Predator loss leads to reduced antipredator behaviours in Bahamas mosquitofish

Questions: How do antipredator behaviours of prey change with the loss of predators? Are these behaviours learned or innate? Hypothesis: Prey fish living without their ancestral predator will exhibit reduced antipredator behaviours compared with those currently living with the predator. The antipredator behaviours will not require learning, as laboratory-reared fish from populations living with predators will exhibit antipredator behaviours even without any exposure to predators during their lifetime. Organisms: We examined behavioural responses of Bahamas mosquitofish (Gambusia hubbsi ) to its primary predator, bigmouth sleeper (Gobiomorus dormitor). Field sites: Six blue holes on Andros Island, The Bahamas: three with the predatory fish and three without. Methods: We used field and laboratory experiments to measure prey behavioural responses to visual cues of a predator. In the field experiment, we tested for differences in behaviours between populations living with and without predatory fish. In the laboratory experiment, we wished to determine whether behavioural responses persisted without exposure to predators, and whether there was significant genetic variation for the behaviours. Results: Fish from blue holes without predators exhibited a considerably muted response to the predator compared with those that lived with the predator. Tests performed with laboratory-raised mosquitofish revealed genetic variation for these antipredator behaviours, and their responses largely mirrored those of wild-caught fish from their blue hole even after two laboratory generations without any predator exposure. Prey species can at least partially lose innate antipredator behaviours in the absence of predation, implying fitness costs of those behaviours.