Changes in physiology,structure and histochemistry occurring during the life-history of the sexually dimorphic isopod Dynamene bidentata (Crustacea: Peracarida)

The main food reserve of the intertidal hebivorous isopod Dynamene bidentata is lipid. Only algal-dwelling juveniles exhibit rhythms of oxygen consumption and defecation related to the tidal cycle. Males undergo the moult to maturity in the algal habitat and are, therefore, able to replenish their food reserves before entering upon a nonfeeding reproductive phase in empty barncle tests and erevices. Storage sites are increased at this moult so that males are able to survive on their food reserves for 2 breeding seasons. Females enter the reproductive habitat in the preovigerous stage and cease to feed. Lipid food reserves are largely used up in the formation of eggs and the final stage cuticle. Consequently, after the ovigerous moult, females are required to utilise lipoprotein-containing tissue as an energy source, and are able to survive only for a single breeding season. At the final moult, the posterior end of the male becomes highly thickened, rugose, and supplied with tegumental glands. These modifications are correlated with the need for self protection, and protection of the vulnerable females, against various physical and biological factors in the intertidal zone. There is a large increase in the dry weight of the brood over the period of incubation, and this is due mainly to the development of the exoskeleton at the last marsupial moult. The source of materials for the weight increase is attributable to a combination of factors, of which salt uptake probably plays the major part.