Locomotor activity rhythm of two sympatric species Talitrus saltator (Amphipoda) and Tylos europaeus (Oniscidea) from Tunisian beaches under continuous light

摘要

Locomotor activity rhythm of the supralittoral species Talitrus saltator and Tylos europaeus was studied under continuous light in populations of Korba and Barkoukech beaches in summer. Results showed that these two species were characterized by a nocturnal behaviour. Under the subjective night, the activity was continuous for T. saltator and interrupted in T. europaeus with the presence of a clear drift towards the right more accentuated for the second species. Whatever the site, using actograms and the waveforms, results showed the absence of bimodal profile in T. europaeus and the plurimodal one in T. saltator. Moreover, the most important activity peaks were observed around the dawn and the dusk, respectively. Furthermore, periodogram and MESA analyzes highlighted the presence of ultradian and circadian components. Whatever the component and the site, the inter-individual variability was more pronounced in T. europaeus. Moreover, whatever the site, individuals of T. europaeus were more active and the locomotor rhythm was more defined in T. saltator. With reference to environmental stability and variability, the differences of locomotor activity characteristics observed between these two species are explained as a need for plasticity to adapt to environmental changes.