Behavioral reactions to novel food odors by intertidal hermit crabs

Background/Question/Methods

Generalist scavengers, such as hermit crabs, routinely encounter novel food items while foraging.  Because hermit crabs rely primarily on olfactory cues to mediate their foraging, their first encounters with novel food items come from the detection of novel food odors.  Hermit crabs are capable of rapid associative learning of food odors.  However, preliminary experiments have shown that exposure to novel food odors elicits strong foraging behaviors by the intertidal hermit crabs Clibanarius digueti and Paguristes anahuacus, suggesting that learning is not necessary for initial attraction to novel foods.  While it is clear that these species show strong reactions to novel food odors at first detection, it remains unclear whether these reactions persist in the absence of stimulus reinforcement (i.e., locating and feeding on the novel food).  It was predicted that the initial attraction to novel food odors in hermit crabs would be lost if the animals repeatedly detected the food odors but never actually located the food reward.  This study tested the behavioral reactions of hermit crabs to previously novel food odors over a series of repeated, unreinforced exposures.

Results/Conclusions

Both C. digueti and P. anahuacus showed significant increases in foraging behaviors following exposure to a novel food odor.  In the absence of stimulus reinforcement, the strength of behavioral reactions by C. digueti to the novel food odor rapidly diminished.  This change in reaction strength was apparent after a single unreinforced odor exposure, and reaction strengths remained low throughout all subsequent exposures.  Behavioral reactions to the odor of a familiar food source (control stimulus) remained strong throughout all exposures.  The behavioral reactions of P. anahuacus to the novel food odor also decreased in strength following unreinforced exposure, but the decline in response was more gradual than that of C. digueti.  The behavioral reactions of P. anahuacus to familiar food odors (control stimulus) remained strong throughout the experiment, although some fluctuation in reaction strength was seen among trials.  The results show that the initial attraction of hermit crabs to novel food odors rapidly diminishes in the absence of stimulus reinforcement.