Pre Copulatory Mate Selection

Sexual selection has long been recognized as a powerful evolutionary process having important consequences on reproductive behaviour, morphology, and fitness (Birkhead and Pizzari, 2002). Sexual selection research has often focused on pre-copulatory mate choice; however, the discovery of female promiscuity and polyandry has lead to the realization that mate choice continues to operate after copulation (Birkhead and Pizzari, 2002). For males, it is obvious that promiscuity has evolved to increase reproductive fitness; however, the potential benefits to females are less understood (Keller and Reeve 1995). Nevertheless, recent studies suggest that females may gain genetic benefits by mating multiply by increasing offspring genetic diversity or …show more content…
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