KABANGE, Zaina / S; HEWS, Diana / K; Indiana State University, Terre Haute; Indiana State University, Terre Haute: Effects of Testosterone and Immune Challenge on White Blood Cell Counts in Male Sceloporus undulatus Lizards

Testosterone affects behavior and morphological traits important in sexual selection. Testosterone also plays 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 the elaboration of secondary sexual traits. Endocrine-immune interactions are well documented in many species, and steroid hormones can be immunoenhancing or immunosuppressive. Relatively little work has examined this in reptiles. Using testosterone implants and/or castration, we asked if circulating levels of testosterone cause changes in immune parameters in adult male Sceloporus undulatus lizards. We assessed how an antigenic challenge (phthalate-conjugated Keyhole Limpet Hemocyanin) affects these measures in males with and without altered testosterone. We calculated the average proportion of each WBC type, total WBC counts, hematocrit, and heterophil to lymphocyte ratio (H:L ratio). The ratio of these two most abundant circulating leukocytes is used in many studies as a diagnostic indicator of stress (Gross, 1981). We found that total WBC counts, the proportion of heterophils, and the H:L ratio differed among treatment groups after testosterone manipulation and immune challenge.