Activity rhythms and orientation in sandhoppers (Crustacea, Amphipoda).

The aim of the present review is to combine knowledge of locomotor activity rhythms with that of compass orientation in littoral arthropods. Talitrid amphipods (the sandhoppers) represent a good biological model in the fields of animal orientation and biological rhythms. The paper examines the activity rhythms of different species of sandhoppers (mainly Talitrus saltator), as well as the chronometric mechanisms of compensation for the apparent motion of the sun and moon that these animals use in zonal recovery based on the two astronomical cues. The two chronometric mechanisms seem to be independent of each other and to operate throughout the 24-hour period. The speed of the chronometric mechanism of solar compensation appears to be related to the hours of light and is entrained by the same stimulus (light-dark alternation) that controls the circadian activity rhythm. Therefore, it is probable that in T. saltator the same mechanism regulates both the circadian locomotor activity and the solar compensation.