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Tree's Leaves Genetically Different From Its Roots
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."
The grafting of fruit trees is very common.
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http://youaskandy.com/questions-answers/25-article-series-1950/16332--why-do-we-have-to-graft-fruit-trees.html ,into peach stock growing in looses sandy soil. So we get peaches and plums growing where they have never grown before.
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
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,.
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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.
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.
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.
Give me Classic Slashdot or give me death!
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.
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.
Some marmosets 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.
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.
But not quite impossible, interestingly.
So called Clonally transmissible cancers 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...
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.
I swear to God...I swear to God! That is NOT how you treat your human!
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.
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.
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.
Sig Battery depleted. Reverting to safe mode.
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.)
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 not produce viable offspring). The only impact the genetic material in the arm could have is to promote or restrict the genome possessed by the reproductive organs.
In principle, a tree branch can compete with another branch in the same tree for light, nutrients, and be capable of producing its own seeds. Or at least it could produce more branches from its side of the tree, unlike say an organ in more complex animals being able to produce more organs if successful enough.
> 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.
Some mornings it's hardly worth chewing through the restraints to get out of bed.
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.
Someone flopped a steamer in the gene pool.
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 parasites in other plants, by growing their tissues through the host plants' tissues... but they had a long evolutionary history separate from their hosts to figure out ways to do this.