**4. Behavioral strategies**

The general objectives of our research are oriented, in this second part, toward understanding the behavioral mechanisms involved in the adaptation of terrestrial isopods to harsh desert conditions. The study model is *P. albinus*; It is found in habitats ranging from coastal sand nebkhas and up to desert ones, hundreds of kilometers away from the sea littoral. The choice of this model is justified by its unique burrowing behavior in the genus *Porcellio* in Tunisia. Based on the knowledge acquired in the terrestrial species model *H. reaumurii,* we propose to 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.

## **4.1. Spatial distribution of burrows**

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 burrows, a place sheltered from the prevailing wind.

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

### **4.2. Burrow morphology**

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

**Life history traits** *P. buddelundi P. albinus* Burrow digging No Yes

Newborns body-mass (spring) 0.44 ± 0.21mg 1.44 ± 0.75 mg

Size of largest female 1.6 cm 2.4 cm Body-mass of largest female 210 mg –

Largest female 18 months 24 months Age at last reproduction 12 months 24 months Itero/Semelparous Iteroparous Iteroparous Breeding activity March-May March-June

Female size 0.65 cm 1.4 cm Female body-mass 41.1 mg 129 mg Female estimated age 3-3.5 months 9 months Length of breeding period (first brood) 28-33 days 28-35 days Fecundity (spring) 60.9 ± 3.5 eggs 36.3 ± 13.8 eggs Fertility 53.13 ± 3.2 mancae 19 ± 9 mancae Reproductive allocation (%) 29.06 ± 12.58 9.94 ± 6.04 Care of offspring No Yes Offspring age estimated at the end of parental care – 2 months

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

September-October September

The general objectives of our research are oriented, in this second part, toward understanding the behavioral mechanisms involved in the adaptation of terrestrial isopods to harsh desert conditions. The study model is *P. albinus*; It is found in habitats ranging from coastal sand nebkhas and up to desert ones, hundreds of kilometers away from the sea littoral. The choice of this model is justified by its unique burrowing behavior in the genus *Porcellio* in Tunisia. Based on the knowledge acquired in the terrestrial species model *H. reaumurii,* we propose to

the expected characteristics of a k-strategist.

**4. Behavioral strategies**

*Body size and newborns mass*

42 Community and Global Ecology of Deserts

*Life span (estimated age)*

*First reproduction*

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

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

**Figure 11.** Parameters used to assess the morphology of the burrows.

containing only one nesting chamber in its deep part (**Figure 12**), or of complex form, a tunnel containing two or more nesting chambers in its deep part (**Figure 13**); generally, in all casts

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

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

45

Locomotor activity of *P. albinus*, deducted from monthly field observation data on the first and the last specimens in activity outside their burrows, was studied in synchrony con with light-dark cycle. During all the sampling period from November 2012 to October 2013, *P. albinus* showed a strict nocturnal activity: only individuals whose size is equal to or exceeds 8 mm began to emerge from their burrows after dusk and return to their shelters before dawn. This circadian rhythm of *P. albinus* is regulated by the rhythmic and natural variations of the duration of the dark period; a positive correlation is observed between the circadian period of the locomotor activity of the species and the duration of the scotophase

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

studied, animals trapped in the cast were confined in the terminal part of the burrow.

**4.3. Daily locomotor activity of** *P. albinus*

**Figure 13.** Burrow with two nesting chamber.

(r = 0.874, p ≤ 0.05).

**5. Discussion**

**Figure 12.** Burrow with a single nesting chamber.

varied between 8 and 62 cm with an average burrow length of 24.04 ± 10.41 cm. The longest length of the burrow was reached in September, considered the hottest month of the year in Zarat area.

A total of 60 resin casts of the burrows of *P. albinus* were made in the coastal nebkha area of Zarat. The study of these casts showed that the burrows are either of simple form, a tunnel Behavioral and Reproductive Strategies of *Porcellio* Species (Oniscidea) in Tunisian Pre-Desert… http://dx.doi.org/10.5772/intechopen.76191 45

**Figure 13.** Burrow with two nesting chamber.

**Figure 11.** Parameters used to assess the morphology of the burrows.

44 Community and Global Ecology of Deserts

Zarat area.

**Figure 12.** Burrow with a single nesting chamber.

varied between 8 and 62 cm with an average burrow length of 24.04 ± 10.41 cm. The longest length of the burrow was reached in September, considered the hottest month of the year in

A total of 60 resin casts of the burrows of *P. albinus* were made in the coastal nebkha area of Zarat. The study of these casts showed that the burrows are either of simple form, a tunnel containing only one nesting chamber in its deep part (**Figure 12**), or of complex form, a tunnel containing two or more nesting chambers in its deep part (**Figure 13**); generally, in all casts studied, animals trapped in the cast were confined in the terminal part of the burrow.

#### **4.3. Daily locomotor activity of** *P. albinus*

Locomotor activity of *P. albinus*, deducted from monthly field observation data on the first and the last specimens in activity outside their burrows, was studied in synchrony con with light-dark cycle. During all the sampling period from November 2012 to October 2013, *P. albinus* showed a strict nocturnal activity: only individuals whose size is equal to or exceeds 8 mm began to emerge from their burrows after dusk and return to their shelters before dawn. This circadian rhythm of *P. albinus* is regulated by the rhythmic and natural variations of the duration of the dark period; a positive correlation is observed between the circadian period of the locomotor activity of the species and the duration of the scotophase (r = 0.874, p ≤ 0.05).
