Regulation of sex-specific feeding behavior in fiddler crabs: physiological properties of chemoreceptor neurons in claws and legs of males and females

Abstract

This study examined properties of chemoreceptor neurons in the claws and legs of the fiddler crabs Uca pugilator and U. pugnax. The primary goal was to establish the neural basis of previously observed greater female sensitivity to feeding stimulants, and secondarily to compare physiological properties of chemoreceptor neurons in these semi-terrestrial crustaceans with those of fully aquatic forms. Sensitivity of chemoreceptor neurons in claws and legs is sex-specific; individual neurons of females respond to lower stimulus concentrations than male chemoreceptor neurons, and equivalent concentrations elicit greater spiking in female vs male chemoreceptor neurons. Thus, the population of chemoreceptor neurons in females expresses lower thresholds and greater average sensitivity than in males. Greater sensitivity of claw neurons explains observations indicating that females continue to feed at food levels too low to stimulate males. Sensitivity differences in leg neurons of males vs females have no clear behavioral correlate, but suggest that females can orient to more dilute stimuli than males. Chemoreceptor neurons of fiddler crabs have low sensitivities and slow rates of adaptation compared to other crustaceans. Also, neurons in claws adapt less slowly than neurons in legs, which may reflect subtle differences in the chemical stimulus environment experienced by claws vs legs.

Role of olfactory appendages in chemically mediated orientation of blue crabs

“…The response was digitally stored on a personal computer using commercial software (Experimenters' Workbench, DataWave) and analyzed off-line to determine the response intensity (# of spikes) for a 4.5 s period following stimulation. Further details of the recording and analysis protocols can be found in Weissburg & Derby (1995). Statistical analyses.…”

“…Decapod crustaceans have chemoreceptors distributed on their mouthparts (Shelton & Lavarack 1970), dactyls and propodus of claws and walking legs (Hatt 1984, Schmidt & Gnatzy 1989, Weissburg & Derby 1995, antennae (Tazaki & Shigenaga 1974, Voigt & Atema 1992, Gomez & Atema 1996, and antennules (Hazlett 1971, Reeder & Ache 1980, Devine & Atema 1982. These groups of sensilla have specialized chemosensory functions (Derby & Atema 1982).…”

Transsexual limb transplants in fiddler crabs and expression of novel sensory capabilities

“…Methods were used as described by Weissburg and Derby (1995). Briefly, claws were autotomized, stripped of all cuticle proximal to the merus to expose the nerve and artery, and placed into a glass and Teflon olfactometer.…”

“…Females have two feeding claws (Crane, 1975). Chemosensory neurons in female claws express greater sensitivity to chemical stimuli than the neurons in male feeding claws (Weissburg and Derby, 1995;Weissburg, 1999), and this disparity appears, in part, to regulate sex-specific behavioral thresholds observed during feeding (Weissburg, 1993). Chemosensory neurons are known to be present in the feeding claws of males and females; male major claws have never been shown to detect chemical cues in either physiological (Weissburg and Derby, 1995) or extensive behavioral (Valiela et al, 1974;Robertson et al, 1981;Weissburg and Zimmer-Faust, 1991;Weissburg, 1993) investigations.…”

“…Sensitivity and dynamic range, among other properties of receptor neurons, set limits on responses to physical stimuli such as light, sound, and chemical cues (see, e.g., Atema et al, 1988;Weissburg and Derby, 1995;Lehrer, 1997). Projection patterns of sensory afferents map various stimulus features onto a spatial dimension in many sensory systems (see, e.g., Konishi, 1986;Hayama and Caprio, 1989;Newland et al, 2000).…”