Collaborative Research: Insulin and Limb-Patterning Pathway Activities in the Horns of Beetles: An Integrative Study of the Mechanisms of Allometry, Dimorphism, Branching & Cur

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The expression of virtually all insect morphological traits is sensitive to nutrition, yet almost nothing is known about the genetic mechanisms that couple trait growth with nutrition. An extreme example occurs in the 'horns' of scarab beetles. Within a single species, beetle horns can vary tremendously in size and shape dependent upon larval nutrition. Beetles with horns include some of the most magnificent and bizarre organisms alive today. The sizes of these horns (relative to the sizes of the beetles that bear them) can dwarf even the most extreme antlers of ungulates, and the diversity of horn forms is breathtaking. Thus, beetle horns are conspicuous structures with known functional significance. With more than a century of interest and observation of these animals and many recent behavioral studies, there is a rich ecological context for the study of horn development.The long-term goal of this research project is to understand the ways that physiology, genetics, and development interact with the environment to generate diversity in animal forms. The objective of this project is to determine the mechanisms responsible for generating variation in the expression of beetle horns. The specific aims are to determine the extent to which (1) the insulin receptor pathway adjusts trait growth in response to nutrition in horned beetles, (2) the insulin receptor pathway and the limb-patterning pathway regulate male dimorphism and sexual dimorphism in horn expression, and (3) the limb-patterning pathway specifies horn shape in beetles with different horn morphologies. The results of this award will provide important new information about how the mechanisms of insect development may be modified to generate biologically meaningful - even spectacular - variation in animal form. In this way, this research will address fundamental and long-standing questions in biology such as: How do novel and complex morphological structures arise? And how are these traits modified to generate diversity in animal form?A core objective of this research collaboration is the cross-training of young scientists in development, genetics, and evolution. Both graduate and undergraduate students involved with this project will spend time in both of the PI's laboratories and will be trained in developmental and genetic methods alike. Numerous aspects of this study lend themselves to independent undergraduate student projects, and the PIs are committed to training students in all aspects of the research process including writing and presenting results at local and national meetings. Both PIs have excellent track records in the training of women and minorities in the sciences. Two of the focal species in this project are very large rhinoceros beetles and worldwide favorites of museums and classrooms, and are perfect for a range of educational programs. This project will use these animals in a variety of educational/outreach activities including visiting local school classrooms, supporting the Washington State University Insect Museum, and aiding with a new Montana insect zoo.