DISSERTATION RESEARCH: The role of integration in driving the morphological diversity of mammalian jaws

哺乳动物是温血动物，因此需要吃相对大量的食物来维持它们的高代谢率。牙齿和下颚是与食物接触的第一个点，不同类型的牙齿和下颚专门用于吃不同种类的食物。这种关系导致了各种各样的下巴形状。例如，食花蜜的蝙蝠有细长的下颚，可以伸进花里，而斑点鬣狗有短而结实的下颚，可以咬碎骨头。其他与进食无关的因素也会影响下颚的形状，比如为了交流而发声的需要，以及挖洞的需要。尽管有这些不同的角色，哺乳动物颌的形状还是受到许多因素的限制。特殊的饮食（如啃碎骨头或以花蜜为食）通常需要非常特殊的下颌形状。下颌形状也由控制下颌生长方式的基因决定。这两个因素缩小了哺乳动物可能拥有的下颌形状的范围。这个项目调查了下巴的形状与饮食的关系，以及这些形状是如何随着时间的推移而进化的。通过这项研究，我们将了解下颌形状如何以及为什么在某些哺乳动物群体中非常多样化，而在其他群体中非常有限。这项研究将为本科生和高中生提供STEM培训机会，包括女性和代表性不足的少数民族，并支持当地社区的科学推广项目。哺乳动物的下颚可以被认为是执行与进食、交流和竞争有关的任务的功能性工具。发育证据表明，有两个主要的区域可以独立进化，或模块，存在于哺乳动物的颚：分支和主体。支是下颌后部的部分，是肌肉附着的部位。牙体是颌的前部，容纳牙齿。当模块变得更加相互独立时，形态多样性的增加就有了更大的空间。然而，模块之间的共变程度在物种内部和物种之间都是不同的。这些差异是由于各种遗传和功能限制而产生的。本研究采用形态计量学和系统发育比较相结合的方法来研究模块化如何影响哺乳动物表现出的下颌形态范围。该项目将测试两个主要假设：1)哺乳动物下颚的进化以不同物种群体之间的饮食相似性（即功能需求）导致的重复趋同为特征；2)哺乳动物下颚的多样性通过降低下颚不同模块之间的共变异水平而得到促进。通过解决这两个假设，本研究旨在了解约束如何影响颌骨多样性以及这种多样性如何在哺乳动物进化支系中分布

Mammals are warm-blooded and so need to eat relatively large quantities of food to maintain their high metabolic rate. Teeth and jaws are the first point of contact with food, and different types of teeth and jaws are specialized for eating different kinds of foods. This relationship has led to a wide range of jaw shapes. For example nectar-eating bats have long and slender jaws for reaching into flowers, whereas spotted hyenas have short and sturdy jaws for crushing bones. Other factors unrelated to feeding can also influence the shape of the jaw, such as the need to make sounds for communication, and digging burrows. Despite these various roles, the shape of mammal jaws is limited by a number of things. Specialised diets (such as bone-crushing or feeding on nectar) often require very specific jaw shapes. Jaw shape is also determined by the genes available to control the way jaws grow. Both of these factors narrow the range of possible jaws shapes that mammals can have. This project investigates how jaw shapes are related to diet and how those shapes have evolved over time. Through this research we will learn how and why jaw shape is very diverse in some groups of mammals and very limited in others. This research will provide STEM training opportunities to undergraduate and high-school students, including women and under-represented minorities, and support science outreach programs in the local community.The mammalian jaw can be thought of as a functional tool for performing tasks related to feeding, communication, and competition. Developmental evidence suggests that there are two primary regions that can evolve independently, or modules, present in the mammalian jaw: the ramus and corpus. The ramus is the back portion of the jaw and serves as the site of muscle attachments. The corpus is the front portion of the jaw and houses the teeth. As modules become more independent of one another there is greater scope for increasing morphological diversity. However, the extent of co-variation among modules can differ both within and between species. These differences arise due to a variety of genetic and functional constraints. This study uses a combination of morphometric and phylogenetic comparative methods to investigate how modularity has influenced the range of jaw morphologies exhibited by mammals. This project will test two primary hypotheses: 1) the evolution of mammal jaws is characterized by repeated instances of convergence as a result of similarity in diets (i.e., functional demands) among different groups of species, and 2) mammalian jaw diversity is facilitated by reducing the level of co-variation among different modules within the jaw. By addressing these two hypotheses, this study aims to understand how constraints have influenced jaw diversity and how this diversity is distributed within the mammal clade