Nav: Home

For females, a little semen may go a long way

March 03, 2016

For most guys in the animal kingdom, sex is a once-and-done event. Females from species like rabbits and cows get sperm from their mates and not much else. But in a Forum article published March 3 in Trends in Ecology & Evolution, researchers suggest that these limited encounters can supply resources to females in seminal fluid, and females might have evolved to seek out such seminal resources, even when the amount of fluid is small.

"Traditionally, the idea is that when this type of mating takes place, there's no resource transfer and there's no paternal care," says senior author Russell Bonduriansky, an evolutionary ecologist at the University of New South Wales (UNSW). "Males contribute DNA to fertilize an egg, but we believe there's something more complex going on."

Bonduriansky and his UNSW colleagues, Angela Crean and Margo Adler, started thinking about evolutionary preferences for seminal fluid--the liquid part of semen, minus the sperm--in 2014, while studying the offspring of female neriid flies (Telostylinus angusticollis) mated with males of varying sizes.

The team found that if a male, either large or small, mated with a female fly before she was fertile, he'd pass his sperm along, but the immature eggs wouldn't be fertilized. The surprise came two weeks later: if the female neriid fly copulated with a second male once her eggs had matured and laid eggs fertilized by his sperm, the resulting offspring would be closer in size to the first male. The lingering effects appeared to stem from chemicals in the first male's seminal fluid, even though he wasn't the father.

If seminal fluid plays a critical role for future offspring regardless of the father's actual identity, says Bonduriansky, then females may have evolved to exploit the benefits. On top of situations where semen is just passing through, some female animals can store semen from multiple males before allowing any of it to fertilize their eggs, and this system could have advantages beyond holding out for the best DNA.

"Females might be choosy even when they don't have eggs ready to be fertilized," Bonduriansky explains. "They might be getting something for future offspring that will be fertilized later on, or they might be getting something for themselves."

This idea has been around for decades when thinking about pairings based on obvious resources. Female gibbons and hawks, for example, have evolved to choose males that provide food, territory, or the promise of parental care, even if they're not ready to have offspring. But, says Bonduriansky, that reasoning hasn't been applied to systems where there's nothing but a small ejaculate being transferred.

And size might not matter as much as previously thought. Seminal fluid is chemically complex, with proteins and RNA floating in the liquid outside of the sperm, so even the effects of a small ejaculate could be significant, giving females a largely unexplored bonus from sex. "It's pretty clear now that seminal fluid is packed with paternal RNA," says Bonduriansky, at least in humans, mice, fruit flies, and nematode worms. "In some systems, mostly nematodes and mice, there's evidence that these RNAs can play a role in early embryonic development," he adds, though the jury is still out on exactly what effects these molecules have.

Researchers typically think of seminal fluid in a small ejaculate as playing different roles, says Bonduriansky, but not as a resource that females purposefully seek out. "And that might not be the case."
-end-
Funding for this work was provided by the Australian Research Council.

Trends in Ecology & Evolution, Crean et al.: "Seminal Fluid and Mate Choice: New Predictions" http://dx.doi.org/10.1016/j.tree.2016.02.004

Trends in Ecology & Evolution (@Trends_Ecol_Evo), published by Cell Press, is a monthly journal that contains polished, concise and readable reviews, opinions and letters in all areas of ecology and evolutionary science. It aims to keep scientists informed of new developments and ideas across the full range of ecology and evolutionary biology--from the pure to the applied, and from molecular to global. For more information, please visit http://www.cell.com/trends/ecology-evolution. To receive Cell Press media alerts, please contact press@cell.com.

Cell Press

Related Sperm Articles:

Novel switch protein that 'turns on' sperm for fertilization
Researchers from Osaka University and Baylor College of Medicine discovered a signaling cascade in which the testicular protein NELL2 travels through the lumen to induce differentiation of the epididymis, secretion of the protease OVCH2, and subsequent sperm maturation.
Study provides first look at sperm microbiome using RNA sequencing
A new collaborative study published by a research team from the Wayne State University School of Medicine, the CReATe Fertility Centre and the University of Massachusetts Amherst provides the first in-depth look at the microbiome of human sperm utilizing RNA sequencing with sufficient sensitivity to identify contamination and pathogenic bacterial colonization.
Diet has rapid effects on sperm quality
Sperm are influenced by diet, and the effects arise rapidly.
Sperm may offer the uterus a 'secret handshake'
Why does it take 200 million sperm to fertilize a single egg?
Long duration of sperm freezing makes no difference to live birth rates in large sperm bank study
Despite a time limit imposed in many countries on the freeze-storage of sperm, a new study from China has found that the long-term cryopreservation of semen in a sperm bank does not affect future clinical outcomes.
An important function of non-nucleated sperm
Some animals form characteristic infertile spermatozoa called parasperm, which differ in size and shape compared to fertile sperm produced by single males.
DNA of sperm taken from testicles of infertile men 'as good as sperm from fertile men'
Scientists have found that sperm DNA from the testicles of many infertile men is as good as that of ejaculated sperm of fertile men.
Let the sperm races begin
For best chances of in vitro fertilization success, the most motile sperm are chosen from semen.
'Old' sperm produces healthier offspring
Research shows that sperm that live for longer before fertilising an egg produce healthier offspring.
Recurrent miscarriage linked to faulty sperm
Multiple miscarriages may be linked to the poor quality of a man's sperm, suggests new research.
More Sperm News and Sperm Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Clint Smith
The killing of George Floyd by a police officer has sparked massive protests nationwide. This hour, writer and scholar Clint Smith reflects on this moment, through conversation, letters, and poetry.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Graham
If former Minneapolis police officer Derek Chauvin's case for the death of George Floyd goes to trial, there will be this one, controversial legal principle looming over the proceedings: The reasonable officer. In this episode, we explore the origin of the reasonable officer standard, with the case that sent two Charlotte lawyers on a quest for true objectivity, and changed the face of policing in the US. This episode was produced by Matt Kielty with help from Kelly Prime and Annie McEwen. Support Radiolab today at Radiolab.org/donate.