Meeting Abstract
As climate change increases globally, vertebrates must cope with increasingly variable and unpredictable environmental conditions. The glucocorticoid stress response enables vertebrates to adjust their behavior and physiology to these changes in the environment, but organisms can respond to environmental stressors only when circulating hormones bind to the glucocorticoid receptor. A variety of environmental stressors influence glucocorticoid receptor expression, but DNA sequence variation in the glucocorticoid receptor gene (Nr3c1) also affects hormone binding affinity and transcriptional activity. Genetic variation in the HPA axis—and particularly in the glucocorticoid receptor—may facilitate adaptation to changing conditions. Here we examined signatures of selection in the glucocorticoid receptor in African starlings (Family: Sturnidae). African starlings occupy a range of environments that vary in precipitation across seasons and years, and many species may be behaviorally and physiologically adapted to environmentally unpredictable habitats. We sequenced Nr3c1 in 27 species of African starlings to investigate whether vertebrates cope with changing environmental conditions via adaptive genetic variation. Although we found low levels of sequence variation in Nr3c1 across species and populations of African starlings, substitution rate (dN/dS) is correlated with variance in precipitation. This relationship suggests that environmental variation does influence evolution of the glucocorticoid receptor in African Sturnidae. During the radiation of African starlings, fluctuating selective pressures as a result of environmental variability may have enabled these birds to adjust their stress response to particular environments.
