Pavlovian conditioning alters reproductive fitness in sperm competition and sperm allocation paradigms

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.