Date of Award

Fall 12-1-2005

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Life Sciences

First Advisor

Diana Hews

Second Advisor

Swapan Ghosh

Third Advisor

Michael Angelitta

Abstract

Sex steroid hormones affect behavior and morphological traits important in sexual selection. Steroid hormones also play a role in the development and functioning of immune system components. The immunocompetence handicap hypothesis (Folstad and Karter, 1992) proposes that tradeoffs, mediated by plasma levels of testosterone, exist between the immune system and elaboration of secondary sexual traits. Endocrine-immune interactions are well documented in birds and mammals, and steroid hormones can be immunoenhancing or immunosuppressive. Relatively little work has examined the ontogeny of immune function, and the interactions between steroid hormones and the immune system in reptiles. The first experiment addressed the question of testosterone regulation of the immune system by assessing variation in immune system components in breeding season adult males Sceloporus undulatus lizards as a result of immune response against an antigenic challenge following hormonal manipulation. Mean values for hematocrit, differential white blood cell (WBC) counts, and total WBC counts were lower in the treatment group with the highest testosterone concentration. The second experiment examined if immune system components are affected by age-related and seasonal variation in circulating levels of steroid hormones in juvenile and adult Sceloporus undulatus lizards after a commonly used antigenic challenge, sheep red blood cells. This experiment evaluated overall immune responses by measuring both humoral and cell-mediated immunity concurrently, which has not been done in reptiles. the first comparison of cellular immunity between juvenile and adult reptiles. Comparing data from adults and juveniles of both sexes during the breeding and postbreeding seasons indicated that immune system components (hematocrit value, differential and total WBC counts) exhibit seasonal variation; and that this variation might be correlated with known seasonal variation in circulating levels of steroid hormones. Together, these results supported for the androgen immunosuppression assumption of the immunocompetence handicap hypothesis. This study provided the first comparison of cellular immunity between juvenile and adult reptiles.

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