Microevolution of the mammalian limb skeleton: from genes and development to morphology and performance

背景：哺乳动物表现出显著的肢体比例多样性，这是为了适应特定类型的运动（例如，冲刺，跳跃）而进化的。我的研究计划的长期目标是揭示使这种骨骼多样性成为可能的发育、功能和进化机制。为了做到这一点，我开发了长腿老鼠，它的胫骨长了15-20%，但体重与随机饲养的对照组老鼠相同。***研究目标：在未来五年内，我将解决三个互补的目标：(1)确定特定的发育遗传途径对长腿的长肢和肢体比例改变的贡献；(2)探讨长腿改良后的肢体形态与运动性能的关系；(3)确定胫骨选择对其他骨骼和软组织性状共同进化的影响。***科学方法：对于目标1，我们将使用组织学和基因表达工具：(1)验证信号因子Dlk1在长骨发育过程中调节生长板中增殖细胞的数量，从而在长腿骨长增加中起主要作用的假设；(2)确定是否有不同的基因途径参与了长腿整体骨骼大小的增加，而不是每个肢体骨骼的大小。对于目标2，我们将使用高速视频和力平台来测试长腿增加的肢骨长度可以提高其跑步和冲刺性能的假设，例如，通过增加其最大冲刺速度和/或耐力。对于目标3，我们将结合显微ct成像和定量遗传学工具，确定长腿身体的其他部位（如头盖骨、内脏）是否以及如何响应胫骨选择而发生变化，以及这是否影响了长腿的整体进化能力。***意义：我的研究项目整合了从基因到形态学到整个生物体性能的数据，以解决关于进化变化机制基础的长期问题。预期结果将通过以下突破对进化生物学及相关领域（如进化发育生物学、生态学、古生物学）产生广泛影响：(1)揭示形态多样性的关键细胞和分子驱动因素；(2)了解生物和灭绝物种如何通过提高有机体性能来适应环境；(3)确定形成生物和化石物种形态多样性的进化限制。拟议的研究还将通过提供进化在行动中的清晰和相关的例子，提高公众对进化的理解，并将有助于培养加拿大下一代生命科学家，他们具有生物信息学、运动科学和数字成像方面的可转移技能。**

Background: Mammals show a remarkable diversity of limb proportions, which evolved as adaptations for specific types of locomotion (e.g., sprinting, hopping). The long-term vision of my research program is to uncover the developmental, functional and evolutionary mechanisms that make this skeletal diversity possible. To do so, I developed the Longshanks mouse, which has 15-20% longer shin bones (tibiae), but the same body mass as random-bred control mice.*** Research Objectives: Over the next five years, I will address three complementary objectives: (1) to define the contributions of specific developmental genetic pathways to the longer limbs and altered limb proportions of Longshanks; (2) to probe the relationship between Longshanks' modified limb morphology and its locomotor performance; and (3) to determine the impact of tibia selection on coevolution of other skeletal and soft tissue traits. *** Scientific Approach: For Objective 1, we will use histology and gene expression tools to: (1) test the hypothesis that the signaling factor Dlk1 regulates the number of proliferating cells in the growth plates during long bone development, and thus plays a major role in increasing bone length in Longshanks, and (2) determine whether different gene pathways are involved in increasing Longshanks' overall skeletal size, vs. the size of each limb bone. For Objective 2, we will use high-speed video and force platforms to test the hypothesis that Longshanks' increased limb bone length improves its running and sprinting performance, e.g., by increasing its maximum sprint speeds and/or endurance. For Objective 3, we will combine micro-CT imaging, and quantitative genetics tools, to determine if and how other parts of Longshanks' body (e.g., cranium, internal organs) have changed in response to tibia selection, and whether this has impacted Longshanks' overall capacity to evolve.*** Significance: My research program integrates data that spans genes to morphology to whole organism performance, to address long-standing questions on the mechanistic basis of evolutionary change. Anticipated outcomes will have broad impacts across evolutionary biology and related fields (e.g., evolutionary developmental biology, ecology, paleontology), through the following breakthroughs: (1) uncovering key cell and molecular drivers of morphological diversity, (2) understanding how species, both living and extinct, adapt to their environments through improved organismal performance, and (3) identifying evolutionary constraints that have shaped morphological diversity in living and fossil species. The proposed studies will also improve public understanding of evolution, by providing clear and relatable examples of evolution in action, and will contribute to the training of Canada's next generation of life scientists, with transferable skills in bioinformatics, movement science and digital imaging. **