**3.4. Life history traits comparison of** *Porcellio albinus* **and** *Porcellio buddelundi*

The study of life history strategies integrates physiological, morphological, and behavioral traits to explain how organisms allocate finite resources to maintenance, growth, and reproduction, under predictable and unpredictable environments [74]. Thus life history patterns, evolved by natural selection, represent an optimization of tradeoffs between growth, survival, and reproduction. One major tradeoff could be between the number of offspring produced and the amount of energy allocated to each one. The timing of the first reproduction is another tradeoff; early reproduction reduces the chances of dying without offspring, but late reproduction can provide healthier offspring or better care. Members of some species breed only once (semelparity), while members of other species can breed several times (iteroparity). The choice of the appropriate strategy may be related to the degree of habitat specialization. Habitat specialists have often shown K-selected traits, while habitat generalists have shown r-selected traits. The xeric species *P. albinus* and *P. buddelundi* well adapted to arid environment differ considerably in their life history traits. These life history traits are summarized in **Table 3**.

To shelter from the extreme heat and dryness in arid environments, *P. albinus* digs burrows, while *P. buddelundi* performs a vertical migration. Both species are iteroparous and started their breeding activity in March with two breeding seasons. The length of the reproductive activity of *P. albinus* longer than 1 month in spring and less than 1 month in autumn than that of *P. buddelundi*. *P. albinus* has a longer development time, and sexual maturity is reached late, at 9 months old, which represents more than a third (37.5%) of its lifetime. *P. buddelundi* grows faster and reaches sexual maturity at 3–3.5 months old which corresponds to almost 20% of its lifetime. In *P. albinus*, there was no difference between ages of oldest female (largest female) and the largest reproductive females. This indicates that in this species, females were able to reproduce until their death, while in *P. buddelundi*, there is a difference between largest female (18 months) and largest reproductive female (12 months) because largest females in this species were not reproductive. *P. albinus* and *P. buddelundi* have a similar length of breeding period at the first brood: 28–35 and 28–33 days, respectively (**Table 3**). Although females of *P. albinus* were larger than those of *P. buddelundi*, they have a lower fecundity range (36.3 ± 13.8 egg) and fertility (19 ± 9 mancae). *P. albinus* also showed the lower mean reproductive allocation (9.94 ± 6.04) but the higher newborn body mass (1.44 ± 0.75 mg). Only *P. albinus* which has few offspring during each reproductive event often gives extensive parental care. This species with this type of high investment strategy uses much of its energy budget to care for its offspring.

**Figure 10.** Reproductive activities of *Porcellio albinus* and *Porcellio buddelundi.*

For both species, breeding starts in March and two breeding activities are defined (**Figure 10**). The first and the most important one was in spring, from March to June in the Zarat population of *P. albinus* and from March to May in Matmata population of *P. buddelundi*. The second was in the fall during the month of September in the first population and from September to

Fecundity estimated by the number of marsupial eggs was lower in *P. albinus* (36.3 ± 13.8 eggs) than that in the *P. buddelundi* species (60.9 ± 3.5 eggs). In the latter species, Medini-Bouaziz et al. [22] have shown that fecundity increases more with increasing ovigerous female body mass in spring than in autumn. A positive correlation between ovigerous female size and

Based on the study of fertility (number of mancae released from the marsupium) and the energy allocated to reproduction for each of the two species (**Table 3**), different tradeoffs were highlighted. The pre-desert species *P. buddelundi* generates a large number of small progeny (53.13 ± 3.2 mancae; newborn body mass = 0.44 ± 0.21 mg), whereas *P. albinus* produces few

Of the two species studied, only *P. albinus* is able to provide care to his offspring. As reported by Medini-Bouaziz et al. [22], the study of the population dynamics of *P. albinus* in Zarat revealed, in all samples taken at night outside the burrows, predominance of larger specimens due to the absence of individuals whose size is smaller than 8 mm. Indeed, after the mancae release and during the first 2 months of life, newborns do not leave the family burrow. During this sensitive period, they depend on their brood-caring mother who provides

large offspring (19 ± 9 mancae; newborn body mass = 1.44 ± 0.75 mg).

October in the second one.

40 Community and Global Ecology of Deserts

**3.3. Care of progeny**

**3.2. Fecundity, fertility and reproductive allocation**

fecundity is noted in both species [22, 24].


analyze the burrowing behavior and to identify the rhythm of activity of *P. albinus*, in order to understand the behavioral mechanisms of adaptations of this species to xeric conditions.

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

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

43

Among the desert-dwelling *Porcellio* species, widespread in southern Tunisia, only *Porcellio albinus* exhibits a burrowing behavior. *Porcellio albinus* shelters from the extreme heat and dryness of its desert habitat in a burrow. One wonders how this species "chooses" the location of its burrows in this type of habitat. What are the abiotic factors that influence this choice?

To answer these questions, several sampling campaigns were carried out in the Zarat station during 2013. The density of burrows, their spatial distribution, and their orientation were studied (see [23] for further details on material and methods). The species was also observed in the field. The analysis of the data collected showed that the distribution of the burrows depends on several factors. *Porcellio albinus* prefers to dig burrows at sandy nebkhas (the mean density of burrows per nebkha was 1.27 ± 1.64 burrows m−2). This preference is justified by the nature of the soil that is easy to dig and the isopod's low ability to do work on harder soils [23, 44]. It is also explained by the sand which has a low water retention capacity associated with a lack of capillarity between the dry surface and the moisture layers which further reduces the evaporation. In each nebkha, the *P. albinus* burrows are located in a circular belt. In this belt, a preferred sector in which the burrows were grouped is oriented toward the southern direction, to avoid the prevailing wind direction E-NE at Zarat: *P. albinus,* leaving its burrow for forage stacks the sand torn from the burrow in front of the opening [44]. This sand, marked with the owner's individual-specific chemical signature, is then used as a landmark to find the burrow after excursion [44]. Thus, to regain infallibly its burrow, *P. albinus* chooses, as the location of its

In addition, *P. albinus* prefers to dig its burrow in nebkhas covered by a mixture of plants. Relating to this last factor, the high densities of burrows determined in nebkhas with a mixture of *Astragalus armatus* and *Stipagrostis pungens* indicate that these nebkhas could be con-

For this study, five burrows located in nebkhas were randomly selected every month, from July 2012 to June 2013 in the sandy coastal area of Zarat, Gabès (in the southeast of Tunisia). For each burrow, three parameters were always determined: sand depth, angle between descending the neck of burrow and horizontal, and burrow length (**Figure 11**). To study the burrow morphology of *P. albinus*, the use of paraffin casting created an in situ, internal mold

The results of this study showed that *P. albinus* is able to dig a burrow, in the habitat of Zarat, at any time of the year. All the burrows of *P. albinus* are dug toward the center of the nebkha; they were generally inclined and make an angle between descending neck of burrow and the horizontal ranging between 2 and 45°; the mean angle was about 22.2 ± 12.87°. Their depth ranged between 1 and 28 cm with a mean depth of 13.89 ± 9.43 cm. The total burrow length

**4.1. Spatial distribution of burrows**

burrows, a place sheltered from the prevailing wind.

**4.2. Burrow morphology**

sidered as a high-quality micro-ecosystem for *P. albinus* [23].

of the burrow structure. The cast is then excavated for analysis.

**Table 3.** Life history traits of the studied xeric species *Porcellio buddelundi* and *Porcellio albinus*.

All these results showed that *P. buddelundi* exhibited a set of characteristics corresponding to those of the r-strategists. In comparison, *P. albinus* displayed opposite trends that fit well with the expected characteristics of a k-strategist.
