Sexual selection reinforces a higher flight endurance in urban damselflies

Abstract

Urbanization is among the most important and globally rapidly increasing anthropogenic processes and is known to drive rapid evolution. Habitats in urbanized areas typically consist of small, fragmented and isolated patches, which are expected to select for a better locomotor performance, along with its underlying morphological traits. This, in turn, is expected to cause differentiation in selection regimes, as populations with different frequency distributions for a given trait will span different parts of the species' fitness function. Yet, very few studies considered differentiation in phenotypic traits associated with patterns in habitat fragmentation and isolation along urbanization gradients, and none considered differentiation in sexual selection regimes. We investigated differentiation in flight performance and flight-related traits and sexual selection on these traits across replicated urban and rural populations of the scrambling damselfly Coenagrion puella. To disentangle direct and indirect paths going from phenotypic traits over performance to mating success, we applied a path analysis approach. We report for the first time direct evidence for the expected better locomotor performance in urban compared to rural populations. This matches a scenario of spatial sorting, whereby only the individuals with the best locomotor abilities colonize the isolated urban populations. The covariation patterns and causal relationships among the phenotypic traits, performance and mating success strongly depended on the urbanization level. Notably, we detected sexual selection for a higher flight endurance only in urban populations, indicating that the higher flight performance of urban males was reinforced by sexual selection. Taken together, our results provide a unique proof of the interplay between sexual selection and adaptation to human-altered environments.

Keywords: eco‐evolutionary dynamics; generalized multilevel path analysis; geometric morphometrics; habitat fragmentation; rapid evolution; scrambling competition.

Figure 1

Mean (±1SE) values for flight‐related traits of Coenagrion puella males originating from urban and rural populations. (a) Relative warp 1, (b) relative warp 2, (c) relative warp 3, (d) centroid size (unitless measure), (e) wing loading (unitless measure), (f) flight muscle ratio and (g) relative fat content. Given are least‐squares means

Figure 2

Mean (±1SE) values for flight performance traits of Coenagrion puella males originating from urban and rural populations. (a) Flight endurance, measured as total flight duration, and (b) flight speed. Given are least‐squares means

Figure 3

Path diagrams depicting the relationships between morphological and physiological traits, flight performance and mating success in urban and rural populations of the damselfly Coenagrion puella. Shown are path diagrams of (a) the “combined model”, where combined data of urban and rural populations were used, and (b) separate models for urban and rural populations. Double‐headed arrows indicate correlations between traits. Path coefficients are given next to the arrows (see text and Table S2 for details). To increase clarity, only significant (p < .05) paths are shown. Paths with quadratic terms are indicated with²