Anas Ayari

Seasonal variation of locomotor activity rhythm of Orchestia gammarellus in the supralittoral zone of Ghar Melh lagoon (North-East of Tunisia)

Locomotor activity rhythm is recorded in individual animals of O. gammarellus from the supralittoral zone of the old harbor of Ghar El Melh lagoon. The rhythm was investigated over the four seasons under two simultaneous experimental regimens; during the first week, animals are kept in light–dark cycle (nLD) in phase with natural diel cycle. During the second week, animals are maintained in constant darkness (DD). Analysis of actograms and waveform curves showed globally that individuals of O. gammarellus concentrated their activity during the experimental and subjective night, respectively during the first and second week of experiment. In addition, animals exhibited circadian and ultradian components. Under light–dark cycle, period is significantly shorter in autumn (τ LD = 23h43′ ± 0h34′) than in the other seasons. Whereas, under constant darkness, the situation is reversed and we noted that the longest circadian period is observed in autumn (τ DD = 26h ± 1h28′). The study of the mean activity times calculated for four seasons showed that whatever the regimen imposed, the most important activity of individuals, observed during autumn, is equal to 15 h 30′ ± 3h24′ and 14h40′ ± 1h21′ under light–dark cycle and constant darkness respectively. In addition, the locomotor activity rhythm is more stable in summer whatever the regimen is.

Effect of age, sex, and mutual interaction on the locomotor behavior of Orchestia gammarellus in the supralittoral zone of Ghar El Melh lagoon (Bizerte, Tunisia)

Freshly collected individuals of Orchestia gammarellus from the supralittoral zone of Ghar El Melh lagoon (Northern of Tunisia) were housed in spring in a controlled-environment cabinet. Locomotor activity rhythm of this species was recorded in spring, at a constant temperature of 18 ± 0.5 °C. In the first experiment, juveniles and adults specimens were kept under light-dark cycle in phase with the natural diel cycle. In the two other experiments (males/females and mixed/unmixed groups), individuals of O. gammarellus were maintained under constant darkness. According to double-plotted actograms, waveforms and periodogram analysis, results revealed different locomotor pattern. However, locomotor rhythm of juveniles was more stable than adults. Also, the locomotor activity rhythm of groups was more defined than that of the isolated individuals. Moreover, the activity of mixed groups as well as unmixed groups was more pronounced than the activity of the isolated individuals. Furthermore, results showed no significant difference between locomotor rhythm pattern of males and females of this species.

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.

Endogenous activity rhythm in Talitrus saltator, Britorchestia brito (Crustacea, Amphipoda) and Tylos europaeus (Crustacea, Isopoda) from Barkoukech Beach (Tabarka, Tunisia)

The locomotor activity rhythm of three supralittoral crustacean species, Tylos europaeus (terrestrial isopod) and Britorchestia brito and Talitrus saltator (amphipod, Talitridea), was investigated in Barkoukech Beach. The rhythm was monitored in individual animals in spring under continuous darkness and constant temperature. Results revealed that whatever the species, actograms and mean activity curves showed that specimens of T. europaeus and T. saltator concentrated their activity during the subjective night; whereas, B. brito concentrated its activity during the subjective day. The three species exhibited a circadian locomotor rhythm with mean circadian period, respectively, equal to 24h41′ ± 0h44′, 24h46′ ± 0h55′ and 25h21′ ± 1h16′. The most stable locomotor rhythm was found in T. saltator (0.444 ± 0.246). Furthermore, individuals of T. europaeus were significantly more active (10h47′ ± 2h52′) than the two amphipods. Differences in the activity patterns of the three species will be discussed as an adaptative strategy to respond to interspecific competitive interactions.

Locomotor activity patterns of two sympatric species Orchestia montagui and Orchestia gammarellus (Crustacea, Amphipoda)

Freshly adult individuals of two sympatric species, Orchestia gammarellus and Orchestia montagui, collected in spring from the supralittoral zone of Bizerte lagoon (Northern of Tunisia) at Menzel Jemil, were housed in a controlled environment cabinet. Locomotor activity rhythm was recorded in isolated individuals and groups by infrared actograph every 20 min by a data-logger, at a constant temperature of 18 ± 0.5 °C under constant darkness. According to double-plotted actograms and waveform curves, results showed the presence of two different locomotor patterns; in fact, individuals of O. gammarellus concentrated their activity during the hours of subjective night, whereas O. montagui were active during the subjective night and beyond the subjective dawn. Furthermore, whatever the species studied, periodogram analysis indicated a distinct circadian pattern of activity. Moreover, whatever the experiment condition is, the most clearly defined rhythms were found in O. gammarellus. In contrary to O. gammarellus, the group effect on the locomotor rhythm parameters seems to be less marked in O. montagui. On the other hand, a highly inter-individual variability was observed in the activity time for these two species and especially for O. montagui groups.

Locomotor activity pattern in pairs of the subsocial desert isopod Hemilepistus reaumurii

Abstract Locomotor activity rhythm of fresh adult of H. reaumurii was recorded in pairs with ovigerous and with non-ovigerous females. According to double-plotted actograms and waveform curves, results showed the presence of different locomotor patterns. In fact, locomotor profiles of pairs with ovigerous females were mainly bimodal whatever the recording conditions, whereas locomotor patterns were trimodal in pairs with non-ovigerous females. Results showed also that locomotor activity rhythm was more stable in the presence of the synchronizer (nLD cycle) than in constant darkness whatever the recording type. Moreover, the most important stability of the locomotor rhythm was observed under constant darkness and individuals were more active in pairs with ovigerous females than in pairs with non-ovigerous females.

Effect of light intensity on the locomotor activity rhythm of Orchestia montagui and Orchestia gammarellus from the supralittoral zone of Bizerte lagoon (North of Tunisia)

Locomotor activity rhythm of Orchestia montagui and Orchestia gammarellus was investigated in populations from the supralittoral zone of Bizerte lagoon. The rhythm was recorded in individual animals in spring, firstly under continuous light with two simultaneous luminous intensities (5 and 140 lux) and secondly under continuous light with four different luminous intensities (5, 35, 75, 140 lux). Thirty specimens were tested for each experiment and for each species. Results revealed that whatever the species and the luminous intensity imposed, actograms showed a clear drift to the right lengthening the circadian period day after day. On the other hand, under continuous light with different luminous intensities, circadian periods determined by periodogram analysis decreased with increasing of luminous intensity for O. montagui whereas for O. gammarellus, circadian period lengthened with increasing of luminous intensity. Concerning ultradian period, it increased with luminous intensity whatever the species studied. Moreover, the stability was important under 5 lux for O. montagui and 140 lux for O. gammarellus. In addition, the study of the mean activity times calculated for these two species showed that the most important activity of individuals was observed under 75 lux for O. montagui and under 140 lux for O. gammarellus.

Seasonal changes of locomotor activity patterns in the desert isopod Hemilepistus reaumuri

The locomotor activity rhythm of the desert woodlouse Hemilepistus reaumurii was monitored as individuals over the four seasons, under entraining and constant darkness conditions. Results indicated that individuals exhibited an endogenous rhythm of locomotor activity with a circadian period longer in spring than the other seasons whatever the regimen. Due to the important inter-individual variability, no significant difference in period was found between seasons as well as between regimens. Periodogram analysis revealed also an ultradian period around 12 h. Activity was mostly confined to the hours of the photophase or to those of subjective day. The activity pattern showed two main peaks. This bimodal circadian rhythm persisted for as long as the experiments were run, and was clearer in summer and autumn than in winter. The most clearly defined rhythms were found in spring and summer recordings, respectively, under entraining and free running conditions. The variation of activity patterns according to the seasons will be discussed.

Effects of light pulses on the locomotor activity rhythm of Orchestia montagui (Amphipoda, Talitridae)

Abstract Animals of the amphipod Orchestia montagui are kept in constant darkness with two short light pulses. One pulse is applied at the beginning of subjective night (around the dusk) and the other one at the end of subjective night (around the dawn). The pulse duration is estimated in the order of one or two hours around the dusk as well as the dawn. The locomotor activity rhythm was monitored in individual animals in summer under constant temperature. Results revealed that whatever the experimental conditions, under continuous or interrupted darkness by pulses, two endogenous components have been highlighted. In fact, Periodogram analysis showed the presence of ultradian and circadian periods around 12 and 24 h, respectively. The shortest circadian period and the most important inter-individual variability was observed under pulse of 2 h around the dusk with mean value equal to τDD+pulse = 24h38′ ± 4h34′. The activity profiles are in majority unimodal. Moreover, the most activity peak showed a slipping of its location from the middle of subjective night under constant darkness to the middle of subjective day under pulse. Globally, the locomotor activity rhythm of O. montagui was better defined under pulses and specimens were significantly more active under continuous darkness. Moreover, a great variability around the activity time was observed especially with pulse of 1 h.

Locomotor behaviour in males, females and groups of Orchestia montagui (Amphipoda, Talitridae) in the supralittoral zone of Bizerte lagoon

Abstract Locomotor activity rhythm of Orchestia montagui was investigated under constant darkness in a population collected in spring from the supralittoral zone of Bizerte lagoon (northern region of Tunisia) at Menzel Jmil in spring. This rhythm was recorded in individual and groups of animal by infrared actography every 20 min by multichannel data loggers, at a constant temperature of 18 ± 0.5 °C. According to double-plotted actograms, wave forms and periodogram analysis, results revealed different locomotor pattern. However, locomotor activity rhythm of males was more stable than females. Furthermore, the mortality was statistically higher in unmixed groups than in mixed groups.