DISSERTATION RESEARCH: Mechanisms of adaptation to saltwater by an amphibian

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This project will investigate the genetic and cellular processes that allow some populations of the American green tree frog (Hyla cinerea) to tolerate high salt concentrations, and how saltwater affects the natural history of amphibians. The ongoing decline of habitat quality and quantity has increased the urgency to understand how organisms adapt to new or changing environments. Evolution might occur rapidly and quickly enough to rescue populations and protect species from being lost in the face of a changing environment, including by the increasing salinization of freshwater wetlands around the world. As wetlands grow saltier, many freshwater wetland organisms such as fish, turtles, and frogs may become locally extinct. However, populations of the American green tree frog have been discovered in brackish wetlands. This project will compare frogs from coastal and inland populations for differences in gene expression, egg hatching, and larval development, among other traits. The results will lead to a much better understanding of the process of adaptation to saline environments. In addition, the project will engage with K-12 students, especially those from groups that are underrepresented in the sciences.To determine whether putatively salt-tolerant frog populations are adaptively diverging from freshwater populations in response to salt exposure, this study uses a common garden, factorial design to investigate endpoints across multiple levels of biological organization across three stages of anuran amphibian development (egg, larval, and post metamorphosis). The study will characterize transcriptomic responses following saltwater exposure and relate these patterns to subsequent protein expression and fitness correlates (e.g., developmental rates, survival). In doing so, the project links selective pressures occurring at the level of the whole organism to the molecular processes that underlie adaptation. The project will identify the mechanisms that underlie salt tolerance and differentiate between competing hypotheses about the role of genetic variation and plasticity in the evolution of adaptive change.