Control of egg hatching in the terrestrial crab

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Embryos of the estuarine terrestrial crab Sesarma haematocheir hatch simultaneously just before they are released into water. Egg hatching occurs synchronously when the embryos are attached to a female, and the role of the female in this synchrony has been investigated. Clusters of embryos(each 200-2000 berries)were detached from the ovigerous females, and their hatching was compared with that of embryos attached to the females. Of the detached embryos in a cluster, either all hatched, or none hatched. Moreover, a remarkable feature was that the success of hatching in these detached eggs depended upon the time of hatching of the eggs still attached to the female. Clusters of embryos that were detached from the female within 48-49.5 h of the projected time of larval release, all hatched successfully, and swimming zoeae appeared. But embryos that were detached from the female for longer time periods did not hatch at all, though they were obviously alive. These results suggest that the pr … More esence of a hatching process different from embryonic development. The female would trigger this process.Furthermore, to investigate which of female and embryo controls the actual timing of hatching, a cluster of embryos was detached and exchanged between two ovigerous females. Hatching of the transplanted eggs were divided into three patterns according to the number of nights until either or both of the females released larvae. In the Pattern I, transplanted clusters independently hatched from the eggs attached to the host female. In the Pattern II, while one of the implanted cluster was not controlled by the host female, hatching of another transplanted clusters was obviously induced. In the Pattern III, not only induction of hatching but also the time of hatching was controlled by the female. Hatching profiles of the transplanted eggs transferred into aerated conditions indicate that hatching requires three nights, and that each embryo also has an endogenous component for hatching. Since hatching of female-attached eggs occurs in a very short time, the female must have some action to enhance hatching synchrony when the actual hatching occurs. A plausible hypothesis to explain the mechanism as the induction and synchronization of hatching in each clutch is discussed. Less