Raja Jelassi

Endogenous locomotor activity rhythm of two sympatric species of Talitrids (Crustacea, Amphipoda) from the supralittoral zone of Bizerte lagoon (Northern Tunisia)

Samples of fresh adults of two sympatric species, Orchestia montagui and Orchestia gammarellus, from the supralittoral zone of Bizerte lagoon (Northern of Tunisia) at Menzel Jmil (37°13′8″N 09°55′1″E) were housed in a controlled environment cabinet. Locomotor activity rhythms were recorded in individual animals in spring, at a constant temperature of 18 ± 1°C; firstly, under light–dark (LD) cycle and constant darkness (DD), and secondly, under continuous light with high (140 lux) and low (5 lux) luminous intensities during the first and second week, respectively. Results showed that whatever the regimen imposed and species studied, periodogram analysis indicated a circadian rhythm with the presence of ultradian component close to 12 h. Double plotted actograms and wave forms highlighted two different locomotor behaviors; in fact, individuals of O. montagui are active during photophase when placed under LD cycle whereas, individuals of O. gammarellus concentrated their activity during the scotophase. The comparison of rhythm characteristics showed that the highest rhythmicity was observed under entraining condition both for O. montagui and O. gammarellus with 77% and 60%, respectively. Moreover, the most important stability and activity time were better defined under continuous light with high luminous intensity for O. montagui and entraining conditions for O. gammarellus. On the other hand, results showed a highly standard deviation explaining the important intraspecific variation. We concluded thus the presence of diurnal and nocturnal trends adopted by these two talitrids. This strategy allowed these concurrent species to minimize their interactions. These two sympatric species, which have the same food preferences, do not share the same temporal niche. This is a strategy to allow the diminution of interspecific competition intensity. This result is discussed in this paper.

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.

Seasonal variation of locomotor activity rhythm of Orchestia montagui in the supralittoral zone of Bizerte lagoon (North of Tunisia)

Locomotor activity rhythms of Orchestia montagui were investigated in a population from the supralittoral zone of Bizerte lagoon. These rhythms were recorded in individual animals over the four seasons under two simultaneous experimental regimens; during the first week, the animals were kept in light–dark cycle in phase with the natural diel cycle. During the second week, animals were maintained in constant darkness (DD). Results revealed that, whatever the season, actograms and mean activity curves showed globally that individuals of O. montagui concentrated their activity during the experimental and subjective day. In addition, animals exhibited a diurnal circadian rhythm of locomotor activity with an ultradian component. Under light–dark cycle, circadian periods determined by periodogram analysis in four seasons were appreciably similar and were close to 24 h. While under constant darkness, circadian period was longer in winter (τDD = 25 h 54′ ± 1 h 14′) and summer (τDD = 25 h 47′ ± 0 h 45′) than in spring (τDD = 24 h 26′ ± 1 h 51′) and autumn (τDD = 24 h 44′ ± 2 h 22′). In addition, the study of the mean activity times calculated for four seasons showed that, whatever the regimen imposed, the most important activity of individuals was observed in summer and it was equal to 11 h 51′ ± 5 h 10′ and 16 h 27′ ± 5 h 44′ under entraining conditions and constant darkness, respectively. With reference to environmental stability and variability, the differences of locomotor activity characteristics observed are explained as a need for plasticity to adapt to environmental changes.

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.

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.

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.

Light pulse effect on the locomotor activity rhythm of Talitrus saltator (Montagu) (Crustacea, Amphipoda)

Abstract The locomotor activity rhythm of the sandhopper Talitrus saltator (Amphipoda Talitridae) was investigated in Madfoun beach. The rhythm was monitored in individual and group animals during 21 days at constant temperature. During the first two weeks, animals were kept under light–dark cycle (d1–d7) and constant darkness (d8–d14). Light pulses of 2 h were applied, at the end of the experimental night, during the first 3 days of the third week (d15–d18). Then, constant darkness was restored for the rest of the experiment (d19–d21). Results revealed that Talitrus saltator individuals as well as groups concentrated their activities in experimental night under light–dark cycle and in the presence of pulses; whereas, a clear drift of activity is observed under constant darkness. Periodogram analysis showed the presence of circadian component whatever the recording type. An ultradian period was revealed in individual recording whatever the regimen, while for groups, this component appeared only under nLD cycle. Furthermore, the locomotor rhythm is more defined under nLD cycle for individuals and in constant darkness for groups.