CHEMORECEPTION BY THE RED-JOINTED FIDDLER-CRAB UCA MINAX (LECONTE) - SPECTRAL TUNING PROPERTIES OF THE WALKING LEGS

The red-jointed fiddler crab Uca minax is one of the most abundant mac roinvertebrates inhabiting the temperate western Atlantic salt marshes , along the eastern and southern coasts of the United States. Dactyl c hemoreception is the primary sensory modality involved in food detecti on. Ninety-six chemoreceptor cells from 69 male and female second and third legs were tested with 20 compounds known to be stimulatory in ot her decapods. Each compound was tested as 1 s pulses at 10(-3) M. Over all, chemoreceptor cells on the dactyls responded strongest to glutama te and ammonium chloride followed by citric acid. Glutamate-and ammoni um 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 mo derately stimulatory. Surprisingly, hexose sugars which cause strong b ehavioural responses in U. minax elicited only weak physiological resp onses. Glutamate sensitivity separates U. minax from other species of fiddler crabs. The results indicate that the chemical response spectru m of U. minax includes compounds that occur naturally in salt marshes as algal and animal constituents, exudates, and decomposition products .