Escape performance decreases during ontogeny in wild crickets.

Increasing the ecological relevance of studies relating to the performance of organisms has been a central issue for functional biologists over the last few years. Of particular concern are changes in performance throughout the life cycle as selective forces act differently on various life stages. We addressed this issue experimentally by following ontogenic variations in the escape performance of crickets threatened by artificial predatory signals. We measured their performance under natural settings, which is a necessary approach yet one that is undocumented in insects. We analysed numeric film sequences obtained using a high-speed video camera at 1000 frames s(-1) to quantify wild cricket performance and behaviour in the field. We detected significant differences in cricket escape performance throughout ontogeny. Escape performances were higher in juvenile crickets than older instars. Complementary behavioural measurements for escaping crickets suggest that these variations may be related to the lower predatory risk perceived by large adults than by juveniles. We expect that our analysis of size-refuge will also improve our understanding in the development of performance, given its importance in community and population ecology theories.