Forced Copulation in Captive Mallards III. Sperm Competition

Abstract

Abstract Previous observations of forced copulation (FC) in captive Mallards (Anas platyrhynchos) showed that most FC attempts were directed at females in prelaying and laying condition and that most FC's occurred in the morning when the females were leaving their nests after egg laying. In order to determine whether or not there is a physiological basis for these observed temporal patterns, sperm competition in captive Mallards was examined using artificial insemination and genetic markers. Results indicated that if a female was inseminated with two competing doses of semen at different time intervals, the proportion of progeny from the first and the second inseminations was not significantly different if these inseminations were simultaneous, 1 h, or 3 h apart. There was a preponderance of progeny (70%) from the second insemination, however, if the inseminations were 6 h apart. Insemination of females less than 1 h after egg laying resulted in 25% of the eggs laid the following morning being fertile. Only 1 of 179 eggs laid the following morning was fertile when the females were inseminated more than 1 h after egg laying. Our experiment demonstrated that there is an insemination "window," a short period when new sperm are least likely to meet competition from sperm already in the oviduct and from sperm introduced later, and it provided a possible explanation for the observed timing of FC attempts.