Browsing by Subject "Sperm competition"
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Item Counter‐perfume : using pheromones to prevent female remating(2018-09-05) Malouines, Clara; Gilbert, Lawrence E.Strong selection to secure paternity in polyandrous species leads to the evolution of numerous chemicals in the male’s seminal content. These include antiaphrodisiac pheromones, which are transmitted from the male to the female during mating to render her unattractive to subsequent males. An increasing number of species have been shown to use these chemicals. Herein, I examine the taxonomic distribution of species using antiaphrodisiac pheromones, the selection pressures driving their evolution in both males and females, and the ecological interactions in which these pheromones are involved. The literature review shows a highly skewed distribution of antiaphrodisiac use; all species currently known to use them are insects with the exception of the garter snakes Thamnophis sirtalis parietalis and T. radix. Nonetheless, many taxa have not yet been tested for the presence of antiaphrodisiacs, in groups both closely and distantly related to species known to express them. Within the Insecta, there have been multiple cases of convergent evolution of antiaphrodisiac pheromones using different chemical compounds and methods of transmission. Antiaphrodisiacs usually benefit males, but their effect on females is variable as they can either prevent them from mating multiple times or help them reduce male harassment when they are unreceptive. Some indirect costs of antiaphrodisiacs also impact both males and females, but more research is needed to determine how general this pattern is. Additional research is also important to understand how antiaphrodisiacs interact with the reproductive biology and sexual communication in different species.Item Pavlovian conditioning alters reproductive fitness in sperm competition and sperm allocation paradigms(2005) Matthews, Rachel Nicolle; Domjan, Michael, 1947-Sperm competition results when sperm from rival males compete to fertilize the ovum of a single female. Typically, paternity rates are proportional to the amount of sperm available during fertilization windows. Two males mating in immediate succession with the same female, transferring similar quantities of sperm, will each sire about 50% of the offspring. The greater the delay, the greater the percentage of offspring sired by the second male. Males engaging in multiple copulations with different females will have exponentially decreasing fertilization success. Manipulations that enable one male to transfer more sperm should provide a paternity advantage, independent of delay or depletion. In a series of experiments, reproductive success was increased with the presentation of a Pavlovian signal prior to copulation. In a study with domesticated quail (Coturnix Japonica), presentation of a Pavlovian signal permitted one of two competing males to predict copulatory opportunity. Using microsatellite-based DNA fingerprinting to identify paternity, signaled males sired 72% of the offspring as compared with control males when no delay was imposed. If five hours separated the two males, the first male sired 26% of the offspring under baseline conditions. Providing a Pavlovian signal overcomes the temporal delay, allowing the first male to sire 43% of the offspring. Further analysis examined the role of Pavlovian conditioning in sperm allocation when a male copulates with two females, separated by a 15-min or 5- hour delay. Baseline rates of paternity increased when a Pavlovian signal preceded the initial (24% to 42%) or second female (6% to 26%). No difference was found when a 5 hour delay was imposed between females. Pavlovian conditioning is a common learning process affecting a variety of sexual behaviors, including sperm output. It has been shown that Pavlovian conditioning provides reproductive advantage in both sexual competition and sperm allocation paradigms. These effects are independent of other factors emphasized in previous explanations, such as mating system or sperm morphology, and were probably mediated by an impact on how sperm were released from sperm stores.Item Sperm competition and the evolution of alternative reproductive tactics in the swordtail Xiphophorus nigrensis (Poeciliidae)(2011-05) Smith, Chad Christopher; Ryan, Michael J. (Michael Joseph), 1953-; Mueller, Ulrich; Juenger, Tom; Bolnick, Daniel; Rosenthal, GilDarwin identified sexual selection as an important evolutionary process resulting from differences among males in their ability to secure mates. In the latter half of the 20th century, it became apparent that females often mate with multiple partners within the same reproductive cycle, leading to the overlap of ejaculates from multiple males and sperm competition for the fertilization of the eggs. Here, I examine how sperm competition has influenced the evolution of Xiphophorus nigrensis, an internally fertilized, livebearing fish with alternative male mating tactics that are dependent upon male size. I find that variation in male tactic is correlated with variation in traits relevant to sperm competition: small males that sneak copulations produce ejaculates with a greater proportion of fertilization-capable sperm (sperm viability) and sperm that is longer-lived following activation compared to large males that court females. Sperm morphology is also divergent between tactics and correlated with sperm performance: smaller males have larger midpieces and midpiece size is positively correlated with sperm velocity and longevity. Social environment also affects ejaculate quality, with sperm velocity rapidly increasing when a small male is exposed to another small male compared to when he is exposed to a large male. Large male ejaculates were invariant across social environments. Next, I demonstrate experimentally that the observed variation in sperm quality has important consequences for the outcome of sperm competition. Males with superior sperm viability sire more offspring, while sperm velocity is negatively associated with sperm competitive ability when sperm are stored within the female prior to fertilization. Finally, I show that sperm competition is likely to have important effects on male reproductive success in the wild by characterizing the genetic mating system of X. nigrensis. I find that 61% of females collected from the Nacimiento Río Choy produce offspring sired by 2-4 males. Paternity is strongly skewed among sires, with an average of 70% of offspring sired by one of the males represented in the brood. These studies illustrate sperm competition can have potent effects on the evolution of animals.