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
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8-Jun-2004