EAR-PF: Are the slow growth and metabolic rates of crocodylians secondarily derived?

Sarah Werning博士已获得NSF地球科学博士后奖学金，在纽约的斯托尼布鲁克大学开展研究和教育计划。她将研究现存和化石种类的鳄鱼（短吻鳄，鳄鱼和凯门鳄）及其已灭绝的祖先的骨组织，以验证在现存鳄鱼中观察到的缓慢生长和低代谢率是次级衍生的假设。像大多数爬行动物一样，所有24种现存鳄鱼的特征是缓慢生长率和低代谢率。这些都反映在他们骨组织的微观结构中。与现存物种相比，鳄鱼的祖先在体型、解剖学、饮食、陆生程度和栖息地方面更加多样化。它们的骨骼组织表明它们生长得更快，代谢率更高;与它们活着的后代相比，这是一种非常不同的生理学。这有力地表明，鳄鱼在经历了一些具有较高速率的进化实验后，重新进化出缓慢的生长和较低的代谢速率。通过对现代鳄鱼的博物馆标本进行骨组织分析，特别是他们灭绝的祖先，Werning博士试图确定何时发生了向更高速率的转变，以及这些生理变化是否与身体大小，解剖学和生态学的变化同时发生。为了做到这一点，她将从现代和化石鳄鱼骨骼中提取骨骼样本，并为显微镜研究准备组织学切片。她将定量分析骨微结构的特征，这些特征已知随生物物种的生长速率和/或代谢速率而变化（例如，血管、骨细胞和胶原纤维的密度、排列和组织、年生长线的数量和年骨沉积率）。Werning博士将重建个体动物寿命的生长轨迹，并汇集来自多个个体的数据，以描述生长和骨组织结构的物种水平变化。她将比较相关的分类群，以阐明鳄鱼谱系内骨组织结构，生长和代谢的进化转变，并确定它们是否与身体大小，形态，生态/Werning博士的项目将生成一个大型骨组织数据集，该数据集将整合现代和化石记录，并建立整个人类的生长和代谢率进化序列。~ 2.5亿年鳄鱼血统的历史。研究结果将为现代物种的生物学和生活史提供深入了解，这些物种的数据很难直接从活体动物中获得。同样，它们将揭示从骨骼解剖学上看不明显的灭绝动物的生物学和生活史信息。对于这两个群体，这些信息包括生长速度，新陈代谢和寿命。该项目将为高中生和本科生提供古生物学方法的教育和培训，并与研究生进行协作互动。该研究使用美国和国际博物馆收藏的现有标本，并通过提供大量数字图像来促进未来的研究，这些图像将通过NSF资助的图像库MorphoBank公开提供。古生物学在教授科学方法和向公众推广进化论方面发挥着至关重要的外展作用。Werning博士将与斯托尼布鲁克大学著名的传播科学中心合作，以提高她现有的外展技能，并将设计一个展览，在斯托尼布鲁克大学医学中心公开展示。

Dr. Sarah Werning has been awarded an NSF Earth Sciences Postdoctoral Fellowship to carry out a research and education plan at Stony Brook University in New York. She will study the bone tissue of living and fossil species of crocodylians (alligators, crocodiles, and caimans) and their extinct ancestors to test the hypothesis that the slow growth and low metabolic rates observed in living crocodylians are secondarily derived.Like most reptiles, all 24 living species of crocodylians are characterized by slow growth rates and low metabolic rates. These are reflected in the microscopic structure of their bone tissues. Compared to living species, crocodylian ancestors were much more diverse in terms of their body size, anatomy, diet, degree of terrestriality, and habitat. Their bone tissue indicates that they grew much faster and had higher metabolic rates; a very different physiology compared to their living descendants. This strongly suggests that crocodylians re-evolved slow growth and lower metabolic rates after going through some evolutionary experimentation with higher rates. By performing bone tissue analyses on museum specimens of modern crocodylians and especially their extinct ancestors, Dr. Werning seeks to determine when the transitions to and from higher rates occurred, and whether these changes in physiology were concurrent with changes in body size, anatomy, and ecology. To do this, she will sample bone from modern and fossil crocodylian skeletons, and prepare histological slides for microscopic study. She will quantitatively analyze the bone microstructure for characteristics known to vary with growth rate and/or metabolic rate in living species (e.g., the density, arrangement, and organization of blood vessels, bone cells, and collagen fibers, the number of annual growth lines, and rates of annual bone deposition). Dr. Werning will reconstruct growth trajectories for individual animals' lifespans and pool data from multiple individuals to describe species-level variation in growth and bone tissue structure. She will compare related taxa to elucidate the evolutionary transitions in bone tissue structure, growth, and metabolism within the crocodylian lineage, and determine whether they co-occurred with transitions in body size, morphology, and ecology/habitat.Dr. Werning's project will generate a large bone tissue dataset that will integrate the modern and fossil records and establish the sequence of evolution of growth and metabolic rates across the entire ~250-million-year history of the crocodylian lineage. The results will offer insights into the biology and life history of modern species for which data are difficult to obtain directly from living animals. Similarly, they will reveal information on the biology and life history of extinct animals that are not apparent from their skeletal anatomy. For both groups, these include information on growth rates, metabolism, and longevity. This project will provide education and training in paleontological methods to high school and undergraduate students, and collaborative interaction with graduate students. The study uses existing specimens in US and international museum collections, and promotes future research by providing a large collection of digital images that will be made publicly-available through the NSF-funded image repository, MorphoBank. Paleontology plays a crucial outreach role in teaching scientific methods and promoting evolutionary theory to the public. Dr. Werning will work with Stony Brook University's renowned Center for Communicating Science to improve her existing outreach skills, and will design an exhibit for public display at the Stony Brook University Medical Center.