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.
Highlights
Urbanization is a major human-induced selective force driving rapid phenotypic change and evolution (Alberti, 2015; Alberti et al, 2017; Sullivan, Bird, & Perry, 2017)
Urban damselfly populations were differentiated from rural populations by having a higher flight endurance
In line with our prediction, the higher flight performance of urban males was reinforced by sexual selection
Summary
Urbanization is a major human-induced selective force driving rapid phenotypic change and evolution Similar findings have been reported in studies comparing edge and core populations of range expanding species: increased dispersal ability is common in the more recently colonized edge populations (Hill, Griffiths, & Thomas, 2011) Both spatial sorting (Shine, Brown, & Phillips, 2011), the process where only the organisms with the best locomotor abilities end up at the range front, and local adaptation (Travis & Dytham, 2002) may contribute to dispersal-enhancing phenotypes at invasion fronts, spatial sorting has been suggested as the main driver (Van Petegem, Boeye, Stoks, & Bonte, 2016). The human-induced changes in mean phenotypic traits in urban habitats (Alberti et al, 2017; Sullivan et al, 2017) can be expected to result in different selection regimes between urban and rural populations This may be especially true for sexual selection in mating systems such as scrambling competition where increased locomotor performance is selected for (Husak & Fox, 2008). Given the expected higher flight endurance in urban populations, and the finding that flight endurance only positively influences mating success above a threshold value in the study species (Gyulavári, Therry, Dévai, & Stoks, 2014), we predicted stronger sexual selection on flight endurance in urban populations
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