Jumat, 01 Juni 2012

Evening primroses reveal the secret of why we evolved sex (and it's not for fun)

Evening primroses reveal the secret of why we evolved sex (and it's not for fun)

By Rob Waugh

PUBLISHED: 11:08 EST, 1 June 2012 | UPDATED: 11:08 EST, 1 June 2012

For human beings at least, sex is fun - but it's hard work, biologically speaking, and a 'risky' evolutionary strategy.

A study of evening primroses has found out 'why' species do it - because it increases resistance to disease.

Species that simply clone themselves can't adapt as quickly as species who have sex to reproduce, mixing characteristics from two individuals.

Now a biologist at Michigan Technological University has found one good reason: sexual reproduction strengthens an organism's ability to adapt; specifically, it may lead to stronger disease resistance

Now a biologist at Michigan Technological University has found one good reason: sexual reproduction strengthens an organism's ability to adapt; specifically, it may lead to stronger disease resistance

Erika Hersch-Green tested the idea on 32 different species of evening primroses.

These native North American wildflowers are unusual in that a number of species reproduce asexually, essentially through cloning themselves.

That allowed Hersch-Green and her colleagues to compare 16 species that reproduce sexually with an equal number that function asexually.

‘We found that the sexual plants have an increased ability for adaptive, positive evolution,’ she said. ‘That's in line with many of the theories of evolution of sex.’

Scientists believe that sexual reproduction offers two big advantages: It can sweep bad mutations out of the gene pool more quickly.

Also, by shuffling parents' genetic material each generation, it increases the likelihood that new genetic combinations will arise that help organisms adapt to their environment.

She alooked at how well 12 different genotypes of the same asexual evening primrose species weathered attacks by powdery mildew.

Those that sustained the most damage from the mildew also were less fit, meaning they produced fewer fruits.

‘This suggests that common pathogens of evening primrose plants are an important selective agent for these plants,’ Hersch-Green said.

‘Furthermore, molecular changes that increase chitinase expression and reduce disease damage are likely to be very good for the plants.’

‘This is in line with the theory that sex provides an evolutionary advantage to organisms,’ Hersch-Green said. ‘Until now, there had been no empirical evidence to support this advantage of new genetic combinations.’

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