Phylogenetic relationships of Phyciodes butterfly species (Lepidoptera: Nymphalidae): complex mtDNA variation and species delimitations

Abstract. Mitochondrial DNA variation was studied in the butterfly genus Phyciodes (Lepidoptera: Nymphalidae) by sequencing 1450 bp of the COI gene from 140 individuals of all eleven currently recognized species. The study focused on four species in particular that have been taxonomically difficult for the past century, P. tharos, P. cocyta, P. batesii and P. pulchella. A cladistic analysis of ninety-eight unique haplotypes showed that Phyciodes forms a monophyletic group with P. graphica as the most basal species. Of the three informal species groups described for Phyciodes, only one (the mylitta-group) is unambiguously monophyletic. Within the tharos-group, seven well supported clades were found that correspond to three taxa, P. tharos, P. pulchella and a grade consisting of P. cocyta and P. batesii haplotypes interdigitated with each other. None of the clades is formed exclusively by one species. The patterns of haplotype variation are the result of both retained ancient polymorphism and introgression. Introgression appears to be most common between P. cocyta and P. batesii; however, these two species occur sympatrically and are morphologically and ecologically distinct, suggesting that the level of current introgression does not seem to be enough to threaten their genetic integrity. The results indicate that mitochondrial DNA sequences must be used with great caution in delimiting species, especially when infraspecific samples are few, or introgression seems to be rampant.