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

Abstract

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.