Fear-based aggression and its relationship to corticosterone responsiveness in three species of python

It has long been known that even closely related species can vary in their antipredator behavior, and in the last two decades there has been mounting interest in how these differences might relate to the hormonal stress response. We tested the relationship between fear-based aggression, a form of antipredator behavior, and plasma corticosterone levels in three species of python [Children's Python (Antaresia childreni), Ball Python (Python regius), Bismarck Ring Python (Bothrochilus boa)]. We recorded the amount of striking in response to perturbation before and after a controlled, stressful confinement. We also measured plasma corticosterone levels prior to confinement, after confinement, and after confinement plus an adrenocorticotropin hormone (ACTH) injection, the later to induce a maximal corticosterone response. We performed among species analyses using two mixed models, and we determined between individual variance within each species to estimate repeatability. Bismarck Ring Pythons struck more than either Ball Pythons or Children's Pythons, and Ball Pythons had a suppressed corticosterone response compared to Children's and Bismarck Ring Pythons. Thus, mean species fear-based aggression correlated with species level differences in corticosterone profile. We also found evidence suggesting behaviors are repeatable within individuals. Our results point to a need for further exploration of aggression, anti-predator behavior, and corticosterone profile.