Complex population differentiation in checkerspot butterflies (Euphydryas spp.)

Gel electrophoresis was used to obtain an estimate of the genetic similarity among populations of Euphydryas anicia, Euphydryas chalcedona, and Euphydryas colon in an effort to determine whether they should be considered separate species or arbitrary groupings of populations in a single polytypic species. The average genetic distances between these entities, which collectively are referred to as the "ACC complex," are of the magnitude found between insect subspecies rather than between insect species. Furthermore, these entities show no unique combinations of morphological or biochemical characters that permit all individuals to be assigned with assurance to a specific taxon. Although cases of apparent reproductive isolation between some sympatric populations within the ACC complex have been reported, they appear to be terminal populations of "rings of races," rather than points of contact between completely isolated reproductive units. We recommend that the ACC complex be treated as a single highly variable species, Euphydryas chalcedona.