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 actually a case of male wing colour shift, apparently
produced by reproductive character displacement. Using double digest
restriction-site associated DNA sequencing and mitochondrial DNA
sequencing we studied four butterfly taxa of the subgenus Cupido
(Lepidoptera: Lycaenidae): Cupido minimus and the taxon carswelli, both
characterized by brown males and females, plus C. lorquinii and C. osiris,
both with blue males and brown females. Unexpectedly, taxa carswelli and
C. lorquinii were close to indistinguishable based on our genomic and
mitochondrial data, despite displaying strikingly different male
colouration. In addition, we report and analysed a brown male within the
C. lorquinii range, which demonstrates that the brown morph occurs at very
low frequency in C. lorquinii. Such evidence strongly suggests that
carswelli is conspecific with C. lorquinii and represents populations with
a fixed male brown colour morph. Considering that these brown populations
occur in sympatry with or very close to the blue C. osiris, and that the
blue C. lorquinii 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 for
conspecific recognition during courtship, we hypothesize that the observed
colour shift may eventually trigger incipient speciation between blue and
brown populations. Male colour seems to be an evolutionarily labile
character in the Polyommatinae, and the mechanism described here might be
at work in the wide diversification of this subfamily of butterflies.