Title

Elucidating the Factors that Modulate the Distribution of Avian Haemosporida Parasites across a Community of Hosts

Document Type

Dissertation

Degree

Doctor of Philosophy

Major

Biology

Date of Defense

12-9-2018

Graduate Advisor

Robert E. Ricklefs, Ph.D.

Committee

Clark, Hewitt B.

Marquis, Robert

Zanne, Amy

Abstract

Parasites are heterogeneously distributed across host species, host populations, and host individuals within populations. A primary aim of infectious disease ecology seeks to uncover the factors that drive this heterogeneity. At a fundamental level, host infection is determined by exposure and susceptibility to a pathogen. My dissertation explores how evolutionary and ecological forces associated with these fundamental determinates of infection shape variation in parasite host breadth and host infection status. Here, I focus on a community of vector-borne avian Haemosporida parasites among suburban birds of Chicago, IL. These parasites exhibit strong variation in their distribution among available hosts, and provide an ideal system to investigate factors that structure parasite-host interactions. I find that while a vector-imposed encounter rate explains variation in the total prevalence of Plasmodium parasites among host species, it does not account for variation in the relationships of individual Plasmodium taxa with different host species. Instead, host species that are more closely related phylogenetically share more parasites. In addition, I present evidence for a trade-off between different parasite host breadth strategies. Specialized Haemosporida taxa reach higher prevalence in their sole host species than generalist Haemosporida taxa, which also infected other host species. In addition, specialists achieved higher prevalence on older host individuals suggesting that they can persist in their hosts longer than generalists. There was no relationship between host breadth and the density of infected hosts. This suggests that specialists infect the same number of hosts as generalists, and compensate for their narrower host ranges by achieving higher prevalence on more abundant hosts. Cumulatively, my dissertation highlights the role that evolutionary forces between the host and parasite play in delimiting the host ranges of vector-borne parasites.

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