Female Choice for Male Immunocompetence: When Is It worth It? 1 2

Running head: Female choice for male immunocompetence 18 19 2 Disease resistance is not determined by any single immune component. Nevertheless, 1 female choice for individual immune components could produce more disease-resistant 2 offspring. Using a mathematical model, we tested whether female choice for male 3 immune responsiveness was maintained or lost in simulated populations. We divided 4 immunity into 3 different components: 2 different types of immune responsiveness 5 (inducible immunity and constitutive immunity) and the ability to recognize pathogens. 6 When the pathogen prevalence fluctuated from generation to generation, female choice 7 for inducible or constitutive immunity was usually lost. Female choice for constitutive 8 immunity was often lost even when choosiness carried no fitness penalty. Choosing for 9 constitutive or inducible immunity produced a fitness advantage, when compared to non-10 choosers, during some generations, but not for others, depending on the identity of the 11 most prevalent pathogens. Choosing for inducible or constitutive immunity led to high 12 mortality when pathogens sensitive to the non-chosen component became prevalent in the 13 population, giving non-choosers the advantage. Given that most animals experience 14 fluctuating pathogen pressure, our model suggests that there may be little selection for 15 female choice for male constitutive and/or inducible immunity in some species. We 16 discuss the implications of our results for the study of female choice for male disease 17 resistance. 18 19 mate choice 21 22 3 Introduction 1 In many species, females actively choose their mates despite the potential costs of 2 being choosy (Andersson, 1994). Mate choice may benefit females by allowing them to 3 select males capable of bestowing 'good genes' on their offspring. By increasing 4 offspring quality, females could enhance their own fitness enough to offset the costs of 5 choice. Disease can drastically reduce female fitness by destroying susceptible offspring. 6 Disease resistance appears to be heritable in a wide variety of species (e.g. Ryder and 7 Siva-Jothy, 2001). Therefore, if females could choose disease-resistant males, more of 8 their offspring would survive. This selection pressure should favour females capable of 9 choosing males based on their disease resistance (i.e. immunocompetence) (Møller et al., 10 1999). 11 In this paper we develop a mathematical model to examine the selection pressure 12 on female choice for superior male immune responses. Immune responsiveness refers to 13 the ability of the immune system to produce cells and/or molecules …