Sexually harassed male antelopes sometimes ration their stud services and spurn females that demand second helpings.

The fittest male African topis find themselves so much in demand that they refuse to couple repeatedly with the same females and often hold out even when pestered for more.

Instead of taking every opportunity to have their way, the males withdraw sexual favours so that they can conserve their sperm for fresh partners.

Males that failed to pace themselves were, a study found, at serious risk of collapsing from sexual exhaustion – putting themselves in danger of beng eaten by predators. The finding challenges the assumption that male mammals seek out mates while females get to choose the most appealing suitors.

Jakob Bro-Jorgensen, who carried out the study in Kenya, said that the role reversal in the process of sexual conflict was likely to be the result of the intense breeding pressures on the promiscuous topis. The rutting season lasts six weeks, but each female is fertile for just one day and needs to mate as often as possible to maximise the chances of conceiving.

With the females being so desperate for repeated satisfaction, the choicest males end up being spoilt for choice and start resisting temptation. The refusal to oblige the females is likely to be driven by the male’s need to conserve its sperm. This, the study published in the journal Current Biology concludes, gives rise to the prime males being harassed, and they are often driven to fight off females.

“I was interested to see that in cases where the male antelope was free to choose between females, he deliberately went for the most novel mate, rather than the most high-ranking,” said the researcher. “However, some pushy females were so aggressive in their pursuit of the male that he actually had physically to attack them to rebuff their advances.” Dr Bro-Jorgensen, of the Zoological Society of London and the University of Jyväshyllä in Finland, said that whereas females were in oestrus for a day the males had to last for the whole mating season. To maximise their chances of fathering calves they needed to mate with as many females as possible.

He added: “It was not uncommon to see males collapsing with exhaustion as the demands of the females got too much for them.”

African topi antelopes, Damaliscus lunatus jimela, live on savannahs and shrublands in the Democratic Republic of Congo, Kenya, Rwanda, Tanzania and Uganda.

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