Meeting Abstract
P1.133 Monday, Jan. 4 The role of thyroid hormone receptors in the evolution of accelerated metamorphosis in desert frogs HOLLAR, A. R.*; BUCHHOLZ, D. R.; University of Cincinnati; University of Cincinnati hollar.amy@gmail.com
Thyroid hormone (TH) has profound yet varied developmental effects in all vertebrates. How such an important developmental hormone can underlie such diverse yet fundamental aspects of development across species is not well understood. Frogs are an excellent organism for the study of TH signaling as metamorphosis is dependent on TH. Because thyroid hormone receptors (TRs) act as mediators of the TH signal, TR expression levels may be a significant target of evolution underlying metamorphic diversity. Spadefoot toads are a closely related group of anurans with known phylogenetic relationships and differing larval period durations whose underlying differences in TH physiology are well established. To test whether TR expression levels correlate with larval period duration, we analyzed TRα and TRβ mRNA expression via quantitative PCR in the tails of three species of spadefoot toad tadpoles with short, intermediate, and long larval period durations. We found that species with shorter larval periods had a greater increase in TRβ expression over the course of metamorphosis. We also induced metamorphosis in two of the species by subjecting them to 8 and 50 nM T3 concentration at Gosner stage 31 (premetamorphosis) and examined the expression of TRα and TRβ mRNA at 12, 24, 48, and 72 hours post-TH induction via qPCR. Our results showed that the species with the shorter larval period had a greater increase in both TRs during TH-induced metamorphosis. Additionally, expression of TRβ reached peak levels quicker in the species with the shorter larval period. Our results provide substantial evidence that larval period duration correlates with increased TR expression in spadefoot toads. We conclude that evolution of shorter larval periods in spadefoot toads may at least partially be due to increased TR expression during metamorphosis.
