Sex: it's a good thing, evolutionarily speaking

May 30, 2012
Sex: it's a good thing, evolutionarily speaking
By comparing sexual and asexual species of evening primroses, pictured, Erika Hersch-Green demonstrated that sexual reproduction offers a significant advantage.

(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.

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 ,” she said. “That’s in line with many of the theories of evolution of .”

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.

To find evidence of those good genetic recombinations, Hersch-Green and her team sequenced the gene chitinase (pronounced KIE-tin-ace) A in each of the 32 species. All plants have the gene, which makes the enzyme chitinase and helps them identify and fight off diseases such as powdery mildew. However, the genes are not exactly the same; there are some differences in their building blocks, called nucleotides, which means that there are slight variations in chitinase from species to species.

Once they knew the sequence of nucleotides in the gene for each species, the researchers compared them using well-established mathematical models. They found that the chitinase A genes in the evening primrose species that reproduce sexually were different in four places from the ancestral gene, while the genes in the asexual species had not changed. In addition, the genes in the sexual plants had a higher expression level, meaning they produced more of the chitinase enzyme used to fight off disease.

She also looked at how well 12 different genotypes of the same asexual evening primrose 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.”

The findings are published in the article “Adaptive Molecular Evolution of a Defence Gene in Sexual but not Functionally Asexual Evening Primroses,” published May 15 online in the Journal of Evolutionary Biology.

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User comments : 6

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JDH
2.1 / 5 (7) May 30, 2012
So, exposing yourself to STDs keeps you disease resistent?

Is it too late for this guy to get a refund on his tuition?
Anorion
3.3 / 5 (7) May 30, 2012
So, exposing yourself to STDs keeps you disease resistent?

Is it too late for this guy to get a refund on his tuition?


exposing a population to an disease will make that those who are more sensitive to it, die of, means their genetics are removed from that populations genetic pool, those who resist better will live and reproduce and pass their resistance genes to next generation.
repeat few generations like that, and at end you have an population who will resist better to that disease. with each generation, the overall resistance of that population increase to that disease. and having 2 individuals contributing to adn of the new individual increase genetic choice , compared when its made without sex. see its pretty simple, and it is observed in nature that it works. just consider all the disease europeans were immune or very resistant, but those same disease wiped out american indians.
or consider how rats or insects or weeds get resistant to poisons we throw at them.
Anorion
3.7 / 5 (6) May 30, 2012
and also consider that keeping immune system on stress, reinforce it. it was observed that people who live in over clean environment, are more sensitive to allergies and parasites and so. while people in more poor countrys who live in dirty environments resist better.
take it as a muscle, if you exercise it, it grows bigger and stronger, if you just sleep and sit all day, it melt down and get weak. same with immune system, if its very active and have to fight against many aggressions, it grows stronger, and if you live in sterile environment, it melt down and grow weaker
kevinrtrs
1 / 5 (4) Jun 04, 2012
Of course there's always the un-answered question:

Just how did the astonishing miracle of sexual difference "evolve"? It would need to be a miracle because of the complexity that's required to "evolve" simultaneously in two different individuals such that the products can come together and perform an even greater miracle.

Now before you shoot off the hip, please first provide a thoroughly scientifically acceptable explanation for the existence of the reproductive differences [yet total compatibility] in male and female counterparts.

Perhaps I should save you some energy: There just isn't any. "Evolution" just has no answer.
Origin
not rated yet Jun 04, 2012
I explained here, the usage of sexual reproduction is optional for many species and its turned on, when the changes of life environment would require faster evolution, than the asexual reproduction provides. The sexual reproduction is connected with elevated risk or cancer and mutations, so its often turned off, when the living conditions would require any mutations at all. or example sharks are living in very stable conditions, so they don't evolve fast, they don't require mutations, so they're cancer resistant and hammerhead shark can reproduce asexually. A endometriosis and/or male associated infertility can be understood as an attempt for evolutionary adaptation of human organism to wealthy life conditions, where the sexual reproduction leads to unnecessary high mutagenity.

It means, for every organism the optimal ratio of sexual and asexual breeding exists.
Origin
not rated yet Jun 04, 2012
For small organisms with fast paced generation cycles the sexual reproduction is usually unwanted luxury, which consumes lotta energy and brings too high number of undesirable mutations. When the population faces the extinction and it lives in diaspora, then the waiting for sexual partner is not the optimal strategy of its survival too.