CONTROL OF EGG HATCHING IN THE CRABRHITHROPANOPEUS HARRISII(GOULD)

Abstract

Ovigerous females of the crab Rhithropanopeus harrisii were collected from an estuary having irregular tides. When monitored under constant conditions in the laboratory, the crabs have a circadian rhythm in larval release. Eggs removed from the female within 2 days of hatching hatched at about the same time as larvae were released by the female. Hatching became increasingly desynchronized with longer removal times. Upon exposure to water in which the larvae hatched, ovigerous females diplayed increased abdomen pumping, a behavior observed at the time of larval release. The active substance was released at the time of egg hatching but not by newly hatched larvae. Homogenized eggs of different ages and homogenized larvae induced similar behavior. There was no change in female sensitivity with clutch age or time of day. Active pumping by the female only induced hatching at times predicted by the larval release rhythm, not at other times during the solar day. These results indicate that an interaction between the eggs and female is responsible for synchronized development while the actual timing of hatching is controlled by the embryo. At this time an active substance is released. This substance induces abdomen pumping by the female which serves to synchronize larval release.