On the importance of geographic and taxonomic sampling in phylogeography: A reevaluation of diversification and species limits in a Neotropical thrush (Aves, Turdidae).

Phylogeographic studies seeking to describe biogeographic patterns, infer evolutionary processes, and revise species-level classification should properly characterize the distribution ranges of study species, and thoroughly sample genetic variation across taxa and geography. This is particularly necessary for widely distributed organisms occurring in complex landscapes, such as the Neotropical region. Here, we clarify the geographic range and revisit the phylogeography of the Black-billed Thrush (Turdus ignobilis), a common passerine bird from lowland tropical South America, whose evolutionary relationships and species limits were recently evaluated employing phylogeographic analyses based on partial knowledge of its distribution and incomplete sampling of populations. Our work employing mitochondrial and nuclear DNA sequences sampled all named subspecies and multiple populations across northern South America, and uncovered patterns not apparent in earlier work, including a biogeographic interplay between the Amazon and Orinoco basins and the occurrence of distinct lineages with seemingly different habitat affinities in regional sympatry in the Colombian Amazon. In addition, we found that previous inferences about the affinities and taxonomic status of Andean populations assumed to be allied to populations from the Pantepui region were incorrect, implying that inferred biogeographic and taxonomic scenarios need re-evaluation. We propose a new taxonomic treatment, which recognizes two distinct biological species in the group. Our findings illustrate the importance of sufficient taxon and geographic sampling to reconstruct evolutionary history and to evaluate species limits among Neotropical organisms. Considering the scope of the questions asked, advances in Neotropical phylogeography will often require substantial cross-country scientific collaboration.