Animals produce a bewildering diversity of ornaments and weapons that function in male contests over reproductive access to females. Two characteristics are common in the most elaborate of these structures: disproportionate growth yielding exaggerated trait sizes, and growth that is more sensitive to nutrition than is the growth of other, non-sexually-selected, structures (e.g. antlers in moose or elk reach extreme sizes in the largest bulls, and antler growth is especially sensitive to the nutritional state of the animal). Despite intense interest in the evolution of these sexually selected traits, almost nothing is known of the genes or the developmental mechanisms responsible for disproportionate/ exaggerated growth, or of the mechanisms linking nutrition with the amount of trait growth. This proposal addresses a fundamental gap in understanding the evolutionary potential of ornaments and weapons of sexual selection: What are the genes and developmental/ physiological processes that underlie nutrition-dependent expression and exaggerated growth? The premise for this project is that to understand the evolution of these structures requires exploration of the details of how they develop. The long-term goal is to understand how physiology and development interact with the environment to generate diversity in morphological and behavioral phenotypes. The objectives are to identify genes and associated physiological pathways responsible for generating exaggerated weapon growth, and nutrition-dependent phenotypic plasticity. The investigators will (1) test whether the mechanisms generating nutrition-dependent expression are the same as those generating exaggerated growth, and (2) compare these mechanisms for two weapons (horns & mandibles) in three lineages of beetle representing three independent origins of enlarged male weapons (dung beetles, rhinoceros beetles, & stag beetles). The integrative approach utilized will shed light on physiological and developmental pathways involved with nutrition-dependent phenotypic plasticity in animals generally, and will provide one of the most comprehensive studies to date linking variation in male condition with the expression of sexually selected traits - a central tenet of current theories of sexual selection.
A core objective is the cross-training of young scientists in genetics, development, physiology and evolution. The postdoc and students involved with this project will spend extensive periods in all three labs actively learning techniques and interacting and collaborating with all three PIs. The PIs are committed to training undergraduates in all aspects of the research process, and will incorporate innovative teaching methods in science that embrace diversity; the very nature of this system lends itself to learner-centered investigations. The focal species are a fantastic resource for outreach activities and the PIs will use these animals in educational programs designed to enhance STEM learning in K-12 students as well as in informal science education environments, including visiting local school classrooms in both WA and MT, supporting the WSU insect museum, and aiding with a new Montana insect zoo.
What generates the striking diversity in animal form in the animal kingdom? This is one of the most fundamental, unanswered questions in evolutionary biology. Our research project addressed this problem by focusing specifically on the exaggerated traits of animals, in our project, we used male beetles. Many species of beetles exhibit remarkably large and ostentatious male-specific traits such as horns and enlarged jaws. These exaggerated male-specific traits are weapons that males use to fight over access to females and ultimately, to sire the most offspring. We and others have found that males with the largest horns and mandibles win fights and have the most offspring. We have also found that the size of these male horns and mandibles is tightly linked to the amount of food they are able to consume when they are in the immature stage. Our goal in this project was to identify the genetic and physiological mechanisms that control the growth of beetle horns and mandibles during development under different nutritional conditions. We used the latest technologies to sequence the genes that are expressed during specific, critical periods during beetle development to identify these mechanisms in three different species of beetles. We chose these three species of beetles because while they all have male-specific exaggerated traits, the type of trait (head horn versus thoracic horn versus enlarged mandibles) is different and are considered to have evolved independently of each other. We also tested the function of genes that we identified to discover the role that these genes have in the development and growth of these traits. Our results are the first comprehensive survey of gene expression from three different beetle weapons that combine function with form. In addition, we have found that the physiological mechanisms and genes that are involved are not all the same. This was not what we expected and it is very exciting for the evolution of sexually-selected traits in general. But more importantly, we can now say that animal diversity in form is not controlled by single genes or single pathways but by complex interactions of genes and physiological signals, even between relatively closely related beetle species! These results are also exciting because we are also showing that animals that are sensitive to the nutrition environment can use different pathways to sense these inputs; in essence, animals are not restricted to one pathway but are flexible in their response depending on their evolutionary history. Finally, our results have important implications for the generality of physiological and genetic interactions in animal communication and signaling in sexually-selected traits. In addition to the scientific achievements that have resulted from our project, we are also very proud of our broader impacts. Specifically we have trained postdoctoral fellows and offered them professional development opportunities, we have mentored graduate students and undergraduate students in authentic research, we have disseminated the results of our work in peer-reviewed publications, invited reviews, and invited presentations around the world and we have conducted outreach and engagement events to K-12 as well as the community in general. We have also been trained, and trained others in exciting new ways to engage women, minorities, and all students in science and science education.
