Meeting Abstract
Much of what we know about the vertebrate stress response to environmental stressors comes from measuring circulating glucocorticoids in free-living animals. However, quantifying glucocorticoid receptor (GR) expression may be equally important as measuring circulating hormones because only when glucocorticoids bind to the receptor does gene transcription begin. GR expression is influenced not only by a variety of environmental stressors, but also by sequence variation in the GR gene (NR3C1) itself, which affects hormone binding affinity and transcriptional activity. Surprisingly, we know little about NR3C1 evolution because few studies have explored GR evolution in free-living, non-model organisms. Here we looked for signatures of selection in the GR in African starlings, a group that inhabits a range of environments from desert to savanna to forest. Previous work in this group has shown that many species may be behaviorally and physiologically adapted to living in environmentally unpredictable environments. To investigate adaptive mechanisms underlying the vertebrate stress response in variable environments, we sequenced all eight exons of NR3C1 in 27 species of African starlings. Sequence variation was analyzed using phylogenetic comparative methods to determine whether substitution rates varied across habitats or were conserved in related species. Preliminary results suggest that the multiple haplotypes of NR3C1 observed in African starlings may reflect adaptation to local environments. This study is the first to examine the molecular mechanisms that underlie the lability of the vertebrate stress response in unpredictable environments. It has important implications for understanding how climate change may impact the evolution of the vertebrate stress response.
