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What is the context of this research?

Horns are conspicuous projections on the heads of many animals, from beetles to buffalo. These structures are thought to have multiple functions, including territorial combat, predator defense, and attracting mates. However, structures with shared functions between animals as distantly related as insects and vertebrates are usually thought to be analogous, the result of convergent evolutionary forces on structures with different genetic and embryological origins, rather than homologous, or shared by descent from a common ancestor. Recent molecular studies have begun to characterize the loci that control horn growth in mammals. The hypothesis that we will test is that horns in vertebrates, namely ungulates and chameleons, are genetically and behaviorally homologous.

What is the significance of this project?

Sexual selection, or competition for mates, leads to differential reproductive success, which is a critical driver of speciation. Speciation is in turn the force that maintains global biodiversity in the face of extinction. The factors that lead to biological diversification continue to be a rich source of ongoing scientific research. Despite the diversity of the family Chameleonidae, with about 200 species, as well as their fascinating and highly derived anatomical and biological adaptations, they remain relatively under-studied although they play important ecological roles in arboreal food webs. We are interested in the factors that have led to diversification within this lineage, and what lessons can be elucidated and applied to other animals with prominent weaponry.

What are the goals of the project?

The short-term goals of this project are to determine the genetic and functional bases of horns in chameleons. We will do this by 1) using PCR primers designed for mammalian horn genes to search for homologous loci in the Jackson’s chameleon, and 2) setting up staged behavioral contests among males with different horn/SVL ratios, to test the idea that longer horns are the best predictor of contest success. Our results will provide critical information for our long term research goals which involve examining the evolution of sexual characters and weapons across the entire Chamaeleonidae family, in addition to the role that sexual characters and weapons play in speciation in this very unique, though poorly characterized group.