. "12 Postcopulatory Sexual Selection: Darwin's Omission and Its Consequences--William G. Eberhard." In the Light of Evolution III: Two Centuries of Darwin. Washington, DC: The National Academies Press, 2009.
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In the Light of Evolution Volume III: Two Centuries of Darwin
influencing CFC (for instance, by packing female storage organs to induce the female not to remate), influencing long-term vs. short-term survival in the female, and defense against female spermicides (Holman and Snook, 2008). The data needed to test these hypotheses are largely lacking [see critical discussions in Swallow and Wilkinson (2002)]. Changes in the percentage of the ejaculate dedicated to parasperm under conditions of different intensities of sperm competition suggest that sperm competition is an important function of parasperm in some species (Oppliger et al., 1998) but not others (Weddell and Cook, 1999).
A similar disconnect regarding sexual selection occurred in studies of semen and of its effects on the female. Insect physiologists developed a tradition of experimentally implanting glandular portions of the male reproductive tract or injecting extracts into the female and determining the effects of these treatments on female behavior and reproductive physiology. Their consistent finding was that these glandular products are diverse (Chen, 1984; Swanson and Vacquier, 2002; Kern et al., 2004) and they induce females to oviposit or resist mating attempts from additional males; additional effects include inducing oogenesis, ovulation, or sperm storage (Chen, 1984; Eberhard, 1996; Andrés et al., 2006). These kinds of data accumulated for many years in the absence of any theoretical expectations, but recognition of the importance of postcopulatory competition among males to trigger such female responses made immediate sense (under both CFC and SAC) of their diversity, their consistent effects on females (Eberhard and Cordero, 1995; Eberhard, 1996), and molecular signatures indicating that they evolved under selection (Swanson et al., 2001; Andrés et al., 2006). The rapid divergence in Gryllus, in which females are thought to benefit (Wagner et al., 2001) rather than suffer from repeated copulations, constitutes evidence against SAC being responsible for this divergence (Andrés et al., 2006). Rapid divergence under selection has also occurred in seminal proteins of both primates and rodents (Dorus et al., 2004; Karn et al., 2008).
Interactions Between Egg and Sperm Molecules
Recent summaries reveal that the genes coding for molecules involved in fertilization in mammals and marine invertebrates such as sea urchins and abalone show a general evolutionary pattern strikingly similar to the patterns seen in male genital morphology: in essentially all steps of animal fertilization where the molecular interactions between sperm and egg proteins have been studied, there is evidence for rapid divergence of