Breeding and population dynamic of Porcellionides sexfasciatus (Crustacea, Isopoda, Oniscidea).

The biology and the population dynamics of Porcellionides sexfasciatus Budde–Lund (1879) were studied on a field and carried out at Garat Naˆam (Kasserine, Tunisia) from July 1996 to June 1998. The reproduction exhibited a seasonal pattern extending from February/March to October/November. The juveniles appeared in the population from April to November. Size frequency distributions were analysed and 14 cohorts were recognised during the sampling period. Six cohorts were identified at the first sampling and eight new ones on the other samplings. Among these latter cohorts, three were tracked till they disappeared. Minimum average length of new cohorts ranged from 3.07 ± 0.35 mm to 3.47 ± 0.2 mm. Maximum average length of cohorts was 10.42 mm. P. sexfasciatus is a semi-annual species (females producing two or three broods per year), with iteroparous and amphogenes females (females reproducing twice or more in their life and producing both males and females), and bivoltine life cycle (two generations per year). The females are able to produce two broods, in the laboratory, without new mating. Fecundity and fertility, corresponding to the number of eggs or embryos per brood, appeared positively correlated with females’ size. Although oscillating throughout the year, the sex ratio was often in equilibrium. [Copyright &y& Elsevier]