Dec. 1, 2004 — At least one species of plant at its northern limits is losing the ability to reproduce sexually due to a "sex versus survival" battle waged under harsh environmental conditions, according to a recent study.

That asexual survival tactic allows species to adapt to inhospitable environments in the short run by becoming "enormous, genetically homogenous superclones," researchers said, but in the longer run, some researchers fear the sterile clones may not be able to move with changing climates.

And because the plant's sterility results from genetic mutations over a short period of time, in this case months or years, the findings are among the first to indicate that complex, formerly beneficial traits, such as sexual reproduction, can erode very quickly.

For the study, scientists studied Decodon verticillatus, a wetlands shrub present throughout eastern North America. The aquatic plant has the ability to reproduce both sexually and asexually. Sexual reproduction involves the spread of pollen by insects. The male organ, the stamen, produces pollen, which functions like sperm. Pollen fertilizes the pistil female organ containing the stigma and ovary. Asexual reproduction involves cloning through branch-tip rooting.

Researchers tracked the reproductive behavior and survival of the shrub in its natural New England setting across Connecticut, Massachusetts, Rhode Island, New Hampshire, and Maine. They also grew some of the plants in a greenhouse for control purposes.

The findings were published in a recent issue of the journal Proceedings of the Royal Society.

The team tracked 780 outdoor plants from 1998-2000. During that time, 479 plants died, with most of the deaths occurring over the winter. Of the survivors, 43 percent were sterile, while 28 percent were fertile.

Christopher Eckert, lead author of the study and a biologist at Queen's University in Ontario, explained that sterility appears to be linked to enhanced heartiness. If given the choice between sex and survival, the plant often chooses sterility, which involves a permanent genetic change.

"We know from detailed analysis of one population that sterility seems to be caused by a single recessive mutation, so perhaps sterility can arise quickly," Eckert told Discovery News.

The result is that the aquatic plant consists of one big clone at its northernmost range.

"These superclones consists of lots of separate plants — often thousands growing around large lakes — that are genetically identical," Eckert said.

He added that while reproduction by cloning can allow the plant to live under harsh conditions, this form of reproduction is not as beneficial to the overall species as sex, which creates genetically diverse populations in which some mutations may allow for geographical and climate range shifts.

"It is generally thought that asexuality is an evolutionary dead end, though we don't know for sure in this case," Eckert said.

Other plants, like bamboo, and animals, such as stony corals, hydras, sponges, starfish and sea cucumbers can produce asexually. Aphids, like Decodon verticillatus, produce both sexually and asexually.

While many gardeners might applaud a drop in the aphid population due to environmental-induced cloning, such a drop could hurt populations of more desirable insects, such as ladybugs, which feed on the aphids.

Paul Licht, director of the U.C. Berkeley Botanical Garden, told Discovery News that sex is always a gamble for plants and animals.

"If we could cut off a piece of our skin to create a baby clone, we would probably experience a huge baby boom because the process would not require much effort and the baby would have a similar survival rate as its parents," he said.

"Cloning also is a way to make sure that nothing changes," he added. "If one plant survives under harsh conditions, then its clones also have a good chance of surviving. The disadvantage is that the species could go extinct if the environment changes."

Thorsten Reusch, a researcher at the Max Planck Institute of Limnology in Germany, agrees with the new study's findings, but does not believe that cloning necessarily will lead to extinctions.

"The only problem would occur if species would be compressed through global change in such a way that there are no sexual members of the population left," Reusch told Discovery News, adding that climate change creates more uncertainty in our futures.

Reusch said, "We are currently conducting a global unreplicated experiment in which the net effect on biodiversity, human well-being and in the potential for life to evolve further is put severely at risk."