Evolutionary ecological genetics of some neotropical birds

Abstract

Most of the current models to explain the diversification of Neotropical birds focus on physical barriers to gene flow. However, for any species the geographic structuring of populations is caused by an interaction between physical barriers to gene flow and a species' propensity to overcome those barriers. The three chapters presented in this dissertation provide three perspectives on this interaction and how it has shaped the diversification of some Neotropical birds. First, the widespread Neotropical lowland forest flycatcher Mionectes oleagineus had three phylogeographic splits across the Andes, resulting in four geographically structured lineages west of the Andes. At least two of these splits post-date Andean uplift, and therefore represent dispersal across the Andes. Coalescent estimates suggest that gene flow occurred with some regularity after the third colonization event several hundred thousand years ago. Secondly, I found that within-population genetic variation in nine codistributed Neotropical landbirds fit a humped distribution, whereby mid-range populations had higher genetic diversity than range-edge populations. This finding is not consistent with a model of increasing genetic diversity with decreasing latitude. Thirdly, I examined variation in genetic differentiation between two populations in 60 codistributed Neotropical landbirds. All species were sampled in southern Belize and central Panama, and I found that the net nucleotide divergence (DA) spanned two orders of magnitude (0.00%--0.085%). Species of frugivores and nectivores had significantly lower DA values than species of insectivores, and in a subsample of 19 species with population-level sampling I found that populations of frugivores and nectivores were significantly more likely to show genetic signals of population expansion than populations of insectivores. These results suggest that foraging ecology plays a fundamentally import role in determining diversification patterns of neotropical birds. These three results should provide important baseline data and new insights into the processes that have led to the neotropical region having the highest avian diversity of all the Earth's biomes.