MSc Candidate, Bonier Lab
Among-species variation in hormone concentrations is associated with urban occurrence in birds
Urbanization of natural areas is increasing worldwide, contributing to rapid biodiversity loss. While most wildlife disappears as habitat becomes urbanized, some species survive and even thrive in cities, though the traits that allow them to do so remain poorly understood. Endocrine phenotypes, such as circulating hormone concentrations and sensitivity of endocrine responses, could underlie aspects of ecology, life history, and behaviour that influence organisms’ ability to cope with the challenges of urban habitats. However, to date, comparisons of endocrine phenotypes across urban and non-urban populations within species have revealed no consistent patterns, suggesting that individual and population-level responses to urbanization are complex and likely largely driven by plastic shifts. Here, we investigated the degree to which evolved variation in endocrine phenotypes among species predicts, and potentially contributes to, among-species variation in urban tolerance using a broad analysis of the association between circulating concentrations of baseline corticosterone, stress-induced corticosterone, and testosterone and estimates of urban occurrence for bird species from across the globe. Our results reveal context-dependent links between circulating glucocorticoids and urban tolerance, and lower testosterone concentrations in females from urban-tolerant species, relative to urban-avoidant species. These findings suggest there are multiple strategies for tolerating urban habitats, and indicate that other aspects of the endocrine phenotype, such as the ability to appropriately attenuate responses to urban challenges, might be more important for success in cities. This study provides the first ever among-species comparison of endocrine phenotypes across bird species that differ in their tolerance of urban habitat, offering novel insight into how evolved differences in endocrine traits may impact species’ ability to cope with ongoing urbanization. As the human population expands and many of the world’s natural habitats continue to be developed into urban environments, this knowledge will be crucial in understanding how wildlife will cope with our changing world.