Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Need Sex? It’s Probably Something About Stress

09.06.2004


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:
http://uanews.org/cgi-bin/WebObjects/UANews.woa/wa/SRStoryDetails?ArticleID=9155

More articles from Life Sciences:

nachricht Water forms 'spine of hydration' around DNA, group finds
26.05.2017 | Cornell University

nachricht How herpesviruses win the footrace against the immune system
26.05.2017 | Helmholtz-Zentrum für Infektionsforschung

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>