The conundrum of species delimitation: a genomic perspective on a mitogenetically super-variable butterfly

The Palearctic butterfly Melitaea didyma stands out as one of the most striking cases of intraspecific genetic differentiation detected in Lepidoptera: 11 partially sympatric mitochondrial lineages have been reported, displaying levels of divergence of up to 7.4%. To better understand the evolutionary processes underlying the diversity observed in mtDNA, we compared mtDNA and genome-wide SNP data using double-digest restriction site-associated DNA sequencing (ddRADseq) results from 93 specimens of M. didyma ranging from Morocco to eastern Kazakhstan. We found that, between ddRADseq and mtDNA results, there is a match only in populations that likely remained allopatric for long periods of time. Other mtDNA lineages may have resulted from introgression events and were probably affected by Wolbachia infection. The five main ddRADseq clades supported by STRUCTURE were parapatric or allopatric and showed high pairwise FST values, but some were also estimated to display various levels of gene...