Short-term mating success in relation to fluctuating wing asymmetry in the male azure damselfly Coenagrion puella

Abstract

As top flying predators, damselflies rely on wing symmetry and functionality. However, already during aquatic larval development, environmental stressors, including anthropogenic ones, can affect their development and impair wing morphology raising the question whether such alterations affect reproductive fitness. To investigate the role of wing morphology in mating success, we collected males of Coenagrion puella observed in copulation wheels (indicating short-term mating success) or actively chasing other wheel or tandem formations (unsuccessful mating attempts at the time of capture). Twenty individuals of each group were collected at two locations differing in environmental and anthropogenic pressures: one regularly used for recreational fishing and surrounded by agriculture in the Rhine Valley and one consisting of research ponds in the Palatinate Forest with restricted public access. Wing morphology and symmetry were assessed via computer-vision by comparing several cell shape and position dependent variables as well as wing size and number of cells and junctions using the recently developed software WingAnalogy. Mating males in the Palatinate Forest exhibited higher cell shape asymmetry than mating males in the Rhine Valley. In these individuals, the cell shape asymmetry was more pronounced in the distal part of the wing than in the proximal part. Mating males had lower body weight (-5%) and smaller wings (-3%) compared to chasing males at both locations. Our results challenge the general theory that stress-induced lower body weight and higher asymmetry diminish short-term mating success. Instead, they underscore the ecological importance of population-specific factors, like female availability or male-male competition, and environmental conditions that shape mating dynamics. Our results suggest that anthropogenic stressors in aquatic habitats have implications for terrestrial food webs by affecting the reproductive interactions of adult amphibiotic top predators, such as damselflies. This highlights the need to consider cross-ecosystem carry-over effects in ecological monitoring and conservation strategies.