Stasis in the adaptive landscape of two ecologically similar and sympatric damselfly species

Abstract

AbstractFollowing the development of regression-based methods to estimate natural and sexual selection, evolutionary biologists have quantified the strength, mode and direction of selection in natural populations. Although this approach has been successful, its limitations include lack of replication across species, compromising the generality of the inferences beyond microevolutionary time scales. Here, we carried out a comparative selection study on wing shape and body size across multiple populations of two closely related and ecologically similar pond damselflies:Enallagma cyathigerumandIschnura elegans(family Coenagrionidae). Our data revealed directional selection on body size in females and weak stabilizing selection on wing shape in both sexes, and these selection regimes were shared between the species. In contrast, sexual selection on male body size was curvilinear and divergent between species. By analyzing selection on the fine-grained spatial scale, we found that selection of male body size was shaped by the local social organization, and the relationship between socioecological indices and directional selection was consistent between the two species. Our study illustrates a case of stasis in the adaptive landscape caused by ecological similarity between taxa, supporting the idea that a shared ecological niche may result in a stable adaptive zone lasting millions of years.