Dehydration as a stressor in toads (Rhinella ornata)

Availability of a humid environment is essential for amphibians to carry out their activities and most species are characterized by low resistance to evaporative water loss. Moreover, dehydration severely compromises amphibian locomotor and foraging performance, representing a relevant selective factor modulating the evolution of its integrative phenotype. In this way, we hypothesized that dehydration is a stressor for toads, inducing a stress response comparable to that elicited by another commonly used stress protocol: restraint challenge. We evaluated changes in plasma levels of corticosterone (CORT), hematocrit (Hct), and neutrophil:lymphocyte (N:L) ratio in adult males of Rhinella ornata, experimentally submitted to different levels of hydration (100%, 90%, and 80% of standard body mass) and to restraint challenge. Our results showed that dehydrating toads by 10% increase CORT to levels equivalent to that obtained by restraint. Moreover, toads dehydrated by 20% show a more pronounced increase in CORT, along with increased Hct and N:L ratio. In this way, we corroborated the hypothesis that dehydration triggers a pronounced stress response in R. ornata.