Limb Autotomy as an Investigatory Tool: Host Molt-Stage Affects the Success Rate of Infective Larvae of a Rhizocephalan Barnacle

Abstract

D. M. Skinner was the first biologist to systematically investigate the effect of multiple limb autotomy on ecdysis in decapod crustaceans. She proposed the existence of (1) limb autotomy factor anecdysis (LAFan) which initiates precocious molting, and (2) limb autotomy factor proecdysis (LAFpro) which postpones proecdysis. Mean time to ecdysis did not differ significantly among groups of small juvenile Callinectes sapidus with zero, two, four, and six limbs removed. Variance was significantly less for the group missing six limbs; i.e., autotomy of six limbs synchronized the molt-cycle. These patterns were consistent with the hypotheses that LAFan exerts an additive effect, i.e. , more anecdysial crabs enter proecdysis as more limbs are autotomized and that a delay of proecdysis occurs above a threshold (>4) of autotomized limbs. Multiple limb autotomy provides investigators with easy access to crabs in metecdysial molt-stages which is useful in studying interactions between rhizocephalan barnacles and their hosts. While 71% of metecdysial C. sapidus exposed to infective larvae of the sacculinid rhizocephalan, Loxothylacus texanus , developed the external stage of the parasite, no similarlysized anecdysial crab was parasitized, suggesting that these crabs are not susceptible to infection during anecdysis. Size of C. sapidus at infection was inversely proportional to the number of ecdyses between infection and emergence of the parasite, but not correlated to final host size. These data suggest that there is a minimum threshold for host size; smaller hosts undergo more ecdyses before attaining the threshold. Rhizocephalans are being considered as biological control agents and there is a need to understand how they find and infect hosts. Because limb autotomy is such a useful research tool, D. M. Skinner's contributions to our understanding of how limb autotomy influences the crustacean molt cycle will continue to pay significant dividends in crustacean biology.