Data from: Growth overshoot and seasonal size changes in the skulls of two weasel species

Ontogenetic changes in mammalian skulls are complex. For a very few species (i.e. some Sorex shrews), these also include seasonally driven, bidirectional size changes within individuals, presumably to reduce energy requirements during low resource availabilities. These patterns are poorly understood, but are likely most pronounced in high-metabolic species with limited means for energy conservation. We used generalized additive models to quantify the effect of location, Julian day, age and sex on the length and depth of 512 and 847 skulls of stoat (Mustela erminea) and weasel (M. nivalis) specimens collected throughout the northern hemisphere. Skull length of both species varies between sexes and geographically, with stoat skull length positively correlated with latitude. Both species demonstrate seasonal and ontogenetic patterns, including a rare, absolute growth overshoot in juvenile braincase depth. Standardized braincase depths of both species peak in their first summer, then decrease in their first winter, followed by a remarkable regrowth that peaks again during their second summer. This seasonal pattern varies in magnitude and timing between geographical regions and the sexes, matching predictions of Dehnel's phenomenon. This suggests implications for the evolution of over-wintering strategies in mammals, justifying further research on their mechanisms and value, with implications for applied osteology research.哺乳动物颅骨的个体发育变化极为复杂。仅极少数物种（如部分鼩鼱属（Sorex）鼩鼱）的个体颅骨会出现受季节驱动的双向尺寸变化，推测此举可在资源匮乏时期降低能量消耗。目前这类变化模式尚不明晰，但在能量保守机制有限的高代谢率物种中，其表现可能最为显著。本研究采用广义加性模型（generalized additive models），量化了采集自北半球全域的512件白鼬（Mustela erminea）与847件伶鼬（Mustela nivalis）颅骨标本的长度、深度受采集地点、儒略日、年龄及性别的影响程度。研究发现，两种鼬类的颅骨长度均存在性别与地理差异，其中白鼬的颅骨长度与纬度呈正相关关系。两类物种均表现出季节性与个体发育相关的变化模式，其中幼年头骨颅腔深度出现罕见的绝对生长超调现象。两类物种的标准化颅腔深度均在首个夏季达到峰值，随后在首个冬季下降，之后出现显著的再次生长，并于第二个夏季再次达到峰值。该季节性变化模式在不同地理区域与性别间的幅度与时间节点均存在差异，符合德恩尔现象（Dehnel's phenomenon）的预测结果。这一发现为哺乳动物越冬策略的演化研究提供了新的启示，也印证了对其背后机制与生物学价值开展深入研究的必要性，同时对应用骨科学研究具有重要参考价值。