A sexually harassed male antelope has been found to ration its stud services and will spurn females which demand second helpings.

The fittest male African topis find themselves so much in demand that they will refuse to couple repeatedly with the same females and will often hold out even when harassed for more. Instead of taking every opportunity to mate the males will withdraw sexual favours so that they can conserve sperm for fresh partners.

Males which failed to pace themselves were, a study found, at serious risk of collapsing from sexual exhaustion - putting them at increased danger of beng eaten by predators.

The finding challenges the assumption that it is male mammals which seek out mates while females pick and choose the most appealing suitors.

The role reversal in the process of sexual conflict is likely to be the result of the intense breeding pressures on the promiscuous topis, says Dr Jakob Bro-Jorgensen, who carried out the study in Kenya.

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 getting pregnant. With the females being desperate to maximise chances of conception, the males, at least the choicest specimens, must refuse to mate more than once with the same female in order to mate with as many different females as possible.

This, the study published in the journal Current Biology concluded, gives rise to the prime males being sexually harassed aggressively by the females and are often driven physically to fight off sex pests.

“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 while females are in oestrus for just a day, the males have to last the whole of the mating season. “It was not uncommon to see males collapsing with exhaustion as the demands of the females got too much for them, ” he said.

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

In his report Dr Bro-Jorgensen said: “Male counterattacks are associated with refusal to mate with the agressive females.

“This study points to reversed sexual conflict as a more significant evolutionary force in promiscuous mammals than previously thought. However, such conflicts probably go unnoticed because males, in contrast to females, can avoid mating without conspicuous resistance.”

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