Abstract
Abstract Although the endocrine system likely plays an important role in orchestrating the transition to a migratory state, the specific mechanisms by which this occurs remain poorly understood. Changes in glucocorticoid signaling are one proposed mechanism that may be important in migratory transitions. Although previous work has focused on the role of changes in circulating glucocorticoids, another potential mechanism is changes in the expression of its cognate receptors. Here, we test this hypothesis by comparing mRNA expression of the genes for the mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) in two brain regions implicated in the regulation of migratory behavior (the hippocampus and hypothalamus) in pine siskins (Spinus pinus) sampled before or after the transition to a spring nomadic migratory state. Compared to pre-migratory birds, migratory birds had body conditions more indicative of physiological preparations for migration (e.g., larger body mass), and greater levels of nocturnal migratory restlessness. However, we found no differences between pre-migratory and migratory birds in the expression of GR or MR mRNA in either the hippocampus or hypothalamus. Thus, differences in expression of receptors for glucocorticoids do not appear to underly the observed differences in physiology and behavior across a migratory transition. Taken together with previous results showing no change in circulating corticosterone levels during this transition, our findings provide no evidence for a role of glucocorticoid signaling in the spring migratory transition of this species.
Highlights
The lives of many vertebrates are organized into annual cycles, made up of different life history stages such as breeding, migration, and wintering
Previous work has focused on the role of changes in circulating glucocorticoids, another potential mechanism is changes in the expression of its cognate receptors. We test this hypothesis by comparing mRNA expression of the genes for the mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) in two brain regions implicated in the regulation of migratory behavior in pine siskins (Spinus pinus) sampled before or after the transition to a spring nomadic migratory state
Migratory indicators and mRNA expression were compared between sampling groups using t-tests when data met the assumption of normality or Mann-Whitney U tests when data were not normally distributed
Summary
The lives of many vertebrates are organized into annual cycles, made up of different life history stages such as breeding, migration, and wintering. The endocrine system plays a central role in orchestrating transitions between these life history stages by coordinating changes in behavior, morphology and physiology [1]. These life history stage transitions provide rich opportunities to resolve the role of endocrine mechanisms in regulating behavior and physiology by comparing endocrine function among animals at different stages. Migration may occur relatively predictably at an anticipated time for which an animal can prepare. This is the case for spring migration in many species of birds, for example. The endocrine mechanisms underpinning these different forms of migration may differ [5], it has been hypothesized that glucocorticoids may play a role in both forms of migration [6,7,8,9,10]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
