Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Need Sex? It’s Probably Something About Stress


Heat turns colonial algae into hotties.

Volvox carteri, a colonial freshwater alga. The small dots are regular cells and the large ones are asexual reproductive cells. Photograph courtesy of Aurora Nedelcu

Hot, stressed volvox flouresces when the dye reacts with oxidants. Photograph courtesy of Aurora Nedelcu and Oana Marcu

When algae find themselves in hot water, the normally asexual organisms get all stressed out and turn sexual.

Blame it on the free radicals, says a team of researchers.

Colonies of the multicellular green alga Volvox carteri exposed to temperatures of 111 degrees Fahrenheit (42.5 degrees Celsius) had twice the amount of free radicals, oxidants that can damage biological structures, as unheated colonies. High levels of oxidants within their cells activated the algae’s sex-inducer gene, the researchers report.

Then the fun starts.

The sex-inducer gene promotes the production of the sex-inducer, a pheromone the colony releases to guarantee willing mating partners.

"We’re the first to show that oxidants are responsible for sex in this organism," said UA professor Richard E. Michod, head of UA’s department of ecology and evolutionary biology and a coauthor on the research. "This is the first demonstration that stress turns on sex-inducer genes."

The research will be published in the June 9 issue of the Proceedings of the Royal Society of London, B. Aurora M. Nedelcu, an adjunct assistant professor at UA and an assistant professor at the University of New Brunswick in Canada, is the lead author of the paper, " Sex as a response to oxidative stress: A two-fold increase in cellular reactive oxygen species activates sex genes." Oana Marcu of the University of California, Irvine, is a coauthor.

It may seem an odd question, but biologists have long puzzled over why have sex.

Besides all the concomitant fuss and muss, sex seems like an inefficient way to pass one’s genes to the next generation.

But sex has been around a long time and lots of organisms do it, so there must be a good reason, scientists figured.

One explanation for sex is that valuable genetic variation is created by the mixing of genes that occurs, first when sperm and eggs are formed and again when they merge.

But about 15 years ago, Michod and some of his UA colleagues proposed an alternative explanation called the DNA-repair hypothesis.

They suggest that the process which divvies out parental genetic material to sperm and eggs also repairs the DNA that goes into those cells. The repair mechanism keeps the hard knocks that life dealt the parents’ DNA from being passed on to the children.

"Sex is all about maintaining the health of the DNA you give your kids," Michod said.

Although there has been work supporting the DNA-repair hypothesis as the reason for sex in single-celled organisms, Michod said the current work is the first evidence that DNA repair is a reason for multicellular organisms to have sex.

"I’d always believed it, but we never had concrete evidence in multicellular organisms until now," he said. "I’m thrilled."

For many organisms, sex is not the main method of reproduction. Instead, sex is a response to stress.

And stress generally increases the production of free radicals, sometimes called oxidants.

While pondering those two facts, Nedelcu, then a research associate in Michod’s lab, wondered whether the signal for sex in such organisms is an increase in oxidants.

To test her idea, she used Volvox, the lab rat of the algal world.

Tiny spheres of gel with individual alga cells spread over the surface of the sphere like polka dots, Volvox colonies can be found in temporary ponds that fill with water in the spring and slowly dry out as summer progresses.

In addition to the outer cells, a colony also has specialized reproductive cells tucked inside the center of the 0.5 millimeter-diameter sphere. Some colonies are male, some are female. The colonies reproduce asexually, by fission of the reproductive cells, about every two days when conditions are good.

As the summer progresses and ponds start heating up and drying out, the colonies become sexual. The sexual colonies have specialized sperm and egg cells that merge to form tough spores that persist until the dried-out pond fills again the following spring. When the spores germinate, the genetic machinery goes through a process called meiosis, which repairs and mixes up the DNA from the parents’ sperm and eggs. The new colonies are asexual.

To simulate such late-summer conditions, Nedelcu put culture plates full of Volvox into water baths for two hours. At several points in time, she added a dye that fluoresces when exposed to oxidants. She then measured the fluorescence, which corresponded to the amount of oxidants the Volvox produced.

After only 10 minutes at 111 F (42.5 C), Volvox colonies had twice as many oxidants when compared with unheated colonies.

"This paper shows that sex is a response to oxidants," she said. "Sex evolved as a way to deal with stress and its consequences -- DNA-damaging oxidants."

Mari N. Jensen | University of Arizona
Further information:

More articles from Life Sciences:

nachricht Gene therapy shows promise for treating Niemann-Pick disease type C1
27.10.2016 | NIH/National Human Genome Research Institute

nachricht 'Neighbor maps' reveal the genome's 3-D shape
27.10.2016 | International School of Advanced Studies (SISSA)

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Etching Microstructures with Lasers

Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.

This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...

Im Focus: Light-driven atomic rotations excite magnetic waves

Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion

Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

How nanoscience will improve our health and lives in the coming years

27.10.2016 | Materials Sciences

OU-led team discovers rare, newborn tri-star system using ALMA

27.10.2016 | Physics and Astronomy

'Neighbor maps' reveal the genome's 3-D shape

27.10.2016 | Life Sciences

More VideoLinks >>>