Consistent seasonal polyphenism in male genitalia of threeLeptideabutterfly species (Lepidoptera: Pieridae)

Abstract

Insect genitalia are important for species identification and taxonomy and are key traits for the evolution of reproductive isolation through their 'lock-And-key mechanism'. Nevertheless, few studies have evaluated intraspecific variation and the impact of seasonal environmental variation on genital morphology. We used geometric morphometric analysis to quantify male genital morphology within and among the three taxa in the Leptidea sinapis cryptic species complex (Lepidoptera: Pieridae). We focused on the potential presence of seasonal polyphenism, i.e. consistent differences among temporally separated generations. As predicted, our analysis revealed that male genitalia differed in size, shape and form (the joint effect of size and shape) among species. More surprisingly, all species harboured consistent genital variation between the spring and summer generations. The interspecific variation in genital structures could function as a mechanical reproductive barrier, although contemporary populations of these butterflies do not engage in heterospecific matings. We suggest that the smaller, but significant, genital differences among conspecific generations provide an opportunity to test empirically whether a seasonal polyphenism in genital morphology could generate raw material for the build-up of reproductive isolation at an early stage of speciation. Collectively, our results provide evidence demonstrating that insect genitalia can indeed harbour ample intraspecific variation. (Less)