Hajer Khemaissia

Amphipod diversity at three Tunisian lagoon complexes in relation to environmental conditions

The amphipod communities of different wetland types belonging to three coastal lagoons complexes in northern Tunisia, Ichkeul (37°06′ to 37°14′ N, 09°35′ to 09°56′ E), Ghar El Melh (37°06′ to 37°10′ N, 10°08′ to 10°14′ E) and Korba (36°34′ to 36°38′ N, 10°52′ to 10°54′ E), were studied with respect to species composition and abundance and their relationship with abiotic environmental characteristics, namely air and soil temperature and humidity, soil grain size and the soil content of organic matter and heavy metals. Both highest abundance and highest diversity of amphipods were observed in the lagoon complex of Ichkeul, which is characterized by higher contents of organic matter but also by higher heavy metal concentrations in the soil than the lagoon complexes of Ghar El Melh and Korba. Although amphipod abundance does not seem to linearly depend on environmental parameters, unimodal Canonical Correspondence Analysis suggests that amphipod abundance is related to grain size of the soil, to the soil content of organic matter and to several heavy metals.

Towards a characterization of the locomotor activity rhythm of the desertic species Porcellio olivieri (Crustacea, Isopoda) from Gabes (South of Tunisia)

Abstract The locomotor activity rhythm of the isopod, Porcellio olivieri, was investigated in Gannouch site in the south of Tunisia. The rhythm was monitored under constant temperature in individual animals in winter under two simultaneous regimens: the light–dark (LD) cycle and the continuous darkness (DD). Results revealed that whatever regimens, actograms, and mean activity curves showed that specimens of P. olivieri concentrated their activity during the experimental and subjective night. The species exhibited a locomotor rhythm period significantly shorter under LD (T = 23h13 ± 0h44) than DD (τ = 24h28 ± 0h58). However, the locomotor activity rhythm was less stable and the individuals were significantly more active under entraining conditions than constant darkness. The activity pattern of this species will be discussed as an adaptative strategy to respond to environmental conditions.

Life history of the sandy beach amphipod Deshayesorchestia deshayesii (Crustacea: Talitridae) from Bizerta beach (North of Tunisia)

Population dynamics and reproductive activity of the amphipod Deshayesorchestia deshayesii were studied monthly from June 2007 to December 2008 in Bizerta beach. During this period, 6577 specimens of D. deshayesii were identified; the sex ratio was female biased, with a mean of the monthly sex ratios equal to 0.21 ± 0.12. Due to the absence of embryos or eggs in the female brood pouches and juveniles in the samples, results suggested that the reproductive season extended from April to November, with a sexual resting period during winter from December to March. Brood size varied between 4 and 17 eggs and fecundity appeared to be correlated with female size. Six cohorts were identified on the first sampling date. Additionally, 12 new cohorts were detected during the study period. Life span was estimated at 5–7 months depending on the time of birth. Cohorts that appeared at the beginning of the reproductive period tended to have shorter lives than those born later in the season. These results suggest that D. deshayesii can be considered as a semi-annual species, with iteroparous females.

Cuticular differences of the exoskeleton relative to habitat preferences among three terrestrial isopods

Terrestrial isopods have adapted to land life by diverse morphological, physiological and behavioral changes. Isopod species exhibit a large variety of preferences ranging from moist to dry habitats. Isopod cuticle is an interesting model for studying adaptations to terrestrial life. The cuticle consists of a hierarchically organized material which provides protection and sites for muscle attachment. The present paper aimed to investigate the structure of the cuticle in three isopod species in order to relate some peculiar features to an adaptive process to environmental constraints. Results showed that general thickness of Ligia italica cuticle was quite similar to that observed in Porcellio lamellatus. Nevertheless, this cuticle was half as thick as in Porcellio laevis. Although the positive relationship found between total body lengths and the total thickness of the cuticle, the exocuticle did not show any differences between the three species. However, it is the development of a thicker endocuticle in P. laevis which make its total cuticle thickness more important.

Heavy Metals Assessment and Their Effects on the Hepatopancreas in Orchestia montagui (Amphipoda, Talitridae)

This study was designed to evaluate the copper and zinc bioaccumulation in Orchestia montagui Audouin, 1826 which was exposed to a contaminated soil during three weeks and to determine the ultrastructural changes in the hepatopancreas of this species. Individuals were weekly weighed and the metals body burdens were determined at the end of the experiment. Furthermore, the bioaccumulation factor (BAF) was calculated showing that this species is considered as a macroconcentrator of these two metals. The highest concentrations of copper and zinc induced significant changes in the ultrastructural organization of S and B cells in the hepatopancreas.

Photoperiod and male-presence effects on the onset of reproduction of Porcellio laevis (Oniscidea)

Abstract A laboratory survey was done to study both day length and male effect on the reproduction of Porcellio laevis Latreille, 1804. Specimens were maintained in six climatic chambers at different photoperiods [Light: Dark (LD) 0: 24, 4:20, 8:16, 12:12, 14:10, 16:8 and 24:0] at constant temperature of 20 ± 1 °C. The characterization of photoperiodic induction on the onset of reproduction in P. laevis females showed that those maintained under LD 16: 8 started reproduction after a delay of 50.27 ± 5.56 days and can perform up to four successive parturial moults. However, females maintained under constant darkness entered in reproduction after 136 ± 5.50 days and underwent only one parturial moult. To evaluate the male-effect on the onset of reproduction, different experiments were conducted highlighting that male presence speeds up the lag-time of females maintained at LD 16:8. We can conclude that long photophases, especially LD 16:8, and male presence stimulate the onset of reproduction.