Control of Hatching in an Estuarine Terrestrial Crab. II. Exchange of a Cluster of Embryos Between Two Females.

Abstract

The eggs of an estuarine terrestrial crab, Sesarma haematocheir (akate-gani), are incubated by the female for about one month. In estuarine crabs larval hatching is synchronized with the nocturnal high tide. To investigate whether the female or the embryo controls the actual timing of the hatching, one cluster of embryos was detached from each of two ovigerous females and reciprocally transplanted. Hatching of the transplanted embryos was divided into the following three patterns according to the number of nights until either (or both) of the females released their larvae. In Pattern I, the transplanted clusters both hatched on the same night that the donor females released their larvae. In Pattern II, the hatching of one of the transplanted clusters was not controlled by the host female, whereas hatching of the other transplanted cluster was obviously induced. Finally, in Pattern III, not only the induction of hatching, but also the time of hatching, was controlled by the female. Hatching profiles of transplanted embryos transferred to aerated conditions indicated that hatching requires three nights, and that each embryo also has an endogenous rhythm for hatching. The female seems to play two roles in hatching: i.e., initiation of the hatching process, and enhancement of hatching synchrony in each embryo. A plausible hypothesis explaining the mechanism of induction and the synchronization of hatching is presented.