Mechanisms of skin resistance to water loss rates in Plethodon salamanders across various body sizes
The ecology and evolution of organisms can often be explained by specific mechanisms involving molecules, genes, and cellular characteristics. By exploring the relationship between these mechanisms, we may gain further insight into how organisms interact with their environment. Being lungless, salamanders require moist skin to breathe. By maintaining moist skin, salamanders lose water to their environment, and consequently, surface activity is primarily determined by the rate at which salamanders lose water to their environment. Salamanders with high skin resistances (and thus lower water loss rates) can be active for longer periods, providing more time to forage and find mates. In lungless salamanders, adults have a distinct advantage over juveniles due to their higher skin resistance to water loss. However, the mechanism by which adult salamanders have higher skin resistances than juveniles remains an unanswered question. Here, we use a variety of histological and lipid assays to determine differences between skin morphology and skin secretion composition between large and small bodied Southern grey cheeked salamanders (Plethodon metcalfi). Skin secretions were collected from live individuals, stained with Sudan Black B, and analyzed using ImageJ to characterize lipid content. Skin samples were stained with hematoxylin-eosin solution to characterize skin morphology.
We found differences in integument thickness and lipid secreting glands between the juvenile and adult salamanders. The adult salamanders had substantially thicker skin and a higher density of lipid secreting glands compared to juvenile salamanders. Additionally, small salamanders excreted a higher concentration of lipids compared to large salamanders. These results suggest that small bodied salamanders might compensate for thinner skin by increasing their lipid secretions. Therefore, interactions between skin morphology and physiology likely determine water loss rates of salamanders. The capacity of salamanders to regulate water loss rates is critical to understanding their ecology. By reducing water loss rates, salamanders might be able to lessen the effects of any environmental change. Therefore, salamanders may be able to persist in some environments, even as they become more unsuitable for organisms that are sensitive to stressful environmental conditions. Further studies could include the analysis of the dimensions of the lipid secreting glands and the composition of the lipid secretions to provide a more comprehensive view of how plethodontid salamanders are regulating skin resistance to water loss.