Karima Nasri-Ammar

Locomotor rhythm phenology of Talitrus saltator from two geomorphologically different beaches of Tunisia: Bizerte (North of Tunisia) and Gulf of Gabes (South of Tunisia)

Locomotor activity of the supra-littoral amphipod Talitrus saltator was studied in spring and autumn. Specimens were collected from two geomorphologically different beaches: Bizerte, in the North of Tunisia and the Gulf of Gabes in the South of Tunisia. The latter has the largest tidal amplitude in the Mediterranean basin. Adult individuals were collected by hand and transferred individually to actographs, equipped with an infrared recording system. These were placed in a controlled environment cabinet, where locomotor activity was monitored over a period of 16 days. The resulting endogenous rhythms of locomotor activity showed unimodal circadian and bimodal periods in amphipods from both Bizerte and Gulf of Gabes beaches. In spring, the unimodal activity pattern predominated at Gabes beach, whereas different patterns of activity (unimodal, bimodal, and plurimodal) were obtained among Bizerte population, with almost equal proportions. Highly significant differences between ultradian and circadian rhythmicities were revealed in both Bizerte and Gabes populations. These results are interpreted in the context of locomotor rhythm adaptation to the geomorphological conditions prevailing at the two collection sites.

Seasonal variation of the endogenous rhythm in two sympatric amphipods: Talitrus saltator and Talorchestia deshayesii from Bizerte beach (northern Tunisia)

The locomotor activity rhythm of the supralittoral sandhoppers, Talitrus saltator and Talorchestia deshayesii, was investigated over four seasons to reveal the impact of environmental variation on these sympatric species collected from Bizerte beach (37°19′N–9°51′E). For each season, thirty adult individuals were collected by hand and transferred to individual actographs equipped with an infrared recording system, where they were subjected to two consecutive experimental light/dark regimens (natural light/dark cycle (LD) and continuous darkness (DD)) in a controlled environment cabinet at 18°C ± 0.5°C. Periodogram analysis of the resulting actograms indicates a predominantly circadian rhythm with a period close to 24 h, with a less predictable semi-diurnal component of about 12 h in both T. saltator and T. deshayesii. A seasonal comparison of the various rhythm characteristics showed that the greater mortality was observed in winter (36.6%) and in spring (70%), respectively, among the population of T. saltator and T. deshayesii; whereas, in summer, this rate was equal to zero whatever the species. Moreover, irrespective of the season and the photoperiodic regimen, circadian rhythmicity was more important than the semi-diurnal one for all seasons and both under natural Light/Dark (nLD) cycle and free-running conditions. In addition, the stability of the circadian rhythm was better defined in spring, whatever the photoperiodic regimen imposed and the species. Similarities and differences observed between T. saltator and T. deshayesii over four seasons reflect an ecological plasticity of their biological clock adapted to different changing environmental conditions.

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.

Towards a characterization of the locomotor activity rhythm of the supralittoral isopod Tylos europaeus.

Freshly collected samples of Tylos europaeus from Korba beach (northeast of Tunisia) were housed in an environmental cabinet at controlled temperature (18°C ± .5°C) and photoperiod. Locomotor activity was recorded under two photoperiodic regimens by infrared actography every 20 min by multichannel data loggers. One regimen simulated the natural light-dark cycle on the day of collection, whereas the second imposed a state of continuous darkness on all individuals. Under entraining conditions, the animals displayed rhythmic activity, in phase with the period of darkness, whereas in continuous darkness these isopods exhibited a strong endogenous rhythm with circadian and semidiurnal components at mean periods of τ (h:min) = 25:09 ± 01:02 h and τ = 12:32 ± 00:26 h, respectively. Under free-running conditions, this endogenous rhythm showed significant intraspecific variability. (Author correspondence: bohli.dhouha@gmail.com)

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.

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.