McKee, Clif, author2017-11-092017-11-092017https://hdl.handle.net/10217/184808Most human infectious diseases have origins in other animal species. Estimating when infectious microbes evolved will help us understand their ability to specialize on a broad range of host species. Using Bayesian phylogenetic techniques, I determine that the bacterial genus Bartonella, a parasite of mammals globally, emerged as a gut symbiont of arthropods 100-200 million years ago. It then diversified after transitioning to a parasitic lifestyle targeting mammals and using blood-feeding ectoparasites as vectors during the Cretaceous, 79-145 millions years ago. Other microbes may be equally old and may reflect a general trend in the evolution of modern diseases.born digitalStudent workspostersengCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.disease ecologyphylogeneticsevolutionBartonellaText