Eat or be eaten? Modifications of Aplysia californica feeding behaviour in response to natural aversive stimuli

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Prey often modify their behaviours to diminish predation risk, but the persistence of such behavioural changes are not well understood. We investigated the effects of predation risk in the aquatic mollusc Aplysia californica to determine whether various natural aversive stimuli alter the expression of feeding behaviour (i.e. bites) over short-term (15 min), intermediate-term (2 h) and long-term (24 h) periods. Aplysia were presented with a variety of natural aversive stimuli that are indicative of predation risk, including exposure to the spiny lobster Panulirus interruptus (a natural predator), the blue crab Callinectes sapidus (a novel predator), and the defensive secretions ink and opaline that are normally released by Aplysia when attacked. Feeding was significantly suppressed immediately after Aplysia were exposed to ink but not to opaline. Additionally, several stimuli, including exposure to lobsters, ink, opaline and attacks from crabs, suppressed feeding, but only for a short time (i.e. 15 min) after the end of the stimulus. No single-exposure treatment elicited intermediate (2 h) or long-term (24 h) changes in feeding, and multiple exposures to ink did not induce long-term feeding suppression. Thus, changes in feeding behaviour in response to predation risk cues appear short-lived in Aplysia, unlike feeding suppression after electric shocks that suppress biting behaviour over longer periods. Since Aplysia possess chemical defences to defend against consumers, it is perhaps unnecessary or too costly to maintain feeding suppression after risk subsides.