Corticosterone, lactate, and circulating leukocyte responses of free-ranging cottonmouth snakes (Agkistrodon piscivorus) vary with the duration and nature of the acute stressor.

Abstract

Exposure to acute stressors can induce multiple physiological changes in vertebrates such as altering circulating hormone and enzyme levels as well as leukocyte counts, and interactions between endocrine and immune function may produce suites of physiological changes following acute stress. Previously, we showed that presence of human observers elicited only a weak elevation of plasma corticosterone levels in cottonmouths. Additional variables, however, must be considered to understand if changes in physiological parameters are highly generalized or vary among sexes or with context. Here we tested effects of more intense acute stressors (i.e., confinement for 2 h or 4 h or repeated blood sampling) on plasma corticosterone and lactate concentrations and the number of circulating leukocytes. In addition to testing for sex differences, we also tested two predictions frequently found in the stress physiology literature: (1) because glucocorticoids are involved in mobilization of leukocytes, corticosterone levels should covary with the heterophil to lymphocyte ratio, (2) since one of the major functions of corticosterone is to mobilize energy stores, baseline corticosterone levels (i.e., in immediately bled snakes) should be elevated in individuals in poor body condition. We found that neither sex nor body condition influenced corticosterone responses to confinement. However, repeated blood sampling had a pronounced effect- snakes bled both upon capture and at 2 h had higher corticosterone levels than snakes bled only once at 2 h or even at 4 h. Plasma lactate and the percent azurophils (but not the heterophil to lymphocyte ratio) were also elevated in confined snakes, and both were positively correlated with plasma corticosterone. Our results indicate a pronounced and nuanced effect of confinement stress on the physiology of cottonmouths.