Meeting Abstract

S8.6  Thursday, Jan. 6  Timing of hatching in Brachyuran crabs: patterns and control CHRISTY, J.S.; Smithsonian Tropical Research Institute, Panama christyj@si.edu

The timing of egg hatching and larval release by over 65 intertidal and shallow subtidal estuarine and coastal Brachyuran crabs (which brood their embryos) occur at particular times in the daylight, lunar or semilunar tidal amplitude, and tidal height cycles that promote larval survival and dispersal. Timing with respect to the tidal amplitude cycle is determined ultimately by when development begins. Daily measurements of reproduction by a tropical fiddler crab over five years show that adults time breeding so that females avoid releasing larvae on crepuscular and moonlit high tides and so that larvae are released on favorable large amplitude tides regardless of seasonal variation in incubation temperatures and development rates. Diurnal and tidal cycle timing of egg hatching results from communication between the female and her embryos. In more terrestrial species, the female signals her mature embryos that favorable conditions are imminent. She then moves to appropriate release sites and, when her eggs have hatched, releases all her larvae within seconds. In subtidal species, embryos largely control the timing of larval release. When they hatch they release a peptide that stimulates larval release behavior by the female. This may be repeated over two or three days until all eggs in a clutch have hatched. Thus, when females must position themselves appropriately for larval release, hatching is cued by the female. In fully aquatic species, embryos respond to cues that cycle with the conditions favorable for hatching. The timing of hatching and larval release is under endogenous control of rhythms in both females and embryos that can be entrained to local conditions. This presumably ensures appropriate timing during natural perturbations in physical cycles and across habitats and tidal regimes in a species’ range.