Gustatory Responses of Ghost Crab Ocypode quadrata to Seawater Extracts and Chemical Fractions of Natural Stimuli

Abstract

The efficacy of seawater-extracted fresh and decomposing blue crab (Callinectes sapidus) claw muscle homogenates as stimulants of feeding behavior by the ghost crab (Ocypode quadrata) was tested with cheliped flexion as a bioassay. Stimulatory components of extracts were heat-stable and <1 kDa. Fresh seawater extracts of muscle tissue homogenate elicited the most responses and decreased in efficacy with decomposition. Ultrafiltrates <1 kDa also became less stimulating with increasing decay of the homogenate. When ultrafiltrates were extracted with ethyl ether, the aqueous phase elicited the most responses. To some degree, active components were soluble in ether. Ion-exchange chromatography of the aqueous phase yielded eluates containing neutral and acidic compounds, which, following a peak in activity, became less stimulatory over time. In contrast, eluates containing amphoteric and basic compounds remained highly effective throughout bacterial degradation. However, their activity was significantly suppressed when they were mixed with neutral and acidic compounds isolated from the same samples. Mixture suppression may function as a mechanism ensuring the consumption of high-quality foods. The ability of O. quadrata to respond to both fresh and decomposing tissues contributes to this species' flexibility in foraging strategies and its success as an inhabitant of sandy beaches.