Ontogeny Versus Phylogeny in Determining Patterns of Chemoreception: Initial Studies with Fiddler Crabs.

Abstract

Fiddler crab (Uca longisignalis) first stage zoea and adults were assayed for behavioral responses to 16 amino acids and sugars. Larval chemosensitivity was examined using computer-video motion analysis of swimming behavior. Adult sensitivity was assayed by determining the substances that elicit feeding. The pattern of chemoreception expressed by U. longisignalis adults is strongly correlated with that measured previously in adult sand fiddler crabs, Uca pugilator. This concordance among abilities probably reflects shared trophic ecologies of the two species. In contrast, a quantitative analysis shows no significant correlation between the sets of compounds inducing chemoreceptive behavior by larval and adult U. longisignalis. The strongest responses (by both stages) are elicited by substances found in potential prey, and differences in prey types among larvae and adults appear responsible for the lack of correlation. Larvae do, however, respond to substances abundant in prey consumed by adults, even though these substances are absent, or occur at low levels, in larval prey. Adults, on the other hand, appear insensitive to compounds that cue only larval food, but which are maximally stimulatory to larvae. Consequently, our results indicate that the abilities of one life-history stage may be constrained, through development, by the requirements of later stages. The patterns of correlation among adults of different species, and among life-history stages within a species, indicate that both ecological context and developmental factors influence patterns of chemosensitivity.