Effects of Colour Morph and Temperature on Immunity in Males and Females of the Common Wall Lizard

Colour polymorphism in reptiles is generally associated with the coexistence of alternative reproductive strategies that involve specific trade-offs among different life history traits. Notably, body temperature trades off with immunocompetence: temperature has relevant effects on immune-response, but maintaining the optimal temperature increases both energetic costs and predatory risk. This trade-off gains complexity by sex, since males and females could optimize fitness by different strategies. Given that there is no single solution for trade-offs, different links among alternative evolutionary stable solutions and morphs might evolve independently in each sex. We tested this hypothesis in the common wall lizard (Podarcis muralis) by means of in vitro cultures of blood cells in order to examine the response of the immune-system to phytohemoagglutinin stimulation in male and female morphs at two different temperatures (i.e. 22 and 32 °C), corresponding to the thermal optima of the two sexes. We found (i) morph-specific immunity in both sexes, i.e. yellow lizards suffer immunosuppression with respect to the other morphs, and (ii) sex-specific immunity under hot conditions, i.e. females of all morphs were immunosuppressed with respect to males. Results support the hypothesis that morphs might differently invest in immunocompetence, according to different set-up for the trade-offs between immunity and other life-history traits, resulting in alternative strategies with different fitness optima.