Altered thyroid hormone signalling in accelerated metamorphosis in desert frogs

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Hormones influence the development of every organ in the body and may underlie the evolution of biodiversity. In particular, thyroid hormone (TH) plays critical roles in brain and skeletal development, yet the role TH plays in development varies widely across vertebrate species. Indeed, evolutionary changes in TH physiology have been implicated in the enormous diversity found in frog and salamander life history. How such an important hormone can change its developmental role in evolution is not known. To more fully understand the role of TH in evolution, this project will examine the role of altered expression of TH receptors (TRs) underlying the evolution of accelerated metamorphosis in desert frogs. Frog metamorphosis is dependent on TH, and desert frog species have shorter larval periods compared to their non-desert relatives. Based on our preliminary data, it is hypothesized that desert species will have a more robust response to TH compared to non-desert species underlying their shorter larval period. Successful completion of this project will functionally test the effect of an evolutionary increase in TR expression on the rate of metamorphosis. The rationale for this research is that knowledge of how altered TR expression affects metamorphosis between frog species will advance our understanding of the developmental and evolutionary roles of this powerful hormone system. Integration of this research project with education will be accomplished by involving undergraduate and graduate students, not only in the research project, but also by enabling presentations of successful research at conferences. The current project enhances infrastructure for research and education through international collaborations and by providing educational material for undergraduate teaching. Results of the proposed research will be disseminated widely by publications in peer-reviewed journals and presentations at professional meetings, and all material used in the project will be deposited in research collections available for the scientific community. Finally, the research is expected to benefit society as a whole, primarily through bringing awareness to the general public of the underpinnings of evolution and biodiversity.