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Mouse lemur mothers-to-be (pictured) trick multiple males into thinking they are the father of their young, to stop their babies being killed off

Promiscuous mothers-to-be encourage 'sperm wars' by tricking multiple partners into thinking they are the father of their young, to stop infants being killed off, scientists claim.

It is already known that that infanticide by male mammals - from mice to gorillas - is common in species where the females live in social groups dominated by one or a few powerful males.

But now experts have uncovered the clever strategy used by females of certain species, such as the mouse lemur, to protect their offspring - and over time, their plan leads to infanticide dying out.

University of Cambridge researchers compared detailed field observations for 260 mammalian species.

They explained that when a rival male takes over groups of animals, they will kill infants to make sure they can produce their own offspring.

To guard against this risk, females mate with as many males as possible in a short amount of time to confuse the paternity of their infants.

The strategy means that any murderous male risks killing off his own offspring.

Dr Dieter Lukas, from the university's department of zoology, explained: 'The finding that females can actually, by mating with multiple males, stop them from killing her offspring, had not been proved before.

'It had been shown in individual species but it wasn't clear that it was in response to infanticide.'

In species such as the mouse lemur, males must concentrate on producing larger quantities of sperm to ensure they can reproduce with lots of females. 

This causes the testis of male mouse lemurs to swell up to 10 times larger than normal in breeding season. 

Female bonobo monkeys can mate with every male in the troop of between 10 and 12 to protect their offspring (stock image) .Male bonobos have testes that are roughly 15 per cent larger than chimpanzees, who are very closely related and do commit infanticide

Dr Lukas explained: 'In species in which infanticide occurs, testis size increases over generations, suggesting that females are more and more promiscuous to confuse paternity.

'Once sperm competition has become so intense that no male can be certain of his own paternity, infanticide disappears - since males face the risk of killing their own offspring, and might not get the benefit of siring the next offspring.'

Closely related species that differ in infanticide and testes size include chimpanzees, where the males commit infanticide, versus bonobos, where males have not been observed to kill offspring.

Bonobos have testes that are roughly 15 per cent larger than those of chimpanzees.

Similarly, male Canadian Townsend voles do not commit infanticide and have 50 per cent larger testes compared to infanticidal males of close relatives the North American meadow voles, Dr Lukas added.