Chemoreception by the red-jointed fiddler crab Uca minax (Le Conte): Spectral tuning properties of the walking legs

The red-jointed fiddler crab Uca minax is one of the most abundant macroinvertebrates inhabiting the temperate western Atlantic salt marshes, along the eastern and southern coasts of the United States. Dactyl chemoreception is the primary sensory modality involved in food detection. Ninety-six chemoreceptor cells from 69 male and female second and third legs were tested with 20 compounds known to be stimulatory in other decapods. Each compound was tested as 1 s pulses at 10(-3) M. Overall, chemoreceptor cells on the dactyls responded strongest to glutamate and ammonium chloride followed by citric acid. Glutamate-and ammonium chloride-best cells formed the most prominent cell populations and were relatively narrowly tuned. Individual cells exhibited a range of tuning breadths based on responses to single compounds. Amines were moderately stimulatory. Surprisingly, hexose sugars which cause strong behavioural responses in U. minax elicited only weak physiological responses. Glutamate sensitivity separates U. minax from other species of fiddler crabs. The results indicate that the chemical response spectrum of U. minax includes compounds that occur naturally in salt marshes as algal and animal constituents, exudates, and decomposition products.