Seasonal Variation in Desert Tortoise Immune Function
Threatened Mojave desert tortoise (Gopherus agassizii) populations may be negatively impacted by upper respiratory tract disease. To more fully understand the general impact of diseases in wild populations, a more complete knowledge of the factors that contribute to immunocompetence in this species is necessary. We analyzed minimal seasonal fluctuations in innate immune function and white blood cell numbers in a colony of captive, healthy tortoises. Bacteriocidal assays measured the ability of constitutive natural antibodies and complement proteins to kill a standard strain of Escherichia coli. Ratios of heterophils to lymphocytes were used to infer relative levels of chronic stress and/or activity among the four seasons. Bacteriocidal capacity was significantly suppressed during winter relative to the other three seasons, but heterophil:lymphocytes did not vary significantly among seasons. These results suggest that tortoises may be inherently immunosuppressed during winter, but elevations in stress do not contribute to this immunosuppression.
Networked Digital Library of Theses and Dissertations