The evolution of female wing pigmentation in dragon- and damselflies (Insecta: Odonata)

Ana Laura Martínez-García, Alex Córdoba-Aguilar y Martín A. Serrano-Meneses

In 1871, Charles Darwin used the theory of sexual selection to explain why males of several animal taxa exhibited extravagant traits. Therefore traits like horns, conspicuous colours, long tails or appendages, protuberances or elongated mandibles were labeled as sexual traits (ST).

A notable ST exhibited by adult males of several dragon- and damselfly taxa (odonates) is wing pigmentation. Although the sexual function of such trait is relatively well documented for several taxa (albeit most studies have concentrated on damselflies, particularly in calopterygids), very little is known about its origins. However, using odonates as a study group, M. A. Serrano-Meneses has recently shown in a phylogenetic comparative study, that male wing pigmentation in male odonates is more likely to evolve if high levels of sexual selection evolve first.

Wing pigmentation, nonetheless, is not exclusively exhibited by males; females of several odonate taxa also exhibit wing pigmentation. The images, for instance, show taxa in which both males and females have pigmented wings (females on the left, males on the right in every image). Although it is known that the trait can signal female reproductive potential in at least one species (in Calopteryx haemorrhoidalis wing pigmentation is negatively correlated with parasite burden), it is not known why wing pigmentation evolves in females.

In this study, Ana Laura Martínez investigated the origin and direction of the evolution of female wing pigmentation in odonates. The main objective was to test whether male and female wing pigmentation evolved in a correlated manner. To this end, Ana Laura Martínez used the photographs of 146 odonate taxa in order to determine whether males and/or females exhibited wing pigmentation (absence: 0; presence: 1). She also used a recent phylogenetic tree, along with a maximum-likelihood method, to first reconstruct the ancestral stages of both males and females. The results of such set of analyses suggest that the ancestral stages did not exhibit wing pigmentation. In a second step, Ana Laura Martínez used a directional phylogenetic comparative method (Bayes Traits - Discrete) in order to test whether male and female wing pigmentation co-evolved.

The results show that male and female wing pigmentation evolved in a correlated manner: females acquired wing pigmentation after males had acquired the trait (due to increasing levels of sexual selection). Nonetheless, once female wing pigmentation is acquired, it may be lost over time...only to be acquired again. Why does this happen? Perhaps the costs associated to maintaining the trait are too high for them. There may be selection against the acquisition of the trait as strong as selection favouring its acquisition via genetic correlation.

Read more »