Life history and behavioral responses to time constraints in a damselfly

Time constraints, imposed by seasonality, are common to life histories. Recent theory in evolutionary ecology predicts independent behavioral and life history responses to such constraints, but this theory remains largely untested. In our two experiments on the damselfly Lestes congener we experimentally alter individual's perception of their proximity to a time constraint and ask whether their behavior and life history respond in the directions predicted by theory. We altered larval perception of their position in the season with light regime. In one group, we hatched larvae from winter diapausing eggs in a light regime that mimics a relatively early time in the season. In the other group we hatched larvae in a light regime that mimics a late time in the season. In the late (time constrained) group, larvae would have very little time to complete development and reach a large size so that they could attain their full reproductive potential prior to winter. In the first experiment, the behaviors we assess are activity rate, which is an indicator of foraging effort and willingness to take risks, and cannibalism, which is a component of the mortality risk of foraging. As predicted, time-constrained larvae increased their activity rates, perhaps in an attempt to increase weight gain, and as a result they suffered higher rates of cannibalism. In the second experiment, we measured development rate as the rate of molting and age at maturity. As predicted, time-constrained larvae accelerated development rate and thereby matured at a significantly earlier age and smaller size. Our analysis demonstrates that the behavioral and life history responses of these larvae were independent, in the sense that the life history responses did not result from the behavioral responses.