Collaborative Proposal: Dental Development and Life History of Malagasy Lemurs

自从阿道夫·舒尔茨的开创性工作以来，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兴趣。最近，化石记录一直是这种比较工作的直接焦点。牙齿微结构方面的新工具可用于梳理已灭绝物种之间生活史差异的方面，并已开始应用于亚化石狐猴，取得了巨大成功。牙齿内保存着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。这不仅对探索已灭绝物种的生活史差异极其有用，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：这项研究将把牙齿微结构的研究和其他新的分析工具应用于最令人着迷的灭绝灵长类动物之一：马达加斯加巨型亚化石狐猴。它们现存的近亲狐猴在牙齿、颅面和躯体生长和发育的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。这些不同的牙齿和骨骼生长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生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(使用磨损分析的新技术)、牙齿发育和萌发(通过X光照相术)和单个成年标本的牙齿显微结构分析的数据，该项目将解决以前从未向灭绝的灵长类动物提出的问题：巨型狐猴的怀孕时间有多长？它们的增长速度有多快？这些物种的断奶是在什么年龄发生的，断奶过渡时间有多长？食果狐猴物种的生长是否像生态风险厌恶假说所预测的那样，比同等大小的食叶动物生长得更慢？灭绝狐猴的季节性生长时间表是否导致成年狐猴在断奶前达到很大比例，还是像现存狐猴那样，婴儿生长率的根本不同是灭绝狐猴类群的特征？最后，基于里程碑的三维几何形态测量学(例如，Morphologika，HETPAD)的进展，加上对特征-年龄矩阵的传统分析，以记录灭绝狐猴的牙齿、大脑和头面部发育之间的关系，使我们能够测试目前关于生活史策略进化的假设，这可能是世界上最独特和最多样化的灵长类适应性辐射。最终，本研究将为理解灵长类生活史变异的进化提供进化发展框架。更广泛的影响：这项研究的一个重要的更广泛的影响是研究生和研究生培训。其中一名PI有一名马达加斯加研究生，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制博士后助理提供理想的培训。此外，在马达加斯加的古生物学、狐猴生态学、生态地貌学、异时性和骨骼个体发育以及牙齿微结构等领域，PI还与其他人进行了持续的合作。我们期望这里描述的工作与其他研究项目相结合，从而为马达加斯加灵长类群落结构的演变、灭绝的模式和原因以及灵长类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.