Frequency and magnitude of wing asymmetry in Central Texas dragonflies (Odonata: Libellulidae)

Bilateral symmetry is a defining characteristic of many animal groups; however, subtle asymmetries in some traits are common. Asymmetry is thought to originate from different combinations of genetic, developmental, and environmental processes. Dragonflies are hemimetabolous predators with aquatic immatures and terrestrial adults. As with most aquatic insects, dragonfly reproduction is a function of the terrestrial adult. In some dragonfly species, a male’s reproductive success depends on the its ability to defend a territory (in some species), obtain a mate, fly in tandem, and guard an ovipositing female. Dragonfly fitness, therefore, is flight-dependent, and symmetrical wings should promote efficient and maneuverable flight. Here, we investigate the frequency and magnitude of wing asymmetry in various dragonfly species. Dragonflies were collected in 2009 and 2010 from the Lake Waco Wetland, Waco, TX and Lake Polk, Temple TX. Right and left wing lengths were measured to the nearest 0.1 mm, and the percent difference in each individual was calculated. We compared wing asymmetries between male and female conspecifics. The frequency of forewing asymmetry was common in all dragonfly species, but the magnitude was subtle. Only a single species exhibited a male/female difference in the amount of asymmetry present. Our results suggest that the frequency of forewing asymmetry is common among dragonflies, but the trait itself, i.e., the reduced magnitude of asymmetry, is likely under strong stabilizing selection pressure.