Data from: Stress hormone receptors change as range expansion progresses in house sparrows

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 mRNA expression of GC receptors (mineralocorticoid, MR and
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 MR mRNA at the range
edge. Reduced MR (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 from this 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.