**Twenty Years of Molecular Biogeography in the West Mediterranean Islands of Corsica and Sardinia: Lessons Learnt and Future Prospects**

Valerio Ketmaier and Adalgisa Caccone

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/55458

### **1. Introduction**

[76] Yayıntaş A. Higuchi M. Tonguç Ö. The moss flora of Istıranca (Kırklareli) mountains in Turkey. Journal of Faculty of Science Ege University. 1996; 19(2): 33-45.

[77] Yayıntaş A. Tonguç Ö. New Moss Records From Thrace for A1. Journal of Faculty of

[78] You-fang W. Ren-liang H. Yu-huan W. Chien G. Deng-ke L. Wei L. He S. Irelend R.R. Moss Flora of China, English version, Volume 7: Amblystegiaceae-Plagiotheciaceae,

[79] Yücel E. Magil R.E. Eskişehir Bölgesi karayosunları (musci) üzerine bir araştırma.

[80] Yücel E. Tokur S. Eskişehir Yöresi Bazı Brydae Alt Sınıfı Türleri Üzerine Floristik

[81] http://www.esu.edu/~milewski/intro\_biol\_two/lab\_2\_moss\_ferns/Mossand‐

Science Ege University. 1994; 16(1): 51-61.

70 Current Progress in Biological Research

Missouri Botanical Garden. USA; 2008.

Anadolu Üniversitesi Fen Fakültesi Dergisi. 1997; 3: 47-54.

Çalışmalar I. Fen Edebiyat Dergisi. 1989; 2(1): 9-16.

Fern\_Diversity.html (accessed 08 October 2012).

The Mediterranean Sea comprises a wide array of insular systems. Sardinia and Corsica are respectively the second and forth-largest islands of the Mediterranean Sea and they are environmentally complex due to their topography and orography. Owing to their central position in the Tyrrhenian Sea (Figure 1) humans started settling on the islands relatively early, during the Mesolithic. Pliny and Ptolemy were among the first to briefly mention the islands' fauna. More systematic surveys of their biodiversity started around 300 years ago, when Sardinia became part of the Kingdom of Sardinia ruled by the House of Savoy and Corsica was incorporated into France [1]. Our current knowledge of the islands' biological diversity can be considered quite accurate; the fauna is relatively species-poor compared to the sur‐ rounding continental areas, still rate of endemism is high, approaching about 7% for Sardinia [2]. Most of the Corsican-Sardinian endemisms show clear affinity with species distributed across that part of Southern Europe that embraces Northern Spain and Southern France. Some of these elements are also closely related to species occurring in Central insular and peninsular Italy (Tuscan Archipelago and coastal areas of Tuscany; Figure 1). These concordant, yet disjunct, distributions (peri-Tyrrhenian hereinto) are shared among a variety of unrelated organisms, from plants to invertebrates and vertebrates (see [3] for a synthesis) all having very low (if any) potential for long distance, over-sea dispersal.

Recurrent patterns in geographical ranges of unrelated species have traditionally attracted the interest of biogeographers because they can be reasonably related to the same underly‐ ing event(s). In the case of the Corsica-Sardinia system, the presence of a pre-Miocene land bridge connecting the different landmasses had been initially hypothesized [4]; affinities of

© 2013 Ketmaier and Caccone; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

nowadays allopatrically distributed lineages were consequently interpreted under a dispersal scenario. The advent of the theory of plate tectonics allowed a detailed reconstruction of the geological history of the islands [5,6] (see Figure 1 and next chapter for details) and in‐ duced many authors to favour vicariance over dispersal as the main process that originat‐ ed the islands' biodiversity [1,3].

Sardinia, with an area of about 24000 km2

**3. Geological history**

the Campidano plain in the southwest part of the island.

the geological evolution of the area is given in Figure 1.

two geological area cladograms are depicted in Figure 2.

, is the second largest island of the Mediterranean

) situated at

and Future Prospects

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Sea. The island is 270 km long and 145 km wide and is almost equally distant from peninsular Italy on the east (187 km) and North Africa (Tunisia) on the south (184 km). Many small islands

Twenty Years of Molecular Biogeography in the West Mediterranean Islands of Corsica and Sardinia: Lessons Learnt

its southwest tip. Most of its territory is mountainous (about 80%) and a number of mountain chains can be identified separated by intervening alluvial plains and flatlands, the largest being

Corsica and Sardinia are old continental islands and their geological evolution has been reconstructedingooddetails.Aconsensusontheoverallprocessofformationofthe twoislands exists. Some questions are still open, though, regarding the timing of final detachment of two islands from the continent and pattern and timing of contacts between them. Traditionally, the split of Corsica and Sardinia from the Iberian Peninsula as a single microplate had been dated at about 29millionyears (Myrs) ago;the rotationofthemicroplate andthedisjunctionofthe two islands started 15 Myrs ago and was completed by 9 Myrs ago [5,6,8,9,10,11,12]. Recently, new geological data challenged this scenario. According to [13,14] the beginning of the split of the microplate should be dated at 24-20 Myrs. The maps presented in [15] support these views but also suggest that the microplate remained connected to the southern edge of Palaeo-Europe during its anti-clock wise rotation through a land bridge that will constitute the future Mari‐ time Alps and the Ligurian Apennines (Italy). The final detachment of the microplate from the continent was contemporary with the onset of the uplift of Tuscany in continental Italy and occurred in the Pliocene (around 5 Myrs ago). The interaction between the Corsica-Sardinia microplate and the Apennines, which were then being formed, caused the emergence of the Tuscan Archipelago, including the islands that later became incorporated in the mainland (the so- called "fossil islands") [11]. Further connections between the Corsica-Sardinia microplate and the continent were probably established during the Messinian Salinity Crisis (5.7-5.3 Myrs) [10,12]. Finally, sea-level oscillations, which occurred repeatedly in the Quaternary at each ice age (from 2 to 0.5 Myr ago), led to connect northern Corsica to Tuscany and southern Corsica to northern Sardinia [16-19]. It is worth noting that all the connections of the two islands to the continentaftertheinitialdetachmentofthemicroplatewereshort-lived,regardlessofhowmany times they happened and when [20,21]. A schematic representation of the alternative views on

In spite of the temporal vagaries outlined in the previous paragraph, the geological cladogram of the area, that is the representation of relationships among areas based on their geological history, can be summarized as follows. The Iberian Peninsula is basal in the cladogram and the two islands are each other's sister areas. When also Balearic Islands, Tuscan Archipelago and continental Italy are considered, then Balearic Islands would be sister to the Iberian Peninsula while Corsica and Sardinia would no longer be sister areas but Sardinia would be basal to a clade formed by Corsica, Tuscan Archipelago and coastal areas of Central Italy. The

and islets surround Sardinia, the largest being the island of Sant'Antioco (109 km2

The uniqueness of a biogeographic situation with several co-distributed, yet unrelated, species all presumably sharing the same history did not escape the attention of molecular evolutionary biologists. The Corsican-Sardinian system offers the opportunity to test explicit biogeographic hypotheses in light of a well-known geological background; the available geological time estimates can be used to test for the clocklike nature of genetic divergence and eventually calibrate rates of molecular evolution. In 1990 the first molecular data ever on a Corsican-Sardinian endemism with Iberian affinities (newts of the genus *Euproctus*) were included as part of a review on molecular island biogeography [7]. Since then a good wealth of molecular work has been done on a variety of terrestrial and freshwater species (both invertebrates and vertebrates) based on different molecular markers (Table 1). The molecular and analytical tools employed in those studies reflect the unparalleled technological and analytical development that the field has witnessed in the last two decades.

In light of the central importance that insular settings have had in the development of the evolutionary thinking, we assembled this review with the aim to specifically address the following points. First, we will present a synthesis of the most representative molecular studies (i.e. explicitly centred on Corsica-Sardinian endemisms and not part of larger phylogenetic studies) conducted on animal groups whose distribution is limited to the Corsica-Sardinia system and surrounding continental landmasses involved in the past geological evolution of the islands. Second, we want to test for each of these groups whether phylogenetic relation‐ ships fit those expected if cladogenetic events were due to vicariance only. Third, we will summarize the available molecular estimates of divergence times to discuss how they relate to current views on the geological evolution of the landmasses. Fourth, we will summarize whether for each group substitution rates accumulate linearly over time or not (if this was tested in original study) and compare rates based on the same markers and calibrated using the very same geological event(s) across taxonomically unrelated groups. Finally, to place this review in a larger context and to ultimately suggest future avenues in the study of the evolution of insular biota we will explore how molecular evidence on the Corsica-Sardinia system relates to comparative phylogeographies available for other insular systems.

### **2. Geographical setting**

Corsica is located in the Tyrrhenian Sea south of France, west of Italy and north of the island of Sardinia. Its surface totals about 8700 km2 extending for 183 km; the island is 83 km wide and it is about 90 km away from Italy (Tuscany), 170 km from Southern France and it is separated from Sardinia by the Strait of Bonifacio (minimum width 11 km). Mountains comprise about two-third of the island forming a single chain that runs in a north-south direction.

Sardinia, with an area of about 24000 km2 , is the second largest island of the Mediterranean Sea. The island is 270 km long and 145 km wide and is almost equally distant from peninsular Italy on the east (187 km) and North Africa (Tunisia) on the south (184 km). Many small islands and islets surround Sardinia, the largest being the island of Sant'Antioco (109 km2 ) situated at its southwest tip. Most of its territory is mountainous (about 80%) and a number of mountain chains can be identified separated by intervening alluvial plains and flatlands, the largest being the Campidano plain in the southwest part of the island.

### **3. Geological history**

nowadays allopatrically distributed lineages were consequently interpreted under a dispersal scenario. The advent of the theory of plate tectonics allowed a detailed reconstruction of the geological history of the islands [5,6] (see Figure 1 and next chapter for details) and in‐ duced many authors to favour vicariance over dispersal as the main process that originat‐

The uniqueness of a biogeographic situation with several co-distributed, yet unrelated, species all presumably sharing the same history did not escape the attention of molecular evolutionary biologists. The Corsican-Sardinian system offers the opportunity to test explicit biogeographic hypotheses in light of a well-known geological background; the available geological time estimates can be used to test for the clocklike nature of genetic divergence and eventually calibrate rates of molecular evolution. In 1990 the first molecular data ever on a Corsican-Sardinian endemism with Iberian affinities (newts of the genus *Euproctus*) were included as part of a review on molecular island biogeography [7]. Since then a good wealth of molecular work has been done on a variety of terrestrial and freshwater species (both invertebrates and vertebrates) based on different molecular markers (Table 1). The molecular and analytical tools employed in those studies reflect the unparalleled technological and analytical development

In light of the central importance that insular settings have had in the development of the evolutionary thinking, we assembled this review with the aim to specifically address the following points. First, we will present a synthesis of the most representative molecular studies (i.e. explicitly centred on Corsica-Sardinian endemisms and not part of larger phylogenetic studies) conducted on animal groups whose distribution is limited to the Corsica-Sardinia system and surrounding continental landmasses involved in the past geological evolution of the islands. Second, we want to test for each of these groups whether phylogenetic relation‐ ships fit those expected if cladogenetic events were due to vicariance only. Third, we will summarize the available molecular estimates of divergence times to discuss how they relate to current views on the geological evolution of the landmasses. Fourth, we will summarize whether for each group substitution rates accumulate linearly over time or not (if this was tested in original study) and compare rates based on the same markers and calibrated using the very same geological event(s) across taxonomically unrelated groups. Finally, to place this review in a larger context and to ultimately suggest future avenues in the study of the evolution of insular biota we will explore how molecular evidence on the Corsica-Sardinia system relates

Corsica is located in the Tyrrhenian Sea south of France, west of Italy and north of the island

and it is about 90 km away from Italy (Tuscany), 170 km from Southern France and it is separated from Sardinia by the Strait of Bonifacio (minimum width 11 km). Mountains comprise about two-third of the island forming a single chain that runs in a north-south

extending for 183 km; the island is 83 km wide

ed the islands' biodiversity [1,3].

72 Current Progress in Biological Research

**2. Geographical setting**

direction.

of Sardinia. Its surface totals about 8700 km2

that the field has witnessed in the last two decades.

to comparative phylogeographies available for other insular systems.

Corsica and Sardinia are old continental islands and their geological evolution has been reconstructedingooddetails.Aconsensusontheoverallprocessofformationofthe twoislands exists. Some questions are still open, though, regarding the timing of final detachment of two islands from the continent and pattern and timing of contacts between them. Traditionally, the split of Corsica and Sardinia from the Iberian Peninsula as a single microplate had been dated at about 29millionyears (Myrs) ago;the rotationofthemicroplate andthedisjunctionofthe two islands started 15 Myrs ago and was completed by 9 Myrs ago [5,6,8,9,10,11,12]. Recently, new geological data challenged this scenario. According to [13,14] the beginning of the split of the microplate should be dated at 24-20 Myrs. The maps presented in [15] support these views but also suggest that the microplate remained connected to the southern edge of Palaeo-Europe during its anti-clock wise rotation through a land bridge that will constitute the future Mari‐ time Alps and the Ligurian Apennines (Italy). The final detachment of the microplate from the continent was contemporary with the onset of the uplift of Tuscany in continental Italy and occurred in the Pliocene (around 5 Myrs ago). The interaction between the Corsica-Sardinia microplate and the Apennines, which were then being formed, caused the emergence of the Tuscan Archipelago, including the islands that later became incorporated in the mainland (the so- called "fossil islands") [11]. Further connections between the Corsica-Sardinia microplate and the continent were probably established during the Messinian Salinity Crisis (5.7-5.3 Myrs) [10,12]. Finally, sea-level oscillations, which occurred repeatedly in the Quaternary at each ice age (from 2 to 0.5 Myr ago), led to connect northern Corsica to Tuscany and southern Corsica to northern Sardinia [16-19]. It is worth noting that all the connections of the two islands to the continentaftertheinitialdetachmentofthemicroplatewereshort-lived,regardlessofhowmany times they happened and when [20,21]. A schematic representation of the alternative views on the geological evolution of the area is given in Figure 1.

In spite of the temporal vagaries outlined in the previous paragraph, the geological cladogram of the area, that is the representation of relationships among areas based on their geological history, can be summarized as follows. The Iberian Peninsula is basal in the cladogram and the two islands are each other's sister areas. When also Balearic Islands, Tuscan Archipelago and continental Italy are considered, then Balearic Islands would be sister to the Iberian Peninsula while Corsica and Sardinia would no longer be sister areas but Sardinia would be basal to a clade formed by Corsica, Tuscan Archipelago and coastal areas of Central Italy. The two geological area cladograms are depicted in Figure 2.

**4. Ecology and endemism**

Corsica and Sardinia have a Mediterranean climate characterized by hot and dry summers and mild and wet winters. Rainfalls are concentrated in autumn and winter with sporadic showers in spring. Owing to the presence of numerous mountains, the Mediterranean climate of the coastal zone (between the sea level and 600 m of altitude) changes into a milder, cooler and wetter climate in the temperate mountain zone comprised between 600 and 1800 m above the sea level. In Corsica, where elevation reaches 2700 m of altitude, it is possible to identify a high alpine zone (between 1800 and 2700 m) where snow-caps and small glaciers are not infrequent.

Twenty Years of Molecular Biogeography in the West Mediterranean Islands of Corsica and Sardinia: Lessons Learnt

and Future Prospects

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Thevegetationofthe islands reflects the climatealtitudinalzones.Inthe coastalareasMediterra‐ nean forests, woodlands, and shrubs predominate with evergreen sclerophylls. Much of the coastal lowlands have been cleared for agriculture, grazing and logging, activities that have considerably reduced the forest cover. Maritime Pines interspersed with forests of deciduous trees are typical of middle elevations. Above 1800 m of altitude (Corsica only), sub alpine shrub lands progressively substitute forests of Corsican Pine, Silver Fir and European Beech. Endem‐ icplantspeciesarechieflyrestrictedtohighaltitudesinCorsicaandtocoastalareasinSardinia[3].

Corsica and Sardinia are faunistically impoverished as compared to potential surrounding continental sources. Based on taxonomic and faunistic considerations a three-phase model of colonization of the islands (pre-Miocene, Messinian and Quaternary; a fourth phase considers species introduced by humans) has been proposed [3]. The first phase would correspond to the detachment of the microplate from the Iberian Peninsula. Most of the endemic species that are nowadays distributed in Sardinia and Corsica (either in common between the two islands or unique to each of them) have differentiated from ancestors that were supposedly codistributed on the microplate and the Iberian Peninsula when these were still forming a single landmass. Thus, the origin of these lineages is at least 29 Myrs old, even thought we cannot exclude that cladogenesis predated geological splits. Invertebrates are particularly well represented. Freshwater planarians of the genus *Dugesia* belong to this stock along with multiple endemic lineages of terrestrial gastropods (genera *Rupestrella*, *Solatopupa*, *Hypnophi‐ la* and *Tacheocampylaea*). Similarly, examples are found among earthworms (genus *Hormogast‐ er*), crustaceans isopods (both epigean and hypogean, aquatic and terrestrial with the genera *Proasellus*, *Stenasellus*, *Helleria*, *Nesiotoniscus*, *Tiroloscia* and *Lucasius*), arachnids (harvestmen of the genera *Parasiro* and *Scotolemon*, the Acari genera *Damaeus* and *Oribatella* and at least five lineages of pseudoscorpions) and centipedes. Insects are present with different orders. Among others, stoneflies and beetles are very interesting biogeographically. The stonefly genus *Tyrrhenoleuctra* includes three endemic lineages; cave Bathysciine beetles are rich in endemism with at least 11 species (genera *Ovobathysciola*, *Patriziella* and *Speonomus*) likewise are scarab beetles with the genera *Elaphocerida*, *Triodonta*, *Cetonia*, *Thorectes* and *Typhoeus*. Amphibians and Reptiles also contributed to this early phase of colonization. Urodela share no species with any of the adjacent continental landmasses and include at least six endemic species (two genera; newt *Euproctus* and salamander *Speleomantes*). The endemic lineages of the lizard genera *Archeolacerta*, *Algyroides* and *Podarcis* also belong to this early stock of colonizers. No mammalian representatives of this ancient stock are still extant; known from fossil records are the perissodactyls *Atalodon* and *Lophiodon* and the ruminant *Amphytragulus boulengeri*.

**Figure 1.** Geological evolution of the peri-Tyrrhenian area. Panels (a) to (e) show reconstructions of the split of the Corsica-Sardinia microplate from the Iberian Peninsula, its subsequent rotation and interaction with the still extant Tuscan Archipelago and the current coastal area of Tuscany (fossil islands; see text). Approximate age of each geologi‐ cal phase is also given. Bottom right inlets in panels (c), (d), and (e) show the interactions between Corsica-Sardinia and Continental Italy between 21 and 5 Myr proposed by [15] as alternative to the classical scenarios shown in the larger panels (grey and white shaded areas correspond to sea and land, respectively). Black and grey triangles indicate oceanic subduction and thrusting. Panel (f) shows the present geographic location of main areas considered in the study: the Iberian Peninsula (I), Balearic Islands (BI), Sardinia (S), Corsica (C), Tuscan Archipelago (TA) and Continental Italy (CI). Maps were drawn on the basis of present geography.

**Figure 2.** Geological area cladograms of the peri-Tyrrhenian area. The cladogram on the left depicts relationships only when the three major landmasses are considered while on the right are expected relationships when additional areas are also included (see text for details).

### **4. Ecology and endemism**

**Figure 2.** Geological area cladograms of the peri-Tyrrhenian area. The cladogram on the left depicts relationships only when the three major landmasses are considered while on the right are expected relationships when additional areas

**Figure 1.** Geological evolution of the peri-Tyrrhenian area. Panels (a) to (e) show reconstructions of the split of the Corsica-Sardinia microplate from the Iberian Peninsula, its subsequent rotation and interaction with the still extant Tuscan Archipelago and the current coastal area of Tuscany (fossil islands; see text). Approximate age of each geologi‐ cal phase is also given. Bottom right inlets in panels (c), (d), and (e) show the interactions between Corsica-Sardinia and Continental Italy between 21 and 5 Myr proposed by [15] as alternative to the classical scenarios shown in the larger panels (grey and white shaded areas correspond to sea and land, respectively). Black and grey triangles indicate oceanic subduction and thrusting. Panel (f) shows the present geographic location of main areas considered in the study: the Iberian Peninsula (I), Balearic Islands (BI), Sardinia (S), Corsica (C), Tuscan Archipelago (TA) and Continental

are also included (see text for details).

Italy (CI). Maps were drawn on the basis of present geography.

74 Current Progress in Biological Research

Corsica and Sardinia have a Mediterranean climate characterized by hot and dry summers and mild and wet winters. Rainfalls are concentrated in autumn and winter with sporadic showers in spring. Owing to the presence of numerous mountains, the Mediterranean climate of the coastal zone (between the sea level and 600 m of altitude) changes into a milder, cooler and wetter climate in the temperate mountain zone comprised between 600 and 1800 m above the sea level. In Corsica, where elevation reaches 2700 m of altitude, it is possible to identify a high alpine zone (between 1800 and 2700 m) where snow-caps and small glaciers are not infrequent.

Thevegetationofthe islands reflects the climatealtitudinalzones.Inthe coastalareasMediterra‐ nean forests, woodlands, and shrubs predominate with evergreen sclerophylls. Much of the coastal lowlands have been cleared for agriculture, grazing and logging, activities that have considerably reduced the forest cover. Maritime Pines interspersed with forests of deciduous trees are typical of middle elevations. Above 1800 m of altitude (Corsica only), sub alpine shrub lands progressively substitute forests of Corsican Pine, Silver Fir and European Beech. Endem‐ icplantspeciesarechieflyrestrictedtohighaltitudesinCorsicaandtocoastalareasinSardinia[3].

Corsica and Sardinia are faunistically impoverished as compared to potential surrounding continental sources. Based on taxonomic and faunistic considerations a three-phase model of colonization of the islands (pre-Miocene, Messinian and Quaternary; a fourth phase considers species introduced by humans) has been proposed [3]. The first phase would correspond to the detachment of the microplate from the Iberian Peninsula. Most of the endemic species that are nowadays distributed in Sardinia and Corsica (either in common between the two islands or unique to each of them) have differentiated from ancestors that were supposedly codistributed on the microplate and the Iberian Peninsula when these were still forming a single landmass. Thus, the origin of these lineages is at least 29 Myrs old, even thought we cannot exclude that cladogenesis predated geological splits. Invertebrates are particularly well represented. Freshwater planarians of the genus *Dugesia* belong to this stock along with multiple endemic lineages of terrestrial gastropods (genera *Rupestrella*, *Solatopupa*, *Hypnophi‐ la* and *Tacheocampylaea*). Similarly, examples are found among earthworms (genus *Hormogast‐ er*), crustaceans isopods (both epigean and hypogean, aquatic and terrestrial with the genera *Proasellus*, *Stenasellus*, *Helleria*, *Nesiotoniscus*, *Tiroloscia* and *Lucasius*), arachnids (harvestmen of the genera *Parasiro* and *Scotolemon*, the Acari genera *Damaeus* and *Oribatella* and at least five lineages of pseudoscorpions) and centipedes. Insects are present with different orders. Among others, stoneflies and beetles are very interesting biogeographically. The stonefly genus *Tyrrhenoleuctra* includes three endemic lineages; cave Bathysciine beetles are rich in endemism with at least 11 species (genera *Ovobathysciola*, *Patriziella* and *Speonomus*) likewise are scarab beetles with the genera *Elaphocerida*, *Triodonta*, *Cetonia*, *Thorectes* and *Typhoeus*. Amphibians and Reptiles also contributed to this early phase of colonization. Urodela share no species with any of the adjacent continental landmasses and include at least six endemic species (two genera; newt *Euproctus* and salamander *Speleomantes*). The endemic lineages of the lizard genera *Archeolacerta*, *Algyroides* and *Podarcis* also belong to this early stock of colonizers. No mammalian representatives of this ancient stock are still extant; known from fossil records are the perissodactyls *Atalodon* and *Lophiodon* and the ruminant *Amphytragulus boulengeri*.

During the Messinian Salinity Crisis (MSC; 5.7-5.3 Myrs) the Mediterranean Sea almost completely dried up. The MSC was short-lived; nonetheless it allowed a number of species to reach the islands. These constitute most of the extant Corsican-Sardinian fauna, although none of them had diversified on the islands into endemic species. The only endemic subspecies is the colubrid snake *Natrix natrix cettii*. Species that reached the islands during the MSC are typical of a warm to hot climate because they had to withstand the harsh conditions of the drained and hyper saline Mediterranean basin. Colonization proceeded along two major paths from south and east. Sardinia and Corsica thus share earthworms, arachnids, insects, reptiles and many fossil mammals with North Africa and Sicily. An eastern wave of colonization from continental Italy carried to the islands land snails, amphibians, reptiles and mammals (the last three groups left representatives almost exclusively in the fossil records).

predicted phylogeographic breaks [26,27]. For *Helleria brevicornis* the same mtDNA haplotype has been found in Southern France, Central Italy and on three islands of the Tuscan Archipe‐ lago. One mtDNA lineage of the Bediagra rock lizard is in common between Sardinia and Corsica. Conversely, no haplotype sharing was detected for any of the other analyzed taxa.

Twenty Years of Molecular Biogeography in the West Mediterranean Islands of Corsica and Sardinia: Lessons Learnt

**Distribution (N of lineages) 2**

<sup>2</sup> <sup>4</sup> I (2)/S (1)/TA (1) Allozymes (26

)/S (3)/C (2)/TA

same lineage

<sup>2</sup> <sup>2</sup> S (1)/ C (1) mtDNA (*12S*,

S (1)/C (2\* )

one lineage is shared with S

\*

<sup>1</sup> Following the criteria in [65]; 2 I= Southern France + Iberian Peninsula; BI = Balearic Islands; S = Sardinia; C = Corsica; TA = Tuscan Archipelago (extant islands); CI = Continental Italy (mostly fossil islands; see Introduction and Figure1); 3 Linearity

**Table 1.** Summary of taxa with a Corsica- Sardinia- Iberian Peninsula distribution studied molecularly. For each group we give the nominal number of species, the number of lineages identified molecularly, the geographical distribution of such lineages, the markers employed, whether linearity of substitution rates has been tested and whether an

11 11 I (4)/ S (7) mtDNA (*COI*) Yes [25]

2 6 I (2)/S (2)/C (1)/ CI (1)

I (1\*

\*

(1\* )/CI (1\* ) **Molecular marker**

loci)

mt- (*12S*, *16S*, *COI*)/ nucDNA (*H3*)

Allozymes (15 loci) mtDNA (*COI*)

mtDNA (*12S*, *16S*, *COI*)

Allozymes (11 loci) mtDNA (*12S*, *COI*)

*16S*, *Cytb*)

mtDNA (*ND4*, *tRNASER, LEU, HIS*)

**Molecular clock3**

**Source**

No [35]

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http://dx.doi.org/10.5772/55458

Yes [37,39]

Yes [33,40,56]

Yes [26]

Yes [34,41]

Yes [23,24]

Yes [27]

**Class Taxa N of**

*Hormogaster*

Oligochaeta Earthworms

Gastropoda Land snails

Malacostraca Aquatic cave

Insecta Stoneflies

Isopods *Stenasellus*

Terrestrial Isopods

Cave beetles *Ovobathysciola Patriziella Anillochlamys Speonomus*

*Archaeolacerta*

of rates tested and/or calibration given in the study source.

Amphibia European newts *Euproctus*

Reptilia Bediagra rock lizard

*Helleria* 1 6

**nominal species**

**N of lineages1**

*Solatopupa* 6 8 I (4)/S (1)/C (2)/TA (1)

*Tyrrhenoleuctra* <sup>3</sup> <sup>5</sup> I (2)/BI (1)/C (1)/ S (1)

1 2

explicit calibration of the molecular clock has been proposed in the original study.

The last connection(s) between our insular system and the adjacent continent (Central Italy) took place during the Quaternary ice ages. These connections were relatively short-lived, allowed dispersal of species adapted to a temperate to cold climate and have originated no extant endemism. Particular abundant is the mammalian fossil record, which includes extinct species of deer, wild boars, dwarf elephants, giant water voles and macaques. The endemic Sardinia pika (*Prolagus sardus*), a primitive lagomorph of Quaternary origin, went extinct in the late 1700s or early1800s, probably due to a combination of habitat loss, predation and competition with introduced alien species [22].

Humans have started introducing species on the islands intentionally or accidentally since historical times. The extinction of much of the pre-Quaternary fauna is due to human activities (hunting above all), competition with alien introduced species or a combination of both. The Barbary partridge (*Alectoris barbara*) is an example of an introduced bird. Among mammals, rats, mice, hedgehogs, martens, weasels, wild cats and boars, follow deer, red deer and mouflons are all introduced. Some of them have been on the islands long enough to acquire unique morphological features that granted them a sub specific rank (the red deer *Cervus elaphus corsicanus* and the mouflon *Ovis orientalis musimon*).

### **5. The data set**

Available molecular data on Corsica-Sardinia endemisms, on their continental Iberian counterparts (and/or insular and continental Central Italian when existing) are summarized in Table 1. They cover four classes of invertebrates and two classes of vertebrates. While a few studies employed simultaneously markers of different origin (mitochondrial and nuclear), the vast majority is based upon mitochondrial DNA (mtDNA) only; *Cytochrome Oxidase subunit I* (*COI*), the large (*16S*) and small (*12S*) ribosomal subunits are the most frequently used genes. Regardless of the type of marker used, number of lineages discovered molecularly exceeds those assumed on the basis of morphology alone (i.e. nominal taxa). Exceptions to this otherwise generalized pattern are cave beetles and newts but for both groups a one-species one-population sampling strategy was used [23-25]. In two circumstances (the terrestrial isopod *Helleria brevicornis* and the Bediagra rock lizard) the same lineage is distributed across predicted phylogeographic breaks [26,27]. For *Helleria brevicornis* the same mtDNA haplotype has been found in Southern France, Central Italy and on three islands of the Tuscan Archipe‐ lago. One mtDNA lineage of the Bediagra rock lizard is in common between Sardinia and Corsica. Conversely, no haplotype sharing was detected for any of the other analyzed taxa.

During the Messinian Salinity Crisis (MSC; 5.7-5.3 Myrs) the Mediterranean Sea almost completely dried up. The MSC was short-lived; nonetheless it allowed a number of species to reach the islands. These constitute most of the extant Corsican-Sardinian fauna, although none of them had diversified on the islands into endemic species. The only endemic subspecies is the colubrid snake *Natrix natrix cettii*. Species that reached the islands during the MSC are typical of a warm to hot climate because they had to withstand the harsh conditions of the drained and hyper saline Mediterranean basin. Colonization proceeded along two major paths from south and east. Sardinia and Corsica thus share earthworms, arachnids, insects, reptiles and many fossil mammals with North Africa and Sicily. An eastern wave of colonization from continental Italy carried to the islands land snails, amphibians, reptiles and mammals (the last

The last connection(s) between our insular system and the adjacent continent (Central Italy) took place during the Quaternary ice ages. These connections were relatively short-lived, allowed dispersal of species adapted to a temperate to cold climate and have originated no extant endemism. Particular abundant is the mammalian fossil record, which includes extinct species of deer, wild boars, dwarf elephants, giant water voles and macaques. The endemic Sardinia pika (*Prolagus sardus*), a primitive lagomorph of Quaternary origin, went extinct in the late 1700s or early1800s, probably due to a combination of habitat loss, predation and

Humans have started introducing species on the islands intentionally or accidentally since historical times. The extinction of much of the pre-Quaternary fauna is due to human activities (hunting above all), competition with alien introduced species or a combination of both. The Barbary partridge (*Alectoris barbara*) is an example of an introduced bird. Among mammals, rats, mice, hedgehogs, martens, weasels, wild cats and boars, follow deer, red deer and mouflons are all introduced. Some of them have been on the islands long enough to acquire unique morphological features that granted them a sub specific rank (the red deer *Cervus*

Available molecular data on Corsica-Sardinia endemisms, on their continental Iberian counterparts (and/or insular and continental Central Italian when existing) are summarized in Table 1. They cover four classes of invertebrates and two classes of vertebrates. While a few studies employed simultaneously markers of different origin (mitochondrial and nuclear), the vast majority is based upon mitochondrial DNA (mtDNA) only; *Cytochrome Oxidase subunit I* (*COI*), the large (*16S*) and small (*12S*) ribosomal subunits are the most frequently used genes. Regardless of the type of marker used, number of lineages discovered molecularly exceeds those assumed on the basis of morphology alone (i.e. nominal taxa). Exceptions to this otherwise generalized pattern are cave beetles and newts but for both groups a one-species one-population sampling strategy was used [23-25]. In two circumstances (the terrestrial isopod *Helleria brevicornis* and the Bediagra rock lizard) the same lineage is distributed across

three groups left representatives almost exclusively in the fossil records).

competition with introduced alien species [22].

76 Current Progress in Biological Research

**5. The data set**

*elaphus corsicanus* and the mouflon *Ovis orientalis musimon*).


<sup>1</sup> Following the criteria in [65]; 2 I= Southern France + Iberian Peninsula; BI = Balearic Islands; S = Sardinia; C = Corsica; TA = Tuscan Archipelago (extant islands); CI = Continental Italy (mostly fossil islands; see Introduction and Figure1); 3 Linearity of rates tested and/or calibration given in the study source.

**Table 1.** Summary of taxa with a Corsica- Sardinia- Iberian Peninsula distribution studied molecularly. For each group we give the nominal number of species, the number of lineages identified molecularly, the geographical distribution of such lineages, the markers employed, whether linearity of substitution rates has been tested and whether an explicit calibration of the molecular clock has been proposed in the original study.

When more than one conspecific population per geographical area was considered, molecules often revealed multiple lineages that are more closely related to one another than they are to any of those distributed on the other landmasses. This suggests that within-area diversification took place after the geological splits.

subterranean aquatic isopod *Stenasellus* (allozymes and mtDNA), stoneflies (*Tyrrhenoleuctra*) and European newts (*Euproctus*). For these groups we have thus to reject the null hypothesis of no association between molecular relationships and the area cladogram. This implies that

Twenty Years of Molecular Biogeography in the West Mediterranean Islands of Corsica and Sardinia: Lessons Learnt

**Taxa Speciation by area Speciation within an area Migratory Sorting** *P\** Earthworms *Hormogaster* 3 2 0 1 0.071 Land snails *Solatopupa* 2 5 0 4 0.610

*Stenasellus* (Allozymes) 4 2 0 1 <<0.001

*Stenasellus* (mtDNA) 4 1 0 1 <0.001 Terrestrial Isopods *Helleria* 1 8 0 9 0.985 Stoneflies *Tyrrhenoleuctra* 4 1 0 0 <<0.001

*Patriziella Anillochlamys* 2 4 0 0 0.410 Cave beetles *Speonomus* 2 2 0 0 0.288 European newts *Euproctus* 2 0 0 0 <<0.001

*Archaeolacerta* 2 7 0 3 0.866

**Table 2.** Summary of the reconstruction of lineage-area assemblage performed in TreeMap [32]. For each group TreeMap sorts the total number of scored events into four categories (columns 2-5; see text for details). The last column reports the significance of the observed fit between the area cladogram (see Figure1) and the molecular

Aquatic isopods of the genus *Stenasellus* are highly adapted to subterranean life, they spend their whole life cycle in subsurface freshwaters and active dispersal can only happen when such a habitat is continuous [33]. Given these characteristics, it was not unexpected to find molecular relationships (regardless of the markers employed) to be remarkably in agreement with the palaeogeography of the area. Stoneflies are very poor fliers and spend most of their life cycle as nymphs in running freshwaters [34]. The terrestrial winged adults are short-lived and tend to stay close to the water edge to reproduce. Considerable oversea dispersal is difficult to hypothesize. Likewise unrealistic would be to invoke between islands sea dispersal for

TreeMap analyses were not significant for earthworms, land snails, terrestrial isopods, cave beetles and rock lizards, groups where the potential for dispersal is also low. For none of these

European newts, given the strict intolerance of amphibians to salt water [23,24].

**Events**

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vicariance has been the main force driving their diversification.

based on 10.000 random permutations; *P* is significant when ≤ 0.05

phylogenies; the null hypothesis is that there is no association between them.

Aquatic cave Isopods

Aquatic cave Isopods

Cave beetles *Ovobathysciola*

Bediagra rock lizard

\*

#### **6. Hypothesis testing and TreeMap analysis**

Was vicariance hence predominant over dispersal in promoting speciation in Corsica-Sardinia-Iberian taxa, as expected given the low dispersal capability of the groups listed in Table 1? If so, relationships within groups should mirror the geological area cladogram of the landmasses they occupy (see the Geological history section and Figure 1 for details). In other words, a vicariance scenario would be supported if the phylogeny of a given group were congruent with the known sequence of vicariant events as determined by geology [28]. To test this hypothesis, we used an approach initially developed to detect co-speciation in host-parasite systems and later on applied to biogeography [29,30]. It should be noted here that we had no access to raw datasets for any of the study cases based on allozymes included in this review. Furthermore, papers based on retrievable sequence data considered, with the sole exceptions of land snails and rock lizards, few populations and individuals (often just a single population per species). All this hampered applicability of the recently developed Approximate Bayesian Computation (ABC) approaches. ABC integrates the many parameters typical of any popula‐ tion genetics study into a Bayesian framework and takes advantage of the flexibility of the Bayesian statistics to derive inferences. ABC, however, arose primarily in the field of popula‐ tion genetics to investigate the demographic history of populations and implicitly assumes a dense sampling in terms of both individuals/populations and loci [31]. We hence limited ourselves to compare branching patterns of molecular phylogenies (as presented in the original papers; Table 1) to the area cladogram to reconstruct the alleged "host-parasite" associations (where the hosts are the geographic areas and the parasites are lineages of a given group). Associations between the molecular phylogenies and the area cladograms as well as all the subsequent statistical analyses were carried out in TreeMap 1.0 [32]. We used the heuristic option to reconcile the area and the group trees and to find a single optimal reconstruction. We tested the significance of the fit between the host and parasite trees by generating 10000 random "parasite" trees with the same number of taxa and "host-parasite" associations. We then measured how the random parasite trees fit the observed parasite trees in comparison with the area cladogram. The proportion of random gene trees that have the same (or greater) number of speciation-separation events as the observed tree is the probability of obtaining the observed value by chance alone. The null hypothesis is that the area cladogram and molecular phylogenetic trees are independent. TreeMap distinguishes and counts the following events: speciation by area, speciation within area, migratory and sorting events. The latter are assumed due to extinction and/or sampling errors; they hence reflect instances where "parasites" were expected to occur but do not.

Results of these analyses are summarized in Table 2. No migratory events were detected for any of the associations tested. The analysis was significant at the 0.05 level or below for the subterranean aquatic isopod *Stenasellus* (allozymes and mtDNA), stoneflies (*Tyrrhenoleuctra*) and European newts (*Euproctus*). For these groups we have thus to reject the null hypothesis of no association between molecular relationships and the area cladogram. This implies that vicariance has been the main force driving their diversification.


\* based on 10.000 random permutations; *P* is significant when ≤ 0.05

When more than one conspecific population per geographical area was considered, molecules often revealed multiple lineages that are more closely related to one another than they are to any of those distributed on the other landmasses. This suggests that within-area diversification

Was vicariance hence predominant over dispersal in promoting speciation in Corsica-Sardinia-Iberian taxa, as expected given the low dispersal capability of the groups listed in Table 1? If so, relationships within groups should mirror the geological area cladogram of the landmasses they occupy (see the Geological history section and Figure 1 for details). In other words, a vicariance scenario would be supported if the phylogeny of a given group were congruent with the known sequence of vicariant events as determined by geology [28]. To test this hypothesis, we used an approach initially developed to detect co-speciation in host-parasite systems and later on applied to biogeography [29,30]. It should be noted here that we had no access to raw datasets for any of the study cases based on allozymes included in this review. Furthermore, papers based on retrievable sequence data considered, with the sole exceptions of land snails and rock lizards, few populations and individuals (often just a single population per species). All this hampered applicability of the recently developed Approximate Bayesian Computation (ABC) approaches. ABC integrates the many parameters typical of any popula‐ tion genetics study into a Bayesian framework and takes advantage of the flexibility of the Bayesian statistics to derive inferences. ABC, however, arose primarily in the field of popula‐ tion genetics to investigate the demographic history of populations and implicitly assumes a dense sampling in terms of both individuals/populations and loci [31]. We hence limited ourselves to compare branching patterns of molecular phylogenies (as presented in the original papers; Table 1) to the area cladogram to reconstruct the alleged "host-parasite" associations (where the hosts are the geographic areas and the parasites are lineages of a given group). Associations between the molecular phylogenies and the area cladograms as well as all the subsequent statistical analyses were carried out in TreeMap 1.0 [32]. We used the heuristic option to reconcile the area and the group trees and to find a single optimal reconstruction. We tested the significance of the fit between the host and parasite trees by generating 10000 random "parasite" trees with the same number of taxa and "host-parasite" associations. We then measured how the random parasite trees fit the observed parasite trees in comparison with the area cladogram. The proportion of random gene trees that have the same (or greater) number of speciation-separation events as the observed tree is the probability of obtaining the observed value by chance alone. The null hypothesis is that the area cladogram and molecular phylogenetic trees are independent. TreeMap distinguishes and counts the following events: speciation by area, speciation within area, migratory and sorting events. The latter are assumed due to extinction and/or sampling errors; they hence reflect instances where "parasites" were

Results of these analyses are summarized in Table 2. No migratory events were detected for any of the associations tested. The analysis was significant at the 0.05 level or below for the

took place after the geological splits.

78 Current Progress in Biological Research

expected to occur but do not.

**6. Hypothesis testing and TreeMap analysis**

**Table 2.** Summary of the reconstruction of lineage-area assemblage performed in TreeMap [32]. For each group TreeMap sorts the total number of scored events into four categories (columns 2-5; see text for details). The last column reports the significance of the observed fit between the area cladogram (see Figure1) and the molecular phylogenies; the null hypothesis is that there is no association between them.

Aquatic isopods of the genus *Stenasellus* are highly adapted to subterranean life, they spend their whole life cycle in subsurface freshwaters and active dispersal can only happen when such a habitat is continuous [33]. Given these characteristics, it was not unexpected to find molecular relationships (regardless of the markers employed) to be remarkably in agreement with the palaeogeography of the area. Stoneflies are very poor fliers and spend most of their life cycle as nymphs in running freshwaters [34]. The terrestrial winged adults are short-lived and tend to stay close to the water edge to reproduce. Considerable oversea dispersal is difficult to hypothesize. Likewise unrealistic would be to invoke between islands sea dispersal for European newts, given the strict intolerance of amphibians to salt water [23,24].

TreeMap analyses were not significant for earthworms, land snails, terrestrial isopods, cave beetles and rock lizards, groups where the potential for dispersal is also low. For none of these groups TreeMap suggested multiple colonization events of the islands. Genetic relationships in the earthworm genus *Hormogaster* do not match the area cladogram, because the lineage from the Elba Island is basal to the Sardinian ones [35], contrary to what expected on the basis of geological considerations alone (Figure 2). These results are likely due to the lack of resolution of the markers employed (allozymes) coupled with an incomplete taxon sampling [35]. Relationships within the genus and the family (Hormogastridae) are problematic and still in need of additional work based on as exhaustive taxon coverage as possible [36]. For land snails of the genus *Solatopupa* we found a relatively high number of within-area speciation and sorting events (Table 2). In particular, *S.guidoni* has diversified within the Sardinia-Corsica-Tuscan Archipelago area into mtDNA lineages that maintained a substantial morphological uniformity in shell and genital traits [37]. These insular lineages are not reciprocally mono‐ phyletic as expected if vicariance had been the only cause of divergence; haplogroups found on Sardinia and Elba Island are embedded within some of those distributed in Corsica. The sorting events detected are likely due to episodes of extinction because the species is nowadays absent from ecologically suitable areas where it has been reported in the past [37,38,39]. The high number of speciation within an area and sorting events as opposed to the very few speciation by area episodes justify the lack of fit between the phylogeographies of both the terrestrial isopod *Helleria brevicornis* and the Bediagra rock lizard and a purely vicariant model of divergence [26,27]. In either case, diversification started in the Pliocene, much later than the completion of the detachment of the Corsica-Sardinia microplate from the Iberian Peninsula. Mitochondrial DNA genealogies support relatively recent between-islands dispersal as demonstrated by the intermingling of haplotypes originating from the two islands. For the isopod, historic human-mediated transport has been also postulated [26]. None of these explanations applies to cave beetles, owing to their strict association with the subterranean environment [25]. In this case, the TreeMap analyses might have been partially distorted by the fact that the lineages considered in [25] are absent from Corsica (hence only two areas could be included in the analyses) and by the strong bias in number of species included in the study in favour of Sardinia. Consequently, speciation-by-area events are either the same or half of those detected within areas.

accumulate substitutions at a relatively faster pace (yet slower than that of other insect orders). In the only case where nuclear DNA sequences were used (land snails *Solatopupa*, histone *H3*

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**Taxa1 Linearity Gene partition Rates**

*Solatopupa* Yes *12S*, *COI* 1st codon pos.\* 0.131, 0.025

*Stenasells* Yes 15 allozymic loci 2-2.1

*Stenasellus* Yes *COI* all pos., *COI* Tv+Ti 3rd codon pos.; *COI* Tv3rd codon pos. 1.25, 0.1, 0.46

Isopods *Helleria* Yes *COI* all codon pos. \*\* N/A

*Tyrrhenoleuctra* Yes 11 allozymic loci 0.8

*Tyrrhenoleuctra* No *12S*, *COI* all codon pos. 0.01-0.25, 0.09-0.79

*Anillochlamys* Yes *COI* all codon pos., *COI* 3rd codon pos., *COI* Tv3rd codon pos. 1.3, 0.86, 0.5

*Speonomus* Yes *COI* all codon pos., *COI* 3rd codon pos., *COI* Tv3rd codon pos. 1.2, 0.98, 0.9

*Archaeolacerta* No *ND4*, *tRNASER, LEU, HIS* 2.74, 1.78

1 Earthworms are not shown here because [35] did not test the molecular clock hypothesis.

*12S* + *16S* all sub., *12S* + *16S* Tv, *Cytb* all codon pos., *Cytb* Tv all

*16S,COI* 2nd and 3rd codon positions and *H3* did not pass the molecular clock test. \*\* *12S* and *16S* not tested for linearity

**Table 3.** Summary of molecular rates for Corsica- Sardinia- Iberian Peninsula lineages. The first column shows whether substitution rates passed a molecular clock test; the second and third columns give the data as partitioned in the original study and the relative rates of substitutions. Rates are given as percentages of substitutions per site per lineage per million years for all partitions but for allozymes where rates are in percentages of genetic divergence *D*

codon pos., *Cytb* Tv3rd codon pos. 0.22, 0.04, 0.38, 0.08, 0.22

gene; [39]), these were not evolving in a clock-like manner.

Land snails

Aquatic cave Isopods

Aquatic cave Isopods

Terrestrial

Stoneflies

Stoneflies

Cave beetles *Ovobathysciola Patriziella*

Cave beetles

European newts *Euproctus* Yes

Bediagra rock lizard

\*

of rates.

[66] per lineage per million years.

#### **7. Divergence times and molecular rates**

The peri-Tyrrhenian area offers at least two independent geological time estimates for calibrating rates of gene evolution (the split of the microplate from the Iberian Peninsula and the split between the two islands) within the same geographical setting across a variety of unrelated taxonomic groups. All the studies centred on this system but one took indeed advantage of this opportunity (Table 1). With the sole exceptions of [40,41], where calibration of sets of allozymic loci was attempted, all other studies exclusively considered mtDNA. Table 3 summarizes the main results. Linearity (i.e. acceptance of the molecular clock hypothesis) of rates was rejected on the whole for stoneflies only [34], while at least some (if not all) of the gene partitions tested in the other studies passed the molecular clock test. A remarkable slowdown in rates was detected for the stonefly *Tyrrhenoleuctra* [34,41]; younger lineages accumulate substitutions at a relatively faster pace (yet slower than that of other insect orders). In the only case where nuclear DNA sequences were used (land snails *Solatopupa*, histone *H3* gene; [39]), these were not evolving in a clock-like manner.

groups TreeMap suggested multiple colonization events of the islands. Genetic relationships in the earthworm genus *Hormogaster* do not match the area cladogram, because the lineage from the Elba Island is basal to the Sardinian ones [35], contrary to what expected on the basis of geological considerations alone (Figure 2). These results are likely due to the lack of resolution of the markers employed (allozymes) coupled with an incomplete taxon sampling [35]. Relationships within the genus and the family (Hormogastridae) are problematic and still in need of additional work based on as exhaustive taxon coverage as possible [36]. For land snails of the genus *Solatopupa* we found a relatively high number of within-area speciation and sorting events (Table 2). In particular, *S.guidoni* has diversified within the Sardinia-Corsica-Tuscan Archipelago area into mtDNA lineages that maintained a substantial morphological uniformity in shell and genital traits [37]. These insular lineages are not reciprocally mono‐ phyletic as expected if vicariance had been the only cause of divergence; haplogroups found on Sardinia and Elba Island are embedded within some of those distributed in Corsica. The sorting events detected are likely due to episodes of extinction because the species is nowadays absent from ecologically suitable areas where it has been reported in the past [37,38,39]. The high number of speciation within an area and sorting events as opposed to the very few speciation by area episodes justify the lack of fit between the phylogeographies of both the terrestrial isopod *Helleria brevicornis* and the Bediagra rock lizard and a purely vicariant model of divergence [26,27]. In either case, diversification started in the Pliocene, much later than the completion of the detachment of the Corsica-Sardinia microplate from the Iberian Peninsula. Mitochondrial DNA genealogies support relatively recent between-islands dispersal as demonstrated by the intermingling of haplotypes originating from the two islands. For the isopod, historic human-mediated transport has been also postulated [26]. None of these explanations applies to cave beetles, owing to their strict association with the subterranean environment [25]. In this case, the TreeMap analyses might have been partially distorted by the fact that the lineages considered in [25] are absent from Corsica (hence only two areas could be included in the analyses) and by the strong bias in number of species included in the study in favour of Sardinia. Consequently, speciation-by-area events are either the same or half of

The peri-Tyrrhenian area offers at least two independent geological time estimates for calibrating rates of gene evolution (the split of the microplate from the Iberian Peninsula and the split between the two islands) within the same geographical setting across a variety of unrelated taxonomic groups. All the studies centred on this system but one took indeed advantage of this opportunity (Table 1). With the sole exceptions of [40,41], where calibration of sets of allozymic loci was attempted, all other studies exclusively considered mtDNA. Table 3 summarizes the main results. Linearity (i.e. acceptance of the molecular clock hypothesis) of rates was rejected on the whole for stoneflies only [34], while at least some (if not all) of the gene partitions tested in the other studies passed the molecular clock test. A remarkable slowdown in rates was detected for the stonefly *Tyrrhenoleuctra* [34,41]; younger lineages

those detected within areas.

80 Current Progress in Biological Research

**7. Divergence times and molecular rates**


1 Earthworms are not shown here because [35] did not test the molecular clock hypothesis.

\* *16S,COI* 2nd and 3rd codon positions and *H3* did not pass the molecular clock test. \*\* *12S* and *16S* not tested for linearity of rates.

**Table 3.** Summary of molecular rates for Corsica- Sardinia- Iberian Peninsula lineages. The first column shows whether substitution rates passed a molecular clock test; the second and third columns give the data as partitioned in the original study and the relative rates of substitutions. Rates are given as percentages of substitutions per site per lineage per million years for all partitions but for allozymes where rates are in percentages of genetic divergence *D* [66] per lineage per million years.

Even though *COI* rates are relatively similar in our dataset, we are by no means implying that these rates could be carelessly applied to other organisms and/or geographic contexts. There are at least two aspects that we think deserve attention; the time-slice we are looking at and the geographic setting. Deep nodes of a phylogeny often suffer from saturation of sequences; choosing the appropriate model of sequence evolution is then crucial to incorporate saturation in the estimates [42]. If sequences are not behaving in a clock-like manner, methods should be used to accommodate acceleration and deceleration of rates along the branches of a given phylogenetic tree without the need to clear the data set of the non-clock data [43,44]. As we move closer in time, the problem of the discrepancy between times of gene and population divergence arises. This is because prior to species divergence, a degree of gene divergence has already accrued in the ancestral species gene pool. This ancestral species divergence can be a large fraction of the total species divergence if the ancestral species was highly structured and, depending on the size of the ancestral population, could impact the first several million of years after divergence [42]. A way to get around this problem is to adopt a genealogical coalescent- based approach in the data analysis because this can robustly take into account the stochastic genealogical component to divergence [45]. Insularity is usually seen as a simplifi‐ cation when it comes to estimate divergence times. Species divergence, however, might precede isolation due to insularity. In other words, species age might be older than island age. If so and the island age is still used as calibration point, we would end up with biased estimates of molecular rates. Galàpagos and Barbados are examples of insular settings harbouring lineages older than the extant islands [46,47].

Figure 3 shows the molecular age estimates for the peri-Tyrrhenian groups considered in the present study arranged by the major geological events that affected the area.

It should be noted that those groups with a significant TreeMap analysis (aquatic subterranean isopods, stoneflies and newts) have ages consistently closer to the older geological estimates of splits of landmasses than groups with a non-significant TreeMap analysis have. The implication is that gene flow within these groups was discontinued at the geological onset of geographical barriers (detachment between the microplate from the Iberian Peninsula and split between the two islands, respectively). For those groups whose distribution includes the Tuscan Archipelago and/or coastal areas of Central Italy, divergence is relatively young in agreement with the recent interaction between those areas and Corsica. The only exception to this otherwise generalized pattern is *Hormogaster* (earthworms). For this group, allozymes indicate the split between Sardinian and Iberian lineages as coeval with the split between Sardinia and Tuscan Archipelago/Central Italy (17.5-13 Myr). If this hypothesis were true, this would imply that gene flow among these lineages ceased sometimes in the Middle Miocene. At the time, Corsica and Sardinia were either completely detached from the continent (classic scenario Figure 1) or connected through a land bridge to the emerging Italian peninsula (alternative scenario; inlets in Figure 1). Since we have to exclude both oversea dispersal for evident ecological reasons and human-mediated transport (genetic divergent would be much lower in that case) we should give credit to the land bridge hypothesis. Alternatively, and perhaps more parsimoniously, we think that the lack of any Corsican population in the data set is responsible [35]. The island is likely to host lineages phylogenetically intermediate between Sardinia and the Tuscan Archipelago/ Central Italy [48].

Comparisons between Corsican and Tuscan (both insular and continental) populations of *Helleria brevicornis* gave very young age estimates and a pattern of relationships without a visible geographic component [26]. MtDNA genealogy, coalescence inferences and distribu‐ tion pattern (the species occurs spottily in Tuscany regardless of the abundance of suitable habitats) suggest historic, human-mediated transport as responsible, possibly due to the intense commercial trades existing in the area when the Tyrrhenian Sea was under Etruscan

**Figure 3.** Within taxonomical group molecular age estimates of cladogenetic splits. Splits are sorted according to the three major geological events in the area (I vs. C/S: detachment of the microplate; C vs. S: separation of the two is‐ lands; C vs. TA/CI interaction between Corsica and coastal Tuscany). Age ranges (when available in the original source) are shown; asterisks indicate that a particular dating was used to calibrate substitution rates. The three uppermost panels illustrate the geological settings of the three events and are simplified versions of panels (b), (d), and (e) of

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All the molecular studies reviewed here consistently support a monophyletic origin for the Corsican-Sardinian lineages, regardless of what the relationships within the system are. Table

control [26].

Figure 1.

**8. Comparisons to other insular systems**

Twenty Years of Molecular Biogeography in the West Mediterranean Islands of Corsica and Sardinia: Lessons Learnt and Future Prospects http://dx.doi.org/10.5772/55458 83

**Figure 3.** Within taxonomical group molecular age estimates of cladogenetic splits. Splits are sorted according to the three major geological events in the area (I vs. C/S: detachment of the microplate; C vs. S: separation of the two is‐ lands; C vs. TA/CI interaction between Corsica and coastal Tuscany). Age ranges (when available in the original source) are shown; asterisks indicate that a particular dating was used to calibrate substitution rates. The three uppermost panels illustrate the geological settings of the three events and are simplified versions of panels (b), (d), and (e) of Figure 1.

Comparisons between Corsican and Tuscan (both insular and continental) populations of *Helleria brevicornis* gave very young age estimates and a pattern of relationships without a visible geographic component [26]. MtDNA genealogy, coalescence inferences and distribu‐ tion pattern (the species occurs spottily in Tuscany regardless of the abundance of suitable habitats) suggest historic, human-mediated transport as responsible, possibly due to the intense commercial trades existing in the area when the Tyrrhenian Sea was under Etruscan control [26].

#### **8. Comparisons to other insular systems**

Even though *COI* rates are relatively similar in our dataset, we are by no means implying that these rates could be carelessly applied to other organisms and/or geographic contexts. There are at least two aspects that we think deserve attention; the time-slice we are looking at and the geographic setting. Deep nodes of a phylogeny often suffer from saturation of sequences; choosing the appropriate model of sequence evolution is then crucial to incorporate saturation in the estimates [42]. If sequences are not behaving in a clock-like manner, methods should be used to accommodate acceleration and deceleration of rates along the branches of a given phylogenetic tree without the need to clear the data set of the non-clock data [43,44]. As we move closer in time, the problem of the discrepancy between times of gene and population divergence arises. This is because prior to species divergence, a degree of gene divergence has already accrued in the ancestral species gene pool. This ancestral species divergence can be a large fraction of the total species divergence if the ancestral species was highly structured and, depending on the size of the ancestral population, could impact the first several million of years after divergence [42]. A way to get around this problem is to adopt a genealogical coalescent- based approach in the data analysis because this can robustly take into account the stochastic genealogical component to divergence [45]. Insularity is usually seen as a simplifi‐ cation when it comes to estimate divergence times. Species divergence, however, might precede isolation due to insularity. In other words, species age might be older than island age. If so and the island age is still used as calibration point, we would end up with biased estimates of molecular rates. Galàpagos and Barbados are examples of insular settings harbouring

Figure 3 shows the molecular age estimates for the peri-Tyrrhenian groups considered in the

It should be noted that those groups with a significant TreeMap analysis (aquatic subterranean isopods, stoneflies and newts) have ages consistently closer to the older geological estimates of splits of landmasses than groups with a non-significant TreeMap analysis have. The implication is that gene flow within these groups was discontinued at the geological onset of geographical barriers (detachment between the microplate from the Iberian Peninsula and split between the two islands, respectively). For those groups whose distribution includes the Tuscan Archipelago and/or coastal areas of Central Italy, divergence is relatively young in agreement with the recent interaction between those areas and Corsica. The only exception to this otherwise generalized pattern is *Hormogaster* (earthworms). For this group, allozymes indicate the split between Sardinian and Iberian lineages as coeval with the split between Sardinia and Tuscan Archipelago/Central Italy (17.5-13 Myr). If this hypothesis were true, this would imply that gene flow among these lineages ceased sometimes in the Middle Miocene. At the time, Corsica and Sardinia were either completely detached from the continent (classic scenario Figure 1) or connected through a land bridge to the emerging Italian peninsula (alternative scenario; inlets in Figure 1). Since we have to exclude both oversea dispersal for evident ecological reasons and human-mediated transport (genetic divergent would be much lower in that case) we should give credit to the land bridge hypothesis. Alternatively, and perhaps more parsimoniously, we think that the lack of any Corsican population in the data set is responsible [35]. The island is likely to host lineages phylogenetically intermediate

present study arranged by the major geological events that affected the area.

between Sardinia and the Tuscan Archipelago/ Central Italy [48].

lineages older than the extant islands [46,47].

82 Current Progress in Biological Research

All the molecular studies reviewed here consistently support a monophyletic origin for the Corsican-Sardinian lineages, regardless of what the relationships within the system are. Table 4 summarizes the main findings deduced from the evolutionary literature available for both continental and oceanic islands.

fair to a deep extent. This is not the case for the Chathams where only a few taxa have been

Twenty Years of Molecular Biogeography in the West Mediterranean Islands of Corsica and Sardinia: Lessons Learnt

and Future Prospects

85

http://dx.doi.org/10.5772/55458

Keeping in mind the above considerations, these studies show that a vicariant, monophyletic origin can be assumed only in the case of the four genera of large flightless insects from the old continental Chatham Islands (cockroaches, crickets and beetles) analyzed by [51]. About 60% of the invertebrates and 20% of the vertebrates Madagascar harbours have an ancient (i.e. Gondwanian; about 80 Myrs old) vicariant origin. On all the oceanic systems, lineages derived from multiple colonization events co-exist with lineages originated through single founding episodes. Multiple lineages of Canarian reptiles were established via independent episodes of colonization, while darkling beetles, brimstone butterflies and fruit flies reached the archipe‐ lago only once [52]. Some representatives of the extant terrestrial fauna of the remote archi‐ pelagos of Hawaii and Galàpagos, perhaps the best studied oceanic insular settings, derives from single colonizing episodes while for others molecular data do not justify such an assumption [47,53]. Groups with a monophyletic origin include some evolutionary paradigms such as the Hawaiian drosophilids and honeycreepers and the Galàpagos giant tortoises and Darwin's finches. The past physical connection, although partial, with the mainland of both West Indies and Philippine Islands facilitated colonization [54,55]. Intriguingly, West Indies have been identified also as source of colonization for the surrounding continents and not only

Frequently lineages diversify on islands. Local lineage production can be repeated many times resulting in a radiation; radiation is sometimes associated with adaptation (adaptive radiation; Table 4). Table 1 shows that Corsica and Sardinia generally host lineages that have diversified locally. It shouldn't be overlooked, however, that only a few studies are based on a dense sampling of populations. We hence suspect the true number of genetic lineages to be under‐ estimated. Keeping in mind the limitations in terms of sampled populations of the studies listed in Table 1, it should be noted that the highest number of detected lineages within either Corsica or Sardinia is seven (cave beetles; [25]). This figure is well below the estimates reported in Table 4, which in some cases exceed 50 (i.e. Hawaiian honeycreepers). Diversification on Corsica and Sardinia was certainly triggered when they became detached from the continent. Subsequent within-island evolution has been documented molecularly but very often it did not produce appreciable morphological differences. Illustrative is the case of the subterranean isopod *Stenasellus* [33,40,56]. The few known populations of this crustacean are virtually indistinguishable morphologically and yet they are deeply divergent from one another at both

Given the available data it is impossible to argue in favour of a Corsica-Sardinia radiation, let alone adaptive radiation. Corsica and Sardinia are not as isolated as the majority of the other insular systems listed in Table 4. Also, they are considerably younger than Madagascar and the Chathams, continental islands that witnessed radiation (with adaptation for Madagascar). Finally, it is not unrealistic to think that when the two islands started moving away from the continent they were not as species-poor as typically are young oceanic islands, which provide plenty of ecological opportunities for immigrants. The number of fossil and extant taxa that can be brought back to the initial phases of insularity of Corsica and Sardinia (see the Ecology

considered.

as a sink [55].

mitochondrial and nuclear loci.


\* West Indies are of continental origin but Lesser Antilles are mostly volcanic. Philippines are the result of tectonic and volcanic activity and progressive uplift.

References: 1[52]; 2[53]; 3[47]; 4[51]; 5[28]; 6[55]; 7[54]; 8[67].

**Table 4.** Summary of phylogeographic reviews available on other insular systems. For each of them information on the origin, age (extant islands only), minimum distance from and past connection to the continent are given. The two last columns indicate whether insular lineages originated through single or multiple events, via vicariance or dispersal and whether there is evidence of within-system radiation and/or adaptive radiation.

We are aware that a crude comparison between islands of different origin would be mean‐ ingless, because intimately different are the ancestry and evolution of the respective biota. Remote oceanic islands can only be colonised through dispersal while both vicariance and dispersal play a role in determining the biological diversity of continental islands [49,50]. The contribution of either factor is related to a large extent to the dispersal ability of organisms. Vicariance is expected to be predominant in poor dispersers (as also shown for the Corsica-Sardinia system) while such a force would be less relevant (if not negligible) in those lineages with a strong vagility. Comparing the studies listed in Table 4 requires additional caution because the molecular data sets they are based upon are quite unbalanced in terms of taxo‐ nomic coverage. Hawaii, Galàpagos, Madagascar and West Indies have been covered from a fair to a deep extent. This is not the case for the Chathams where only a few taxa have been considered.

4 summarizes the main findings deduced from the evolutionary literature available for both

**Connection with the continent**

**Colonization Single (S)/ Multiple (M) Process Vicariance (V)/ Dispersal (D)**

No S/M-D Yes/Yes

No S/M-D Yes/Yes

No S-V Yes/?

Partial S/M-D/V(?) Yes/Yes

Partial M-D Yes/Yes

**Radiation/ Adaptive radiation**

**Minimum distance from the continent**

> 3000 km (North America)

960 km (South America)

800 km (New Zealand)

81 km (North America)

800 km (Asian mainland)

Madagascar5 Continental 88 400 km (Africa) Yes S/M-V/D Yes/Yes

West Indies are of continental origin but Lesser Antilles are mostly volcanic. Philippines are the result of tectonic and

**Table 4.** Summary of phylogeographic reviews available on other insular systems. For each of them information on the origin, age (extant islands only), minimum distance from and past connection to the continent are given. The two last columns indicate whether insular lineages originated through single or multiple events, via vicariance or dispersal

We are aware that a crude comparison between islands of different origin would be mean‐ ingless, because intimately different are the ancestry and evolution of the respective biota. Remote oceanic islands can only be colonised through dispersal while both vicariance and dispersal play a role in determining the biological diversity of continental islands [49,50]. The contribution of either factor is related to a large extent to the dispersal ability of organisms. Vicariance is expected to be predominant in poor dispersers (as also shown for the Corsica-Sardinia system) while such a force would be less relevant (if not negligible) in those lineages with a strong vagility. Comparing the studies listed in Table 4 requires additional caution because the molecular data sets they are based upon are quite unbalanced in terms of taxo‐ nomic coverage. Hawaii, Galàpagos, Madagascar and West Indies have been covered from a

Canary Islands1 Volcanic 21-1 110 km (Africa) No S/M-D Yes/?

continental and oceanic islands.

84 Current Progress in Biological Research

**Island system Origin Age (Myr)**

Hawaiian Islands2 Volcanic 29-0.40

Islands3 Volcanic 4-0.5

Chatham Islands4 Continental 70

West Indies6 Mixed\* 48-20

Islands7,8 Mixed\* 28-2.5

volcanic activity and progressive uplift.

References: 1[52]; 2[53]; 3[47]; 4[51]; 5[28]; 6[55]; 7[54]; 8[67].

and whether there is evidence of within-system radiation and/or adaptive radiation.

Galàpagos

Philippine

\*

Keeping in mind the above considerations, these studies show that a vicariant, monophyletic origin can be assumed only in the case of the four genera of large flightless insects from the old continental Chatham Islands (cockroaches, crickets and beetles) analyzed by [51]. About 60% of the invertebrates and 20% of the vertebrates Madagascar harbours have an ancient (i.e. Gondwanian; about 80 Myrs old) vicariant origin. On all the oceanic systems, lineages derived from multiple colonization events co-exist with lineages originated through single founding episodes. Multiple lineages of Canarian reptiles were established via independent episodes of colonization, while darkling beetles, brimstone butterflies and fruit flies reached the archipe‐ lago only once [52]. Some representatives of the extant terrestrial fauna of the remote archi‐ pelagos of Hawaii and Galàpagos, perhaps the best studied oceanic insular settings, derives from single colonizing episodes while for others molecular data do not justify such an assumption [47,53]. Groups with a monophyletic origin include some evolutionary paradigms such as the Hawaiian drosophilids and honeycreepers and the Galàpagos giant tortoises and Darwin's finches. The past physical connection, although partial, with the mainland of both West Indies and Philippine Islands facilitated colonization [54,55]. Intriguingly, West Indies have been identified also as source of colonization for the surrounding continents and not only as a sink [55].

Frequently lineages diversify on islands. Local lineage production can be repeated many times resulting in a radiation; radiation is sometimes associated with adaptation (adaptive radiation; Table 4). Table 1 shows that Corsica and Sardinia generally host lineages that have diversified locally. It shouldn't be overlooked, however, that only a few studies are based on a dense sampling of populations. We hence suspect the true number of genetic lineages to be under‐ estimated. Keeping in mind the limitations in terms of sampled populations of the studies listed in Table 1, it should be noted that the highest number of detected lineages within either Corsica or Sardinia is seven (cave beetles; [25]). This figure is well below the estimates reported in Table 4, which in some cases exceed 50 (i.e. Hawaiian honeycreepers). Diversification on Corsica and Sardinia was certainly triggered when they became detached from the continent. Subsequent within-island evolution has been documented molecularly but very often it did not produce appreciable morphological differences. Illustrative is the case of the subterranean isopod *Stenasellus* [33,40,56]. The few known populations of this crustacean are virtually indistinguishable morphologically and yet they are deeply divergent from one another at both mitochondrial and nuclear loci.

Given the available data it is impossible to argue in favour of a Corsica-Sardinia radiation, let alone adaptive radiation. Corsica and Sardinia are not as isolated as the majority of the other insular systems listed in Table 4. Also, they are considerably younger than Madagascar and the Chathams, continental islands that witnessed radiation (with adaptation for Madagascar). Finally, it is not unrealistic to think that when the two islands started moving away from the continent they were not as species-poor as typically are young oceanic islands, which provide plenty of ecological opportunities for immigrants. The number of fossil and extant taxa that can be brought back to the initial phases of insularity of Corsica and Sardinia (see the Ecology and Endemism section) do not depict these islands as blank slates available for colonization and subsequent diversification but rather like hosting already structured biota.

Accurate sampling at the population level should then be coupled with a thorough screen of multiple molecular markers to minimize the gap between gene and species trees. This is being made easier by the escalating availability at reduced costs of high-throughput secondgeneration sequencing. Only until a few years ago, avoiding the limitations idiosyncratic to the single locus approach (as that applied to most of the peri-Tyrrhenian organisms reviewed here) would have required considerable investments in terms of both working time and financial resources. Nowadays, we are in the position to easily isolate batteries of highly polymorphic nuclear markers (microsatellites) [58]. Multi-locus Single Nucleotide Polymor‐ phisms (SNPs) are emerging as even more powerful tools than microsatellites to infer structure of natural populations [59] and they are becoming increasingly popular as the technical challenges associated with their optimization subside. Thousands of SNPs can be identified in a relatively easy manner by using high-throughput sequencing of restriction-site-associated DNA tags (RAD tags); these markers have proved able to supply resolution sufficient to infer patterns of population relatedness [60]. For Corsica-Sardinia organisms we could take advantage of the molecular phylogenies already available. These could be used as guidelines to develop SNPs that are fixed or nearly fixed within populations but variable among them [61]. The genome-wide sample of genotype data is likely to overwhelm most of the sampling error (if any) and, hence, to produce better estimates of phylogeographic relationships without

Twenty Years of Molecular Biogeography in the West Mediterranean Islands of Corsica and Sardinia: Lessons Learnt

and Future Prospects

87

http://dx.doi.org/10.5772/55458

The flourishing of new methods to harness large numbers of tailored-to-the-scope molecular markers has proceeded in parallel with (and partially stimulated) the development of sophis‐ ticated phylogeographic analytical tools [62]. At the same time, the rise of the coalescence theory is causing a shift in the treatment of phylogeographic data from exploratory to modeldriven [62,63]. In an exploratory framework, phylogeographic inferences are based on qualitative interpretations of (often) single-locus gene genealogies. Molecular data, coupled with external information such as species ecology and landscape context, are used directly to infer the demographic history of taxa. This approach is necessary when an *a priori* phylogeo‐ graphic hypothesis for the taxon (or the area) of interest is not available and has to be generated anew. In the fortunate circumstance that such *a priori* hypotheses exist, alternative scenarios could be discriminated statistically and the one that fits the data best be chosen [64]. In doing that we obviously restrict ourselves to a subset of the whole possible scenarios but with the advantage to accurately estimate key components of the species demography and history of divergence ([62] and references therein). Under a model-driven approach, gene genealogies are not anymore central to the phylogeographic analysis but they rather represent variables for connecting data to demographic parameters under an explicit statistical coalescent model [63]. The peri-Tyrrhenian area offers a unique opportunity to use the model-driven approach and to test its strengths and weaknesses because its geological history is well understood and relatively simple, thus restricting considerably the number of possible alternative phylogeo‐ graphic scenarios, granted that the appropriate taxon is chosen (i.e. poor disperser). A further advantage is that the insular condition is per definition simpler than any continental one and, hence, complexity of models could be reduced at limited costs in terms of model misspecifi‐

any prior investment in genomic resources being necessary.

cation risk.

#### **9. Conclusions**

Studies conducted so far on organisms with a peri-Tyrrhenian distribution have confirmed the area as one of primary interest for evolutionary research. It offers, in fact, the opportunity to test hypotheses in a well-defined biogeographical context due to the uniqueness of its fauna and the detailed knowledge of its past geological evolution. Available molecular data, along with the analyses carried out *de novo* for this review, suggest that diversification was predom‐ inantly driven by vicariance. Allopatry can be safely assumed for organisms strictly bound to freshwaters (both superficial and subterranean; crustacean isopods, stoneflies and newts). Nonetheless, we do believe that these researches have only started scraping the surface of a scenario that is emerging as more complex than previously thought.

The studies reviewed here were meant to unveil relationships at the species or even at the genus level; therefore sampling designs were rarely conceived to disentangle processes below those levels. The few studies designed at the population level failed in retrieving one-landmass onemonophyletic-lineage associations (land snail *Solatopupa guidoni*, terrestrial isopod *Helleria brevicornis*, Bediagra rock lizard *Archaeolacerta bediagrae*) [26,27,37]. This suggests that disper‐ sal could dim the historical signal even in taxa that are apparently not well equipped for substantial movements over long distances. The number and kind of molecular markers used inrelationtothe evolutionarytimescale theyare tryingtotargetisyetanother criticalissue.Most ofthe studies reviewedhere arebasedona single locus (oftenmtDNA).Suchanapproachworks well to resolve old splits, but as one moves towards more recent events the information content of a single locus (which provides us with a gene tree) is rapidly blurred by the random noise typicallyassociatedwithstochasticpopulationprocesses.Hence,thediscordancebetweenwhat we have in hands (a gene tree) and what we should aim to (the species tree) is maximized.

From what emerges from this and other reviews (Table 4), it is evident that an accurate under‐ standing of evolutionary processes on islands could be better attained when co-distributed taxonomically independent taxa are investigated in a comparative manner. For the Corsica-Sardinia system we are already in a good position because the work done so far in the area has already identified a number of species that could be used for the scope and for which we have fairly accurate phylogenetic reconstructions. We would now need samplings at the popula‐ tion level to maximize the likelihood to retrieve an accurate representation of their evolution‐ ary histories. Studies conducted on insular endemisms (i.e. Galápagos tortoises, *Anolis* lizard) [47,55] have taught us that size of the island and within-island potential barriers to gene flow correlates positively with number of evolutionary independent lineages. In the case of Sardi‐ nia, the phylogeographic structure of the endemic carabid beetle *Percus strictus* [57] was found toaccuratelyreflectthesubdivisionoftheislandintothreeseparatedlandmassesatthebeginning of the Pliocene. This potential source of genetic regionalism shouldn't be overlooked when planning further genetic studies. Ideally, samplings should include multiple populations to contrast genetic structuring on either side of the putative barriers to that across them.

and Endemism section) do not depict these islands as blank slates available for colonization

Studies conducted so far on organisms with a peri-Tyrrhenian distribution have confirmed the area as one of primary interest for evolutionary research. It offers, in fact, the opportunity to test hypotheses in a well-defined biogeographical context due to the uniqueness of its fauna and the detailed knowledge of its past geological evolution. Available molecular data, along with the analyses carried out *de novo* for this review, suggest that diversification was predom‐ inantly driven by vicariance. Allopatry can be safely assumed for organisms strictly bound to freshwaters (both superficial and subterranean; crustacean isopods, stoneflies and newts). Nonetheless, we do believe that these researches have only started scraping the surface of a

The studies reviewed here were meant to unveil relationships at the species or even at the genus level; therefore sampling designs were rarely conceived to disentangle processes below those levels. The few studies designed at the population level failed in retrieving one-landmass onemonophyletic-lineage associations (land snail *Solatopupa guidoni*, terrestrial isopod *Helleria brevicornis*, Bediagra rock lizard *Archaeolacerta bediagrae*) [26,27,37]. This suggests that disper‐ sal could dim the historical signal even in taxa that are apparently not well equipped for substantial movements over long distances. The number and kind of molecular markers used inrelationtothe evolutionarytimescale theyare tryingtotargetisyetanother criticalissue.Most ofthe studies reviewedhere arebasedona single locus (oftenmtDNA).Suchanapproachworks well to resolve old splits, but as one moves towards more recent events the information content of a single locus (which provides us with a gene tree) is rapidly blurred by the random noise typicallyassociatedwithstochasticpopulationprocesses.Hence,thediscordancebetweenwhat we have in hands (a gene tree) and what we should aim to (the species tree) is maximized.

From what emerges from this and other reviews (Table 4), it is evident that an accurate under‐ standing of evolutionary processes on islands could be better attained when co-distributed taxonomically independent taxa are investigated in a comparative manner. For the Corsica-Sardinia system we are already in a good position because the work done so far in the area has already identified a number of species that could be used for the scope and for which we have fairly accurate phylogenetic reconstructions. We would now need samplings at the popula‐ tion level to maximize the likelihood to retrieve an accurate representation of their evolution‐ ary histories. Studies conducted on insular endemisms (i.e. Galápagos tortoises, *Anolis* lizard) [47,55] have taught us that size of the island and within-island potential barriers to gene flow correlates positively with number of evolutionary independent lineages. In the case of Sardi‐ nia, the phylogeographic structure of the endemic carabid beetle *Percus strictus* [57] was found toaccuratelyreflectthesubdivisionoftheislandintothreeseparatedlandmassesatthebeginning of the Pliocene. This potential source of genetic regionalism shouldn't be overlooked when planning further genetic studies. Ideally, samplings should include multiple populations to

contrast genetic structuring on either side of the putative barriers to that across them.

and subsequent diversification but rather like hosting already structured biota.

scenario that is emerging as more complex than previously thought.

**9. Conclusions**

86 Current Progress in Biological Research

Accurate sampling at the population level should then be coupled with a thorough screen of multiple molecular markers to minimize the gap between gene and species trees. This is being made easier by the escalating availability at reduced costs of high-throughput secondgeneration sequencing. Only until a few years ago, avoiding the limitations idiosyncratic to the single locus approach (as that applied to most of the peri-Tyrrhenian organisms reviewed here) would have required considerable investments in terms of both working time and financial resources. Nowadays, we are in the position to easily isolate batteries of highly polymorphic nuclear markers (microsatellites) [58]. Multi-locus Single Nucleotide Polymor‐ phisms (SNPs) are emerging as even more powerful tools than microsatellites to infer structure of natural populations [59] and they are becoming increasingly popular as the technical challenges associated with their optimization subside. Thousands of SNPs can be identified in a relatively easy manner by using high-throughput sequencing of restriction-site-associated DNA tags (RAD tags); these markers have proved able to supply resolution sufficient to infer patterns of population relatedness [60]. For Corsica-Sardinia organisms we could take advantage of the molecular phylogenies already available. These could be used as guidelines to develop SNPs that are fixed or nearly fixed within populations but variable among them [61]. The genome-wide sample of genotype data is likely to overwhelm most of the sampling error (if any) and, hence, to produce better estimates of phylogeographic relationships without any prior investment in genomic resources being necessary.

The flourishing of new methods to harness large numbers of tailored-to-the-scope molecular markers has proceeded in parallel with (and partially stimulated) the development of sophis‐ ticated phylogeographic analytical tools [62]. At the same time, the rise of the coalescence theory is causing a shift in the treatment of phylogeographic data from exploratory to modeldriven [62,63]. In an exploratory framework, phylogeographic inferences are based on qualitative interpretations of (often) single-locus gene genealogies. Molecular data, coupled with external information such as species ecology and landscape context, are used directly to infer the demographic history of taxa. This approach is necessary when an *a priori* phylogeo‐ graphic hypothesis for the taxon (or the area) of interest is not available and has to be generated anew. In the fortunate circumstance that such *a priori* hypotheses exist, alternative scenarios could be discriminated statistically and the one that fits the data best be chosen [64]. In doing that we obviously restrict ourselves to a subset of the whole possible scenarios but with the advantage to accurately estimate key components of the species demography and history of divergence ([62] and references therein). Under a model-driven approach, gene genealogies are not anymore central to the phylogeographic analysis but they rather represent variables for connecting data to demographic parameters under an explicit statistical coalescent model [63]. The peri-Tyrrhenian area offers a unique opportunity to use the model-driven approach and to test its strengths and weaknesses because its geological history is well understood and relatively simple, thus restricting considerably the number of possible alternative phylogeo‐ graphic scenarios, granted that the appropriate taxon is chosen (i.e. poor disperser). A further advantage is that the insular condition is per definition simpler than any continental one and, hence, complexity of models could be reduced at limited costs in terms of model misspecifi‐ cation risk.

About twenty years of molecular work on these fascinating Mediterranean islands have unveiled their potential as yet another natural laboratories for the study of evolutionary processes. This review, besides summing up what has already been done, wants to stimulate further research in the area. With both the methodological and analytical progresses that evolutionary biology has witnessed in recent years, it is not difficult to envision the Corsica-Sardinia system as an exceptional playground to investigate phylogeographic patterns at an unprecedented level.

[6] Alvarez W. Sardinia and Corsica, one microplate or two? Rendiconti del Seminario della Facoltà di Scienze dell'Università di Cagliari. Cagliari: Libreria Cocco; 1972. [7] Sbordoni V, Caccone A, Allegrucci G, Cesaroni D. Molecular island biogeography. In: Azzaroli A (ed.) Biogeographical aspects of insularity, Atti dei Convegni Lincei,

Twenty Years of Molecular Biogeography in the West Mediterranean Islands of Corsica and Sardinia: Lessons Learnt

and Future Prospects

89

http://dx.doi.org/10.5772/55458

[8] Bellon H, Coulon C, Edel JB. Le déplacement de la Sardigne: synthèse des donnees géochronologiques, magmatiques et paléomagnétiques. Bulletin de la Societe Géolo‐

[9] Bonin B, Chotin P, Giret A, Orsini JB. Etude du bloc corso-sarde sur documents satel‐ lites: Le problème des mouvements différentiels entre les deux iles. Revue de Geo‐

[10] Esu D, Kotsakis T. Les vertebres et les mollusques continentaux du Tertiarire de la Sardaigne: Palaeobiogeographie et biostratigraphie. Geologica Romana 1983; 22: 177-

[11] Lanza B: Sul significato biogeografico delle isole fossili, con particolare riferimento all'Arcipelago pliocenico della Toscana. Atti della Societa' Italiana di Scienze naturali

[12] Boccaletti M, Ciaranfi N, Cosentino D, Deiana G, Gelati R, Lentini F, Massari F, Mor‐ atti G, Pescatore T, Lucchi FR, Tortorici L. Palinspatic restoration and palaeogeo‐ graphic reconstruction of the peri-Tyrrhenian area during the Neogene.

[13] Carmignani L, Decandia FA, Disperati L, Fantozzi PL, Lazzarotto A, Liotta D, Oggia‐ no G. Relationships between the Tertiary structural evolution of the Sardinia-Corsi‐ ca-Provencal Domain and the Northern Apennines. Terra Nova 1995; 7: 128-137. [14] Robertson AHF, Grasso M. Overview of the late Tertiary-Recent tectonic and palaeoenvironmental development of the Mediterranean region. Terra Nova 1995; 7:

[15] Meulenkamp JE, Sissingh W. Tertiary palaeogeography and tectonostratigraphic evolution of the Northern and Southern Peri-Tethys platforms and the intermediate domains of the African-Eurasian convergent plate boundary zone. Palaeogeography

[16] Lipparini T. Per la storia del popolamento delle isole dell'Arcipelago Toscano (con‐ tributo geo-paleontologico). Lavori della Societa' Italiana di Biogeografia 1976; 5:

[17] Cherchi A, Montadert L. Oligo- Miocene rift of Sardinia and the early history of the

Palaeogeography Palaeoclimatology Palaeoecology 1990; 77: 41-50.

Palaeoclimatology Palaeoecology 2003; 196: 209-228.

western Mediterranean basin. Nature 1982; 298: 736- 739.

Volume 85. Accademia Nazionale dei Lincei. Roma; 1990. p55-83.

graphie Physique et de Geologie Dynamique 1979; 21: 147-154.

gique de France 1977; 7: 825-831.

206.

114-127.

13-25.

1984; 125: 145- 158.

### **Acknowledgements**

We wish to thank Francesca Pavesi for producing the maps inFigures 1 and 3.

### **Author details**

Valerio Ketmaier1,2 and Adalgisa Caccone3

\*Address all correspondence to: ketmaier@uni-potsdam.de

1 Institute of Biochemistry and Biology, University of Potsdam, Potsdam, Germany

2 Department of Biology and Biotechnology "Charles Darwin", University of Rome "La Sa‐ pienza", Rome, Italy

3 Department of Ecology & Evolutionary Biology, Yale University, New Haven, USA

### **References**


[6] Alvarez W. Sardinia and Corsica, one microplate or two? Rendiconti del Seminario della Facoltà di Scienze dell'Università di Cagliari. Cagliari: Libreria Cocco; 1972.

About twenty years of molecular work on these fascinating Mediterranean islands have unveiled their potential as yet another natural laboratories for the study of evolutionary processes. This review, besides summing up what has already been done, wants to stimulate further research in the area. With both the methodological and analytical progresses that evolutionary biology has witnessed in recent years, it is not difficult to envision the Corsica-Sardinia system as an exceptional playground to investigate phylogeographic patterns at an

We wish to thank Francesca Pavesi for producing the maps inFigures 1 and 3.

1 Institute of Biochemistry and Biology, University of Potsdam, Potsdam, Germany

3 Department of Ecology & Evolutionary Biology, Yale University, New Haven, USA

2 Department of Biology and Biotechnology "Charles Darwin", University of Rome "La Sa‐

[1] Baccetti B. Per una storia dell'esplorazione biogeografica delle isole che circondano la

[2] Minelli S, Ruffo S, Stoch F. Endemism in Italy. In: Ruffo S, Stoch F (eds.) Checklist and distribution of the Italian fauna. Memorie del Museo Civico di Storia Naturale di

[4] Jeannel R. Les Psélaphides de l'Afrique du Nord. Essai de Biogéographie berbère.

[5] Alvarez W. Rotation of the Corsica- Sardinia microplate. Nature 1972; 235: 103-105.

[3] Baccetti B. Biogeografia sarda venti anni dopo. Biogeographia 1980; 8: 859-870.

Memoirs du Museum d'Histoire Naturelle 1956; 14: 1-233.

unprecedented level.

88 Current Progress in Biological Research

**Acknowledgements**

**Author details**

pienza", Rome, Italy

**References**

Valerio Ketmaier1,2 and Adalgisa Caccone3

\*Address all correspondence to: ketmaier@uni-potsdam.de

Sardegna. Biogeographia 1995; 18: 1-26.

Verona. Verona; 2006. p29-31.


[18] Burgassi PD, Decandia FA, Lazzarotto A. Elementi di stratigrafia e paleogeografia nelle colline metallifere (Toscana) dal Trias al Quaternario. Memorie della Societa' Geologica Italiana 1983; 25: 27-50.

[31] Csilléry K, Blum MGB, Gaggiotti OE, François O. Approximate Bayesian Computa‐ tion (ABC) in practice. Trends in Ecology and Evolution2010; 25: 410-418.

Twenty Years of Molecular Biogeography in the West Mediterranean Islands of Corsica and Sardinia: Lessons Learnt

and Future Prospects

91

http://dx.doi.org/10.5772/55458

[32] Page RDM. Parallel phylogenies: reconstructing the history of host-parasite assemb‐

[33] Ketmaier V, Argano R, Caccone A. Phylogeography and molecular rates of subterra‐ nean aquatic Stenasellid Isopod with a peri-Tyrrhenian distribution. Molecular Ecol‐

[34] Fochetti R, Sezzi E, Tierno de Figueroa JM, Modica MV, Oliverio M. Molecular sys‐ tematics and biogeography of the Western Mediterranean stonefly genus *Tyrrheno‐ leuctra* (Insecta, Plecoptera). Journal of Zoological Systematics and Evolutionary

[35] Cobolli Sbordoni M, De Matthaeis E, Alonzi A, Mattoccia M, Omodeo P, Rota E. Spe‐ ciation, genetic divergence and palaeogeography in the Hormogastridae. Soil Biology

[36] Novo M, Almodóvar A, Fernández R, Giribet G, Díaz Cosín DJ. Understanding the biogeography of a group of earthworms in the Mediterranean basin- The phylogenet‐ ic puzzle of Hormogastridae (Clitellata: Oligochaeta). Molecular Phylogenetics and

[37] Ketmaier V, Manganelli G, Tiedemann R, Giusti F. Peri-Tyrrhenian phylogeography in the land snail *Solatopupa guidoni* (Pulmonata). Malacologia 2010; 52: 81-96.

[38] Giusti F. Biogeographical data on the malacofauna of Sardinia. Malacologia 1977; 16:

[39] Ketmaier V, Giusti F, Caccone A. Molecular phylogeny and historical biogeography of the land snail genus *Solatopupa* (Pulmonata) in the peri-Tyrrhenian area. Molecular

[40] Ketmaier V, Argano R, Cobolli M, De Matthaeis E. Genetic divergence and evolution‐ ary times: calibrating a protein clock for South- European *Stenasellus* species (Crusta‐

[41] Fochetti R, Ketmaier V, Oliverio M, Tierno de Figueroa JM, Sezzi E. Biochemical sys‐ tematics and biogeography of the Mediterranean genus *Tyrrhenoleuctra* (Plecoptera,

[42] Arbogast BS., Edwards SV, Wakeley J, Beerli P, Slowinski JB. Estimating divergence times from molecular data on population genetic and phylogenetic time scales. An‐

[43] Sanderson MJ. A non-parametric approach to estimating divergence times in the ab‐ sence of rate constancy. Molecular Biology and Evolution 1997; 14: 1218-1231.

cea, Isopoda). International Journal of Speleology 1999; 26: 63-74.

nual Review of Ecology Evolution and Systematics 2002; 33: 707–740.

Insecta). *Insect Systematics and Evolution* 2004; 35: 299-306.

lages. Cladistics 1994; 10: 155-173.

ogy 2003; 12: 547-555.

Research 2009; 47: 328-336.

Evolution 2011; 61: 125-135.

125-129.

and Biochemistry 1992; 24: 1213-1221.

Phylogenetics and Evolution 2006; 39: 439 – 451.


[31] Csilléry K, Blum MGB, Gaggiotti OE, François O. Approximate Bayesian Computa‐ tion (ABC) in practice. Trends in Ecology and Evolution2010; 25: 410-418.

[18] Burgassi PD, Decandia FA, Lazzarotto A. Elementi di stratigrafia e paleogeografia nelle colline metallifere (Toscana) dal Trias al Quaternario. Memorie della Societa'

[19] La Greca M. The insect biogeography of west Mediterranean islands. Atti dei Con‐

[20] Duggen S, Hoernle K, van den Bogaard P, Rupke L, Morgan JP. Deep roots of the

[21] Lambeck K, Antonioli F, Purcell A, Silenzi S. Sea-level change along the Italian coast for the past 10,000 year. Quaternary Science Reviews 2004; 23: 1567–1598.

[22] Smith AT, Johnston CH. Prolagus sardus. IUCN Red List of Threatened Species. Ver‐

[23] Caccone A, Milinkovitch MC, Sbordoni V, Powell JR. Molecular biogeography: using the Corsica- Sardinia microplate disjunction to calibrate mitochondrial rDNA evolu‐ tionary rates in mountain newts (*Euproctus*). Journal of Evolutionary Biology 1994; 7:

[24] Caccone A, Milinkovitch MC, Sbordoni V, Powell JR. Mitochondrial DNA rates and biogeography in European newts (genus *Euproctus*). Systematic Biology 1997; 46: 126-

[25] Caccone A, Sbordoni V. Molecular biogeography of cave life: a study using mito‐

[26] Gentile G, Campanaro A, Carosi M, Sbordoni V, Argano R. Phylogeography of Hel‐ leria brevicornis Ebner 1868 (Crustacea: Isopoda): old and recent differentiations of

[27] Salvi D, Harris DJ, Bombi P, Carretero MA, Bologna MA. Mitochondrial phylogeog‐ raphy of the Bedriaga's rock lizard, *Archaeolacerta bedriagae* (Reptilia: Lacertidae) en‐ demic to Corsica and Sardinia. Molecular Phylogenetics and Evolution 2010; 56:

[28] Yoder AD, Nowak MD. Has vicariance or dispersal been the predominant biogeo‐ graphic force in Madagascar? Only time will tell. Annual Revue of Ecology Evolution

[29] Durand JD, Bianco PG, Laroche J, Gilles A. Insight into the origin of endemic medi‐ terranean ichthyofauna: Phylogeography of *Chondrostoma* genus (Teleostei, Cyprini‐

[30] Ketmaier V, Bianco PG, Durand JD. Molecular systematics, phylogeny and biogeog‐ raphy of roaches (*Rutilus*, Teleostei, Cyprinidae). Molecular Phylogenetics and Evo‐

an ancient lineage. Molecular Phylogenetics and Evolution 2010; 54: 640-646.

chondrial DNA from Bathysciine beetles. Evolution 2001; 55: 122-130.

Geologica Italiana 1983; 25: 27-50.

sion 2011.2 [www.iucnredlist.org]

227- 245.

144.

690-697.

Systematics 2006; 37: 405-431.

lution 2008; 49: 362-367.

dae). Journal of Heredity 2003; 94: 315-328.

Messinian salinity crisis. Nature 2003; 422: 602–606.

vegni Lincei 1990; 85: 459-468.

90 Current Progress in Biological Research


[44] Sanderson MJ. Estimating absolute rates of molecular evolution and divergence times: A penalized likelihood approach. Molecular Biology and Evolution 2002; 19: 101-109.

*lus racovitzai* (Crustacea, Isopoda) from Corsica, Tuscany and Sardinia. Archiv fuer

and Future Prospects

93

http://dx.doi.org/10.5772/55458

[57] Ketmaier V, Casale A, Cobolli M, De Matthaeis E, Vigna Taglianti A. Biochemical systematics and phylogeography of the *Percus strictus* subspecies (Coleoptera, Cara‐

Twenty Years of Molecular Biogeography in the West Mediterranean Islands of Corsica and Sardinia: Lessons Learnt

[58] Santana QC, Coetzee MPA., Steenkamp ET, Mlonyeni OX, Hammond GNA, Wing‐ field MJ, Wingfield BD. Microsatellite discovery by deep sequencing of enriched ge‐

[59] Glover KA, Hansen MM, Lien S, Als TD, Hoyheim B, Skaala O. A comparison of SNP and STR loci for delineating population structure and performing individual genetic

[60] Hohenlohe PA, Bassham S, Etter PD, Stiffler N, Johnson EA, Cresko WA. Population genomics of parallel adaptation in threespine stickleback using Sequenced RAD

[61] Emerson KJ, Merz CR, Catchen JM, Hohenlohe PA, Cresko WA, Bradshaw WE, Hol‐ zapfel CM. Resolving postglacial phylogeography using high-throughput sequenc‐

[62] Garrick RC, Caccone A, Sunnucks P. Inference of population history by coupling ex‐ ploratory and model-driven phylogeographic analyses. International Journal of Mo‐

[63] Hickerson MJ, Carstens BC, Cavender-Bras J, Crandall KA, Graham CH, Johnson JB, Rissler L, Victoriano PF, Yoder AD. Phylogeography's past, present, and future: 10 years after Avise, 2000. Molecular Phylogenetics and Evolution 2010; 54: 291-301. [64] Knowles LL. The burgeoning field of statistical phylogeography. Journal of Evolu‐

[65] Avise JC, Arnold J, Ball RM, Bermingham E, Lamb T, Neigel JE, Reeb CA, Saunders NC. Intraspecific phylogeography: the mitochondrial DNA bridge between popula‐ tion genetics and systematics. Annual Review of Ecology Evolution and Systematics

[66] Nei M. Estimation of average heterozygosity and genetic distance from a small num‐

[67] Heaney LR, Rickart EA. 1990 Correlations of clades and clines: geographic, elevation‐ al and phylogenetic distribution patterns among Philippine mammals. In Peters G, Hutterer R (eds.) Vertebrates in the Tropics. Bonn: Museum Alexander Koenig; 1990.

ing. Proceedings of the National Academy of Sciences 2010; 107: 16196–16200.

assignment. BMC Genetics 2010; 11: doi: 10.1186/1471-2156-11-2

Tags. PLOS Genetics 2010; 6: doi: 10.1371/journal.pgen.1000862

bidae), endemic to Sardinia. The Italian Journal of Zoology 2003; 70: 339-346.

Hydrobiologie 2000; 147: 297-309.

lecular Science 2010; 11: 1190-1127.

tionary Biology 2004; 17: 1-10.

ber of individuals. Genetics 1978; 89: 583- 590.

1987; 18: 489–522.

p321-332.

nomic libraries. BioTechnique 2009; 46: 217-223.


*lus racovitzai* (Crustacea, Isopoda) from Corsica, Tuscany and Sardinia. Archiv fuer Hydrobiologie 2000; 147: 297-309.

[57] Ketmaier V, Casale A, Cobolli M, De Matthaeis E, Vigna Taglianti A. Biochemical systematics and phylogeography of the *Percus strictus* subspecies (Coleoptera, Cara‐ bidae), endemic to Sardinia. The Italian Journal of Zoology 2003; 70: 339-346.

[44] Sanderson MJ. Estimating absolute rates of molecular evolution and divergence times: A penalized likelihood approach. Molecular Biology and Evolution 2002; 19:

[45] Rosenberg NA, Feldman MW. The relationship between coalescence times and popu‐ lation divergence times. In Slatkin M, Veuille M. (eds.) Modern developments in the‐

[46] Thorpe RS, Reardon JT, Malhotra A. Common garden and natural selection experi‐ ments support ecotypic differentiation in the Dominican anole (*Anolis oculatus*).

[47] Parent CF, Caccone A, Petren K. Colonization and diversification of Galàpagos ter‐ restrial fauna: a phylogenetic and biogeographical synthesis. *Philosophical Transac‐*

[48] Omodeo P, Rota E. Earthworm diversity and land evolution in three Mediterranean districts. Proceedings of the California Academy of Sciences 2008; 59: 65-83.

[49] Poulakakis N, Russello M, Geist D, Caccone A. Unravelling the peculiarities of island life: vicariance, dispersal and the diversification of the extinct and extant Galàpagos

[50] Sequeira AS, Stepien CC, Sijapati M, Roque Albelo L. Comparative genetic structure and demographic history in endemic Galàpagos weevils. *Journal of Heredity* 2012; 103:

[51] Trewick SA. Molecular evidence for dispersal rather than vicariance as the origin of flightless insect species on the Chatham Islands, New Zeland. Journal of Biogeogra‐

[52] Juan C, Emerson BC, Oromí P, Hewitt GM. Colonization and diversification: towards a phylogeographic synthesis for the Canary Islands. Trends in Ecology and Evolu‐

[53] Cowie RH, Holland BS. Molecular biogeography and diversification of the endemic terrestrial fauna of the Hawaiian Islands. Philosophical Transactions of the Royal So‐

[54] Jones AW, Kennedy RS. Evolution in a tropical archipelago: comparative phylogeog‐ raphy of Philippine fauna and flora reveals complex patterns of colonization and di‐

[55] Ricklefs R, Bermingham E. The West Indies as a laboratory of biogeography and evo‐ lution. Philosophical Transactions of the Royal Society B 2008; 363: 2393-2413.

[56] Ketmaier V, Messana G, Cobolli M, De Matthaeis E, Argano R. Biochemical biogeog‐ raphy and evolutionary relationships among the six known populations of *Stenasel‐*

versification. Biological Journal of the Linnean Society 2008; 95: 620-639.

oretical population genetics. Oxford: Oxford University Press; 2002. p130-164.

101-109.

92 Current Progress in Biological Research

206-220.

phy 2000; 27: 1189-1200.

tion 2000; 15: 104-109.

ciety B 2008; 363: 3363-3376.

American Naturalist 2005; 165: 495-504.

*tions of the Royal Society B* 2008; 363: 3347-3361.

giant tortoises. Molecular Ecology 2011; 21: 160-173.


**Chapter 5**

**The Biogeography of the Butterfly Fauna of Vietnam**

Long term studies of Vietnamese Rhopalocera suggest that by using a taxonomic composition analysis of the modern fauna, with ecological and biogeographical characteristics and comparative data with butterfly faunas of adjacent regions, it is possible to offer a plausible account of the history and derivation of the Vietnamese fauna. In former works on the butterfly fauna of Vietnam and of the Oriental tropics generally, we completed the first steps in understanding possible derivation mechanisms for the group. In particular, all Vietnamese butterfly species have been classified according to their global geographical ranges (Holloway, 1973; 1974; Spitzer *et al*., 1993; Monastyrskii, 2006; 2007), from the most restricted to the most widespread (Methods). A similar approach for notodontid moths in Thailand has been adopted by Schintlmeister & Pinratana (2007). Moreover, depending on the representation of various species distribution range categories, a scheme of biogeographical zonation has been

In continuing studies on the specificity and derivation of the modern Vietnam butterfly fauna, aspects of species range configuration and other parameters of butterfly distribu‐ tions are considered in the current work. For example, it is possible to assign genera to groups according to both their overall range and variation of their species-richness across that range (Holloway, 1969, 1974) or according to representation of particular species range types within the genera (Holloway, 1998). Application of the first approach led to recogni‐ tion of several generic distribution types within the Oriental Region that provide a foundation for the discussion of species ranges presented in this paper, such as: genera with a species-richness generally distributed from Assam to Sundaland (Indo-Burmese in this paper); genera with their greatest richness in Sundaland (Sundanian in this paper); and genera with a strong centre of richness in western China and the eastern Himalaya (Sino-

and reproduction in any medium, provided the original work is properly cited.

© 2013 Monastyrskii and Holloway; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

**With a Focus on the Endemic Species (Lepidoptera)**

A.L. Monastyrskii and J.D. Holloway

http://dx.doi.org/10.5772/55490

suggested (Monastyrskii, 2006; 2007).

**1. Introduction**

Additional information is available at the end of the chapter
