STARVATION RESISTANCE IN LARVAE OF A SEMITERRESTRIAL CRAB, SESARMA-CURACAOENSE (DECAPODA, GRAPSIDAE)

Starvation resistance in the larvae of a semiterrestrial grapsid crab, Sesarma curacaoense De Man, 1892, was studied by point-of-no-return (PNR) and point-of-reserve-saturation (PRS) experiments. S. curacaoense shows an abbreviated larval development (only two zoeal stages) and a high degree of lecithotrophy. In complete absence of food, larval development is possible from hatching to the megalopa stage. Thus, no PNR or PRS can be given for individual zoeal stages of this species. However, late effects of early starvation indicate that lecithotrophy is only facultative in S. curacaoense zoeae: food is not essential but will be eaten when available. The endotrophic potential decreases from the first to the last larval stage: while the zoea I is entirely independent of external food sources, the zoea II shows increasingly delayed development after increased periods of initial food deprivation, and the megalopa can develop independent of food only if the preceding zoeal stages were fed continuously. Besides ontogenetic changes, significant variability was observed also in starvation resistance of larvae originating from different females. In an experiment with a particularly starvation-resistant hatch, development in the zoea II was accelerated during continuous lack of food or when starvation followed brief initial feeding periods. This effect was interpreted as a mechanism which should be specific to facultative lecithotrophy: starvation may induce a change in energy partitioning, from a preference for growth (uptake and accumulation of additional energy reserves) to accelerated development (mobilization of internal reserves, rapid termination of the planktonic larval phase). Enhanced starvation resistance in S. curacaoense zoeae compared with that in most planktotrophic marine decapod larvae is considered an adaptation that allows for retention of the larvae within a nutritionally unstable environment where the adult populations live. These ontogenetic traits corroborate the assumption that S. curacaoense may be the closest relative of an ancestral Sesarma species from which adaptive radiation of endemic Jamaican freshwater and terrestrial crabs began.