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

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

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