Meeting Abstract
Traits that mediate vertebrate range expansions are only just being revealed, and such information may help mitigate the negative impacts of pest species on native communities as well as the challenges of global climate change on the distributions of endemics. Here, we summarize recent work we have conducted on the house sparrow (Passer domesticus) in Kenya. The species was introduced about 1950 to the coastal city of Mombasa, but has since spread across much of the country. We have found that range expansion was apparently mediated by adjustments in the regulation of the stress hormone, corticosterone, and the receptors integral to its effects (glucocorticoid (GR) and mineralocorticoid (MR)). Moreover, we have found that variation in stress hormone regulation is related to variation in behaviors relevant to range expansion. Birds at the range edge release much more corticosterone in response to restraint, and they are also much more exploratory, less neophobic (or more neophilic), and better able to consolidate (spatial) memories than birds from older sites; intriguingly though, birds at range edges are less innovative than birds from old sites. To discern whether these patterns are due directly to circulating corticosterone, we implanted individuals from one old, one new and one intermediate site with either a high or a low dose of corticosterone or a sham control, and assessed effects of the steroid treatments on some of the above behaviors. Analyses are still ongoing, but preliminary analyses indicate weak effects of corticosterone on behaviors, suggesting that any effects of this hormone might be correlated to behavior for unknown reasons or organized early in life.
