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Cloning in nature has terrible trade-offs

/ Source: Discovery Channel

Plants which clone themselves to live for eons may be cheating death, but at a terrible price, say researchers who have studied seemingly immortal aspen trees in British Columbia.

Like many other plants, an aspen can reproduce sexually or by growing clones of itself from lateral roots — sometimes creating large stands of trees of more than 100 acres that are essentially the same tree grown over and over again. Some aspens may have used this tactic to survive up to a million years, according to some estimates.

But the longer an aspen depends on cloning to survive the worse it is at sexual reproduction, says California State University, San Diego biologist Dilara Ally, who discovered this trade-off in male aspens while doing her doctoral work at the University of British Columbia.

The advantages of reproducing by cloning are easy to spot — you can just keep spreading a genetically identical plant without all the trouble of flowers, seeds and getting the seeds dispersed.

"They don't have to go to the trouble that we do (to reproduce)," explained Ally, whose paper on the matter, co-authored by Kermit Ritland and Sarah Otto, appears in this week's issue of the journal PLoS Biology.

There are some big disadvantages to cloning as well, however. Perhaps the biggest disadvantage is mutations, or genetic errors, that gradually and steadily build up in the genetic material of the plants cells.

"The longer you clone yourself the more mutations you build up," Ally explained.

By counting the accumulated mutations of more than 700 trees belonging to 20 different male aspen clones via what are called genetic microsatellite markers, Ally and her colleagues were able to use them as a sort of clock to gauge the age of the original tree that started all the cloning. They then compared the ages of the clones to different measures of the trees' fertility.

They found that long-lived aspen clones do indeed suffer reduced sexual fitness with age.

In other words, even seemingly eternal trees like aspens are still subject to the harsh realities of natural selection, sooner or later.

"Plants cannot escape," said plant aging researcher Deborah Roach of the University of Virginia. "Selection can't create the perfect organism."

But the new study is also important in another way, Roach told Discovery News.

"This is a big leap in terms of looking at whole organisms as opposed to the plant part," said Roach. A lot of previous work focused on leaf senescence, for instance, she said, rather than how an entire tree ages.

Now aging in plants like aspens can be used as a model for other organisms, Roach said.