Chickens, by ejecting the sperm of the males after mating, control fertilization of their eggs.
It is often ignored, but in a barn, a battle of the sexes rages on. The hens are solicited by the roosters, the dominant subordinates, and couplings are frequent, sometimes even “a little forced.” However, females have a means of controlling fertilization: they may expel semen received through the muscles of their cloaca, the body (common birds, reptiles and amphibians) which lead to the intestine, ureters of the urinary tract and the oviduct of the reproductive tract, Rebecca Dean, University of Oxford and colleagues studied among a group of wild chicken, the circumstances of this response to coercion.
They were interested in risk (the probability that ejaculate is eliminated) and intensity (the proportion of seeds removed) of the ejection. First, the ejection of semen discharges an average of 80 percent of the sperm content. Then, more semen volume, the more it may be repressed. Finally, the intensity of the crowding is even higher than the male’s social status is low. Thus, the hens have a selection pressure on genes active males, but after mating.