Influence of extracts of adult crabs on molting of fiddler crab megalopae (Uca pugnax)

Abstract

Larvae of many benthic invertebrates metamorphose in response to habitat cues, which include the presence of adult conspecifics. Prior research showed that fiddler crab [Uca pugnax (Smith)] megalopae advance molting to the first crab stage in seawater in which conspecific adult crabs were maintained. In the present study, extracts of adult crabs were prepared and the specificity and protein content were characterized. U. pugnax megalopae were reared in the laboratory to minimize their prior exposure to potential molting cues. Then they were presented with extract solutions (in 1995, 1996, 1997, and 2000) to determine the specificity of the molting response to extracts of several crab species and the effects of the protein concentration of the extract, age of the megalopae at exposure to extract, and the duration of exposure on the molting response. Megalopae of U. pugnax molted sooner in seawater containing extract from adult conspecifics than in filtered seawater without extract or in seawater containing extract from the congener U. minax. Extract from the mud crab Dyspanopeus sayi retarded molting of U. pugnax megalopae. The stimulatory effect of U. pugnax extract on molting of megalopae was dependent on extract concentration. U. pugnax megalopae did not respond to extract until 6 days after molting, and only 1 day of exposure was sufficient to stimulate molting. The boiled extract was effective after being frozen (−15°C) for 2 years. The preparation of stable extract provides a uniform stimulus for multiple experiments examining the specificity of molting cues for brachyuran crustacean larvae and the onset of receptivity to cues.