Post-fight levels of plasma lactate and corticosterone in male copperheads, Agkistrodon contortrix (Serpentes, Viperidae): differences between winners and losers.

During the mating seasons (late summer and spring), male copperheads (Agkistrodon contortrix; Serpentes, Viperidae) engage in aggressive physical interactions for priority of access to females. These fights generally involve two individuals and are characterized by prominent vertical displays, a high degree of physical contact, and the absence of biting. Ritualized aggression does not occur in females. Although intrasexual aggression in conspecifics has obvious energetic costs (e.g., lactate accumulation) that can affect subsequent behavior, few studies have addressed these costs in reptiles, and no studies have examined snakes. Moreover, recent studies suggest psychoneuroendocrine (catecholamines, glucocorticoids) regulation of metabolism during and following aggressive episodes. There were three main questions addressed in this study. Do winners and losers of staged, pair-wise encounters show differences in post-fight (60-min) levels of plasma lactate and corticosterone (CORT)? Are levels of plasma lactate correlated with levels of plasma CORT? Is fight duration correlated with levels of plasma lactate and CORT? Two different control groups (cage and arena) were used. Body length, body mass, duration of fighting, and season of testing were not correlated with levels of plasma lactate and CORT. At 60-min post-fight, losers had significantly higher levels of mean plasma lactate and CORT when compared to levels in winners and controls, and there were no significant differences between winners and controls. From our results, we suggest the following conclusions. First, elevated levels of CORT in losers, but not winners, result from psychoneuroendocrine factors rather than simple exercise. Second, elevated levels of CORT in losers retard metabolic recovery resulting in higher lactate levels in losers, whereas winners return to pre-fight levels within 60-min post-fight. Last, the CORT response has a net negative effect on metabolic recovery and may be implicated in the protracted suppression of aggressive behavior in losers.