Endogenous Rhythmicity Associated with Larval Hatching in the Lobster Homarus Gammarus

Abstract

A nocturnal larval hatching rhythm is described for the lobster Homarus gammarus. In natural illumination cycles, hatching takes place shortly after darkness with the hatching process lasting for about 1 min or less. One female lobster can release batches of larvae each successive night for periods of from 2 to 6 weeks, depending on size and water temperature during the period of hatching. The hatching rhythm persists, though slightly out of phase, when lobsters that have been releasing larvae for some time are kept in constant darkness, but in constant illumination hatching may be delayed for 2 or 3 days and when it does occur it is erratic and non-rhythmic. Larvae that do hatch in constant illumination appear to do so without parental assistance. Onset of darkness synchronizes the rhythm but an endogenous component is involved in controlling it.