Meeting Abstract
Animals that live in variable climates are often exposed to stressful conditions. Variable temperatures can be a harmful stressor due to the production of tissue-damaging chemicals, such as reactive oxygen species. Melanin production is one means by which animals protect tissues from cellular damage caused by exposure to warm temperatures. We investigated the immunological and physiological responses to temperature and humidity as stressors in an abundant terrestrial salamander (Plethodon metcalfi). We exposed individuals to cycling temperature and humidity treatments over a period of four weeks in the laboratory. Nocturnal activity was simulated by moving salamanders to open-air containers that exposed individuals to cycling temperatures and vapor pressure deficits (VPDs). We maintained the same VPDs across temperature treatments to ensure temperature and humidity were not confounded in the study. We sampled blood smears to assess the stress response and production of melanin in the liver before and after the experiment. We tested for a generalized stress response by measuring neutrophil to lymphocyte (NL) ratios in the blood smears. Melanin production increased dramatically across the experiment, with low levels of melanin at the beginning and high levels at the end of the experiment. In response to temperature, individuals produced more melanin under warm treatments than individuals from cool treatments. The NL ratios indicated equally low levels of stress across all treatments, suggesting an absence of a stress response across the treatments. We also found very limited evidence of liver damage, such as irregular arrangement of liver parenchyma and hepatocytes. These results suggest that physiological responses, such as the production of melanin, might be an important response involved in limiting stress under warm temperatures.
