Chemical Mediation of Larval Release Behaviors in the Crab Neopanope sayi

Control of egg hatching was investigated in ovigerous females of the crab Neopanope sayi. Larval release is a brief event, generally lasting less than 15 min, during which females perform stereotypic behaviors involving vigorous abdomen pumping. Substances released by hatching eggs (pumping factors) of N. sayi, Rhithropanopeus harrisii, and Uca pugilator, but not Sesarma cinereum, evoked these stereotypic behaviors (pumping response) in ovigerous N. sayi. Spontaneous pumping and responsiveness to pumping factors varied with the age of the embryos. These results indicate that the eggs release pheromones around the time of hatching, which supports the general model for egg-hatching control described for R. harrisii (Forward and Lohmann, 1983). The chemistry of N. sayi pumping factors was investigated, and the pumping response was used as a bioassay in this study. Pumping factors adsorbed to Amberlite XAD-7 resin and could be eluted from it with methanol. Size fractionation by cascade pressure dialysis showed that the active molecules were <1000 daltons. Acid hydrolysis followed by reverse-phase HPLC amino acid analysis showed that the biologically active fraction contained peptides. Cysteine, glycine, methionine, and isoleucine were the four most common amino acids in these peptides. The responsiveness of N. sayi to hatch water from R. harrisii, the general similarity of adsorptive characteristics of hatch waters from the two species toward XAD-7 resin, and the amino acid compositional analysis suggest that the pumping factors from both species are similar. This supports the hypothesis that N. sayi pumping factors are also small peptides, as was suggested for those of R. harrisii (Rittschof et al., 1985, 1989).