The Effects of Exogenous Corticosterone and Testosterone on Juvenile Eastern Fence Lizards, Sceloporus undulatus

Open Access
Author:
Norjen, Courtney M
Area of Honors:
Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Tracy Lee Langkilde, Thesis Supervisor
  • James Harold Marden, Honors Advisor
Keywords:
  • corticosterone
  • testosterone
  • fence lizards
  • maternal affects
  • growth
  • sex ratios
  • hatching success
  • size at hatching
  • survival
Abstract:
Hormones, such as corticosterone (CORT) and testosterone (T), play a critical role in an animal’s stress response, sexual maturation, and growth and development. These hormones interact through the hypothalamic-pituitary-adrenal (HPA) axis, and have reciprocal effects. Maternal levels of CORT and T can have important effects on juveniles through two pathways: 1) maternal hormones can enter the eggs and directly affect the developing offspring and/or 2) these hormones can affect maternal behavior or maternal allocation of nutrients to the eggs, thereby indirectly affecting the developing offspring. We used the Eastern Fence Lizard, Sceloporus undulatus, to test the effects of CORT and T on hatching success, size at hatching, sex, growth rate, and survival of offspring. We topically applied exogenous hormones to pregnant female Fence Lizards and to eggs from unmanipulated females post-laying, to distinguish between direct effects of these hormones and effects caused by hormonally-driven changes in maternal behavior or allocation. Hormone application to the mothers, but not direct application to the eggs, affected hatching success and size at hatching, suggesting that these changes were driven by maternal responses to CORT and T rather than being a direct effect of these hormones on the developing embryos. Offspring survival was affected both by application of hormones to the eggs and to the mothers, suggesting this might be a direct hormonal effect. CORT and T differentially affected these traits: offspring of CORT-dosed mothers had higher hatching success and were larger at hatching than control-dosed mothers, whereas dosing mothers with T had the opposite effect. Similarly, applying CORT to eggs or mothers increased survival over 4-months, whereas applying T decreased survival, relative to controls. Applying CORT or T to both the mothers or the eggs did not affect the sex ratio of the offspring. Our findings suggest that maternal levels of CORT and T can have significant effects on fitness-relevant traits in offspring, both directly and via hormonally-driven changes in maternal behavior or allocation.