Activity is an important behavioral trait that in most animals mediates a trade-off between obtaining food for growth and avoiding predation. Active individuals usually experience a higher encounter-rate with food-items and predators, and as a consequence grow faster and suffer a higher predation-pressure than less active individuals. We investigated how predator-induced mortality and growth of the damselfly Coenagrion hastulatum depends on activity at the level of genotype. Larvae from six different C. hastulatum families were reared in two different predator treatments; predator present or absent. Families differed in activity and active families grew to a significantly larger size than less active families. Within families there was a plastic response to predators, since larvae reared without predators were more active and grew larger than the less active larvae reared with a non-lethal predator. In the presence of a lethal predator the active families experienced a higher mortality than the less active families. The results illustrate that the growth/predation-risk trade-off was mediated by activity and clearly show a cost of antipredator behavior. They also indicate that the variance in activity level might be genetically regulated and could explain why C. hastulatum are abundant in aquatic systems both with and without potential predators.
