From the horns of Hercules beetles to antlers of elk, intense selection arising from competition for access to reproduction has driven the evolution of extreme animal weapons. Extreme weapons often evolve faster than other body parts, and they tend to be more diverse among species than other body parts. Yet few studies have directly measured selection on weapons in natural populations, and almost nothing is known about the genes and developmental pathways responsible for rapid weapon evolution. This project capitalizes on populations of rhinoceros beetle that differ dramatically in the relative size of a weapon, a "pitchfork" horn projecting from the heads of males. By rigorously studying beetle behavior in divergent populations, the investigators will test whether local differences in the intensity of selection have driven rapid, recent evolutionary changes in weapon size. Studies of the distribution of relevant genes in these populations of beetles, along with identification of additional genes associated with these extreme traits and their location within the genome will further our understanding of the genetic basis of weapon evolution, building on a decade of prior research by these investigators and their collaborators on the developmental mechanisms regulating horn growth in this species. This project will train post-doctoral, graduate, and undergraduate students, expand an international collaboration with research labs in Japan, and contribute both regionally and nationally to high school science education and public knowledge of evolutionary biology and animal behavior.
Specifically, the PIs will combine QTL and divergence mapping approaches to screen for genes associated with increased weapon size (AIM 1); contrast gene expression in proliferating horn tissues of beetles from recently diverged short- and long-horned populations, identifying candidate genes and transcripts that are differentially expressed, and then investigating their function in the evolution of this weapon (AIM 2); and they will use field studies of behavior to compare the intensity of selection on horns in divergent populations (AIM 3). This study will impact society through education and outreach by (1) establishing a pipeline for undergraduate researchers from Gonzaga University to work at Washington State University and the University of Montana, (2) engaging a high school biology teacher in an authentic research project, (3) contributing to displays and student docent volunteer training at the new Missoula Butterfly House and (4) developing Process Oriented Guided Inquiry Learning (POGIL) activities targeted to high school biology students. Data will be deposited and available in the Dryad repository (http://datadryad.org), and at Traces (http://trace.ncbi.nlm.nih.gov/Traces/sra/), NCBI GEO (www.ncbi.nlm.nih.gov/geo/info/seq.html), and GenBank (www.ncbi.nlm.nih.gov/genbank/tsa/).
