虽然很多树木的寿命比我们人类要长,但是这也并不代表它们拥有永恒的生命,树木无法克隆自己,它们也需要同类来帮助它们繁衍生息。
1 g8 y2 Z# F4 {5 y Certain trees are able to clone themselves, which raises the tantalising possibility that they could effectively "live forever".* q) Y# Y& u: \
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But a study published in the journal PLoS Biology has dashed that hope.$ o8 x8 @# X) F* r9 ?$ y
- P3 m1 v& c1 r" T Dr Dilara Ally and her team at the University of British Columbia, Canada, found that the fertility of clones declines with age.6 K- D0 J& l* ~, K! h% _$ N9 l2 L
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This means that a tree cannot clone itself indefinitely; it must eventually sexually reproduce, or it will die.4 \1 y- E$ _: Y& Q0 k Z( x; ^
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The secret of eternal life has been sought by human alchemists for centuries, but certain trees were thought to have evolved the knack, through cloning.
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) V# k! {+ o# A: A2 k1 q As all keen gardeners know, many trees have the ability to clone themselves. Transplant a "leaf cutting" and up pops a genetically identical plant without the need for sexual reproduction.! i9 Q, y+ J4 s4 d- c' k1 q
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In the wild, trees resort to cloning when there are no members of the same species nearby with which to sexually reproduce. It is a strategy that has helped them avoid extinction.
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In the new study, Dr Ally and her team studied populations of trembling aspen to investigate the effects of cloning on tree fertility. X; N4 {9 f" i1 N
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The aspen is particularly renowned for its ability to clone itself. Clones sprout from the roots and each is considered part of the same parent tree.
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The single largest aspen clone - named Pando meaning "I spread" - is believed to be 80,000 years old and weighs 6,000 tonnes, which if confirmed would make it the world's oldest and heaviest organism.+ \) V/ w) j" [. P+ m7 S& v
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8 s( |' W, ^5 k Dr Ally's team found that genetic mutations gradually build up with each subsequent generation of clone, resulting in a decline in fertility. This means that the aspen cannot clone itself indefinitely, but eventually must reproduce sexually or die.
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The researchers used a novel "molecular clock technique" to work out the age of individual clones before measuring fertility./ w+ l3 {$ y! L8 u; Q; N
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This meant comparing the DNA of the clones to that of the parent to calculate the time since the clones first sprouted.
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$ a0 P; q- R. z9 M D i. q Prior to the advent of this method, clone age had to be determined by observing populations over long periods. With the aspen this would have been impractical.: j2 w# ^; k+ \# D3 y
5 V0 \ d, A9 y, y "Imagine trying to follow cohorts of plants that live on average 100 years of age and don't start reproducing until they are 25; it's impossible within the timeframe of a PhD or even over an entire career," said Dr Ally. |