INFANTE, C.R.*; HANKEN, J.; Museum of Comparative Zoology, Harvard University: Thryoid hormone receptor expression and the metamorphosis and evolution of anuran jaws

Most anuran amphibians exhibit a complex, biphasic life history consisting of a free-living aquatic larva (tadpole) and a terrestrial adult. Metamorphosis in anurans is characterized by extensive remodeling of larval tissues via growth or resorption and the de novo formation of many adult structures. This process is dependent on thyroid hormone, which initiates – via nuclear receptors – a cascade of gene expression in responding tissues. It has been hypothesized that changes in the thyroid hormone-regulated metamorphic program mediate the evolutionary diversification of larval and adult morphology. This could be accomplished via temporal changes in tissue sensitivity and responsiveness to thyroid hormone on a tissue or organ-specific level. We are interested in the role that thyroid hormone response plays in the diversification of a specific tissue, Meckel’s cartilage, a prominent skeletal element in the larval lower jaw. We investigated the presumed ancestral pattern of thyroid hormone receptor (TRα and TRβ) expression during tadpole development and metamorphosis, and compared this to patterns in other species with varied jaw morphologies associated with larval feeding adaptations. Additionally, we assessed whether patterns of cell death and proliferation correlate with thyroid hormone response. This study will contribute to our understanding of the biphasic developmental program of anuran amphibians and its role in the generation of anuran diversity.