Immunocompetence and sexual selection in insects

Abstract

Males of many species have extravagant morphological and behavioral secondary sexual traits, and female choice of mates is often based on these traits. It has been postulated that such traits are reliable indicators of male quality since the costs of these traits select against cheating. The immunocompetence handicap hypothesis is a recently proposed mechanistic explanation of these costs: it states that males carry sexual ornaments at the expense of their resistance to diseases and parasites, and this resistance is heritable. In this thesis I show that visual, acoustic, and chemical sexual ornaments as well as some behavioral traits in insects may reflect male immunocompetence. Moreover, I show that both immunocompetence and sexual ornaments are condition dependent using experimental manipulations of condition and recording pheromone attractiveness. This provides an explanation for the positive correlation between the expression of sexual ornaments and immunocompetence found at the population level. In addition, I show that in the resource holding polygyny mating system, where females choose territories based on the quality and quantity of resources, the outcome of male-male competition can be used to predict male immunocompetence. A number of studies in insects have proven that immunocompetence is heritable. Thus, by preferring males with elaborate secondary traits or males possessing the best territories females might benefit indirectly by increasing the parasite resistance of their offspring.