Interrelations among Multiple Metrics of Immune and Physiological Function in a Squamate, the Common Gartersnake (Thamnophis sirtalis).

The field of ecoimmunology has made it clear that individual and ecological contexts are critical for interpreting an animal's immune response. In an effort to better understand the relevance of commonly used immunological assays, we tested how different metrics of immunity and physiological function were interrelated in naturally parasitized individuals of a well-studied reptile, the common gartersnake (Thamnophis sirtalis). Overall, we found that bactericidal ability, an integrative measure of innate immunity, was often correlated with more specific immunological and physiological tests (lysis and oxidative stress) but was not related to tissue-level inflammation that was determined by histopathology. The only hematological metric that correlated with tissue-level inflammation was the prevalence of monocytes in blood smears. Finally, using histological techniques, we describe natural parasitism throughout the organ systems in these individuals, finding that neither the presence nor the burden of parasite load affected the physiological and immune metrics that we measured. By performing comprehensive assessments of physiological and immune processes, we are better able to draw conclusions about how to interpret findings from specific assays in wild organisms.