Biological clock in seasonal reproductive cycle in the ditch shrimp Palaemonetes varians leach. II. Ovarian state-dependent response to non-diel light-dark cycles

Abstract

Responses of females of Palaemonetes varians were described under various non-diel light-dark cycles according to their oogenesis stages. Two experimental designs were chosen, one which applied a complete photophase with a non-circadian periodicity and the other which applied a random light-dark cycle. These conditions provoked an internal desynchronization of the biological clock involved in time-measurement. Two effects concerning reproduction were described: a lack of the photoperiodic stimulation for the onset of reproduction and a fall of the number of the reproductive females. Nevertheless, in some cases the reproductive physiological metabolism predominated over the photoperiodism effect so that the responses of the females were modified. In this context, the efficiency of the biological clock was maximal when the Zeitgeber period is less than 24 h. This clock was involved in both the date of onset of reproduction and the rate of reproductive activity. The formulation of a circadian organization is advanced as an explanation of the reproductive strategy in P. varians. Comparisons of circadian rhythms involved in behaviour such as locomotor activity are made with other caridean Decapods.