Doctor of Philosophy (PhD)


Biological Sciences

Document Type



The high biodiversity found in the Amazon Basin has long captivated the attention of naturalists and evolutionary biologists seeking to explain its origins. Early observations by Alfred Wallace highlighted the role of rivers in delimiting the geographic ranges of many species; furthermore, where rivers narrow towards their headwaters, he noted that some species cross rivers freely. A major goal of this dissertation is to investigate how these and other observations about riverine barriers might inform our understanding of how speciation unfolds in Amazonia. My approach involved generating genomic data with dense geographic sampling for manakins in the genus Lepidothrix, particularly the Blue-capped Manakin (Lepidothrix coronata). Using these data, I first estimated a phylogeny of the genus, clarifying evolutionary relationships and facilitating testing of biogeographic hypotheses. Based on the newly generated phylogeny, I selected the monophyletic Blue-capped Manakin of the western Amazon Basin for an investigation of patterns of genetic connectivity around riverine barriers. I tested the hypothesis that genetic connectivity between populations is greater across narrow river headwaters and found evidence that this was the case in headwater regions of northern Peru, Ecuador, and Colombia, although I found exceptions as well. My findings suggest that river barriers as currently observed on the landscape are unlikely to fully account for cycles of allopatry and diversification of Amazonian species. However, I emphasize that Amazonian rivers are dynamic over time and there is mounting evidence to support the hypothesis that river channel movements can promote speciation in Amazonia. I conclude my dissertation by discussing how river channel movements help account for multiple patterns in Amazonian biogeography, and I describe the avian biogeography around a recent, well-dated river avulsion in Peru provide that provides a suitable context for testing hypotheses of Amazonian speciation.



Committee Chair

Brumfield, Robb T.