Parasites can exert strong selection on traits known to affect mate choice (Hamilton and Zuk, 1982; Poulin and Thomas, 1999; MacColl, 2009) and in some cases the genes involved also have immune functions, such as genes of the MHC (Milinski et al., 2005; Milinski, 2006; Eizaguirre et al., 2009 Eizaguirre et al., , 2011 . MHC genes www.frontiersin.org have been considered as possible "magic traits" in sticklebacks, influencing both defense and mate choice (Matthews et al., 2010) . MHC divergence in a closely related and sympatric pair of cichlid species from Lake Malawi has been proposed to be a result of local host-parasite-coevolutionary associations, and to have influenced odor-mediated mate choice, and ultimately to have favored speciation (Blais et al., 2007) .