Featured Research

from universities, journals, and other organizations

Sex, Cleaner Of Genomes

Date:
February 20, 2006
Source:
Indiana University
Summary:
When sexual species reproduce asexually, they accumulate bad mutations at an increased rate, report two Indiana University Bloomington evolutionary biologists in this week's Science. The researchers used the model species Daphnia pulex, or water flea, for their studies.

When sexual species reproduce asexually, they accumulate bad mutations at an increased rate, report two Indiana University Bloomington evolutionary biologists in this week's Science. The researchers used the model species Daphnia pulex, or water flea, for their studies.

The finding supports a hypothesis that sex is an evolutionary housekeeper that adeptly reorders genes and efficiently removes deleterious gene mutations. The study also suggests sexual reproduction maintains its own existence by punishing, in a sense, individuals of a species that meander into asexuality.

"It is known that sex is common in plants and animals, and that asexual species are typically short-lived, but why this should hold throughout evolutionary time is a great mystery," said Susanne Paland, who led the study. "Our results show that asexual deviants are burdened by an ever-increasing number of genetic changes that negatively affect the function of their proteins. It appears sex is important because it rids genomes of harmful mutations."

Coauthor Michael Lynch added, "Although there has been solid theory on the matter for quite some time, these results provide the first definitive proof at the molecular level that sexual reproduction magnifies the efficiency of natural selection in eliminating deleterious mutations from populations."

Sexual reproduction is biologically costly and at times complicated. In mammals, sex is usually preceded by intricate mating behaviors. It requires the compatibility of sexual structures, an insertion event, fertile eggs and sperm, and the successful unification of egg and sperm into a viable zygote. All of this adds up to a big energy investment -- energy an organism might have used for other purposes. Scientists have long been left to ponder, what is it about sex that justifies its big energy investment?

Biologists have come up with a wide variety of competing (and, in some cases, complementary) hypotheses to explain why sex continues to exist in the midst of recurrently evolving asexual competitors. The most widely accepted explanation has been that sexual reproduction confers the benefit of "unlinking" genes, meaning bad versions of genes won't always get to ride the coattails of good versions, and vice versa. In essence, the theory holds that natural selection operates best when parts of the genome are free to shuffle.

The present report provides evidence this is so. In the case of Daphnia pulex, sex appears to have enabled the separation of beneficial and deleterious versions of genes, so natural selection could act more efficiently in favoring the good and weeding out the bad.

The scientists used mitochondrial genome data to compose a phylogenetic tree depicting relationships among sexual and asexual strains of Daphnia pulex sampled from 75 ponds as far west as Illinois and as far east as Nova Scotia, Canada. This family tree reveals that sexual populations have recently and repeatedly spun off asexual strains.

The scientists sequenced the entire mitochondrial genomes for a subset of these sexual and asexual lines of Daphnia pulex, and by comparing rates of protein evolution, they found the asexual lines have accumulated bad mutations four times faster than sexual lines.

Paland and Lynch reason that if a switch to asexuality causes a big increase in the number of protein defects, a mechanism for removing those defects must somehow be missing when sex, too, is missing. The present report supports the notion that it is sex -- or genetic recombination that is a component of sexual reproduction -- which is the purifying force that helps get rid of genetic mishaps that harm the overall evolutionary health of a population.

The ability to reproduce asexually may be useful to organisms that can't get mates, but its long-term benefits are questionable.

"Ultimately, we would like to know how long a species can abstain from sex without going extinct," Lynch said.

###

The research was supported by grants from the National Science Foundation, the National Institutes of Health, and a German Academic Exchange Service Hochschulsonderprogramm III doctoral fellowship. Computer support was provided by IU University Information Technology Services, which are funded in part by the Indiana Genomics Initiative and the Lilly Endowment.

"Transitions to Asexuality Result in Excess Amino Acid Substitutions," Science, Vol. 311, Iss. 5763


Story Source:

The above story is based on materials provided by Indiana University. Note: Materials may be edited for content and length.


Cite This Page:

Indiana University. "Sex, Cleaner Of Genomes." ScienceDaily. ScienceDaily, 20 February 2006. <www.sciencedaily.com/releases/2006/02/060220102301.htm>.
Indiana University. (2006, February 20). Sex, Cleaner Of Genomes. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/2006/02/060220102301.htm
Indiana University. "Sex, Cleaner Of Genomes." ScienceDaily. www.sciencedaily.com/releases/2006/02/060220102301.htm (accessed July 28, 2014).

Share This




More Plants & Animals News

Monday, July 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Traditional African Dishes Teach Healthy Eating

Traditional African Dishes Teach Healthy Eating

AP (July 28, 2014) Classes are being offered nationwide to encourage African Americans to learn about cooking fresh foods based on traditional African cuisine. The program is trying to combat obesity, heart disease and other ailments often linked to diet. (July 28) Video provided by AP
Powered by NewsLook.com
Raw: Sea Turtle Hatchlings Emerge from Nest

Raw: Sea Turtle Hatchlings Emerge from Nest

AP (July 27, 2014) A live-streaming webcam catches loggerhead sea turtle hatchlings emerging from a nest in the Florida Keys. (July 27) Video provided by AP
Powered by NewsLook.com
Russia Saves Gecko Sex Satellite, Media Has Some Fun With It

Russia Saves Gecko Sex Satellite, Media Has Some Fun With It

Newsy (July 27, 2014) The satellite is back under ground control after a tense few days, but with a gecko sex experiment on board, the media just couldn't help themselves. Video provided by Newsy
Powered by NewsLook.com
Trees Could Save More Than 850 Lives Each Year

Trees Could Save More Than 850 Lives Each Year

Newsy (July 27, 2014) A national study conducted by the USDA Forest Service found that trees collectively save more than 850 lives on an annual basis. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins