Recent speciation in the orchard oriole group: Divergence of Icterus spurius spurius and Icterus spurius fuertesi

Abstract

New World orioles (Icterus) include several closely related species and subspecies pairs that provide excellent opportunities for studying recent speciation. We examined a subspecies pair in the Orchard Oriole group: Orchard Oriole (l. spurius spurius), a longdistance migrant that breeds in eastern North America, and Fuertes's Oriole (l. s. fuertesi), a shortdistance migrant that breeds in a restricted range in Veracruz, Mexico. We sequenced parts of the mitochondrial cytochromeb gene (925 base pairs) and control region (344 base pairs) freom 23 Orchard Orioles and 7 Fuertes's Orioles. Subspecies are not reciprocally monophyletic. Instead, our data suggest that at least one taxon is paraphyletic or polyphyletic. We found little support for any further phylogenetic structure, including whether one subspecies might be derived freom the other. However, haplotype freequency analysis suggests that there is little or no current gene flow between the taxa. The phylogenetic relationship between Orchard and Fuertes's orioles is likely a result of recent divergence and incomplete lineage sorting. That interpretation is consistent with theoretical models of speciation, which predict patterns of nonmonophyly at early stages of taxon divergence. Our findings suggest that Orchard and Fuertes's orioles are separate species and provide a case study for evaluating the importance of monophyly in defining species limits.