Data from: Profound reversible seasonal changes of individual skull size in a mammal

Animals typically cope with seasonal environments through changes in anatomy, physiology and behaviour. Such anatomical adaptations rarely include size changes of the skeleton once animals are fully grown. Here, we document extensive individual seasonal size changes in the braincase of free-ranging common shrews (Sorex araneus), previously only documented post-mortem and at population level. Using x-ray images of recaptured shrews we show that individuals shrink their braincases in anticipation of winter by an average -15.3% (individual maximum -20.1%). They then partially regrow their braincases in spring by 9.3% (individual maximum 13.2 %). Thus, this pattern is not caused or enhanced by seasonal size-dependent mortality, but reflects profound individual changes in bone anatomy. We hypothesize that this is linked to an alternative wintering strategy to hibernation or migration. Our findings are important for understanding the evolution of adaptations to extreme conditions in a small high-metabolic animal and have tremendous potential for applied research on mature mammalian bones and nervous systems.动物通常借助解剖结构、生理机能与行为模式的适应性变化来应对季节性环境。这类解剖学适应性变化在动物完全成熟后，极少涉及骨骼尺寸的改变。本研究首次记录了野生普通鼩鼱（Sorex araneus）个体脑颅广泛存在的季节性尺寸变化——此前该类变化仅在死后样本及种群层面被报道。通过对重捕鼩鼱拍摄的X射线（X-ray）影像分析，我们发现个体在入冬前会收缩脑颅尺寸，平均收缩幅度达15.3%（个体最大收缩幅度可达20.1%）。随后在春季，其脑颅会部分再生，平均再生幅度为9.3%（个体最大再生幅度可达13.2%）。由此可见，该变化模式并非由季节性体型依赖性死亡所导致或加剧，而是反映了个体骨骼解剖结构的显著改变。我们推测，这一现象与冬眠或迁徙之外的另类越冬策略存在关联。本研究结果对于理解高代谢小型动物对极端环境的适应性演化具有重要意义，同时在成熟哺乳动物骨骼与神经系统的应用研究领域具备广阔潜力。