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.绝大多数脊椎动物在达到成体体型后，其产后体型变化均为单向且有限的。仅在少数情形下，体长可因恶劣环境条件出现变化。这类反应性改变与季节性、通常为预期性的形态变化存在显著差异——例如部分成年鸟类大脑的可逆尺寸调整。学界已针对红齿鼩鼱与部分鼬科动物的躯体、头骨及脑容量，报道过一种名为德恩尔现象（Dehnel’s phenomenon）的独特深度解剖结构变化模式。基于种群水平的死后提取头骨样本的研究显示，最常用的替代观测指标——颅腔高度会出现季节性20%的缩减与15%的回弹。此前，量化个体内的此类变化在方法学上难以实现。本研究对野外重捕的普通鼩鼱（Sorex araneus）开展了全周期跟踪，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，我们发现个体在入冬前的颅腔尺寸平均缩减15.3%，春季时颅腔会出现9.3%的部分回弹；体质量则下降17.6%，春季时大幅回升83.4%。综上，本研究证实德恩尔现象所引发的剧烈变化，可发生于个体的骨骼与其他组织中。