Interspecific Variation in Innate Immune Defenses and Stress Response of Toads from Botucatu (São Paulo, Brazil)

ABSTRACT. Glucocorticoid hormone levels increase in the blood stream in response to a large range of social and physical stressors, affecting variables associated to fitness, such as reproductive output and immunocompetence. Although quantification of plasma levels of glucocorticoids has been used as an indicator of environmental stress in different clades of vertebrates, the existence of interspecific differences in magnitude of stress response, their functional bases and ecological correlates remain poorly investigated. In the present study, we tested the following hypotheses: (1) phyllogenetically close species of Bufonids differ in innate immunocompetence, baseline activity of the hypothalamic-pituitary-interrenal (HPI) axis, and response of the HPI axis to stressors; and (2) species showing higher baseline activity of the HPI axis are characterized by lower innate immunocompetence. To test these hypotheses, we compared plasma bactericidal ability against Escherichia coli, baseline field levels of cor...