Male agility in relation to mating success in two non-territorial damselflies

Male body size is usually correlated with mating success in insects. In non-territorial species, smaller males may have an advantage because small body size may predict agility and maneuverability. Consequently, selection for male size may drive the evolution of female-biased sexual size dimorphism (SSD). Here, we investigated whether male size is an indicator of male agility and if it may be used to predict male reproductive success. To this end, we conducted a field study using two species of damselflies, Acanthagrion truncatum Selys, 1876 and A. lancea Selys, 1876 (Zygoptera, Coenagrionidae). We compared the body size and wing length of mated and unmated males, and between sexes, to describe their patterns of SSD. Males of A. truncatum adopt a sit-and-wait mating strategy, while the males actively search for females in A. lancea. Our results suggest that wing length can be used as a proxy for male body size and agility. However, we have found no evidence for small male advantage that could explain wing dimorphism in both species. In conclusion, this study corroborates other studies that suggest agility cannot explain SSD in non-territorial damselflies but fail to support the small male advantage hypothesis.