Hens reject Bad Mates’ Sperm

By Mark Brown, Wired UK

Feral chickens have developed an effective countermeasure to avoid being fertilized by a forceful, sub-standard mate.

 Zoologists from Oxford University observed hens forcibly ejecting sperm after copulation, as if to lower a male’s chances of fathering the next generation, and putting a selective pressure on chicken dads.
On average, 80 percent of the ejaculate is expelled. Large quantities suffered a higher risk of ejection, but a larger proportion of smaller ejaculates were expelled leaving less sperm to fertilize an egg.

“Sperm ejection imposes on males an evolutionary dilemma,” says Rebecca Dean, of Oxford University Department of Zoology in a press release. “This trade-off between ejection risk and amount of sperm ejected could generate opposing selection on the evolution of sperm allocation strategies in males.”

Females don’t treat all males equally. The hens were more likely to dump sperm after a few matings, favoring their first partners over later ones. Socially inferior males also got the ejection criteria, as females gave dominant males the advantage.

Female counter-measures to fertilization are not entirely uncommon, and especially prevalent in animals where males are able to force females into mating. It has been found in worms, insects, and even primates.

Male ducks, for example, have large corkscrew penises — lined with ridges and latching spines — that they can extend to a fully-erect 20cm in a a third of a second. To avoid being fertilized by a forceful duck, female ducks have evolved long and twisting maze-like vaginas which spiral in the opposite direction and have dead-end pockets and frightful kinks — it’s like a genitalia arms race.

Image: sk8geek/Flickr

Source: Wired.co.uk

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