Temporal changes in cranial size in South African vlei rats (<i>Otomys</i>): evidence for the ‘third universal response to warming’

Using museum collections and recently collected specimens we studied geographical and temporal (from 1906 to 2013) changes in skull size of two sibling species of rodents, <i>Otomys auratus</i> and <i>O. angoniensis</i>, in northern South Africa occupying distinct temperate grassland (<i>O. auratus</i>) and subtropical savanna (<i>O. angoniensis</i>) biomes. We hypothesised that cranial size should vary in space and time within species according to Bergmann's Rule, which predicts an inverse relationship between body size and temperature. We used the greatest length of the skull (GLS) as a robust indicator of body size. Cranial size of both <i>O. auratus</i> and <i>O. angoniensis</i> decreased significantly over the past 100 years, as expected given historical evidence of warming across northern South Africa since the 1950s. In terms of geographical patterns, GLS was inversely correlated with both latitude and longitude in <i>O. auratus</i> but these trends were correlated with annual rainfall rather than mean annual temperature. Conversely, cranial size of <i>O. angoniensis</i> was weakly positively correlated with longitude but with no climatic variables. Our results demonstrate rapid morphological changes in two herbivorous South African rodents over the past 100 years. Whilst the general decline in size with time in relation to increased temperature is consistent with Bergmann's Rule, multiple drivers may underlie geographical trends in the two species.

本研究依托博物馆馆藏标本与新近采集的样本，针对南非北部两种姊妹种啮齿动物——金非洲攀鼠（*Otomys auratus*）与安戈尼非洲攀鼠（*O. angoniensis*）的头骨尺寸，分析其在1906年至2013年间的地理与时间维度变化。两种鼠分别栖息于独特的温带草原与亚热带稀树草原生物群系。
我们提出假说：依据贝格曼法则（Bergmann's Rule），同一物种的头骨尺寸应在空间与时间维度上发生变异——该法则预测体型与温度呈负相关关系。本研究以头骨最大长（greatest length of the skull, GLS）作为体型的稳健指示指标。
研究结果显示，在过去百年间，金非洲攀鼠与安戈尼非洲攀鼠的头骨尺寸均出现显著下降，这与南非北部自1950年代以来气候变暖的历史记录相符。
就地理格局而言，金非洲攀鼠的头骨最大长与纬度、经度均呈负相关，但该相关趋势与年降雨量关联更为紧密，而非年平均温度。与之相反，安戈尼非洲攀鼠的头骨尺寸仅与经度呈弱正相关，且未与任何气候变量呈现显著关联。
本研究结果证实，过去百年间南非的两种植食性啮齿动物发生了快速的形态演变。尽管体型随温度升高而减小的整体趋势符合贝格曼法则，但两个物种的地理格局变化可能受到多重驱动因素的影响。

搜集汇总

背景与挑战

背景概述

该数据集研究了南非水鼠（Otomys auratus和O. angoniensis）在1906年至2013年间头骨大小的时空变化，以检验伯格曼规则对气候变暖的响应。研究发现，两种物种的头骨大小在过去100年中显著减少，这与南非北部气候变暖趋势一致，支持了‘第三普遍变暖响应’假说；同时，地理分布模式显示头骨大小与气候变量（如降雨和温度）的关联在物种间存在差异，表明多种驱动因素可能影响形态变化。