Boldness in anti-predator behaviour and immune defence in field crickets

Questions: Are prey animals’ behavioural responses against predation associated with their ability to resist parasites and pathogens, and if so, how is this adjusted in different populations? Methods: We studied the association between anti-predator behaviour and immune defence (encapsulation response and lytic activities of the haemolymph) using laboratory-reared male field crickets originating from two wild populations that differ in predation and parasitism risk. The anti-predator behaviours that we measured were as follows: (1) the animal’s latency to become active inside a safe refuge, (2) its latency to emerge from a safe refuge after disturbance, and (3) the animal’s freezing time following a separate alarm cue. Results: Crickets originating from a high-parasitoid, high-predation risk population (Arizona) had higher encapsulation responses than crickets from a low-parasitoid, lowpredation risk population (California). Lytic activity correlated negatively with freezing time. Encapsulation response was positively correlated with the latency to become active and latency to emerge from a safe refuge in the high-predation risk population, but not in the low-predation risk population. Conclusion: Predation and parasitoids may increase the cricket’s investment in parasite resistance, despite the potential costs of anti-predator behaviour.