Age effect on the locomotor activity rhythm of Armadillidium granulatum (Crustacea, Isopoda)

摘要

In this present paper, we propose to characterize the locomotor behavior of the Oniscidea Armadillidium granulatum Brandt, 1833 and to highlight the effect of age on its locomotor patterns. Individuals of A. granulatum were collected from the supralittoral zone of Sebkha El Ouafi. Adult and young specimens were maintained in spring under two successive regimens: the light-dark (LD) cycle and the constant darkness (DD) at a constant temperature. Whatever the age, double-plotted actograms and waveforms showed that specimens of A. granulatum concentrated their activity during the experimental and subjective nights. In addition, the majority of locomotor activity patterns were unimodal; whereas, adults and juveniles intensified their activities respectively around the dusk and in the middle of the night. Through periodogram analysis, circadian and ultradian components were determined. The first one was significantly longer under DD than under natural LD cycle for adults as well as for juveniles. These last were characterized by the most stable and well-defined locomotor activity rhythm. Furthermore, Adult specimens were more active under entraining conditions contrary to juveniles that showed an important activity time under DD. With reference to environmental stability and variability, the differences of locomotor activity characteristics observed between juveniles and adults were explained as a need for plasticity to adapt to environmental changes.