SG: Eco-evolution in a concrete jungle: how rapid urbanization affects host-parasite interactions in the Galapagos Islands

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Human population size is increasing exponentially and, in turn, the urban environment is one of the few ecosystems that is rapidly expanding. A recent example of urbanization is in the Galapagos Islands, which is home to the iconic Darwin’s finches. The Galapagos currently hosts 225,000 tourists each year and is home to over 21,300 permanent residents. Consequently, humans have altered the natural habitat and introduced parasites to the Galapagos, such as a parasitic nest fly (Philornis downsi), which causes significant mortality to baby finches. However, recent work shows that small ground finches (Geospiza fuliginosa; a species of Darwin’s finch) in urban areas are healthier and less affected by the parasite compared to finches in non-urban areas, which suggests that birds are better defended against the parasite in urban areas. The goal of the research is to determine why Darwin’s finches in urban areas are less affected by the parasitic nest fly than finches in non-urban areas. The research will first explore what specific immune responses are being produced by the urban finches to lower their parasite burden. The work will then determine whether these heightened immune responses are driven by: 1) the environment, such as through urban food supplementation that could increase allocated energy to immunity, or 2) heritable genetic changes to the immune system within the urban population. Overall, the research seeks to understand bird-parasite interactions in response to urbanization by identifying the potential environmental or evolutionary basis of immunity to a novel parasite in a novel environment. The proposed work will also include broader impacts from a local to international scale through the development of in-class K-12 activities, public presentations, and online videos related to the research.The research will use a series of experimental field studies to determine the immunological changes potentially occurring in Darwin’s finches in response to urbanization and whether these changes are driven by environmental conditions or adaptive evolution. First, the work will determine what mechanisms of immunity differ between urban and non-urban finches by experimentally manipulating the parasite and characterizing gene expression of candidate immune genes in the finches across locations. Second, the research will determine whether environmental factors, such as increased food availability, in the urban area are driving differences in finch immunity by experimentally supplementing urban and non-urban finches with human-based food, then determining finch immunity and parasite burden. Lastly, the research will determine whether urban finches have adaptively evolved immunity to the parasite using a common garden experiment, whereby urban and non-urban finch young will be cross fostered in their original or new area, then their immunity and parasite burden will be quantified. The Galapagos system is powerful to address fundamental questions in urban eco-evolution because of the significant amount of established groundwork, the ability to perform experiments in the field, and the relatively recent urbanization of the islands.This project is co-funded by the Evolutionary Processes cluster in the Division of Environmental Biology and the Symbiosis, Defense and Self-recognition Program in the Division of Integrative Organismal Systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.