Date of Award

Summer 8-1-2005

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Diana K. Hews

Second Advisor

Swapan K. Ghosh

Third Advisor

Michael J. Angilletta, Jr.

Abstract

The immunocompetence handicap hypothesis (IHH) was proposed by Folstad and Karter ( 1992) to describe the role of the endocrine system in ensuring honesty of sexual signaling. Numerous studies have investigated the assumptions of the IHH, but currently there is mixed evidential support in favor of the IHH. The first chapter of this thesis is a review examinining these studies, their limitations, and proposed alternative models and future directions. The second chapter of this thesis presents a study in which we experimentally assesss the testosterone immunosuppression assumption in adult male Sceloporus undulatus lizards. We manipulated circulating androgen levels (Day 0) by surgical castration/implantation, and then sequentially measured two aspects of immune function (in three tests) reflecting humoral and cellular responses, respectively. The four treatment groups were: no operation; sham surgery with blank implants; sham surgery with testosterone implants; and castrate with blank implants. Males were then immunized with the antigen, phthalateKLH to measure secondary antibody responses with a competitive ELISA at Day 34. We compared this to secondary antibody responses produced using the sheep RBC hemagglutination protocol (Day 160). To estimate cell-mediated immune responses, we also used a delayed-type hypersensitivity test (Day 120) involving subcutaneous injections of antigen (pt-KLH) versus saline and measuring differences in swelling 24-hrs post-injection. To validate the hormone manipulations, we measured plasma levels of testosterone and corticosterone using radioimmunoassay,. Males with elevated testosterone levels had reduced cell-mediated immune responses compared to the other treatment groups. However, we failed to detect any evidence of suppressed humoral responses (both pt-KLH and SRBC immunizations) in males with elevated testosterone. Thus, testosterone was not consistently immunosuppressive in this species.

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