Mechanisms of crustacean egg hatching: Evidence for enzyme release by crab embryos

Abstract

During the summer of 1989, we examined mechanisms of egg hatching in three species of brachyurans that occupy different habitats as adults near Beaufort, North Carolina, USA:Neopanope sayi (Smith) (subtidal),Uca pugilator (Bosc) (intertidal) andSesarma cinereum (Bosc) (supratidal). Results of casein assays indicated that embryos of all species release proteolytic enzymes near the time of egg hatching. Species differences in specific enzyme activity were suggested, with increased activity in the more terrestrial crabs. Embryos ofN. sayi released enzymes several hours before larval release by the female, whileU. pugilator andS. cinereum released enzymes closer to the time of larval release; enzyme release coincided roughly with time of egg-membrane breakage in all species. Direct observations of hatching showed a sequence of outer-membrane breakage apparently followed by inner-membrane breakage and emergence of the larva. Egg volumes increased most during early and/or mid-stages of development, with a marked slowing of the increase during the several days before hatching. Thus, a gradual osmotically-driven increase in water content may also be involved in egg hatching.