Chemical Senses Vol.14 no.l pp. 121-130, 1989 Stimulation of feeding behavior in three species of fiddler crabs by hexose sugars Dan Rittschof and C.Ursula Buswell Duke University Marine Laboratory, Beaufort, NC 28516, USA Abstract. Feeding responses to five hexoses were examined in three closely related species of fiddler crabs, Uca minax, U.pugnax and U.pugilator. Htxoses tested were glucose, galactose, sorbose, fructose and mannose. Intact crabs and eyestalk-ablated crabs were tested. Responses to sugars were species specific. Eyestalks are directly involved in vision and overall neural integration as well as with chemosensory and metabolic pathways associated with feeding. Overall, eyestalk-ablated crabs were more sensitive uian intact crabs. Studies of responses of individuals within a population to hexoses showed tiiere are individual U.pugnax that respond to galactose and others that do not. Similarly, there were U.pugilator individuals that were mannose responsive and others that did not respond to mannose. An additional study of differences in population responses to hexoses would provide valuable tools in studying geographic relationships between fiddler crab populations. Introduction Fiddler crabs of the genus Uca are obvious semiterrestrial members of low energy intertidal environments in many parts of the world (Crane, 1975). Fiddler crabs usually forage on exposed substrata in large groups (Teal, 1958; Miller, 1961). Fine grained sand or mud is brought to the buccal region with the chelae and sorted into material that is either swallowed or rejected. The rejected feeding pellets (Miller, 1961) have been used to quantify feeding activity and to test for chemosensory responses (Robertson et al., 1980, 1981). Among living prey, diatoms, ciliates and bacteria stimulate feeding (Robertson etal, 1981). Robertson et al. (1981) showed that chemical components in the substratum upon which sand fiddler crabs {U.pugilator) walk elicit feeding responses. On natural substrata, crab foraging intensities were well correlated with food levels (Robertson et al., 1980). Amino acids, proteins (casein) and especially sugars and sugar polymers such as dextrin were found to be strong stimulants of feeding activity (Robertson et al., 1981). Although individual compounds were effective in eliciting feeding responses, mixtures were more effective (Robertson et al., 1980). Robertson et al. (1981), and others (Hazlett, 1971a,b; Hartman and Hartman, 1977; Zimmer-Faust et al., 1979) have suggested crustaceans orient to specific chemicals that reflect major dietary components. Thus, differences in response by different species of fiddler crabs might reflect differences in quantity or quality of food in the habitat that each species occupies. Hexoses are specific excretion products and components of the exopolymers of food items such as diatoms (White and Benson, 1984). Crabs could use hexoses to detect food. In contrast to most aquatic crustaceans whose antennules are central to food search behavior (Hazlett, 1971a; Carr and Derby, 1986) fiddler crab antennules are separated from the food containing substratum by air. Thus, food search is mediated by dactyl chemoreception rather than antennule chemoreception (Robertson etal., 1981). Antennular chemoreception is known to be mediated by neurosecretory complexes in © IRL Press 121 at duke university medical ctr on November 25, 2013 http://chemse.oxfordjournals.org/ Downloaded from