A preliminary study on female-limited colour polymorphism in Lestes sponsa

Abstract

Female-limited colour polymorphisms are widespread in Odonata, usually showing an androchrome and one or more gynochromes. Androchromes have been hypothesized to function as male mimics with a consequent decrease of male harassment, although males may also learn to recognize the different female colour morphs. In the Eurasian damselfly Lestes sponsa, the occurrence of two female colour morphs (androchrome and gynochrome) has been known since the beginning of the twentieth century, although this has been generally overlooked. In this work, we studied a Swedish population of L. sponsa by counting the number of females of each morph during nine consecutive days, as well as the number of tandems. Androchromes showed blue pruinescence at similar body parts as males, although more limited at the tip of the abdomen. Moreover, androchromes also showed bright blue coloured eyes as males. We found no indication that androchromes might be a result of age changes in female coloration. The androchrome morph accounted for 19% of the female population. Androchromes did not form tandems at a lower frequency than expected in the population, given the frequency of presence of each morph. Therefore our results suggest that either androchromes in this species do not function as male mimics, or that the population has reached equilibrium with equal fitness for each morph. Other aspects of male harassment and learned mate-recognition, as well as female morph behaviour, would shed light on the evolutionary and ecological significance of female morphs in this species.