Which endocrine factors influence reproductive decisions in the multiennially breeding viviparous lizard, Tiliqua nigrolutea?

An animal's energy intake must be partitioned between the requirements for growth and maintenance and the requirements of reproduction. For females in particular, a successful reproductive episode may result in an energy debt such that those animals are not able to reproduce again until energy stores are restored. Male blue-tongued lizards (Tiliqua nigrolutea) do become reproductively active every year; however females reproduce only at intervals of two, three, or even four years. Vitellogenesis occurs rapidly after spring emergence: thus reproduction depends on resources accumulated before hibernation. This implies that in females there is some physiological mechanism that signals to the reproductive system when sufficient fat reserves are available to fuel reproduction. The adrenal steroid corticosterone is a major metabolic hormone in reptiles, and appears to be important for regulating lipid cycling. In this study we compared the annual cycle of plasma corticosterone in male and female blue-tongued lizards. In males, plasma corticosterone is high during the spring mating period, lowest during summer, and rising to a significant peak during late hibernation. In both reproductive and non-reproductive females, plasma corticosterone is minimal in spring. In pregnant females corticosterone peaks during late gestation, falling sharply around the time of birth: this pattern i not seen in non-pregnant females. Both groups showed a peak during late hibernation but this was not as marked as that seen in males. We suggest that these patterns primarily reflect the role of corticosterone in the regulation of metabolic reserves.