Promiscuity lowers extinction risk

Posted By Ian Randall on 4th March 2010

Females who keep multiple partners may be playing a vital role in staving off the threat of extinction, biologists believe. A joint study by the Universities of Exeter and Liverpool, published this week in Current Biology, shows that such promiscuity, which is common in the animal world, greatly reduces the risks caused by all-female broods.


A fruitfly. Picture credit - Sanjay Acharya

The presence of sex-ratio distortion chromosomes in animals can cause the death of all Y chromosome sperm before they have the chance to fertilise an egg – this leads to an entirely female set of offspring, all of whom continue to pass the sex-ratio chromosome to their children, reducing the number of males of the species with each generation. If there are no males left, the entire population will inevitably die out.

The researchers studied changing populations of the fruitfly Drosophila pseudoobscura – allowing some flies to mate with multiple partners – as they would normally – while the rest were restricted to one mate alone. The study showed that polyandry, having multiple mates, limits the spread of the sex-ratio chromosome and thus prevents the species becoming extinct.

“We were surprised by how quickly a population could die out as a result of females only mating with one partner… this study is the first to suggest that it could actually save a population from extinction,” said Professor Nina Wedell, an evolutionary biologist at the University of Exeter.

This is because sex-ratio distorted males are only able to produce half the sperm of normal males – thus the chance for the affected sperm to fertilise an egg is reduced when polyandry introduces competition from healthy males.

In the study, five of the twelve monogamous fruitfly populations were made extinct by the sex-ratio chromosome; whilst none of the polyandrous groups were affected.

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