Dissertation Research: Sick in the city? Hosts and parasites in urban and non-urban habitats

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As cities grow larger and more species of animals make their homes in urban habitats, it becomes increasingly important to understand the effects of city life on animal health. Parasite infections can have significant impacts on animal survival and physiology, and urban habitats may change parasite infections in several ways. For example, urban habitats may change both the stressors that animals experience and their immune resistance to parasites. However, little is known about parasites in urban vs non-urban populations of vertebrate animals, including how they affect animal health and whether urban animals have different levels of stress hormones or immunity to parasites. This research will provide critical knowledge about the parasites that birds must withstand in order to survive in urban areas, which will inform future conservation efforts in urban habitats. This work will also help protect human health, since urban birds are potential reservoirs of human diseases; for example, urban birds are more likely to be infected with West Nile Virus than non-urban birds. Understanding what parasites urban birds are infected by, and what physiological states are associated with these infections, can help us better prevent disease spread from birds to humans. In order to better understand the effects of urbanization on parasitism and host physiology, the researchers will study a songbird, the Dark-eyed Junco (Junco hyemalis), from multiple cities and non-urban habitats across California. Previous research has found considerable variation in phenotype and parasitism between an urban and neighboring non-urban population of juncos. In a non-urban population, there was higher prevalence of parasites that require vectors for transmission. In the neighboring urban population, there was greater prevalence and intensity of directly and environmentally transmitted parasites, including an intestinal parasite, coccidia (Isospora sp.). Urban hosts also differed in endocrine physiology from non-urban birds. This project will combine extensive field surveys and aviary experiments to test 1) whether urbanization consistently results in these same patterns for environmentally transmitted versus vector-borne parasites; and 2) whether the observed difference in coccidia infection intensity between the urban and non-urban populations is due to traits of the host (relating to stress response and immune function) or traits of the parasite. By combining approaches from disease ecology and eco-immunology, this project will address the critical links among habitat characteristics, parasitism, and host phenotypes.