Collaborative Proposal: Dental Development and Life History of Malagasy Lemurs

自从阿道夫·舒尔茨（Adolf Schultz）的开创性工作以来，灵长类动物学家一直对灵长类动物生活史变异的骨骼发育相关性及其对理解生活史进化的影响表现出持续的兴趣。最近，化石记录已经成为这种比较工作的直接焦点。牙齿微观结构的新工具可用于梳理已灭绝物种的生活史变化方面，并已开始成功地应用于亚化石狐猴。牙齿保存了它们发育的永久记录，使研究人员能够从单个成年标本中检索纵向发育数据。这不仅对探索灭绝物种之间的生活史变化非常有用，而且有望彻底改变我们对现存物种生活史的某些方面的理解。科学价值：这项研究将带来牙齿微观结构的研究和其他新的分析工具来研究最令人着迷的灭绝灵长类动物之一：马达加斯加的巨型狐猴亚化石。它们的近亲，现存的狐猴，在牙齿、颅面和躯体的生长和发育时间上表现出显著的差异，所有这些都是在高度季节性和不可预测的环境中进行的。这些牙齿和骨骼生长的不同模式与狐猴生活史策略的变化有关，特别是与成年雌性生存和繁殖努力之间的权衡有关。通过结合食物加工的行为个体发生（使用使用磨损分析的新技术）、牙齿发育和出牙（通过放射照相）以及单个成年标本的牙齿微观结构分析的数据，该项目将解决以前从未问过的关于灭绝灵长类动物的问题：巨型狐猴的妊娠期有多长？它们的成长速度有多快？这些物种在什么年龄断奶，断奶过渡期有多长？是否像生态风险规避假说所预测的那样，食果狐猴比同等大小的叶食性狐猴生长得更慢？是已灭绝狐猴的季节性生长计划导致在断奶前达到成年狐猴体型的很大比例，还是已灭绝狐猴类群与现存狐猴类群的婴儿生长速度根本不同？最后，基于地标的三维几何形态计量学（例如，Morphologika， HETPAD）的进步，以及对特征年龄矩阵的传统分析，以记录已灭绝狐猴牙齿，大脑和颅面发育之间的关系，使我们能够测试关于生活史策略进化的当前假设，这可能是世界上最独特和多样化的灵长类动物适应性辐射。最终，本研究将为理解灵长类动物生活史变异的进化提供进化发育框架。更广泛的影响：本研究的一个重要的更广泛的影响是研究生和研究生培训。其中一个pi有一个马达加斯加研究生，他正在研究狐猴，并表示有兴趣学习这里描述的技术。这里要求的微观结构工作也将为两年的博士后提供理想的培训。此外，pi还在马达加斯加的古生物学、狐猴生态学、生态形态学、异时性和骨骼个体发育以及牙齿微观结构等领域与其他机构进行合作。我们希望这里描述的工作能与其他研究项目有益地交叉，从而为马达加斯加灵长类动物群落结构的进化、灭绝的模式和原因以及灵长类动物的进化发育生物学的研究提供信息。

Ever since the pioneering work of Adolf Schultz, primatologists have shown a sustained interest in the skeletal developmental correlates of life history variation among primates, and in their implications for understanding the evolution of life history. More recently, the fossil record has been the direct focus of such comparative work. New tools in dental microstructure are available for teasing out aspects of life history variation among extinct species and have begun to be applied with great success to subfossil lemurs. Teeth preserve within them a permanent record of their development enabling researchers to retrieve longitudinal developmental data from single adult specimens. This is not merely extremely useful for exploring life history variation among extinct species, but it promises to revolutionize our understanding of some aspects of the life histories of extant species as well. Scientific merit: This study will bring the study of dental microstructure and other new analytical tools to bear on one of the most fascinating groups of extinct primates: the giant subfossil lemurs of Madagascar. Their closest living relatives, the extant lemurs, show remarkable variation in the timing of dental, craniofacial, and somatic growth and development, all within the context of a highly seasonal and unpredictable environments. These differing patterns of dental and skeletal growth relate to variation in lemur life history strategies - in particular, to the trade-off between adult female survival and reproductive effort. By combining data on the behavioral ontogeny of food processing (using new techniques in use-wear analyses), dental development and eruption (via radiography), and dental microstructural analyses of single adult specimens, this project will address questions never before asked of extinct primates: How long was gestation in giant lemurs? How rapidly did they grow? At what age did weaning occur in these species, and how prolonged was the weaning transition? Do frugivorous lemur species grow more slowly than like-sized folivores, as predicted by the ecological risk aversion hypothesis? Does the seasonal scheduling of growth in extinct lemurs cause a large proportion of adult size to be achieved before weaning, or do fundamentally different rates of infant growth characterize extinct lemur taxa as they do extant lemurs? Finally, advances in landmark-based 3-D geometric morphometrics (e.g., Morphologika, HETPAD), along with conventional analysis of trait-age matrices to chronicle the relationships between dental, brain and craniofacial development in extinct lemurs, allows us to test current hypotheses regarding the evolution of life history strategies in what is perhaps the world's most unique and diverse adaptive radiation of primates. Ultimately, this study will provide the evolutionary developmental framework for understanding the evolution of life history variation in primates. Broader impact: An important broader impact of this study is graduate and postgraduate training. One of the PIs has a Malagasy graduate student who is studying lemurs and has expressed an interest in learning the techniques described here. The microstructural work required here will also provide ideal training for a two-year postdoctoral associate. Furthermore, the PIs have ongoing collaborations with others in the realms of Madagascar's paleobiology, lemur ecology, ecomorphology, heterochrony and skeletal ontogeny, and dental microstructure. We expect the work described here to intersect profitably with other research projects, and thus to inform research on the evolution of primate community structure in Madagascar, the patterns and causes of extinction, and the evolutionary developmental biology of primates.