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Macroevolutionary dynamics of bill evolution and diversification in tanagers (Passeriformes: thraupidae)
Vinciguerra, Nicholas T.
Burns, Kevin J.
Reeder, Tod W.Pryde, Philip R.
A fundamental pattern of biodiversity is that it is unevenly distributed across the tree of life, both in terms of species richness and morphological disparity. Understanding the relationship between species richness and morphological disparity, therefore, is a central goal of evolutionary biology. Many ideas have been put forth to explain patterns of morphological disparity and species richness, some of which include clade age or differential diversification via adaptive radiation. Ecological opportunity is hypothesized to be the primary catalyst of adaptive radiation, but the role of this process in generating species and morphological diversity across broad spatial and taxonomic scales remains unclear. In this thesis, I investigated the tempo and mode of bill evolution and diversification in tanagers (Passeriformes: Thraupidae, 377 species), an ecologically and morphologically diverse continental assemblage of Neotropical songbirds. The first objective of my thesis was to test one of the central predications of an adaptive radiation, rapid morphological evolution, using a species-level molecular phylogeny of tanagers and comparative methods. For bill size, the pattern of trait evolution and disparity through time was no different than expected from a constant rate Brownian motion process. In contrast, I found evidence for an early burst of bill shape disparity in the evolutionary history of tanagers, which is consistent with a model of adaptive radiation and the filling of ecomorphological space. My second objective was to investigate links between bill morphology and speciation in tanagers. I tested three hypotheses: (1) a particular bill shape (e.g. insectivorous, granivorous) influences speciation rate (trait-dependent speciation), (2) bill size and shape divergence is associated with speciation events (speciational evolution), and (3) speciation rates are correlated with rates of bill evolution. I found no evidence of trait-dependent speciation and no association between rates of bill evolution and the rate of speciation. However, I did find support for a mixed model of speciational and gradual trait change. These results indicate that bill size and shape diversify in association with the speciation process, but not through an association with speciation rate itself.
San Diego State University
Master of Science (M.S.) San Diego State University, 2020
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