Abstract
Species delimitation is a difficult problem that has implications across organismal biology, yet no single method has proved wholly satisfactory. We tested the utility of combining species‐delimitation methods based on phylogeny and gene flow statistics using two parapatric members of the Coenonympha tullia group as an example: the endangered maritime ringlet butterfly ( Coenonympha nipisiquit McDunnough) and the common inornate ringlet butterfly ( Coenonympha inornata Edwards). We reconstructed the phylogeny of the nearctic C. tullia ‐group taxa from mitochondrial DNA (mtDNA) sequences (cytochrome oxidase I and mitochondrial control region) to explore the ancestry of the C. nipisiquit lineage within the group. We investigated the extent of gene flow between the two taxa with F ‐statistics using 587 nuclear amplified fragment length polymorphism markers, accounting for the effect of potential scoring ‘collisions’ where a marker may represent more than one DNA fragment. Combining species‐delimitation methods was especially effective because it uncovered both historical and recent evolutionary patterns. Phylogenetic analysis of mtDNA revealed the early divergence of C. nipisiquit from other C. tullia ‐group taxa, including the morphologically similar C. inornata. F ‐statistics and gene‐by‐gene introgression profiles demonstrated clear isolation between the two taxa and revealed strong population structure within C. nipisiquit. C. nipisiquit is the first taxon in the nearctic C. tullia group showing strong evidence of genetic isolation. The methods we used are relatively inexpensive and can be widely used to delimit taxonomic boundaries near the species level, both generally and in particular for taxa that may be targets of conservation efforts.