Stress hormone receptors change as range expansion progresses in house sparrows

Abstract

As ranges expand, individuals encounter different environments at the periphery than at the centre of the range. Previously, we have shown that glucocorticoids (GCs) vary with range expansion: individuals at the range edge release more GCs in response to restraint. Here, we measured hippocampal mRNAexpression ofGC receptors (mineralocorticoid,MRand glucocorticoid, GR) in eight house sparrow (Passer domesticus) populations varying in age.We found that individuals closest to the range edge had the lowest expression of MR relative to GR; in all likelihood, this relationship was driven by a marginal reduction of MRmRNA at the range edge. ReducedMR (relative to GR) might allow enhanced GC binding to GR, the lower affinity receptor that would enhance a rapid physiological and behavioural response to stressors. The insights gained fromthis study are not only enlightening to introduced species, but may also predict how certain species will react as their ranges shift owing to anthropogenic changes. © 2013 The Author(s) Published by the Royal Society.