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

Postnatal size changes in most vertebrates are unidirectional and finite once the individual reaches full size. In rare cases, changes of body length may occur in response to harsh environmental conditions. Such reactionary changes are distinct from seasonal, often anticipatory morphological changes, such as the reversible size change of some adult bird brains. A unique pattern of profound anatomical change known as Dehnel’s phenomenon has been described for the body, skull and brain size of red-toothed shrews and some mustelids. The seasonal 20% decrease and 15% re-growth of the most common proxy, braincase height, were documented at population level from extracted skulls post-mortem. Quantifying intra-individual change had so far been methodologically prohibitive. Here, we followed the intra-individual change in skull size and body mass throughout the full cycle in wild recaptured shrews (Sorex araneus). Using X-ray images we showed that individuals decreased the size of their braincases in anticipation of winter by an average of 15.3%. Braincases then partially regrew in spring by 9.3%. Body mass decreased by 17.6% and then dramatically increased by 83.4% in spring. Thus, we demonstrate that the dramatic changes incurred by Dehnel’s phenomenon occur in the individual’s bone and other tissues.多数脊椎动物在个体达到成年体型后，产后体型变化呈单向且有限的特征。极少数情况下，个体可因恶劣环境条件出现体长改变。此类应激性变化与季节性、多为预见性的形态变化截然不同，例如部分成年鸟类大脑的可逆性尺寸波动。针对红齿鼩鼱与部分鼬科动物的体型、头骨及大脑尺寸，学界已报道过一种被称为德恩尔现象（Dehnel’s phenomenon）的独特深度解剖学变化模式。该研究最常用的替代指标——颅腔高度——会出现季节性20%的缩减与15%的复增，该结果基于种群层面的死后提取头骨样本所记录。迄今为止，量化个体内部的尺寸变化在方法学上一直难以实现。本研究对野外重捕的普通鼩鼱（Sorex araneus）开展全周期跟踪，记录其头骨尺寸与体质量的个体内变化。通过X射线影像分析，我们发现个体为应对冬季提前将颅腔尺寸平均缩减15.3%；春季时，颅腔尺寸会部分复增9.3%。体质量则先下降17.6%，随后在春季大幅攀升83.4%。综上，本研究证实德恩尔现象所引发的剧烈变化，发生于个体的骨骼与其他组织之中。