Nav: Home

Pregnancy loss and the evolution of sex are linked by cellular line dance

August 01, 2017

MADISON, Wisconsin - After Dan Levitis and his wife lost two pregnancies, before having their three children, he was drawn to investigate why pregnancy loss is so common, and whether other living beings face the same struggle his family did.

Levitis, a scientist in the University of Wisconsin-Madison Department of Botany, had one main suspect in mind: meiosis, which organisms use to produce sperm and eggs for sexual reproduction. He describes meiosis as an intricate cellular line dance, one that mixes up chromosomes to reshuffle genes. This rearrangement helps create offspring that are different from their parents, offspring that might be better equipped to survive in a changing world.

But meiosis is also one of the most complex processes that cells undergo, and a lot can go wrong as chromosomes tangle and untangle themselves. Levitis figured that this complexity might lead to problems creating healthy progeny.

In new research published this week (Aug. 1, 2017) in the Proceedings of the Royal Society B, Levitis and his collaborators report that meiosis takes a heavy toll on the viability of offspring. And not just for humans. Creatures from geckos to garlic and cactuses to cockroaches pay a price to undergo sexual reproduction.

The work provides deeper context on the fundamental biological causes behind pregnancy loss, and suggests that the advantages of sexual reproduction must overcome the severe constraints imposed by meiosis.

"It's known that for humans, the primary cause of pregnancy loss is chromosomal abnormalities arising from meiosis," says Anne Pringle, a professor of botany at UW-Madison and another author of the research. "But what wasn't at all clear was whether meiosis is a leading cause of inviability not just in humans, but wherever it occurs."

To answer this question, Levitis compared the viability of offspring produced by three different kinds of reproduction. Sexual reproduction, where two players make a genetic contribution, always requires meiosis. On the other hand, asexual reproduction -- where the offspring are clones of their parents -- usually uses the much simpler mitosis, a comparatively easy cloning of cells, no genetic reshuffling required. When asexual reproduction does use meiosis, it is even more complicated than sex.

In this three-way comparison, Levitis found that more complex reproduction resulted in lower offspring survival. For example, asexual lizards that use meiosis had lower viability than sexual lizards that also use meiosis because asexual meiosis was more complicated. Yet the organisms that used the simpler mitosis, like palm trees and damselflies, produced healthier offspring.

This pattern held true in 42 of 44 species. "When you get a result that consistent across such a wide range of organisms, it's suspicious," says Levitis. But even after a second look, the data checked out. Something about meiosis, seemingly its complexity, kills offspring.

"If you're making your tally sheet, all the pluses and minuses of sex, the fact that sex requires this deadly process is pretty clearly a disadvantage," says Levitis.

Regarding the evolution of sex, Levitis' findings suggest that the advantages of going through meiosis must be significant enough to balance that tally sheet. The reshuffling of genes between two parents during sex might provide even more of an advantage than previously thought.

The other takeaway, says Levitis, is that although it's easy to think that natural selection can solve every problem -- and that we might wish it had, such as for high rates of pregnancy loss -- sometimes it comes up against fundamental constraints. Meiosis seems to be one of those insurmountable barriers.

Yet the tradeoff, offspring that are truly unique, with novel genetic combinations to face a challenging world, must be worth it.
-end-
This work was funded in part by National Science Foundation grants DGE0644491 and DGE1144152 and by the Max Planck Society for the Advancement of Science.

--Eric Hamilton, (608) 263-1986, eshamilton@wisc.edu

University of Wisconsin-Madison

Related Reproduction Articles:

Proteins linked to HIV transmission could actually be beneficial for reproduction
Protein fragments found in semen, and previously only known for their ability to enhance HIV infection, also appear to play an important role in reproductive biology.
Human reproduction likely to be more efficient than previously thought
How difficult is it to conceive? According to a widely-held view, fewer than one in three embryos make it to term, but a new study from a researcher at the University of Cambridge suggests that human embryos are not as susceptible to dying in the first weeks after fertilization as often claimed.
Researchers find crucial clue to manipulating reproduction in plants
A team of researchers, led by a UC Riverside plant cell biologist, has for the first time identified a small RNA species and its target gene that together regulate female germline formation in plants -- crucial knowledge for manipulating plant reproduction in order to improve agriculture.
Why does so much of nature rely on sex for reproduction?
Why is sex so popular among plants and animals, and why isn't asexual reproduction, or cloning, a more common reproductive strategy?
The genetic basis for timing of reproduction in the Atlantic herring revealed
Animals need to breed at the time of year when their progeny have the best chance of survival.
Oxford University Press to publish Biology of Reproduction
Oxford University Press is pleased to announce its partnership with the Society for the Study of Reproduction to publish Biology of Reproduction.
Which chemicals are hazardous to reproduction?
Regulatory authorities around the world can in future instruct manufacturers of chemicals and drugs to check their products for harmful effects on reproduction by means of a new test with molluscs.
Could assisted reproduction reduce birth defects for older women?
Babies born to women aged 40 and over from assisted reproduction have fewer birth defects compared with those from women who conceive naturally at the same age, according to new research from the University of Adelaide.
Male chemistry primes females for reproduction -- but at a cost
A research team led by a Northwestern University scientist has discovered that male animals, through their invisible chemical 'essence,' prime female animals for reproduction but with the unfortunate side effect of also hastening females' aging process.
Tracing the evolution of bird reproduction
What really came first -- the chicken or the egg?

Related Reproduction Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#SB2 2019 Science Birthday Minisode: Mary Golda Ross
Our second annual Science Birthday is here, and this year we celebrate the wonderful Mary Golda Ross, born 9 August 1908. She died in 2008 at age 99, but left a lasting mark on the science of rocketry and space exploration as an early woman in engineering, and one of the first Native Americans in engineering. Join Rachelle and Bethany for this very special birthday minisode celebrating Mary and her achievements. Thanks to our Patreons who make this show possible! Read more about Mary G. Ross: Interview with Mary Ross on Lash Publications International, by Laurel Sheppard Meet Mary Golda...