Changes in life history characteristics of Porcellio laevis (Isopoda: Oniscidea) along a cadmium pollution gradient in Sfax (Central Tunisia)

Abstract

This study aimed to determine the effect of cadmium pollution on some life history traits of Porcellio laevis populations sampled along a contamination gradient in the region of Sfax (central Tunisia). To characterize each population, woodlice were collected in the spring and parameters such as the number of individuals, sex-ratio, body length and cephalothorax width of the different categories of individuals were determined. Since the sampling period coincided with the reproduction period of the species, number and diameter of eggs, embryos, and mancas were counted and measured for ovigerous females of each of the studied population. Relative growth was estimated using a morphometric relationship between the body length and the cephalothorax width to determine the type of relationship (isometric/allometric). The number of eggs, embryos and mancas varied between the sampled populations and ranged between 13.25 ± 7.18 and 58.85 ± 36.37; 25 ± 8.71 and 40.9 ± 11.47; 11.5 ± 7.77 and 29 mm, respectively. The mean size of eggs, embryos and mancas ranged between 0.491 ± 0.077 and 0.558 ± 0.098 mm, 0.697 ± 0.070 and 0.918 ± 0.206 mm, and 0.945 ± 0.248 and 1.554 ± 0.236 mm, respectively. Body length, cephalothorax width, eggs and embryos sizes, were lower in the population sampled from the most polluted site compared to the other populations. Additionally, based on the Pearson’s correlation, negative and non-significant correlations were found between the number and the size of the different reproductive stages (eggs, embryos and mancas), and cadmium soil content. The morphometric parameters showed a significant correlation between the body length and the cephalothorax width, and globally a negative allometry was observed.