One way to measure the impact of climate change on amphibians is with skin resistance. Skin resistance is a numerical measurement defined as an organism’s resistance to evaporative water loss through the skin. This can be achieved through a number of biological mechanisms, but the result is the same: the higher an individual’s skin resistance, the better it is at resisting evaporation from its skin. For my senior thesis project, I wanted to measure whether skin resistance exhibits plasticity in response to environmental change in salamanders local to California, which is steadily becoming hotter and drier. I selected the Southern long-toed salamander (Ambystoma macrodactylum sigillatum) to test my hypothesis that acclimating individuals to a higher temperature would increase their skin resistance. These salamanders are terrestrial as adults, and inhabit a range from southwestern Oregon to northern and central California.
Ambystoma macrodactylum sigillatum individual in the lab.
I kept three groups of A. m. sigillatum individuals in the laboratory at three different acclimation temperatures: 15, 18, and 21oC. These represent a situation typical of the current climate (15oC), a scenario with slight warming (18oC), and a scenario with more severe warming (21oC). Next, I conducted trials where I dehydrated the salamanders at one of five trial temperatures. I weighed each salamander to determine how much water it lost after spending 10 minutes in a chamber with a dry air flow, and compared this to the water loss of an agar model. An empty chamber was also included to monitor environmental conditions.
Salamander (left), agar (center), and empty (right) chambers during a 10-minute dehydration trial.
After collecting data, I used the water loss from each trial to calculate skin resistance, then tested which factors had a significant effect on skin resistance values. Interestingly, acclimation temperature had a significant impact, but trial temperature, while showing a correlation, did not. I also plotted the skin resistance from each trial against the temperature used in that trial to create a type of graph known as a thermal performance curve, or TPC. I fitted TPCs to each of the three acclimation temperature groups.
A visual analysis of the TPCs shows that the 15oC and 21oC curves are a similar shape, but the 18oC curve is flatter. The 18oC curve also extends slightly past the maximum point of the 15oC curve. The 18oC population seems to be thermally generalist – that is, having a higher skin resistance at a wider range of temperatures but with a lower overall fitness – whereas the 15oC population is specialist, favoring certain temperatures within its range with much higher relative skin resistance. Comparing the 15oC and 21oC curves, the two populations have very similar resistance levels at lower temperatures, but the 21oC group has an extended maximum range, resulting in higher resistance at higher temperatures. There appears to be no reduction in fitness at lower temperatures to compensate; in other words, the trend has not shifted, but rather expanded to include higher temperatures.
TPCs of skin resistance for the 15, 18, and 21oC acclimation groups. Individual trial data is not pictured.
My research suggests that increasing acclimation temperature can cause a response in Ambystoma macrodactylum sigillatum’s skin resistance, but that this response can differ depending on how much warmer the acclimation temperature is. It is possible that the slight increase in skin resistance at higher temperatures may compensate for increased evaporation, and provide a small buffer for A. m. sigillatum against the effects of climate change. My findings provide additional evidence supporting the idea that skin resistance is plastic in amphibians, which could aid in their survival in the years to come.
I would like to thank the Norris Center for providing funding for my senior thesis project.
