Chemosensory proteins as putative semiochemical carriers in the desert isopod Hemilepistus reaumurii.

The order Isopoda contains both aquatic and terrestrial species, among which Hemilepistus reaumurii, which lives in arid environments and is the most adapted to terrestrial life. Olfaction has been deeply investigated in insects while it has received very limited attention in other arthropods, particularly in terrestrial crustaceans. In insects, soluble proteins belonging to two main families, Odorant Binding Proteins (OBPs) and Chemosensory Proteins (CSPs), are contained in the olfactory sensillar lymph and are suggested to act as carriers of hydrophobic semiochemicals to or from membrane-bound olfactory receptors. Other protein families, namely Nieman-Pick type 2 (NPC2) and Lipocalins (LCNs) have been also reported as putative odorant carriers in insects and other arthropod clades. In this study, we have sequenced and analysed the transcriptomes of antennae and of the first pair of legs of H. reaumurii focusing on soluble olfactory proteins. Interestingly, we have found 13 genes encoding CSPs, whose sequences differ from those of the other arthropod clades, including non-isopod crustaceans, for the presence of two additional cysteine residues, besides the four conserved ones. Binding assays on two of these proteins showed strong affinities for fatty acids and long-chain unsaturated esters and aldehydes, putative semiochemicals for this species.

Physiological and behavioral responses of Orchestia gammarellus (Amphipoda, Talitridae) towards trace elements contamination soil.

Effects of trace elements on the hepatopancreas ultrastructure and on the locomotor activity rhythm were investigated in the amphipod talitrid Orchestia gammarellus collected from Bizerte lagoon banks situated in the north of Tunisia. Animals were exposed to a series of contaminated soil with different concentrations of cadmium and zinc. The locomotor activity rhythm was studied under constant darkness. Histopathological analysis showed that the trace elements, especially the Cd, induced significant changes in the morphology and in the ultrastructural organization of hepatopancreatic cells. The significant alterations obtained were dose dependent. Concerning the behavioral response, results revealed the presence of two components whatever the experimental conditions. In addition, a great inter-individual variability of the locomotor rhythm was observed. Patterns were in majority bimodal for the control individuals and became unimodal and multimodal when exposed under Cd and Zn, respectively. Furthermore, ultradian and circadian periods were determined. The circadian period lengthened after Zn exposure. In addition, the locomotor activity rhythm was more stable for control individuals. However, those exposed to Cd were less active.

Effects of Heavy Metals Artificial Contamination on Porcellio laevis (Latreille, 1804) (Crustacea: Isopoda: Oniscidea).

This study aimed at determining the competition of cadmium (Cd), lead (Pb), zinc (Zn) and copper (Cu) on their assimilation, on the food consumption and the growth of terrestrial isopod Porcellio laevis. Individuals were exposed to artificially contaminated litter of Quercus for 4 weeks and were weekly weighed. At the end of the experiment, the concentration of Cd, Pb, Zn and Cu in individuals were measured by atomic absorption spectrometry. Biological parameters such as growth, and bioaccumulation factor (BAF) were calculated and results from the various treatments were compared. Depending on metals, weight loss or gain were recorded for isopods during the four weeks of exposure. A weight loss was measured on individuals exposed to Cd-contaminated litter whereas a weight gain was highlighted for those exposed to the Zn-contaminated litter. BAF values revealed that P. laevis was macroconcentrator of Zn and Cu and deconcentrator of Cd and Pb.

Measure of environmental stress on Porcellio laevis Latreille, 1804 sampled near active Tunisian industrial areas.

This study aimed to observe the type of asymmetry exhibited by Porcellio laevis sampled from 15 sites belonging to Tunisian industrialized areas. Physicochemical parameters such as pH, organic matter and CaCO3 contents were measured in soils. Moreover, Cd, Pb, Zn, and Cu concentrations were determined in both soils and woodlice. Additionally, 10 metrical traits were measured to evaluate the type of asymmetry on individuals: the basis, the second and the third articles of the antenna, the first article of the flagellum of the antenna and the merus, the carpus, and the propodus of the sixth and the seventh pereopods. Among the 531 measured individuals, 432 exhibited fluctuating asymmetry (FA) while the remaining individuals exhibited antisymmetry or directional asymmetry. The data obtained were analyzed using a multivariate statistical analysis. Contrary to our hypothesis, the results showed that individuals from contaminated sites have a low FA level, whereas those from uncontaminated sites have a high FA level, particularly females but with some exceptions. Variations in FA level in the traits and populations studied and its usefulness as a stress indicator were discussed.

Hierarchical organization of the cuticle of the subsocial desert isopod, Hemilepistus reaumurii.

The crustacean cuticle is a hierarchically organised material which provides protection and sites for muscle attachment. The physical properties of this exoskeleton envelope are adapted to the function and the eco-physiological requirements of the species. This paper aimed to study, using the TEM, the structure of the tubercle and the tergite cuticle of the arid species Hemilepistus reaumurii in a comparison with a subhumid isopod in order to relate some peculiar features to an adaptive process to environmental constraints. Results showed that wild H. reaumurii cuticles were twice as thick in comparison with Porcellio variabilis which is a subhumid zone isopod. It is suggested therefore that the thick cuticle of wild H. reaumurii can be an adaptation to terrestrial life and a protection against osmotic stress and water loss in an arid environment. In addition the inside of the tubercle showed a high number of lipid droplets stacked into an adipose tissue which suggest that tubercles were used for storage for nutritive material in wild H. reaumurii.