The water flea Daphnia pulex is a commonly used model organism among ecologists and other environmental scientists.
Copyright Holder: P.D.N. Hebert, University of Guelph
Posted on 06/22/2008 2:11:51 AM PDT by neverdem
The water flea Daphnia pulex is a commonly used model organism among ecologists and other environmental scientists.
Copyright Holder: P.D.N. Hebert, University of Guelph
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.
Source : Indiana University
Indeed.
I would think that some environmental stress would cause the spin off of an asexual strain. Perhaps a die off of prey or a particularly cold year.
Doh! :-O
Is this where can I get me one of those sex licenses?
“When sexual species reproduce asexually, they accumulate bad mutations at an increased rate”
Take note. CLONING is reproducing asexually, so CLONING will cause big trouble with abnormal mutations.
Guilty.
No kidding.
Doesn't have a clue, does he? And people wonder why scientists are considered to be nerds.
This is confusing. At least in humans, mitochondrial DNA is supposed to be asexually reproduced, coming only from the mother. Is that not the case with water fleas?
New recommended pick up line, "Want to take part in an insertion event?"
Doesn't have a clue, does he? And people wonder why scientists are considered to be nerds.
Chantilly Lace had a pretty face and a ponytail hangin' down
A wiggle in her walk and a giggle in her talk
Make the world go 'round
Ain't nothing in the world like a big eyed girl
To make me act so funny, make me spend my money
Make me feel real loose like a long necked goose
Like a--oh baby, that's a-what I like!
Don’t forget smelly.
Thanks neverdem for both of these.
Chromosome rearrangements not as random as believed
Children’s Hospital of Philadelphia via biologynews.net | February 16, 2006 | NA
Posted on 06/22/2008 3:02:05 AM PDT by neverdem
http://www.freerepublic.com/focus/f-news/2034639/posts
|
|
|||
Gods |
Thanks neverdem. |
||
|
· Mirabilis · Texas AM Anthropology News · Yahoo Anthro & Archaeo · · History or Science & Nature Podcasts · Excerpt, or Link only? · cgk's list of ping lists · |
|||
Ah, good ol' Daphne Pulex.
Good times. Good times.
Sex, cleaner of genes???
I know a gal whose jeans I’d like to...
ummm... do some bioengineering with.
She was dating both of us at the time, though...
Even ugly water fleas
Do it
If I sit here long enough, I'll double in size?
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.