Meeting Abstract
Most of what is known about the mechanisms regulating the transition to a migratory state comes from studies of species that make obligate migrations – regular and predictable movements to and from the same locations. In contrast, very little is known about the regulation of nomadic migrations, which occur unpredictably in space and/or time. For some nomadic migrants, there is a seasonal component to their movements, with a temporal window when migration is most likely to occur. In one such nomadic species, the pine siskin (Spinus pinus), we have found that increasing spring day lengths stimulate physiological preparations for migration and expression of migratory restlessness. Here, we examine the potential role of changes in glucocorticoid signaling – implicated in other forms of migration – in the transition to a nomadic migratory state. Using captive wild-caught pine siskins, we compared circulating corticosterone levels and expression of glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) mRNA in key brain regions in birds before and after the onset of spring migratory restlessness. We found no change in circulating corticosterone levels as birds transitioned to a migratory state. We similarly found no differences in the expression of GR or MR in the hypothalamus or hippocampus of birds expressing spring migratory restlessness compared to those sampled before the onset of migratory restlessness. Our results do not suggest a significant role for changes in glucocorticoid signaling in the expression of a seasonal window for nomadic migration in pine siskins. These results are in contrast to evidence for a role of glucocorticoid signaling in some obligate migrations and in other forms of facultative migration.
