1987; Jacob et al. 2002; Milinski et al. 2005). While there have been several studies examining the effect of MHC genotype on pre-copulatory mate choice (reviewed in Tregenza and Wedell, 2000), there is evidence the MHC may also play a role in post-copulatory sexual selection, presumably through egg-sperm interactions (Wedekind et al. 1996; Rülicke et al. 1998; Yeates et al. 2009). Salmonid species are an excellent model system for the study of post-copulatory sexual selection, specifically sperm competition and CFC, because fertilization occurs externally, allowing in vitro fertilizations under controlled settings. Furthermore, the structure of the teleosts egg consists of an outer envelope (the chorion), and unlike mammals, only a single sperm is allowed entry into the egg via the micropyle (Kamler, 1992). Therefore, teleost eggs offer a unique opportunity for investigating sperm competition because having only a single entrance available for fertilization should dramatically elevate sperm competition, subsequently leading to the evolution of characteristics that increase sperm competitiveness. The micropyle may also facilitate CFC. During sperm attraction and movement through the funnel-shaped micropyle, the potential exists for the egg to favor certain sperm over others, thus leading to mate choice based on genetic compatibility at loci such as the MH genes (Skarstein et al. 2005; Yeates et al. 2009). Yeates et al. (2009) found that during competitive fertilization experiments in Altantic salmon (Salmo salar), males with more similar MH genotypes relative to the female outcompeted males with more dissimilar MH genotypes. Conversely, in other species, studies have found that female prefer males with more
1987; Jacob et al. 2002; Milinski et al. 2005). While there have been several studies examining the effect of MHC genotype on pre-copulatory mate choice (reviewed in Tregenza and Wedell, 2000), there is evidence the MHC may also play a role in post-copulatory sexual selection, presumably through egg-sperm interactions (Wedekind et al. 1996; Rülicke et al. 1998; Yeates et al. 2009). Salmonid species are an excellent model system for the study of post-copulatory sexual selection, specifically sperm competition and CFC, because fertilization occurs externally, allowing in vitro fertilizations under controlled settings. Furthermore, the structure of the teleosts egg consists of an outer envelope (the chorion), and unlike mammals, only a single sperm is allowed entry into the egg via the micropyle (Kamler, 1992). Therefore, teleost eggs offer a unique opportunity for investigating sperm competition because having only a single entrance available for fertilization should dramatically elevate sperm competition, subsequently leading to the evolution of characteristics that increase sperm competitiveness. The micropyle may also facilitate CFC. During sperm attraction and movement through the funnel-shaped micropyle, the potential exists for the egg to favor certain sperm over others, thus leading to mate choice based on genetic compatibility at loci such as the MH genes (Skarstein et al. 2005; Yeates et al. 2009). Yeates et al. (2009) found that during competitive fertilization experiments in Altantic salmon (Salmo salar), males with more similar MH genotypes relative to the female outcompeted males with more dissimilar MH genotypes. Conversely, in other species, studies have found that female prefer males with more