A molecular phylogeny of forktail damselflies (genus Ischnura) reveals a dynamic macroevolutionary history of female colour polymorphisms

Colour polymorphisms are popular study systems among biologists interested in evolutionary dynamics, genomics, sexual selection and sexual conflict. In many damselflies, such as in the globally distributed genus Ischnura (forktails), female colour polymorphisms occur in some species. Female-polymorphic species contain two or three female morphs, one of which is male-coloured (androchrome or male mimic) and co-exists with sexually dimorphic (heterochrome) females. These female colour polymorphisms are considered to be maintained by frequency-dependent sexual conflict, but their macroevolutionary histories are unknown, due to the lack of a robust molecular phylogeny. Here, we present the first time-calibrated phylogeny of Ischnura, using a multispecies coalescent approach (StarBEAST2), incorporating both molecular data and fossil information of 41 extant species (55% of the genus). We estimate the age of Ischnura to be between 13.8 and 23.4 millions of years, i.e. Miocene. We infer the an...