Salt and the Rough-Skinned Newt (\u3ci\u3eTaricha granulosa\u3c/i\u3e): Evolutionary Investigations of Local Adaptation to an Anthropogenic and Natural Stressor

Amphibians are osmotically-challenged due to their highly permeable skin and egg membranes. As such, biologists have mostly ignored their occurrence in saline habitats. The goal of this dissertation was to investigate the ability of amphibians to adapt to inhabit these osmotically-stressful environments. As freshwater resources are increasingly salinized due to a combination of anthropogenic and natural stressors, including road-deicing salt application, coastal storm events, and sea-level rise, it is important to understand the abilities and constraints of sensitive organisms, like amphibians, to persist in these environments. I began by exploring what is known about amphibians inhabiting saline habitats around the world, and reviewed information dating from the 1800s to the present, documenting over 100 species inhabiting inland and coastal environments. I then proceeded to investigate the evolutionary potential for one species in particular, the rough-skinned newt (Taricha granulosa) to adapt to increased salinity in its habitat. I documented the negative effects of salinity (both NaCl and MgCl2 – the two most commonly-used road deicers) on embryonic and larval survival and development through a series of experiments, and explored the importance of both developmental and evolutionary history with a stressor on survival. I investigated the evolutionary potential of salt-naïve populations through examining intrapopulation and interfamily variation in critical early life-history traits, and determined that there is high interfamily variation in the salt tolerances of offspring of individual females within a population, providing the raw material for natural selection and local adaptation. Finally, I discovered a population of newts living in the tidal area of a coastal stream, with a natural source of salinity. Through conducting a series of laboratory salt challenges and assays on osmotic, stress, and immune physiology, I was able to determine that newts in the tidal area appear to be physiologically adapted to increased salinity compared to newts in a freshwater area upstream. All this information suggests that amphibians, while still osmotically-challenged, may also not be helpless in the face of salinization, and populations may be able to locally adapt to habitats impacted by natural and anthropogenic sources of salinity