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

August 1, 2017 by Eric Hamilton, University of Wisconsin-Madison
Credit: CC0 Public Domain

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: , which organisms use to produce sperm and eggs for . 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 , 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."

Why do so many offspring die? Credit: Iris Levitis, Anne Pringle and Kolea Zimmerman

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 does use meiosis, it is even more complicated than sex.

In this three-way comparison, Levitis found that more complex 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, that are truly unique, with novel genetic combinations to face a challenging world, must be worth it.

Explore further: Researchers identify traffic cop mechanism for meiosis

More information: Is meiosis a fundamental cause of inviability among sexual and asexual plants and animals? Proceedings of the Royal Society B, rspb.royalsocietypublishing.or … .1098/rspb.2017.0939

Related Stories

Researchers identify traffic cop mechanism for meiosis

December 12, 2013

Researchers at NYU and the Whitehead Institute for Biomedical Research have identified the mechanism that plays "traffic cop" in meiosis—the process of cell division required in reproduction. Their findings, which appear ...

New steps in the meiosis chromosome dance

January 23, 2017

Where would we be without meiosis and recombination? For a start, none of us sexually reproducing organisms would be here, because that's how sperm and eggs are made. And when meiosis doesn't work properly, it can lead to ...

Recommended for you

Houseplants could one day monitor home health

July 20, 2018

In a perspective published in the July 20 issue of Science, Neal Stewart and his University of Tennessee coauthors explore the future of houseplants as aesthetically pleasing and functional sirens of home health.

LC10 – the neuron that tracks fruit flies

July 20, 2018

Many animals rely on vision to detect, locate, and track moving objects. Male Drosophila fruit flies primarily use visual cues to stay close to a female and to direct their courtship song towards her. Scientists from the ...

Putting bacteria to work

July 20, 2018

The idea of bacteria as diverse, complex perceptive entities that can hunt prey in packs, remember past experiences and interact with the moods and perceptions of their human hosts sounds like the plot of some low-budget ...

0 comments

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.