Within-season variation in sexual selection on flight performance and flight-related traits in a damselfly

Abstract

While selection is a key mechanism of evolution, our understanding of within-season variation in sexual selection remains limited. Here, we studied within-season sexual selection on two key performance traits, flight speed and flight endurance, and a set of morphological and physiological phenotypic traits in a natural population of the territorial damselfly Chalcolestes viridis. We applied a path analysis approach to address whether the flight-related traits affected mating success directly or indirectly through their effect on the flight performance traits, and whether these selection patterns differed between the first and second half of the reproductive season. While some trait means did not differ between both parts of the season (flight speed, wing loading and non-allometric wing shape), most traits showed within-season differences (flight endurance, fat content, flight muscle ratio, wing centroid size, body mass and the allometric wing shape). Despite the within-season temporal differences in flight endurance, sexual selection consistently favoured males with a higher flight endurance. None of the detected patterns of sexual selection on the flight-related traits were consistently significant in both periods: while we detected selection on wing loading and wing centroid size in the first half of the season, we detected selection on body mass in the second half of the season. More studies focusing on understudied traits such as performance traits are needed to refine our knowledge of the temporal dynamics of selection patterns in nature. This is important to arrive at a better understanding of the adaptive evolutionary dynamics of traits in natural populations.