Evolution by Individual Trees

[scotspine1]

So an Oak lives for hundreds of years. Defoliating insects might have two generations a year. You'd think that the insects have the upper hand, they're mobile, breed fast, and can adapt over generations to any defences the tree might have. So how come the tree gets to live out its days???

 

It evolves. Trees can't run away from trouble or look for better environments. They change or die (or struggle for years then die).

 

Trees (as you're probably aware) are generating systems. They don't heal wounds, they seal them with new tissue. The damage is always there just compartmentalised.

 

Trees are also modular. Stems, limbs, branches, twigs, leaves and buds are in competition with each other - the perfect capitalist market economy. Those parts that are profitable last another day. Those parts that can't pull their weight get surbordinated or binned.

 

 

Ok - I've been rambling, but there is a point.

 

Every part of a tree, grows from meristematic tissues. Those tissues can mutate during normal cellular division. This means that a bud can be genetically different to the others.

 

This means that whatever that bud turns into will be genetically different as well. So bud becomes leaf, flower, twig. All the parts that arise from that new growth will be genetically distinct also.

 

This means that mature trees can be made up of a 'mosaic' of genes.

 

This allows natural selection to act on parts of the tree. Reversion is a good example, reverted leaves are more productive and will outcompete the variegated, purple, cut-leafed types. Buds mutate back to their wild type and just do their thing.

 

To go back to where I started - leaves under attack from defoliating insects produce chemicals to defend themself. Leaves that are better at doing it don't get eaten. A genetic mosiac of foliage keeps the tree one step ahead.

 

Also adventitous buds lie dormant until released by changes in hormones or sunlight. These can also be mutate but won't be expressed until needed. Evolution in a bottle!! Stored for a rainy day.

 

Tony, what your talking about is not evolution, just adaptation that takes place within a single trees life. Tree's dont build up a cumulative knowledge of how to interact or react to insects or fungi the insects and fungi do the controlling and exploit the tree to their benefit, mychorrizae is a good example or galls of cynipid wasp.

[Amelanchier]

I remember reading about genetic mosaics a couple of years ago in "Trees: A natural history" by P. Thomas.

 

Then it cropped up in a conversation about natural chimeras (organisms composed of more than one genetically distinct tissue) at my Prof Dip session. So I dug up the above paper.

 

Andy's picture below shows one limb on an Ash in the top left that has retained its colour a bit longer than the reat of the tree... Genetically distinct??? Perhaps!!

[Amelanchier]

Tony, what your talking about is not evolution, just adaptation that takes place within a single trees life. Tree's dont build up a cumulative knowledge of how to interact or react to insects or fungi the insects and fungi do the controlling and exploit the tree to their benefit, mychorrizae is a good example or galls of cynipid wasp.

 

Tim. Evolution is successive adaptation over time. Don't get teleological. Read the paper, I may not have done it justice. I'm popularising it!!!

[Dagmar]

It seems that 'Leaf signal theory' and its apparent evidence of coevolution, originally postulated by the late William Hamilton, a biologist at the University of Oxford, has been effectively disproved by Marco Archetti also of Oxford and his colleagues at the University of Talca in Chile.

 

Journal of Evolutionary Biology,

http://dx.doi.org/10.1111/j.1420-9101.2007.01469.x

[Amelanchier]

It seems that 'Leaf signal theory' and its apparent evidence of coevolution, originally postulated by the late William Hamilton, a biologist at the University of Oxford, has been effectively disproved by Marco Archetti also of Oxford and his colleagues at the University of Talca in Chile.

 

Journal of Evolutionary Biology,

http://dx.doi.org/10.1111/j.1420-9101.2007.01469.x

 

And once again Karl Popper looks smug...

 

Thanks for the info Dagmar.

[scotspine1]

Evolution is successive adaptation over time.

 

Could that mean that ring porous trees are a successive adaptation to summer drought?

[Bundle 2]

Ha ha..I've just read Dagmar's signature.....

[cerneARB]

thats got me thinking Tony. Thanks.

 

food for thought.

[Andy Collins]

Tony, is it not also possible that the top left twiggy limb bit has a better supply of nutrients than the rest of the tree, therefore retains its youthfull looks longer than the rest of the tree? Apart from that, this is waaaaaay over my head!

[Will Hinchliffe]

This is something that I am particularly interested in. Funnily enough it also came up on wendnesday on my tech cert course in relation to reiterations. Apparently a reasearch group in the tropics has proved that reiterations can be geneticly distinct.

 

When I was at University I did an experement where I tried to disprove the genetic mosaic Hypothysis. I measured various dimensions of hazel nuts and there cupules, recording which branch they came from and which tree. I measured thousands of hazelnuts in the Burren in Ireland. Then I ran a nested analysis of variance on the data set.

 

We found that you could accept that there was variety within trees and between trees. But that somatic variation was less than variation caused by sexuall recombination.

 

Hazel nuts where chosen because the nut is not influenced by the pollen that fertilizes the ovule (it is derived from the ovum) and because of its importance to the plant its form is not effected by environmental factors.

 

Obviously there are many flaws to this experiment when it comes to addressing the Genetic mosaic Hypothesis but I found it Fascinating.

 

There was a great picture in an old (1980s) edition of nature that had a plantation of Eucalyptus that had been defoliated by insect damage. All that remained was one branch on one tree completly un touched!!!

 

A paper that I found very interesting was one written by Losey In the 60's 70's called The Genetic Mosaic Hypothesis.

 

There are of course other stagies that plants have evolved to allow themselves to keep one step ahead of pathogens with incredibly fast life cycles.

 

Now this is coming from the back of my memory (and is not likley to be 100% accurate) but I think there is a section on it in the Agrios plant pathology book (that I sold when I was Skint:sad:). The book talks about it in relation to the evolotion of powdery mildew on barley. Protiens that are pressent in the cell membrane recognise the powdery mildew spores and then trigger a systemic response from the plant and also programed cell death in the cells imediatly surronding the inoculation site. The powdery mildew evolves to evade these protiens. The genes that code for these protiens have high quantities of "junk" DNA except that it is not junk. The repetitive nature of the junk DNA found in genes that are responsible for resistance means that when sexual recombination occurs these genes are more likely to mutate and throw up protiens that result in resistance

 

Probably a bit rambling to understand but I tried:confused1: