Late Cenozoic climatic impact on body size evolution in large mammals

由于体型大小与物种的许多基本生物学特性相互作用，体型大小的进化可能是与不断变化的环境相关的生物多样性产生和维持的重要组成部分。然而，在大范围内驱动体型进化的原因尚不清楚。特别是，由于进化发生在当时的生物地理环境中，环境条件的异质性在多大程度上影响了物种体型的时空格局，这是理解体型进化的关键问题；这也是一个及时的问题，考虑到当前面临预计的气候变化的生物多样性危机。在确定进化动力的驱动因素方面，化石记录已经并将继续发挥关键作用，因为灭绝的分类群是至关重要的，但对于依赖于现存多样性的研究方法来说，将它们纳入研究仍然是一个挑战。为了深入了解体型进化，我建议利用化石记录进行全面调查，以确定过去2300万年中大型哺乳动物将气候变化与体型进化联系起来的主要机制。这一时期是全球气候变冷的历史时期，在此期间，许多分类群都观察到体型的明显增加，包括两个哺乳动物目（偶蹄目和异蹄目）。通过增加食肉目、灵长类目和长鼻目3个不同的生态角色和功能目，建立跨时空生物多样性和气候数据的跨学科古生物学数据库，该项目将进一步探索气候变化与体型进化之间的生物学机制。首先，我将采用一种基于谱系动力学的宏观进化方法，评估气候变化对新第三纪时期与地理范围动态和饮食偏好相关的体型时间变化的影响。其次，我将把新近纪的动态发现与较短但气候变化更剧烈的更新世的动态发现进行比较，为预测当前生物多样性的未来提供更多相关知识。第三，采用生物地理学的方法研究不同体型的类群在新第三纪和更新世全球气候变化的不同时期的空间分布。拟议项目的这三个组成部分将相互补充，为哺乳动物体型的进化史提供有价值的见解，并阐明控制生命进化的一般原则。

Because body size interacts with many fundamental biological properties of a species, body size evolution can be an essential component of the generation and maintenance of biodiversity in relation to the ever-changing environment. Yet, what drives body size evolution at a broad scale remains unclear. In particular, because evolution takes place within the biogeographic setup at the time, to what extent the heterogeneity in environmental condition contributes to shaping the temporal as well as spatial patterns of species body size is a key question for understanding body size evolution; it is also a timely question, given the current biodiversity crisis in the face of projected climate change. In identifying drivers of evolutionary dynamics, the fossil record has played and will continue to play a pivotal role, because extinct taxa are crucial to consider but incorporating them remains a challenge for research approaches relying on extant diversity. To gain a deep understanding of body size evolution, I propose a comprehensive investigation using the fossil record to pinpoint the dominant mechanism linking climate change to body size evolution in large mammals during the last 23 million years. This time period was a history of global climate cooling during which an apparent increase in body size has been observed in many taxa, including two mammalian orders (Artiodactyla and Perissodactyla) based on my recent work. Adding three additional orders of diverse ecological roles and functions (Carnivora, Primates and Proboscidea), and building an interdisciplinary paleontological database containing biodiversity and climatic data across space and time, the proposed project will take several steps further to search for the biological mechanisms that connect climate change to body size evolution. First, I will take a macroevolutionary approach, based on linage dynamics, to assess the influence of climate change on the temporal variation in body size in relation to geographic range dynamics and dietary preferences during the Neogene. Second, I will compare findings of the Neogene dynamics to those in the shorter but climatically more dramatic Pleistocene to provide more relevant knowledge for anticipating the future of the current biodiversity. Third, I will take a biogeographic approach to investigate how taxa of different body sizes are distributed spatially during different times as the global climate changed throughout Neogene and Pleistocene. These three components of the proposed project will complement each other to provide valuable insights into the evolutionary history of mammal body size and shed much light onto the general principles governing the evolution of life.