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

背景：哺乳动物显示出显著的肢体比例多样性，这是为了适应特定类型的运动而进化的（例如，冲刺、跳跃）。我的研究计划的长期愿景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，我开发了长腿小鼠，它的胫骨长了15-20%，但体重与随机繁殖的对照小鼠相同。 研究目的：在接下来的五年里，我将致力于三个互补的目标：（1）确定特定的发育遗传途径对长腿长肢和改变肢体比例的贡献;（2）探索长腿的修改肢体形态和运动性能之间的关系;（3）确定胫骨选择对其他骨骼和软组织性状的共同进化的影响。*** 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）检验信号因子Dlk 1在长骨发育过程中调节生长板中增殖细胞的数量，从而在长腿的骨长度增加中起主要作用的假设，以及（2）确定不同的基因途径是否参与增加长腿的整体骨骼尺寸，与四肢骨骼的大小相比较。对于目标2，我们将使用高速视频和力量平台来测试长腿的肢体骨骼长度增加可以改善其跑步和短跑性能的假设，例如，通过增加其最大冲刺速度和/或耐力。对于目标3，我们将结合联合收割机显微CT成像和定量遗传学工具，以确定长腿身体的其他部位（例如，头骨，内脏）在胫骨选择的反应中发生了变化，以及这是否影响了长腿的整体进化能力。 重要性：我的研究项目整合了从基因到形态到整个生物体性能的数据，以解决进化变化的机械基础上的长期问题。预期的结果将对进化生物学和相关领域产生广泛的影响（例如，进化发育生物学、生态学、古生物学），通过以下突破：（1）揭示形态多样性的关键细胞和分子驱动因素，（2）了解物种，无论是活的还是灭绝的，如何通过改善有机体性能来适应环境，以及（3）识别塑造活的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清晰和相关的进化实例，提高公众对进化的理解，并将有助于培训加拿大下一代生命科学家，使他们具备生物信息学、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. **