Body size evolution in mammals: complexity in tempo and mode

Body size correlates with virtually every aspect of species' biology, so understanding the tempo and mode of its evolution is of key importance in macroecology and macroevolution. Here we use body-mass data from 3473 of 4510 extant mammalian species and an almost complete species-level phylogeny to determine the best model of log(body-mass) evolution across all mammals, split taxonomically and spatially. An early-burst model fits better across all mammals than models based on either Brownian motion or an Ornstein-Uhlenbeck process, suggesting that mammals experienced a burst of morphological evolution relatively early in their history followed by slower change subsequently. We also use spatial models to investigate rates of body-mass evolution within ecoregions. These models show that around 50% of the variation in rate can be explained by just a few predictors. High estimated rates are associated with cold, low lying, species-poor, high energy, mainland ecoregions. We conclude that the...

体型几乎与物种生物学的所有方面均存在显著关联，因此探究其演化的速率与模式，在宏观生态学（macroecology）与宏观演化学（macroevolution）领域具有核心研究价值。本研究利用4510种现生哺乳动物中3473种的体质量数据，结合近乎完整的物种水平系统发育树（phylogeny），旨在筛选出适用于全哺乳动物类群的log(body-mass)演化最优模型，并分别从分类学与空间维度开展拆分分析。相较于基于布朗运动（Brownian motion）或奥恩斯坦-乌伦贝克过程（Ornstein-Uhlenbeck process）的演化模型，早爆发模型（early-burst model）对全哺乳动物类群的拟合效果更优，这表明哺乳动物在演化历史的相对早期经历了一轮形态演化爆发，后续的演化速率随之逐渐放缓。本研究同时利用空间模型探究了不同生态区（ecoregion）内的体质量演化速率，结果显示演化速率约50%的变异仅可通过少数几个预测因子（predictors）得到解释。较高的估算演化速率与寒冷、低海拔、物种贫乏、高能量的大陆型生态区（mainland ecoregion）显著相关。本研究最终得出结论：