Influence of human activity on gut microbiota and immune responses of Darwin's finches in the Galapagos Islands

Urbanization can influence animal traits, including immunity and gut microbiota. Over the past several decades, the Galapagos Islands have seen rapid resident human population growth and tourist activity, leading to varying levels of human activity across Islands. Consequently, diet, gut microbiota, and immunity of endemic animals, such as Darwins finches, may have changed. The goal of this study was to determine the effect of land use on the immune response, gut microbiota, and body measurements of Darwins finches in 2008, at a time of rapidly increasing human activity in the Islands. Specifically, we compared proxies of immunity (lysozyme activity, and haptoglobin, complement antibody, and natural antibody levels), gut microbiota (bacterial diversity, community structure and membership, and relative abundance of bacterial taxa), and body measurements (body mass, tarsus length, and scaled mass index) across undeveloped, agricultural, and urban areas for medium ground finches (Geospiza fortis) and small ground finches (G. fuliginosa). We found that lysozyme activity was lower and observed bacterial species richness was higher in urban areas compared to non-urban areas across both finch species. For small ground finches, relative abundances of three bacterial genera (Pseudoxanthomonas, Cloacibacterium, and Dietzia spp.) were higher in urban areas compared to non-urban areas, but this pattern was not observed in medium ground finches. Medium ground finches were smaller in undeveloped areas compared to the other two areas, but body measurements of small ground finches did not differ across areas. Our results suggest that human activity can impact immune measures and gut microbiota of Darwins finches.