COLLABORATIVE RESEARCH: Integrative Approaches to the Turtle Body Plan: Evolutionary Origins of Structural Complexity in an Enigmatic Lineage

龟壳确实是结构和进化生物学的奇迹。这是一个复合特征，包括一系列只有海龟才知道的骨头，但它也整合了大量的椎骨、肋骨和肩带元素。海龟的肩胛骨（肩胛骨）位于胸腔内，而所有其他爬行动物和哺乳动物的肩胛骨都在肋骨外，这清楚地表明，要理解这种明显戏剧性的进化变化是如何发生的，海龟代表着一个挑战。海龟究竟是如何以及为什么获得了如此奇特的身体结构，这是比较生物学历史上存在时间最长的问题之一，也是一个尚未解决的问题。澄清海龟起源的最大障碍是缺乏将海龟与其他已知爬行动物群联系起来的过渡化石。关于海龟祖先的直接证据的缺乏导致了关于海龟在爬行动物生命树中的位置，现代海龟身体结构的哪些特征首先进化，以及这些特征为海龟祖先提供了哪些选择优势等惊人的不同假设。该项目将通过协调来自最近发现的化石的新的解剖学数据，更详细地了解调节海龟特定特征产生的发育机制，以及来自多种爬行动物的基因序列模式来解决这些问题。最终的产品将是一个高度精细的海龟进化模型，这不仅有助于我们对海龟起源的理解，而且将作为如何解决复杂进化问题的指南。海龟，尤其是化石海龟的广泛吸引力，也确保了这个项目将通过博物馆展览和外展活动为所有年龄和背景的人提供令人兴奋的教育机会。基因组数据的获取和分析相对容易，这为推断发育系统的进化及其产生的表型提供了前所未有的机会。这种范式面临着最大的挑战，因为冠状枝被极其长的茎系分开，其中一个更著名的例子是海龟的起源和它们的壳状身体计划。我们的项目建立在最近在发育、系统学和化石记录方面的发现之上，以推进我们对早期海龟进化的理解，以及它与比较生物学中广泛问题的相关性。该项目的目标可以概括为四个目标：(1)利用高分辨率成像和进化分析，基于化石记录建立龟茎谱系骨骼表型特征转化的身份、功能和进化动力学；(2)利用密集取样的现代龟和羊膜外群个体发生序列，结合实验发育方法，建立龟冠群和总群形态发生、调控和生长的祖先模式；(3)利用不同的分析方法解决泛龟类在现存和灭绝的羊膜动物中的系统发育地位，并阐明一个时间校准的进化模型，该模型整合了形态学，发育和遗传数据，以描述龟的出现及其特征。该项目致力于了解脊椎动物身体结构的基本原理，以及该结构发生巨大变化的机制，与美国国家科学基金会的十大理念之一“理解生命的规则：从基因型预测表型”高度一致。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The turtle shell is truly a wonder of structural and evolutionary biology. It is a compound feature that includes a series of bones known only in turtles, but it also integrates a large number of vertebrae, ribs, and shoulder girdle elements. That the turtle scapula (shoulder blade) lies inside of the rib cage, whereas all other reptiles and mammals have the scapula on the outside of the ribs, is a clear indication that turtles represent a challenge to understand how such apparently dramatic evolutionary change occurs. Exactly how and why turtles acquired such a peculiar body plan is one of the longest standing problems in the history of comparative biology, and one that remains very much unresolved. The largest impediment to clarifying the origin of turtles has been the lack of transitional fossils linking turtles to other known reptile groups. This absence of direct evidence regarding turtle ancestry has resulted in strikingly disparate hypotheses as to where turtles sit within the reptile tree of life, what features of the modern turtle body plan evolved first, and what selective advantages these features provided turtle ancestors. This project will address these problems by coordinating novel anatomical data from recently discovered fossils, a more detailed understanding of the developmental mechanisms that regulate the production of turtle-specific traits, and the patterns of genetic sequences from a wide diversity of reptiles. The end product will be a highly refined model of turtle evolution that will not only facilitate our understanding of turtle origins but will serve as a guide for how to tackle difficult evolutionary problems across deep time. The broad appeal of turtles, and especially fossil turtles, also ensures that this project will deliver exciting educational opportunities for people of all ages and backgrounds through museum exhibits and outreach activities.The relative ease with which genomic data can now be acquired and analyzed provides unprecedented opportunities for inferring the evolution of developmental systems and their resultant phenotypes. This paradigm faces its greatest challenge where crown clades are separated by extremely long stem lineages, with one of the more famous examples being the origin of turtles and their shelled body plan. Our project builds on recent discoveries in development, systematics, and the fossil record to advance our understanding of early turtle evolution and its relevance for broad-based questions in comparative biology. The goals of the project can be summarized under four objectives: (1) use high-resolution imaging and evolutionary analyses to establish the identity, functionality, and evolutionary dynamics of character transformations in the skeletal phenotype of the turtle stem lineage based on the fossil record; (2) use densely sampled ontogenetic series of modern turtles and amniote outgroups, integrated with experimental approaches in development, to establish ancestral patterns of morphogenesis, regulation, and growth for the turtle crown and total group; (3) use diverse analytical approaches to address the phylogenetic position of Pan-Testudines among both extant and extinct amniotes and to articulate a time-calibrated evolutionary model that integrates morphological, developmental, and genetic data in describing the emergence of turtles and their characteristic features. In its pursuit to understand the basic principles that underlie the vertebrate body plan and the mechanisms through which large changes to this plan can occur, this project is highly congruent with one of NSF’s 10 Big Ideas — “Understanding the Rules of Life: Predicting Phenotype from Genotype.”This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.