Novel Intron Phylogeny Supports Plumage Convergence in Orioles (Icterus)

Abstract

A recent study of New World orioles (Icterus spp.), which traced a large number of plumage characters onto a mitochondrial DNA phylogeny, reported high frequencies of evolutionary convergence and reversal of plumage characters (Omland and Lanyon 2000). Although those results are consistent with other smaller scale studies that have documented plumage homoplasy, the mitochondrial genome is inherited as a single linkage group, so mitochondrial data represent only one gene tree. The mitochondrial (mt) DNA tree may not reflect the true evolutionary history of a lineage; therefore, it remains possible that the plumage characters could reflect the true species phylogeny. Other rapidly evolving regions of DNA can provide independent phylogenetic hypotheses useful for evaluating mitochondrial gene trees. A novel phylogenetic marker, a region of the nuclear gene ornithine decarboxylase (ODC) spanning from exon 6 to exon 8, was sequenced in 10 oriole species. The resultant nuclear gene tree reconstructs the same three major oriole clades as the mtDNA tree (Omland et al. 1999), supporting the conclusion that plumage evolution in the New World orioles has been highly homoplastic. Although most phylogenetic studies that have employed introns report greatest resolution at the genus or family level, ODC appears to offer some degree of phylogenetic resolution for infrageneric analyses. However, that intron has clearly not sorted to monophyly within or between closely related species.