A tale of two haplotype groups: Evaluating the New World Junonia ring species hypothesis using the distribution of divergent COI haplotypes.

The New World Junonia butterflies are a possible ring species with a circum-Caribbean distribution. Previous reports suggest a steady transition between North and South American forms in Mesoamerica, but in Cuba the forms were thought to co-exist without interbreeding representing the overlapping ends of the ring. Three criteria establish the existence of a ring species: a ring-shaped geographic distribution, gene flow among intervening forms, and genetic isolation in the region of range overlap. We evaluated mitochondrial cytochrome oxidase I haplotypes in Junonia from 9 species in the Western Hemisphere to test the Junonia ring species hypothesis. Junonia species are generally not monophyletic with respect to COI haplotypes, which are shared across species. However, two major COI haplotype groups exist. Group A predominates in South America, and Group B predominates in North and Central America. Therefore, COI haplotypes can be used to assess the degree of genetic influence a population receives from each continent. Junonia shows a ring-shaped distribution around the Caribbean, and evidence is consistent with gene flow among forms of Junonia, including those from Mesoamerica. However, we detected no discontinuity in gene flow in Cuba or elsewhere in the Caribbean consistent with genetic isolation in the region of overlap. Though sampling is still very limited in the critical region, the only remaining possiblity for a circum-Caribbean discontinuity in gene flow is at the Isthmus of Panama, where there may be a transition from 98% Group B haplotypes in Costa Rica to 85-100% Group A haplotypes in South America.