Meeting Abstract

37.2  Jan. 5  Metamorphic remodeling and the evolution of larval morphology in the carnivorous tadpole Lepidobatrachus laevis INFANTE, C.R.; Harvard University los@oeb.harvard.edu

Members of the frog subfamily Ceratophryinae (Anura: Leptodatylidae) are known for the enlarged heads, massive jaws, and aggressive predatory natures of their adult forms. As tadpoles, however, each of the three genera that comprise the group exhibits very distinct larval feeding ecologies and accompanying morphologies. Most striking among these are the tadpoles of the genus Lepidobatrachus which feature laterally expanded jaws used to consume other tadpole prey whole. In terms of both behavior and morphology, Lepidobatrachus tadpoles appear to be expressing adult characteristics at the larval stage. I am interested in how the regulation of the metamorphic remodeling program has changed to accommodate the unique larval jaw morphology of these tadpoles. 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 (TH), which initiates – via nuclear receptors – a cascade of gene expression in responding tissues. It has been hypothesized that changes in the TH-regulated metamorphic program mediate the evolutionary diversification of larval and adult morphology. This could be accomplished via temporal changes in tissue sensitivity to TH, or TH concentration on a tissue or organ-specific level via the local activity of deiodinases. To investigate these hypotheses in regard to the unique jaws of Lepidobatrachus tadpoles, I have used studies of receptor expression and enzyme activity during natural metamorphosis and in tissue culture. These studies demonstrate that deiodinase inactivation of TH protects the lower jaw during metamorphosis and the delayed morphological remodeling and ossification of the lower jaw correlates with deiodinase activation of TH.