Abstract

A recent phylogenetic survey of the New World orioles (genus Icterus; Omland et al. 1999) suggested that the Baltimore Oriole (I. galbula) and the Black-backed Oriole (I. abeillei) are sister taxa. That survey examined mitochondrial DNA (mtDNA) from a single representative of each species in the genus. Here, we examine mtDNA sequences from 15 Blackbacked and 20 Baltimore Orioles. The two species appear to be very recently diverged, with average sequence divergences for both cytochrome b (cyt b) and the control region indicating a probable late Pleistocene split. Despite this very recent divergence, there is one fixed base-pair difference between the species in cyt b and another in the control region, suggesting that one or both species have undergone a bottleneck during or since speciation. This molecular evidence of recent divergence suggests that male plumage differences between Black-backed and Baltimore Orioles evolved very rapidly.