The effects of diet on plasma and yolk steroids in lizards (Anolis carolinensis)

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Abstract
Steroids present in egg yolk have been shown to vary as a result of numerous social and environmental influences and to produce both positive and negative phenotypic outcomes in offspring. In the present study, we examined how quality of the diet affects plasma and yolk steroids in the green anole (Anolis carolinensis), a lizard species with genotypic sex determination. We documented the effects of body condition on plasma testosterone (T) and corticosterone (CORT)—steroids with frequently opposing effects—in breeding females and on the T and CORT content of their eggs. We chose to manipulate body condition via diet because resource availability is a relevant, fluctuating variable in the environment to which females can be expected to respond. Field-collected females were housed in the laboratory and kept on either a reduced, standard, or enhanced diet (differing in nutritional quality and/or quantity) for ten weeks. Although females did not differ in body condition at the beginning of the study, we found these diet regimes effective in producing females that differed in condition by the end of the study. Females on diets of enhanced quality were in better condition, produced more, but not heavier, eggs, and had higher plasma T concentrations than did females on a standard diet or one of reduced quality. There was also a significant positive relationship between laying sequence of eggs and yolk T for females on diets of enhanced quality, but not for the females on diets of standard or reduced quality. There were no effects of quality of diet on CORT in plasma or yolk, but yolk T and yolk CORT exhibited a strong positive correlation irrespective of treatment. Females on diets of reduced quality did not differ from females on standard diets either with respect to reproductive output or to endocrine profiles, in spite of being in worse body condition. These results demonstrate that females’ body condition, physiology, and reproductive output can be manipulated by quality of diet, and that changes in deposition of yolk steroids in response to diet may be minimal.