Probing evolutionary patterns in neotropical birds through DNA barcodes

Abstract

Background: The Neotropical avifauna is more diverse than that of any other biogeographic region, but our understanding of patterns of regional divergence is limited. Critical examination of this issue is currently constrained by the limited genetic information available. This study begins to address this gap by assembling a library of mitochondrial COI sequences, or DNA barcodes, for Argentinian birds and comparing their patterns of genetic diversity to those of North American birds.

Methodology and principal findings: Five hundred Argentinian species were examined, making this the first major examination of DNA barcodes for South American birds. Our results indicate that most southern Neotropical bird species show deep sequence divergence from their nearest-neighbour, corroborating that the high diversity of this fauna is not based on an elevated incidence of young species radiations. Although species ages appear similar in temperate North and South American avifaunas, patterns of regional divergence are more complex in the Neotropics, suggesting that the high diversity of the Neotropical avifauna has been fueled by greater opportunities for regional divergence. Deep genetic splits were observed in at least 21 species, though distribution patterns of these lineages were variable. The lack of shared polymorphisms in species, even in species with less than 0.5M years of reproductive isolation, further suggests that selective sweeps could regularly excise ancestral mitochondrial polymorphisms.

Conclusions: These findings confirm the efficacy of species delimitation in birds via DNA barcodes, even when tested on a global scale. Further, they demonstrate how large libraries of a standardized gene region provide insight into evolutionary processes.

Figure 1. Frequency histogram of COI sequence variation for birds of Argentina.

Distance to nearest congeneric neighbour for 282 species from genera represented by multiple taxa (black) and mean intraspecific distance for the 389 species of birds with two or more sequence records (white).

Figure 2. Maps detailing the different distributional patterns of divergent barcode lineages.

Species ranges are highlighted in green and circles indicate collection sites. Hollow and filled in circles correspond to lineages represented on superimposed neighbour-joining trees (shaded circles represent sites with overlap). (A) Barcode lineages are allopatric and coincide with disjunctions in the distribution of populations (e.g. Thamnophilus ruficapillus). (B) Barcode lineages are allopatric, but species distribution appears continuous (e.g. Cinclodes fuscus). (C) Barcode lineages are parapatric (e.g. Vireo olivaceus). (D) Barcode lineages are sympatric (e.g. Manacus manacus).