Relationship of escape performance with predator regime and ontogeny in fishes

Populations exposed to sustained differences in predation pressure often diverge in morphological, behavioural or physiological features. However, predation pressures can also change throughout ontogeny, as individuals grow and/or migrate to new habitats. We examine how anti-predator traits differ in relation to predator regime through a comparative study of juvenile and adult waterfall-climbing goby fishes. On Hawai'i, gobies can migrate out of the range of aquatic predators, whereas on La Reunion aquatic predators and goby prey coincide. We predict that species and life stages that are freed from predation pressure would have reduced escape behaviour and performance. Because greater thrust production improves escape performance, we also predict that fishes coinciding with predators would have taller bodies than fish freed from predation. We simulated predator attacks and evaluated escape performance for juvenile and adult prey fishes from Hawai'i and La Reunion. Juvenile gobies of all species responded more frequently and had higher peak accelerations than adults. Additionally, fish released from predation pressures had the slowest peak accelerations and wider caudal peduncles than fish exposed to greater predation pressure. These results suggest that fishes released from predation pressure may have morphologies and performance that are more aligned with holding station than with the production of thrust to evade predators.