Understanding the causes of range expansions in abundant species can help predict future species distributions. During range expansions, animals are exposed to novel environments and are required to cope with new and unpredictable stressors. Glucocorticoids (GCs) are mediators of the hormonal and behavioural mechanisms allowing animals to cope with unpredictable changes in the environment and are therefore expected to differ between populations at expansion edge and the historic range. However, to date, very few studies have evaluated the relationship between GCs and range expansion. The Egyptian mongoose has been rapidly expanding its range in Portugal over the past 30 years. In this study, we applied an information theoretic approach to determine the most important spatial and environmental predictors of hair GCs (hGCs) in the population, after controlling for normal patterns of hGC variation in the species. We observed a decrease in hGC as distance from the historic range increased (i.e. closer to the expansion front). This distance term was present in all of the top models and had a 95% confidence interval (95% CI) that did not overlap with zero, strongly supporting its influence on hGC. We estimated a 0.031 pg/mg (95% CI: −0.057, −0.004) decrease in hGCs for each kilometre distance to the Tagus River, which was once the limit of the species’ distribution. Our results indicate that the species’ expansion is unlikely to be limited by mechanisms related to or mediated by the physiological stress response. The decrease in hGC levels towards the expansion edge coupled with limited evidence of a negative effect of human population density suggests that the species’ northward expansion in Portugal could continue.

中文翻译：

---

向扩张前沿降低糖皮质激素水平表明陆地哺乳动物正在进行扩张

了解丰富物种范围扩大的原因可以帮助预测未来的物种分布。在范围扩大期间，动物会暴露在新的环境中，并且需要应对新的和不可预测的压力源。糖皮质激素 (GC) 是激素和行为机制的介质，使动物能够应对环境中不可预测的变化，因此预计在扩张边缘和历史范围内的种群之间会有所不同。然而，迄今为止，很少有研究评估 GC 与范围扩展之间的关系。在过去的 30 年里，埃及猫鼬一直在迅速扩大其在葡萄牙的活动范围。在这项研究中，我们应用信息论方法来确定人群中头发 GCs (hGCs) 最重要的空间和环境预测因子，在控制了物种中 hGC 变异的正常模式之后。我们观察到随着与历史范围的距离增加（即更接近扩张前沿），hGC 下降。该距离项存在于所有顶级模型中，并且具有不与零重叠的 95% 置信区间 (95% CI)，强烈支持其对 hGC 的影响。我们估计到塔霍河每公里距离，hGCs 减少 0.031 pg/mg（95% CI：-0.057，-0.004），这曾经是物种分布的极限。我们的研究结果表明，物种的扩张不太可能受到与生理应激反应相关或介导的机制的限制。