Liow Lee Hsiang, Fortelius Mikael, Bingham Ella, Lintulaakso Kari, Mannila Heikki, Flynn Larry, Stenseth Nils Chr
Center for Ecological & Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, P.O. Box 1066 Blindern, N-0316 Oslo, Norway.
Proc Natl Acad Sci U S A. 2008 Apr 22;105(16):6097-102. doi: 10.1073/pnas.0709763105. Epub 2008 Apr 15.
Do large mammals evolve faster than small mammals or vice versa? Because the answer to this question contributes to our understanding of how life-history affects long-term and large-scale evolutionary patterns, and how microevolutionary rates scale-up to macroevolutionary rates, it has received much attention. A satisfactory or consistent answer to this question is lacking, however. Here, we take a fresh look at this problem using a large fossil dataset of mammals from the Neogene of the Old World (NOW). Controlling for sampling biases, calculating per capita origination and extinction rates of boundary-crossers and estimating survival probabilities using capture-mark-recapture (CMR) methods, we found the recurring pattern that large mammal genera and species have higher origination and extinction rates, and therefore shorter durations. This pattern is surprising in the light of molecular studies, which show that smaller animals, with their shorter generation times and higher metabolic rates, have greater absolute rates of evolution. However, higher molecular rates do not necessarily translate to higher taxon rates because both the biotic and physical environments interact with phenotypic variation, in part fueled by mutations, to affect origination and extinction rates. To explain the observed pattern, we propose that the ability to evolve and maintain behavior such as hibernation, torpor and burrowing, collectively termed "sleep-or-hide" (SLOH) behavior, serves as a means of environmental buffering during expected and unexpected environmental change. SLOH behavior is more common in some small mammals, and, as a result, SLOH small mammals contribute to higher average survivorship and lower origination probabilities among small mammals.
大型哺乳动物的进化速度比小型哺乳动物快，还是相反呢？由于这个问题的答案有助于我们理解生活史如何影响长期和大规模的进化模式，以及微进化速率如何放大到宏观进化速率，因此受到了广泛关注。然而，目前仍缺乏一个令人满意或一致的答案。在这里，我们利用一个来自旧世界新近纪（NOW）的大型哺乳动物化石数据集，重新审视这个问题。我们控制了采样偏差，计算了跨界者的人均起源和灭绝速率，并使用标记重捕（CMR）方法估计了生存概率，发现了一个反复出现的模式：大型哺乳动物属和物种的起源和灭绝速率更高，因此持续时间更短。鉴于分子研究表明，较小的动物由于其较短的世代时间和较高的代谢率，具有更高的绝对进化速率，这种模式令人惊讶。然而，较高的分子速率不一定转化为较高的分类群速率，因为生物和物理环境都与表型变异相互作用，部分由突变推动，从而影响起源和灭绝速率。为了解释观察到的模式，我们提出，进化并维持诸如冬眠、蛰伏和穴居等行为的能力，统称为“睡眠或隐藏”（SLOH）行为，是在预期和意外环境变化期间作为一种环境缓冲手段。SLOH行为在一些小型哺乳动物中更为常见，因此，SLOH小型哺乳动物有助于提高小型哺乳动物的平均存活率，并降低其起源概率。
