**5. Discussion**

According to our results, among terrestrial isopods dwelling in xeric, semiarid, and arid habitats [75], the genus *Porcellio* with five species in Tunisia [76] ranks second after the genus *Hemilepistus* with nine species [50]. The *Porcellio* species discussed in this chapter showed a geographical distribution which depends on many ecological factors mainly climatic and orographic and of less importance edaphic. All of them were distributed south of the Tunisian Dorsal; the distribution of both xeric species *P. simulator* and *P. buddelundi* was limited, in the North, by the 500 mm isohyets. The distribution of *P. olivieri* was restricted to arid environments, while the rare species *P. albicornis* and *P. albinus* tolerate remarkably high temperatures and were able to reach the Sahara. Woodlice showing comparably effective adaptations to desert environments are *H. reaumurii* [26] and *Venezillo arizonicus* [77]. The latter two species possess protection against water loss through the cuticle which corresponds to a thicker and more calcified cuticle, thus reducing water evaporation in arid environments [53] and indicating that permeability to water has been reduced during adaptation to habitats with periodically or permanently low water availability. These physiological adaptations were, however, insufficient for coping with the harsh conditions of desert environments.

*H. reaumurii* and other desert species from the Middle East characterized by a single spring or autumn breeding season [45, 72, 83]. Our results about reproductive traits of both species showed that *P. buddelundi* exhibited a set of characteristics corresponding to those of the r-strategists: a shorter life span, a smaller size, early sexual maturity, higher fertility, and a reproductive allocation to maximize brood size. In comparison, *P. albinus* displayed opposite trends to which parental care was added which corresponds well to expected characteristics of a k-strategist. These results reinforce the Sutton et al. [25] observations and those of Quadros et al. [74] by showing that *P. buddelundi* and *P. albinus* have opposite life history traits that correspond to their degree of habitat specialization: the steneodynamic species corresponds to a K-selected habitat specialist and the eurydynamic species to an r-selected habitat generalist. According to the study of life history traits of the two species, *P. albinus* with its capacity to dig burrows displays a fairly developed social behavior compared to other species of the genus which allowed him to be the most advanced of the *Porcellio* genus

Behavioral and Reproductive Strategies of *Porcellio* Species (Oniscidea) in Tunisian Pre-Desert…

http://dx.doi.org/10.5772/intechopen.76191

47

The quite diverse *Porcellio* genus in arid regions is an integral part of pre-desert macro-arthropod communities. In a single square meter of soil of desert ecosystems, as many as four species of *Porcellio* may be collected [76]. Under comparable conditions where earthworms are absent, ant communities may comprise up to 28 species [84]. All of these *Porcellio* species as many other terrestrial isopods [7, 13–15, 17], termites, and ants contribute to the consumption and mineralization of a significant part of litter (litter transformers) in arid areas [1, 16, 85]; they build holorganic structures (their fecal pellets) that serve as incubators for microbial activities [Lavelle, 1996]. The burrowing and digging activity of *P. albinus* as well as the vertical migration of the other pre-desert species of the genus *Porcellio* may influence the infiltration properties of the soil and, thus, on the whole process of water movement within the soil profile and on the subsurface flow process. This was studied in the genus *Hemilepistus* from arid region of southeastern Russia, at an estimated population density of 1.4 million individuals ha−1; the animals were deemed capable of transporting, from a depth of up to 1 m to the surface, 5–6 tonnes of soil, of a different granulometrical and chemical composition, annually [86]. Macroporosity related to the activity of other arthropod groups such as ants and termites demonstrated prodigious earth-moving abilities, which may contribute importantly to soil formation. For example, in the Chihuahuan desert, four species of ants which have relatively short-lived colonies transported between 21 and 86 kg ha−1 yr.−1 of subsurface soil to the surface, and some species of termites produce erodible surface galleries different in composition from the surface soil [16]. As result of "ecosystem engineers'" work, topsoil was improved and was able to support

Future prospects, which could be considered from our research and have led to the following

• The reproductive phenology of desert *Porcellio* species other than *P. buddelundi* and *P. albinus*,

such as *P. olivieri* and *P. simulator*, and their reproductive strategies.

but remain less evolved than *H. reaumurii*.

a more diverse and dense vegetation.

**6. Future prospects**

questions, are as follows:

To survive in the harsh conditions of the desert and escape the danger of desiccation, the *Porcellio* survive the high temperature during the day in summer and autumn, either by vertically migrating (*P. buddelundi*, *P. simulator*, *P. olivieri*, and *P. albicornis*) or in a burrow which *P. albinus* dig in loose soil at any time of the year unlike *H. reaumurii* [26] who dig new burrows only in early spring. The maximum density of burrows, in nebkhas, was recorded in the southern sector to avoid the main wind direction [23]. *P. albinus* showed no daily activity; all year long it is a strictly nocturnal species. Individuals whose size is more than 8 mm started their activity after dusk to forage and return to their shelter before dawn. This nycthemeral rhythm of *P. albinus* is regulated by the rhythmic and natural variations of the duration of the scotophase. The circadian rhythm in *P. albinus* is probably generated by an internal clock that is synchronized to light-dark cycles and other cues in an organism's environment; this intrinsic timer was apparent in *Tylos europaeus* [78] and *H. reaumurii* [79, 80]. Nocturnal activity of *P. albinus* was correlated to a lower evaporation rate. In burrows, *P. albinus* breed and take care of their offspring for about 2 months [22]. Given the importance of a burrow for this species, the sand, scraped from the burrow and piled outside, when the member of a family started their activity, was used to close the burrow during the day probably as an antipredatory strategy. In addition, *P. albinus* used mechanisms similar to those found in *H. reaumurii* [55, 81], using combination of celestial mechanisms and the sand scraped from the burrow to relocate the burrows after foraging [44]. Burrows of *P. albinus*, in nebkhas of Zarat area, showed a simple or complex tunnel with one nesting chamber in its deep part for the first and with two nesting chamber for the second. *P. albinus'* burrow length reached its maximum in September.

In addition to behavioral adaptations, the pre-desert and desert species of *Porcellio* have developed reproductive strategies that allow them to better succeed in the colonization of arid environments. The study of the reproductive phenology of the populations of the two *Porcellio* species from pre-desert ecosystems in Tunisia allowed to bring new fundamental knowledge on the dynamics of these populations as well as on the reproductive traits of the xeric *Porcellio* species *P. albinus* and *P. buddelundi*. The reproduction of these two iteroparous *Porcellio* was characterized by two breeding seasons: the most important one in spring and the other in autumn distinctly separated by a sexual rest phase [22, 24]. This reproductive phenology differs from that of (1) mesic species such as *P. variabilis* [33, 82], which generally shows a breeding period spread over several months followed by a sexual rest and (2) *H. reaumurii* and other desert species from the Middle East characterized by a single spring or autumn breeding season [45, 72, 83]. Our results about reproductive traits of both species showed that *P. buddelundi* exhibited a set of characteristics corresponding to those of the r-strategists: a shorter life span, a smaller size, early sexual maturity, higher fertility, and a reproductive allocation to maximize brood size. In comparison, *P. albinus* displayed opposite trends to which parental care was added which corresponds well to expected characteristics of a k-strategist. These results reinforce the Sutton et al. [25] observations and those of Quadros et al. [74] by showing that *P. buddelundi* and *P. albinus* have opposite life history traits that correspond to their degree of habitat specialization: the steneodynamic species corresponds to a K-selected habitat specialist and the eurydynamic species to an r-selected habitat generalist. According to the study of life history traits of the two species, *P. albinus* with its capacity to dig burrows displays a fairly developed social behavior compared to other species of the genus which allowed him to be the most advanced of the *Porcellio* genus but remain less evolved than *H. reaumurii*.

The quite diverse *Porcellio* genus in arid regions is an integral part of pre-desert macro-arthropod communities. In a single square meter of soil of desert ecosystems, as many as four species of *Porcellio* may be collected [76]. Under comparable conditions where earthworms are absent, ant communities may comprise up to 28 species [84]. All of these *Porcellio* species as many other terrestrial isopods [7, 13–15, 17], termites, and ants contribute to the consumption and mineralization of a significant part of litter (litter transformers) in arid areas [1, 16, 85]; they build holorganic structures (their fecal pellets) that serve as incubators for microbial activities [Lavelle, 1996]. The burrowing and digging activity of *P. albinus* as well as the vertical migration of the other pre-desert species of the genus *Porcellio* may influence the infiltration properties of the soil and, thus, on the whole process of water movement within the soil profile and on the subsurface flow process. This was studied in the genus *Hemilepistus* from arid region of southeastern Russia, at an estimated population density of 1.4 million individuals ha−1; the animals were deemed capable of transporting, from a depth of up to 1 m to the surface, 5–6 tonnes of soil, of a different granulometrical and chemical composition, annually [86]. Macroporosity related to the activity of other arthropod groups such as ants and termites demonstrated prodigious earth-moving abilities, which may contribute importantly to soil formation. For example, in the Chihuahuan desert, four species of ants which have relatively short-lived colonies transported between 21 and 86 kg ha−1 yr.−1 of subsurface soil to the surface, and some species of termites produce erodible surface galleries different in composition from the surface soil [16]. As result of "ecosystem engineers'" work, topsoil was improved and was able to support a more diverse and dense vegetation.
