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.

绝大多数脊椎动物的出生后体型变化均为单向且有限的，当个体达到成体体型后，便不再发生显著改变。极少数情况下，体长变化可能因恶劣环境条件而发生。此类反应性变化与季节性、多为前瞻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变化。科研人员已在红齿鼩鼱与部分鼬科动物的躯体、颅骨及大脑尺寸变化中，观测到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。此前研究通过死后提取的颅骨样本，在种群层面记录到该类群最常用的替代指标——脑颅高度——出现季节性20%的缩减与15%的回弹生长。但截至此前，量化个体内部的体型变化在方法学上均难以实现。本研究对野外重捕的普通鼩鼱（*Sorex araneus*）开展完整周期追踪，分析其颅骨尺寸与体质量的个体内变化。借助X光影像，我们发现普通鼩鼱会为应对冬季主动缩减脑颅尺寸，平均缩减幅度达15.3%；随后在春季，脑颅实现9.3%的部分回弹生长。其体质量则会下降17.6%，并在春季出现83.4%的显著回升。综上，本研究证实德恩尔现象所引发的剧烈变化，确实发生在个体的骨骼与其他组织之中。