Female choice for male immunocompetence: when is it worth it?

Disease resistance is not determined by any single immune component. Nevertheless, female choice for individual immune components could produce more disease-resistant offspring. Using a mathematical model, we tested whether female choice for male immune responsiveness was maintained or lost in simulated populations. We divided immunity into three different components: two different types of immune responsiveness and the ability to recognize pathogens. Immune responsiveness was divided into constitutive immunity (CI) and inducible immunity (IN) to simulate the fact that mounting an effective immune response requires independently regulated components. By using an immunologically relevant division, empirical data were available to constrain the model parameters. When the pathogen prevalence fluctuated from generation to generation, female choice for IN or CI was usually lost. Female choice for CI was often lost even when choosiness carried no fitness penalty. Choosing for CI or IN produced a fitness advantage over nonchoosers during some generations, but not for others, depending on the identity of the most prevalent pathogens. Choosing for IN or CI led to high mortality when pathogens sensitive to the nonchosen component became prevalent in the population, giving nonchoosers the advantage. Given that most animals experience fluctuating pathogen pressure, our model suggests that there may be little selection for female choice for male CI and/or IN in some species. We discuss the implications of our results for the study of female choice for male disease resistance. Copyright 2005.