Adaptation to predators in a new community: Swimming performance and predator avoidance in damselflies

Species evolve in response to the abiotic and biotic interactions they experience in a community, and so studying the adaptation of species in a community context is a necessary component for understanding the development of community structure. Previous studies have suggested that Enallagma damselflies (Odonata: Coenagrionidae) invaded aquatic habitats with large dragonflies as the top predators at least twice, and large changes in morphological structures (e.g., caudal lamellae acid abdomen), which should increase swimming speed, are associated with these invasions. This is significant because these species swim away from attacking predators, whereas species in the ancestral habitat (habitats with fish as the top predators) do not swim from attacking predators. We quantified swimming speed over a large ontogenetic size range for larvae of seven Enallagma species, two in dragonfly lakes and five in fish lakes. Results of analysis of covariance and a modification of Felsenstein's method of evolutionary contrasts indicate that a large evolutionary increase in the slope of the ontogenetic relationship between swimming speed and log(e)(body length) is associated with invasions into dragonfly lakes, and this shift results in larvae of dragonfly-lake species being faster swimmers, especially in larger size classes, than larvae of fish-lake species. We also present experimental results demonstrating that damselflies with larger lamellae are faster swimmers and have higher survival when exposed to dragonfly predation. The results of this study indicate that the change in selective environment associated with habitat shifts into dragonfly lakes promoted adaptations for increased swimming speed in Enallagma lineages. The potential ramifications of this adaptation for community structure are discussed.