CHAKRABORTY, Mukta *; HEWS, Diana K.; Indiana State University; Indiana State University: Endocrine-immune interactions in male Sceloporus lizards: testing assumptions of the immunocompetence handicap hypothesis

Variation in male secondary sexual traits contributes to explaining variation in reproductive success. Regulation of secondary sex traits is often mediated by the endocrine system, especially testosterone. Although high testosterone can enhance sexual characters and competitive ability, it may also prejudice immune function, a key assumption of the “immunocompetence handicap hypothesis”. Little work in reptiles has tested these assumptions. We experimentally assessed the testosterone immunosuppression assumption in adult male Sceloporus undulatus lizards captured during the breeding season. We manipulated circulating androgen levels and then measured two aspects of immune function that reflect humoral and cellular responses, respectively. We surgically castrated males and/or implanted them with testosterone capsules to alter plasma androgen levels. Following primary and secondary immunizations with a standard immunogen (phthalate-conjugated Keyhole Limpet Hemocyanin, pt-KLH), we measured humoral antibody responses with a competitive ELISA. We compared this to humoral responses produced using the sheep RBC hemagglutination protocol, to assess the efficacy of each protocol. To estimate cell-mediated immune responses, we used a delayed-type hypersensitivity test involving subcutaneous injections of antigen (pt-KLH) versus saline and measuring differences in swelling 24-hrs post-injection. Swelling primarily reflects T-cell migration into the injection site. Using radioimmunoassay, we measured plasma levels of testosterone and corticosterone to validate the hormone manipulations and to assess any immunosuppressive effects of high corticosterone, which could increase due to immune challenges and/or surgery treatments.