Testing for Direct and Indirect Effects of Mate Choice by Manipulating Female Choosiness

Despite a massive research effort, our understanding of the evolution of female mate choice remains incomplete [1, 2]. A central problem is that the predominating empirical research tradition has focused on male traits, yet the key question is whether female choice traits are maintained because of direct effects on female fitness or because of indirect genetic effects in offspring that may be associated with such traits. Here, we address this question by using a novel research strategy that employs experimental phenotypic manipulation of a female choice trait in an insect model system, the seed beetle Callosobruchus chinensis (Coleoptera: Bruchidae). We show that females with increased efficiency of choice enjoy strongly elevated fitness compared to females with reduced choice efficiency. In contrast, we found no effects of female choice efficiency on offspring fitness. Our results show that female choice is maintained by direct selection in females in this system, whereas indirect selection is relatively weak at most. We suggest that phenotypic engineering of female choice traits can greatly advance our ability to elucidate the relative importance of direct and indirect selection for the maintenance of female choice.