Auditory stimulation dishabituates anti-predator escape behavior in hermit crabs (Coenobita clypeatus).

Responses to innocuous stimuli often habituate with repeated stimulation, but the mechanisms involved in dishabituation are less well studied. Chan et al. (2010b) found that hermit crabs were quicker to perform an anti-predator withdrawal response in the presence of a short-duration white noise relative to a longer noise stimulus. In two experiments, we examined whether this effect could be explicable in terms of a non-associative learning process. We delivered repeated presentations of a simulated visual predator to hermit crabs, which initially caused the crabs to withdraw into their shells. After a number of trials, the visual stimulus lost the ability to elicit the withdrawal response. We then presented the crabs with an auditory stimulus prior to an additional presentation of the visual predator. In Experiment 1, the presentation of a 10-s, 89-dB SPL noise produced no significant dishabituation of the response. In Experiment 2 we increased the duration (50s) and intensity (95dB) of the noise, and found that the crabs recovered their withdrawal response to the visual predator. This finding illustrates dishabituation of an antipredator response and suggests two distinct processes-distraction and sensitization-are influenced by the same stimulus parameters, and interact to modulate the strength of the anti-predator response.