The future of coastal amphibian populations: Local adaptation or local extinction?
Sea level rise (SLR) is expected to be a major consequence of global warming. While the magnitude of effects will vary regionally, SLR will impact coastal ecosystems around the world. Currently, however, we know far too little about how SLR will impact coastal freshwater wetlands and the biotic communities that they sustain. It is often assumed that freshwater species in historically freshwater coastal wetlands will become locally extirpated as the environment transitions into higher salinities, yet few studies have examined the potential for local adaptation to elevated salinities to buffer some species against the negative effects of SLR and climate change. We use anuran amphibians, a salt-sensitive group of freshwater wetland inhabitants, to explore this question. Specifically, we characterized responses to a common salinity gradient among different populations and species to determine whether coastal anuran populations that persist in chronically salt-intruded wetlands exhibit physiological and behavioral phenotypes consistent with adaptations that allow them to inhabit SLR affected wetlands.
Due to their permeable skin and reliance on freshwater, it is broadly accepted that elevated salinities will adversely affect amphibian populations, however, we demonstrate that coastal populations of anuran amphibians (adults and larvae) are persisting in saltmarsh habitats with high salinities. Further, we experimentally determined that individuals from coastal populations demonstrate responses consistent with the hypothesis that they are locally adapted to elevated salinities. In particular, we found distinct differences among our populations and species in mass loss and blood plasma osmolality after exposure to a gradient of saltwater. Frogs from high salinity habitats had lower rates of mass loss and lower plasma osmolality in higher salinity treatments (>8ppt) than inland (saltwater-naïve) frogs. In addition, we are finding changes in the abundance of key osmoregulatory proteins (e.g. NKA, NKCC, and AQPs) in skin, bladders and kidneys consistent with this hypothesis. While it is widely assumed that stressors associated with climate change will result in widespread biodiversity loss, we may be overlooking the capacity of some organisms to rapidly adapt to the changing environment. This research takes an important step in understanding how frogs and possibly other freshwater organisms can respond to the changing environment.