Females that have multiple mates reduce the risk of producing a brood of offspring without males..!!!

Promiscuous females
‘could prevent species becoming extinct’

Promiscuous females could prevent their species becoming extinct, scientists have found.

According to research by the Universities of Exeter and Liverpool, females that have multiple mates reduce the risk of producing a brood of offspring without males.

The study, published today in Current Biology, says an all-female brood could occur when all the ‘male’ Y chromosome sperm are killed before fertilisation, because of a sex-ratio distortion (SR) chromosome.

Scientists believe all-female broods will pass the chromosome on to their sons, which will in turn produce more female-only broods and eventually there will be no males and the population will die out.

Known as ‘polyandry’ among scientists, the phenomenon of females having multiple mates is shared across most animal species, from insects to mammals.

For this study, the scientists worked with the fruitfly Drosophila pseudoobscura.

They gave some populations the opportunity to mate naturally, meaning that the females had multiple partners. The others were restricted to having one mate each.

Several generations of these populations were bred so researchers could see how each fared over time.

Over 15 generations, five of the 12 populations that had been monogamous became extinct as a result of males dying out.

The SR chromosome was far less prevalent in the populations in which females had the opportunity to have multiple mates and none of these populations became extinct.

Having multiple mates can suppress the spread of the SR chromosome, making all-female broods a rarity, the researchers suggest.

This is because males that carry the SR chromosome produce only half as many sperm as normal males. When a female mates with multiple males, their sperm will compete to fertilise her eggs.

The few sperm produced by males carrying the SR chromosome are out-competed by the sperm from normal males, and the SR chromosome cannot spread.

Lead author Professor Nina Wedell, of the University of Exeter, said: ‘’We were surprised by how quickly - within nine generations - a population could die out as a result of females only mating with one partner.

‘’Polyandry is such a widespread phenomenon in nature but it remains something of an enigma for scientists. This study is the first to suggest that it could actually save a population from extinction.’’

(C) The Telegraph Group London 2010


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