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Tree's Leaves Genetically Different From Its Roots 80

ananyo writes "Black cottonwood trees (Populus trichocarpa) can clone themselves to produce offspring that are connected to their parents by the same root system. Now, after the first genome-wide analysis of a tree, it turns out that the connected clones have many genetic differences, even between tissues from the top and bottom of a single tree. 'When people study plants, they'll often take a cutting from a leaf and assume that it is representative of the plant's genome,' says Brett Olds, a biologist at the University of Illinois at Urbana-Champaign who was involved in the study. 'That may not be the case. You may need to take multiple tissues.' The finding also challenges the idea that evolution only happens in a population rather than at an individual level. As one tree contains many different genomes, natural selection and evolution could happen within a single organism."
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Tree's Leaves Genetically Different From Its Roots

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  • And yet most fail to be monstrous or metal at all.

  • by Anonymous Coward

    Are they saying some parts of the tree will survive to reproduce and other parts will not? I don't understand how "evolution could happen within a single organism."

    • Re:Uh... Howzat? (Score:4, Interesting)

      by Russ1642 ( 1087959 ) on Monday August 13, 2012 @11:32AM (#40973623)
      Sounds like that's what they're saying. Different tissues reproduce in different ways. For example a tree can make seeds or produce offshoots from the roots. One way could be more successful than another so areas with different genes within a single tree could produce a differing number of offspring.
      • Re:Uh... Howzat? (Score:5, Interesting)

        by icebike ( 68054 ) * on Monday August 13, 2012 @01:47PM (#40975373)

        Well what they are really saying is that the upper parts of a tree can diverge from each other and from their root stocks via natural methods.

        Any orchard owner knows that its easy to graft dissimilar branches on a common root stock, producing, for example, two different types of apples from the same tree. Its easy, and farmers have been doing it for years. Who knows where this idea arose.

        Now it turns out that nature can do roughly the same thing, without all the cutting and splicing, but rather, by gene mutation or cross pollination or what ever.

        Clearly every seed germinates to a single plant, but over time, it appears that significant divergence can take place on a single living tree. This might be a significant evolutionary advantage, as some branches may survive frost, drought, or pests better than other branches. A built in diversity in a single tree.

        Perhaps we have to start thinking of some of these trees as colonies of organisms rather than a single individual.

        • by pspahn ( 1175617 )

          Or, at a different level, consider how large colonies of trees can share the same root system, specifically the poplar family.

          This would allow a shared root system to adapt independently of the trunks/limbs/leaves so that you get a root stock adapted to its specific soil type, while at the same time you get mutations up top which introduce better adaptations for the world above.

          Trees are awesome.

        • Grafting and all that, as well as most genetic agriculture, comes from a monk who spent time splicing together different bean plants and breeding them. I can't remember his name, it's been a long time since I had a biology class. His work led to that square gene-expression thing we used to figure out with genes would be dominant. I'm surprised I remember any of that at all...

          Either way, "As one tree contains many different genomes, natural selection and evolution could happen within a single organism." i

          • by icebike ( 68054 ) *

            I assume you refer to Gregor Mendel, http://en.m.wikipedia.org/wiki/Gregor_Mendel [wikipedia.org] but I have to point out that grafting had been used for centuries before he did his work.

            Other things that were considered to be a single organism have turned out to be colonies of organisms. I believe there is s a type of fungus/mushroom in Wisconsin or Michigan that was found to be all connected under ground, and when taken as a whole ended up being the world's largest living organism.

            We know some tree species have undergr

      • There are so many varieties of coleus because it is relatively common for a plant to produce a 'branch' that is of a completely different appearance from the the rest of the plant. Cut it off, root it and you have new strain. I don't know if the seeds from the new strain would revert to the parent, however. Now that we are looking, we may find that most organisms we think of as distinct are really co-ops. We have that part of the mind we think of as our self but there is that sub self which oft times seems
    • Trees can produce seeds almost anyplace they could produce leaves, so I don't think this really sounds all that far-fetched: something like that could happen. For organisms that have more centralized reproductive systems, it would be a lot more difficult.

      • Re:Uh... Howzat? (Score:5, Informative)

        by fuzzyfuzzyfungus ( 1223518 ) on Monday August 13, 2012 @11:50AM (#40973883) Journal

        But not quite impossible, interestingly.

        So called Clonally transmissible cancers [wikipedia.org] are particularly growth-oriented cells from some progenitor organism that managed to beat the odds and, instead of just killing their luckless host as cancers tend to, spread to other members of the species.

        There is also Henrietta Lacks; but she lives more or less exclusively in laboratory environments and might not be said to count...

      • Re:Uh... Howzat? (Score:4, Informative)

        by TheLink ( 130905 ) on Monday August 13, 2012 @01:14PM (#40974883) Journal
        I think it's more of immune systems than reproductive systems.

        Trees do not have "active" immune systems like animals, that cause "transplant rejection". The tree needs leaves and it needs roots, but as long as the leaves do reasonably "leafy" stuff they could be genetically different and the rest of the tree will go on fine. That's why you can often graft the top of one tree species onto the bottom part of another tree.

        In contrast it's not trivial to put a related human's kidney into another human. You'd likely still have to suppress the immune system.

        It could be because a tree doesn't need as much per in terms of resources (energy etc) per mass/volume, and it doesn't need to move. So some inefficiencies due to "cancer" (strange growths) are less likely to kill the tree. Thus it does not need to kill cancer as urgently.

        Whereas strange growths are likely to kill you - once they are large enough so you can't move about, feed or breathe you're going to die.
        • It's not just the large growths that kill you either, often it is the proliferation throughout the circulatory system. I don't know if anyone has ever seen this in plants - tumeruos tissues spreading by circulation.
          • Plant cells are unable to move about and so any cancer will be self-limiting. When the local tissue growth outstrips the food supply, the tissue dies and that is the end of the plant cancer. There are infectious plant cancers that are triggered by bacteria which hitch a ride inside things like aphids, as well as others which are triggered by the growth of fungus. In all cases it is another organism which is spreading and causing locally cancerous plant tissue to form.

            There are plants which live as par

        • Re: (Score:3, Insightful)

          by Anonymous Coward

          While that is a good point, that an active immune system would prevent genetic diversification within an individual, the diversification alone is not sufficient for evolution within an individual. For example, if you had some chimeric human where your arm had genetic differences from the rest of you, regardless of how viable or not the abilities of your arm are, that genetic material will not get passed on (some slashdotters should have experimentally figured out by now that hand-person relationships do no

          • by TheLink ( 130905 )
            That's a good point too. Each part of the tree is more independent from the rest when compared to the more complex animals.

            Chop off a branch, stick it in the ground under favorable conditions and it might become a new tree. It takes amazingly "favorable" conditions to do something similar with humans (aka cloning)...
    • Re:Uh... Howzat? (Score:5, Interesting)

      by Anonymous Coward on Monday August 13, 2012 @11:39AM (#40973747)

      Actually, yes. That's exactly it. Think about the times you've seen a tree with a plenty of leaves, but with dead branches mixed in.

      Given the way that trees grow, this actually makes sense. Tissues in the trunk are only grown in a very narrow band located between the bark and the wood. If a mutation happens at some point during the tree's growth, it's possible that the new tissues will be more/less likely to survive given the current environmental circumstances. Those new tissues carrying beneficial mutations would be more common as the tree continues to grow. Leaves are an even more extreme example. If a given branch has tissues with a given mutation, the leaf buds on the tree will carry it, and the leaves will carry it. Branches with more productive leaves will live longer/better as a result. Given that trees can grow for hundreds of years, it's possible that the same tree may have had dozens of mutations in its genetic structure some of which were passed on to branches at different points in time, multiple of which could still be 'active' as a result.

      This is less likely to be the case for animals, since their tissues undergo complete replacement over a comparatively short period of time. That means a genetic sample from an animal would almost always only reflect the *current* genetic state of the animal.

      • Thinking of it this way, studying a single large tree (at multiple points along its growth) might reveal a lot of interesting information about how evolution works. As you head from the tips of the branches to the trunk and leaves, it would be like looking back in time.

    • Re:Uh... Howzat? (Score:4, Interesting)

      by Rhaban ( 987410 ) on Monday August 13, 2012 @11:44AM (#40973817)

      A mutation could happen in single cell, ar a group of cells during the tree growth, and then a leaf or an entire branch spawns from this cell.

      If cells in tree nodes are for some reason likely to be the subject of mutations, it's easy to imagine natural selection occuring at a cell level, with a branch growing from the fittest cells.

  • by RichMan ( 8097 ) on Monday August 13, 2012 @11:27AM (#40973537)

    The grafting of fruit trees is very common.


    There are other advantages to grafting. A grafted fruit tree may be made to grow in new places. A peach likes sandy, wellsanded soil. The plum tree likes poorly drained soil. Peach can be grafted onto plum stock growing in soggy soil. Plum can be grafted ,into peach stock growing in looses sandy soil. So we get peaches and plums growing where they have never grown before.

    Grafting also helps to keep down plait pests and disease. Some fruit trees cannot be hurt by this pest or that disease. These trees form fine stock, though the fruit may be poor,.

    • Taking cuttings from plants in general is even more common.

      I'm curious to see these examinations performed on a larger variety of plant types and species..

    • But completely irrelevant to the article. This is talking about own-root trees.
      • by bennomatic ( 691188 ) on Monday August 13, 2012 @01:19PM (#40974951) Homepage
        Maybe not completely irrelevant. Perhaps, in a given population of a species of tree, there is not only cross-pollination, but also cross-grafting. Maybe insects or higher animals move leaves or seeds from tree to tree, and for some reason, this species is more likely to accept the new introduction without complex grafting techniques.

        To wit: Tree A spawns tree B through pollination with tree C, so B is indeed genetically unique. B is close to A, though, and a bird gathering shoots for its nest brings over something viable from B to A and sticks it in the crook of a branch and it grafts. B' is born, effectively a grandchild AND parasite of A.

        I'm just letting my imagination wander here, but it certainly would be interesting if that were the case.
      • by pspahn ( 1175617 )

        Not necessarily.

        If you ever look at a large nursery catalog, you may see that a specific apple tree is available with a variety of root stocks (often patented/trademarked). These various root stocks aren't necessarily from different species of trees, but instead come from different cultivars of that same tree.

        What you end up with is the ability to buy a truck-load of apple trees with an apple root stock that has adapted to better survive cold winters (at the expense of larger fruit, for example).

    • Grafting of fruit flies less so.
    • I was thinking more of the bud sports used in grafting. Sometimes plants produce a branch with a spontaneous mutation that has a useful trait, like an apple that fruits differently, a pale grape, or an earlier peach. These mutants are grafted for their useful traits, and because of this, even though there is only one umbrella variety, like Gala [wikipedia.org], there can be multiple different strains of sports used in different orchards (like Gale Gala or Ultima Gala). I don't see how something horticulturalists have be

  • Yeah, but I bet it has a lousy sex life.

  • by Hatta ( 162192 ) on Monday August 13, 2012 @11:36AM (#40973695) Journal

    The finding also challenges the idea that evolution only happens in a population rather than at an individual level. As one tree contains many different genomes, natural selection and evolution could happen within a single organism."

    Nobody ever thought that. Evolution happens with any sort of imperfect replicator subjected to selection. Period. A good example of this happening within our own bodies would be cancer.

    • From the article:

      The findings have parallels to cancer studies. Earlier this year, scientists showed that separate parts of the same tumour can evolve independently and build up distinct genetic mutations, meaning that single biopsies give only a narrow view of the tumour's diversity

      However, it seems to me that cancer mutations are usually not germline, whereas these mutations in trees might well be... dare we use the term "Lamarckian"?

      • However, it seems to me that cancer mutations are usually not germline, whereas these mutations in trees might well be... dare we use the term "Lamarckian"?

        Poor Lamarck, after a century of darwinism his time has come.

      • The cancer mutations are definitely germline, for the cancer itself.
    • You could argue (I would) that even in this example of trees (and of cancer) that evolution IS the change of populations over time. Our bodies and those of trees are made up of a population of cells. The cells genetics changes due to a number of factors, and the those changes can be replicated to new cells. Cancer is the perfect example of this in our own bodies. Now it seems that Tree's go through this as well.

      It would be interesting to see if the evolution of cells in a tree keeps the tree population
    • by mcgrew ( 92797 ) *

      Have you ever read Asimov's Playboy and the Slime Gods? [wikipedia.org] The aliens in that story reproduce asexually, which Asimov (a biochemist who did cancer research at Boston University) figured would evolve very slowly. Unfortunately (or fortunately if you want to actually read the story in the book Nightfall) the wikipedia synopsis is awful offal.

      • Those who want to read it need not settle for a wikipedia editor's summary.

        The story was originally printed in the March 1962 issue of Amazing Stories. Scan available here [mediafire.com].

        Also, Asimov's original title for the story, "What Is This Thing Called Love?" is restored in his short story collection, "Nightfall and Other Stories".

        • by mcgrew ( 92797 ) *

          Thanks for the link to the scan, I didn't know any of his works were online. "Nightfall" is one of the two dozen books in my Asimov collection. I wish I had copies of all 500+ of them!

        • by mcgrew ( 92797 ) *

          I went to your link and saw nothing but advertising.

  • Cancer (Score:4, Insightful)

    by Dachannien ( 617929 ) on Monday August 13, 2012 @11:38AM (#40973725)

    That's essentially what cancer is, a genetic mutation in a cell that evolves it into an undying, eternally reproducing organism that parasitically gets its nutrients from its host organism/ancestor.

    • Well, cancers aren't very good at hijacking the reproductive mechanisms to make immortal babies. (SF plot idea, anyone?) There are lots of viruses and even bacteria that will do things like that. Ticks pass Rocky Mountain spotted fever to their eggs. River blindness is a bacterium passed by nematodes through biting flies and humans that give a reproductive advantage to the flies from the bug they carry. Malaria promotes the reproduction of the mosquitos that carry it (in competition with uninfected mosquit
      • Re:Cancer (Score:5, Informative)

        by wierd_w ( 1375923 ) on Monday August 13, 2012 @01:08PM (#40974833)

        Not entirely true.

        There exists a naturally occurring "disease" in dogs that is a sexually transmitted cancer. [wikipedia.org]

        It could be considered a highly successful parasitical mutation of the canid genome, which has evolved to make use of the reproductive behaviors of its host organism to perpetuate itself.

        IIRC, genetic analysis of the genome for the tumor suggests that it is several thousand years old.

        • That CTVT example is one of just three TVTs, which rather makes my case. But the real point is that TVTs don't help the host propagate better, just the tumor. They're purely parasitic, not symbiotic. In that sense, they're less successful adaptions than malaria, RMSF, or river blindness are.
        • The Tasmanian devil population is currently suffering through a plague of transmissible mouth cancers, from reports it appears to be a relatively new disease, not sure how it is transmitted though.
          • Analysis of the tumors suggests it was derived from a Schwann cell tumor. The transmission is mediated by the tendency for Tasmaninan Devils to bite each other on/around the head in their frequent and loud squabbles.

            The few other observed transmissible cancers cover a range of mechanisms (venereal [wikipedia.org]; mosquito [nih.gov]).

    • by Hentes ( 2461350 )

      Evolution is a combination of mutation and selection, the latter which isn't really present in cancer because it is a product of a single dramatic mutation, not normal cells slowly evolving into cancer cells. It couldn't have a continuous evolution anyway for its time is limited: either it dies or its host, killing both of them. Clonal tree colonies, on the other hand, can live for eternity.

      • Depends on your POV: you could think of potentially cancerous cells as being species of one-celled organisms, with the successful ones being those which go on to form actual tumors, which do of course reproduce within the body. Eventually, they do kill the host and thus themselves, but this is really no different from a species going extinct when it uses up the resources available in its local ecosystem.

      • The sexually transmitted cancers, like canine venereal tumor, move from host to host before being destroyed by the host's immune system. This places it firmly in the realm of natural selection for reproductive fitness:

        It has to easily detach from the host tissue.
        It has to easily integrate into the new host tissue.
        It has to withstand the host's immune response for extended periods until it can reproduce itself in a new host.

        This, in addition to energy consumption fitness and other evolutionary pressures.


    • That's essentially what cancer is, a genetic mutation in a cell that evolves it into an undying, eternally reproducing organism that parasitically gets its nutrients from its host organism/ancestor.

      Cancer is caused by a small number of mutations and does not behave in a way that is healthy to the entire organism. These cottonwood trees, on the other hand have "variation within a tree... as great as the variation across unrelated trees" all within a healthy organism.

  • by fuzzyfuzzyfungus ( 1223518 ) on Monday August 13, 2012 @11:40AM (#40973759) Journal

    Some marmosets [pnas.org] are naturally chimeric some substantial portion of the time. This leads to wacky fun for researchers because it is perfectly possible(depending on how the different cell populations ended up distributed in the mature monkey) for an individual to show one genotype on blood tests; but produce offspring that appear to be genetic descendants of their brother or sister....

    Just to be sure, we'll probably have to homogenize any animals and/or small children we wish to study in the future. [zork.net]

  • This is one of the coolest things ever.

  • No big surprise that an organism that reproduces by seed as well as by rhizome cloning has evolved two distinct ways of coding these strategies. I would not be surprised if many plants that reproduce underground like this have tailored their genes to do so.
  • I wonder if they did a sample from a toe and a sample from the head if they would come up with different genetics. My assumption would be that there would be slight differences.
    • Re: (Score:2, Interesting)

      by Anonymous Coward

      The current theory, is that you would not in a "normal" human. The gene sequences should be identical in all healthy cells, with only the pattern of currently active genes changing between cells. Mutations later in life tend to result in cancer, not functional human tissue.

      However, there are known ways for this to not be true. Typically it has to do with the subject having absorbed siblings while in the womb. It would be interesting to find out how common that actually is in humans.

  • by GodfatherofSoul ( 174979 ) on Monday August 13, 2012 @01:04PM (#40974783)

    People think that nature is a bunch of animals running around a green backdrop. But, plants have their own pretty interesting evolution. I took a botany class in college and it gives you a whole new appreciation for the "scenery" in your nature documentaries.

    • The time I appreciate plants the most is when a drought breaks, we had a deep and long drought here in Oz recently that lasted several years. My house is near the beach so for most of that time the yard was just bare sand. When the drought broke a couple of years ago, somehow the grass "knew" and instead of coming up in patches like it did after a storm during the drought, it came up like a carpet of barely perceptible green fuzz, within a month the city had their lawn mowers out again. I've been through se
  • With innovations in the introduction of parthenogenesis to new species' perhaps this discovery is good news for only about 50% of the population.
  • by tilante ( 2547392 ) on Monday August 13, 2012 @02:08PM (#40975663)

    I'm sure that I remember reading about most trees being genetic mosaics more than ten years back. And I know for certain that I heard about a case of it happening in people at a conference on Neurofibromatosis more than ten years ago.

    (Presentation at the conference had a bit about a family where several of the children had NF Type 1, even though neither of the parents did. NF1 is a genetically dominant mutation, but having two copies of the gene is lethal -- thus, if one parent has NF1, you expect that roughly half the children will... but if neither parent has it, the chance of a child having it should be very small. In this case, though, about half the children had NF1, even though tests said neither of the parents had the gene.

    Eventually, it was discovered that part of the father's body had NF1 -- including the testes. Most of his body, however, did not have the gene. Thus, while tests using cells taken from other parts of his body showed him as not having NF1, for reproductive purposes, he did.

    As I recall, at the time, the prevailing belief among the geneticists working on the disease was that neurofibromas - lumps on the nerves associated with NF1 - were themselves manifestations of cellular-level mutations. Essentially, when a nerve cell in the body mutated in such a way as to lose its working copy of the NF1 gene, a neurofibroma resulted. Not sure if that's still what's believed, though, since that was over a decade ago.)

  • 'How lovely trees are.'

  • by Kozar_The_Malignant ( 738483 ) on Monday August 13, 2012 @02:52PM (#40976245)

    > The finding also challenges the idea that evolution only happens in a population rather than at an individual level.

    I'm not sure where this statement comes from. Evolution by means of natural selection has always been understood to act at the individual level. You are favored in reproduction or not. There are all kinds of nifty mathematical ways to describe the effect of this on populations that lead to talk of "populations evolving," but that is a sloppy way of describing the cumulative effect of individual evolutionary events.

  • Maybe a plant biologist could weigh in here but I wonder if this diversification couldn't lead to different parts of the plant being more or less resistant to various pests? I mean, these trees get pretty old so it seems like a good way to ensure survival of the whole tree since some parts of it may have resistance. Also, if the tree is hermaphroditic (sorry, I don't know enough about cottonwood to know) the resistant parts could cross-fertilize, resulting in seeds potentially even more resistant, right? Wo
  • The human brain itself is famous for its mosaic aneuploidy (http://en.wikipedia.org/wiki/Aneuploidy#Somatic_mosaicism_in_the_nervous_system), which is similar to having different genes in that the number of chromosome copies have a lot of gene expression significance (think of trisomy 21, for example). So as wonderful it sounds, it's nothing out of the ordinary. In biology, you can start research by going against something like the central dogma and finding counterexamples. Retrovirus, platypus, photosynthe

"This is lemma 1.1. We start a new chapter so the numbers all go back to one." -- Prof. Seager, C&O 351