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.
鈥淲hen biologists talk about the 鈥榖attle of the sexes鈥� they often tacitly assume that the battle is between persistent males who always want to mate and females who don鈥檛,鈥� says Jakob Bro-J酶rgensen 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-J酶rgensen has observed such behaviour among the African topi antelope (Damaliscus lunatus) in Kenya.
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Competitive mating
Herds of African topi can number in the thousands. Typically females travel in large groups to mating hotspots 鈥� called leks 鈥� where about 10-20 males guard small territories, each measuring about 30 metres in diameter. Smaller males that fail to grab some of this prime real estate miss out on being able to participate in the intense mating, or lekking, that takes place.
Bro-J酶rgensen, 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-J酶rgensen.
Disruptive females
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-J酶rgensen says that he has seen a male topi antelope copulate 36 times in just one day, leaving the animal 鈥渢otally exhausted鈥�, and possibly with depleted sperm.
鈥淔or so long we have assumed that sperm is in unlimited supply,鈥� comments Paul Verrell at Washington State University in Pullman, US. 鈥淭hat old dogma is falling by the wayside.鈥�
Journal reference: (DOI: 10.1016/j.cub.2007.11.026)
