DISSERTATION RESEARCH: The relative roles of selection and constraint in convergent ear loss across the true toads (Bufonidae)

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Middle and outer ear structures are used for hearing sound and are shared by most land animals. Although frogs and toads use hearing to find a mate, many frogs and toads have lost their middle and outer ear structures. This project aims to discover the genetic changes that have resulted in the evolution of ear loss in toads. Since the middle and outer ears of other land animals (including humans) use similar developmental pathways, understanding the genetic changes that result in ear loss in toads will illuminate potential causes of middle and outer ear loss and malformation in other animals. The genetic data produced by this study will help us better understand the relationships between toad species and provide novel genetic data for future research. In addition to graduate training, interactive museum displays will be created from the specimens and data generated from the project, and a series of K-12 classroom exercises will be developed to explain the ear structure evolution in toads.This project investigates the selection pressures and genetic constraints that generate convergent loss and potential regain of middle and outer ear structures across the family of true toads (Bufonidae). Sequence data for 60 bufonid species (16 earless, 44 eared) spanning seven ear loss events will be analyzed to identify signatures of selection and parallel genetic changes across 50 genes involved in middle and outer ear development. The dataset will assess the effects of various selection pressures and look for evidence of constraint at the genetic level, complementing the large amount of evidence for selection and constraint at the phenotypic level that has previously been collected by the research team. Results of this project will delineate the roles of selection and constraint in driving ear loss across Bufonidae, and elucidate common genetic pathways by which selection can act in a constrained, potentially costly, trait loss.