Research affirms sexual reproduction avoids harmful mutations

January 12, 2015 by Elaine Smith
Sex and the Single Evening Primrose
Oenothera grandis plant (Showy evening primrose) Credit: Marc Johnson

(Phys.org)—Sex or no sex? Using various species of the evening primrose (Oenothera) as his model, Jesse Hollister, a former University of Toronto post-doctoral fellow, and his colleagues have demonstrated strong support for a theory that biologists have long promoted: species that reproduce sexually, rather than asexually, are healthier over time, because they don't accumulate harmful mutations.

"These findings allow us to understand why an enormous diversity of around the world go through the laborious process of sexual reproduction," says Hollister, who completed the research while working at U of T Mississauga's Department of Biology and U of T St. George's Department of Ecology & Evolutionary Biology.

The research, published online recently by the journal Molecular Biology and Evolution, was authored by Hollister, along with his supervisors, Professor Marc Johnson at U of T Mississauga and Professor Stephen Wright at U of T St. George. Hollister is now an assistant professor at Stony Brook University in New York.

For decades, evolutionary found to be a paradox. Mathematically, asexual reproduction seemed to make more sense. Each organism – not just half the population—could produce offspring, and all its genes were passed on, rather than the 50 per cent from each parent in offspring from sexual unions.

One key issue they didn't take into account, says Hollister, was the accumulation of harmful mutations over time. New mutations occur naturally in every species from one generation to the next. When species reproduce sexually, their genes are separated, shuffled and recombined in various ways, so each offspring doesn't receive all of their parents' mutations in addition to the naturally occurring ones. In asexual reproduction, however, the species copies the existing genome as a whole, effectively cloning itself. Therefore, they pass on all the mutations that naturally accumulate from generation to generation.

"Asexual reproduction leads to a buildup of deleterious mutations over time; it's called Muller's Ratchet," Hollister says. "The species' average fitness is reduced and they are less able to compete in the ecological arena than sexual species, so they have an increased probability of extinction."

The primrose was the ideal system for studying the evolutionary importance of sex, Hollister noted, because about 30 per cent of the species in the genus have evolved to reproduce asexually, each at a different time. With the assistance of the 1,000 plant transcriptome project, led by Gane Ka-Shu Wong at the University of Alberta, and sequencing aid from the BGI-Shenzen in China, the U of T researchers were able to examine 30 pairs of species. One species in the pair reproduced sexually; the other, asexually. Some of the asexually reproducing species were younger than others in evolutionary terms, allowing the researchers to see the effects of over time.

"What we found was exactly what we predicted based on theory," says Hollister. "The power of our study is that we examined many independent transitions to asexuality over different time scales and were able to take a snapshot in the present of the genetic variation in species pairs."

Johnson, a professor in the Department of Biology at UTM, says this research has shed new light on the paradox of sex.

"This is the first solid genetic support for the theory that a significant cost to being asexual is an accumulation of deleterious ," Johnson says. "This study has allowed us to unlock part of the mystery of why sex is so common: it's good for your health, at least if you are a plant."

Explore further: Sexual reproduction can increase genetic variation but reduce species diversity

Related Stories

Sex: it's a good thing, evolutionarily speaking

May 30, 2012

(Phys.org) -- Sure, sex may be fun, but it’s a lot of work, and the payoff is by no means certain. Scientists have speculated for a long time on why all living things don’t simply make like amoebas and split.

Researcher argues that sex reduces genetic variation

July 7, 2011

Biology textbooks maintain that the main function of sex is to promote genetic diversity. But Henry Heng, Ph.D., associate professor in WSU's Center for Molecular Medicine and Genetics, says that's not the case.

Recommended for you

Mice can smell oxygen

December 2, 2016

The genome of mice harbours more than 1000 odorant receptor genes, which enable them to smell myriad odours in their surroundings. Researchers at the Max Planck Research Unit for Neurogenetics in Frankfurt, the University ...

How single-celled organisms navigate to oxygen

December 2, 2016

A team of researchers has discovered that tiny clusters of single-celled organisms that inhabit the world's oceans and lakes, are capable of navigating their way to oxygen. Writing in e-Life scientists at the University ...

Natural nomads, leatherback turtles opt to stay in place

December 2, 2016

Endangered leatherback sea turtles are known for their open-ocean migratory nature and nomadic foraging habits – traveling thousands of miles. But a Cornell naturalist and his colleagues have discovered an area along the ...

Neural stem cells serve as RNA highways too

December 1, 2016

Duke University scientists have caught the first glimpse of molecules shuttling along a sort of highway running the length of neural stem cells, which are crucial to the development of new neurons.

7 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Vietvet
4.5 / 5 (8) Jan 12, 2015
Jamie K will be along soon to call the author a science idiot and spout his "microbes to men" bs.
jsdarkdestruction
5 / 5 (6) Jan 13, 2015
Wow. Jvk isn't here yet? Wowzers. I hope he is taking my advice and instead of crying about "science idiots" and is putting the time in to advance his ideas further by researching further and contacting the experts and working on how he can convince them to convert.
Whydening Gyre
5 / 5 (5) Jan 14, 2015
Agreed. This one has "JVK must provide input" written all over it... (at least, for him...)
ubavontuba
1 / 5 (1) Jan 14, 2015
"This is the first solid genetic support for the theory that a significant cost to being asexual is an accumulation of deleterious mutations,"
I don't understand. Aren't the majority of earth's species (both prokaryotes and eukaryotes) asexually reproducing (a large percentage, particularly the prokaryotes, being microorganisms)? Haven't these populations generally tended to be quite stable, and not overrun by supposedly superior, sexually reproducing species?

So, does this mean this rule generally only applies to multicellular organisms? What about species that have secondarily lost this feature? Has this weakened them in some respect?

What about heterogamy (the ability to reproduce both sexually and asexually)? Why wouldn't having the best of both be far superior to either or? Why aren't we being overrun by species with this capability?

I'm concerned there may be a confirmation bias here. It seems to me if this was true, it should be more obvious.

Whydening Gyre
not rated yet Jan 14, 2015
don't understand. Aren't the majority of earth's species (both prokaryotes and eukaryotes) asexually reproducing (a large percentage, particularly the prokaryotes, being microorganisms)? Haven't these populations generally tended to be quite stable, and not overrun by supposedly superior, sexually reproducing species?

Would this indicate some sort of "immunological response" mechanism?

What about heterogamy (the ability to reproduce both sexually and asexually)? Why wouldn't having the best of both be far superior to either or? Why aren't we being overrun by species with this capability?


In due time, Uba...:-)
The short, more logical route to this would be to have both sets of sex organs in a single organism (thereby doubling the chance of some action on a Saturday night...)...
cjn
5 / 5 (2) Jan 14, 2015
Its not just sexual reproduction, but being diploid which allows for the suppression of mutations within a population. It is the ability to express the common dominant or superior dominant (or even reduced expression of a superior recessive) which enables resilience in the individual within the population.

If it was merely that "genes are separated, shuffled and recombined in various ways, so each offspring doesn't receive all of their parents' mutations in addition to the naturally occurring ones (FTA)", then you'd just have shuffled deleterious mutations.
Whydening Gyre
5 / 5 (1) Jan 14, 2015
Its not just sexual reproduction, but being diploid... ... which enables resilience in the individual within the population.

This is a key factor in maintaining organismal stability...
nicely described, cjn...

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.