Active in the sac: damselfish embryos use innate recognition of odours to learn predation risk before hatching

Predation-induced mortality rates of aquatic species are much higher in larvae than in adults. Consequently, the ability of an organism to recognize relevant predators as early as possible could increase its chance of survival, especially in areas with high predator diversity. Heart rates of embryonic cinnamon clownfish, Amphiprion melanopus, were monitored to assess their reaction to damage-released conspecific alarm cues. These cues were then combined with a predator odour in a conditioning trial to establish whether the embryos were capable of learning a predatory threat. Results showed that A. melanopus embryos were not only able to detect and react to conspecific chemical alarm cues, but were also capable of using this information to learn about predation risk before they hatched. This recognition could lead to a number of antipredator behavioural adaptations, such as modifications of habitat choice at settlement, and could affect development and behaviour in postembryonic individuals, all of which may increase their chance of survival.