From New Scientist:
Male antelopes play hard to get
* 11:15 29 November 2007
* NewScientist.com news service
* Roxanne Khamsi
Women have a reputation for being choosy when it comes to mates, but a study of African topi antelopes shows that males can be discriminating too. The study found that some males fight off advances from aggressive females that they have already mated with, so that they can pursue newer mates.
“When biologists talk about the ‘battle of the sexes’ they often tacitly assume that the battle is between persistent males who always want to mate and females who don’t,” says Jakob Bro-Jørgensen at the Zoological Society of London, UK.
But previously, researchers had observed female gorillas interfering with copulating pairs to compete for the male. Now, Bro-Jørgensen has observed such behaviour among the African topi antelope (Damaliscus lunatus) in Kenya. …
Bro-Jørgensen, who has observed the African topi for a decade, analysed the mating habits of 98 females. They could be distinguished from one another by physical traits, such as natural markings on their horns, and scars on their ears.
The females are typically in oestrus for only one day a year. During that brief time they compete with other fertile females to mate with the fittest males as frequently as possible to ensure conception.
On average, the females mate with four males 11 times during this day. This is possible because the actual sexual act takes only a few seconds, says Bro-Jørgensen.
He also observed that when a female saw a desirable male about to mate with another, she often charged at the couple with her horns. As a result, the male was sometimes forced to mate with the aggressor. But the researchers also noted that if the male had already mated with the aggressive female, he would fight her off.
The researchers suggest that the males get picky because they want to conserve their sperm and mate with as many females as possible, and thus maximise their chances of bearing offspring. Bro-Jørgensen says that he has seen a male topi antelope copulate 36 times in just one day, leaving the animal “totally exhausted”, and possibly with depleted sperm.
“For so long we have assumed that sperm is in unlimited supply,” comments Paul Verrell at Washington State University in Pullman, US. “That old dogma is falling by the wayside.”