ABSTRACT
Hormones play key, functional roles in mediating the tradeoff between survival and reproduction. Glucocorticoid hormones can inhibit reproduction and improve chances of survival during periods of stress. However, glucocorticoid hormones are, at times, also associated with successfully engaging in energetically costly courtship and mating behaviors. Corticosterone (CORT), a primary glucocorticoid hormone in amphibians, reptiles and birds, may be important in activating or sustaining energetically costly mating behaviors. We used a non-invasive, water-borne hormone assay to measure CORT release rates of male and female red-spotted newts (Notophthalmus viridescens) collected when either engaged in amplexus or when not engaged in amplexus. Because amplexus is energetically costly for males, we predicted that males would have higher CORT release rates than females. We also predicted that females in amplexus would have elevated CORT release rates because the restraint of amplexus prevents foraging and breathing and may be costly. Here we show that an acute increase in CORT is associated with amplexus behavior in both male and female red-spotted newts. Additionally we demonstrate that males have higher overall CORT release rates both in and out of amplexus than do females. Our results support the hypothesis that glucocorticoid hormones are associated with energetically costly courtship and mating behaviors for both sexes.
