Rapid colour shift by reproductive character displacement in Cupido butterflies
Reproductive character displacement occurs when competition for successful breeding imposes a divergent selection on the interacting species, causing a divergence of reproductive traits. Here, we show that a disputed butterfly taxon is but a case of rapid male wing colour shift, apparently produced by reproductive character displacement. Using genomic ddRAD and mtDNA sequencing we studied four butterfly species of the subgenus Cupido (Lepidoptera: Lycaenidae): Cupido carswelli and C. minimus, both characterized by brown males and females, as well as C. lorquinii and C. osiris, both with blue males and brown females. Unexpectedly, C. carswelli and C. lorquinii were virtually indistinguishable in their nuclear and mitochondrial genomes, albeit the striking difference in male colouration. We report and analysed a brown male within the C. lorquinii range, which demonstrates that the brown morph is present at low frequency in C. lorquinii. These evidences strongly suggest that the taxon carswelli is conspecific with C. lorquinii and represents populations with a fixed male colour morph. Given that these brown populations occur in sympatry with the blue C. osiris, and that the lorquinii blue populations never do, we propose that the taxon carswelli could have lost the blue colour due to reproductive character displacement with C. osiris. Since male colour is important in mate choice for females, we hypothesize that the observed colour shift may eventually trigger incipient speciation between blue and brown populations. Considering that male colour seems to be an evolutionarily labile character in the Polyommatinae, the mechanism described here might be at work in the broad diversification of this group of butterflies.