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Native American elms and evolution against diseases

Posted by jujujojo 8 (My Page) on
Wed, Mar 20, 13 at 10:06

Many native elms are sick and dying. But they are resistant enough to produce seeds for many years. New plants grow out of the seeds with the illness and are able to produce seeds again.

If you do not cut down the native elms, but let them stand in illness, then after millions and millions of years, the native elms will be resistant to this disease. Those more resistant will survive better, over time.

The changes are here and there over an extremely long clock.

However, this natural course may not be cooperative with the interests of humans.

What do you think?


Follow-Up Postings:

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RE: Native American elms and evolution against diseases

I do not think you are off base.

Perhaps it will happen even quicker though.


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RE: Native American elms and evolution against diseases

Think about what?


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RE: Native American elms and evolution against diseases

WxDano, think about the following and let me know:

(a) Do you observe the same?

(b) Do you agree with my prediction that evolution is giving elms resistance?

(c) Supply your evidences supporting your judgement in (a) and (b).


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RE: Native American elms and evolution against diseases

In cities, jujujojo, letting diseased trees stand allows the disease to continue. It also increases risk of damage from failure.

Presuming that it is useful to allow the progeny of diseased trees in cities to grow to maturity presumes a lot.

So for a) We don't have evidence at these time scales that the seeds are developing resistance. for b) given enough time elms may develop resistance before succumbing to the disease. But it is not a guarantee.

And the risks borne by letting them stand are greater than the chance of developing resistance.

This post was edited by WxDano on Wed, Mar 20, 13 at 12:23


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RE: Native American elms and evolution against diseases

First, I am assuming that the reference is to the many elm diseases, but as an example I will focus on one - DED.
American elm is native in this region. One can still see the occasional old, old American elm still standing with relatively good health. It would be hard to imagine that these trees have never been exposed to DED and so they indeed must have genetic resistance. I would suspect that their progeny, or at least some of their progeny would be resistant and in turn pass that trait on. Eventually the majority of these elms would be resistant as the non-resistant elms would gradually decline.
I don't think that it takes millions of years, maybe hundreds or a few thousand.
Having said that, removing diseased trees in cities does perhaps slow the spread of disease but also slows the evolutionary change toward resistance by reducing the rate of spread. Removal of these trees serves the more immediate needs of us humans as opposed to the strengthening of a species' genetics.
Not saying they shouldn't be removed, just looking at it from the species' perspective. Ma Nature can take care of herself...
hortster


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RE: Native American elms and evolution against diseases

Agree with Hortster. IMHO, it MAY take ONLY several more decades for a large portion of American Elm to become resistant to DED (other Elm disease, are another story). I say this because there is obviously at least partial resistance present in the native population. It is much easier o quickly select for resistance if resistance is already present. Much hard if no resistance is present as in the case of American Chestnut. Even so, there is another selection pressure operating here, that is almost always overlooked. The beetles..... Every time a host tree dies from DED, the beetle vector loses reproductive capacity, as there are few hosts on which to reproduce. So for the beetles standpoint, if they somehow do not vector the disease, then their host survives longer, allow better reproduction of the beetle, thereby selecting for beetles that are less effective as vectors. Therefore there is also ongoing selection pressure on the beetles, and their life cycles are far shorter than that of the Elm. Of course the DED has it's own selection pressures. And in fact a well adapted parasite rarely does significant harm to it's host, because its normally in the parasites best interest for the host to survive, so that the parasite survives longer, producing more offspring. A good example of this would be the common cold in humans. You catch it, but don't feel bad enough to stay home, so you get out spread the virus to allot of other people, who then follow suit. If you stay home, the virus does not spread as well. Result harm to the virus. BUT, if it doesn't make you all that sick, you will remain active and do a far better job of spreading it. Therefore the selection pressure is for the virus not to make you too sick.

Point is, there is a great deal more evolving going on than one see at first glance. Eventually these co-evolutionary pressures should result in a stale mate of sorts, in which all organisms "win" (co-exist).

Arktrees


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RE: Native American elms and evolution against diseases

I agree with Arktrees & Horster...decades to several hundred years.

The species ability to reproduce at a young age has saved it (unlike American Chestnut) but it also means that lots of non-DED resistant pollen and seed is produced, hampering the progression to a naturally occurring DED resistant strain.

Another problem...we provide a lot of suitable habitat for early successional species like American Elm. This allows DED and non-DED resistant trees to co-exist and grow rapidly and increases Elm Bark Beetle populations. As forests mature and move to a later successional composition, the diseased elms will disappear, insect pressure decreases, and the DED resistant elms will be the sole seed source remaining. If we continue cutting trees and creating disturbed sites, we will slow the evolution towards DED resistant elms.


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RE: Native American elms and evolution against diseases

Most of our landscapes are managed already. They have been disturbed by man. DED is an invasive brought in by man. Surely if given enough time it is likely these trees will adapt and some will be resistant. There is a scale mismatch between tree adaptation and human societies.

But similar to what is happening in Britain with ash trees, it is better to control the spread, especially in built environments.


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RE: Native American elms and evolution against diseases

A dying tree is not genetically resistant nor will it's seeds magically gain a resistance due to it's dying. Genetic mutations do not work that way. A diverse gene pool in a given area may contain a tree or trees that are resistant and as other trees die, that gene pool is allowed to prosper. But a dying tree can not react by changing it's DNA.

tj


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RE: Native American elms and evolution against diseases

tsuga, IMHO I think the intent of the argument is to let as many progeny as possible grow out in hopes one has a resistant gene.

That prospect is made harder in cities, as far fewer seedlings grow to a size in a place where they weren't purposely planted.


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RE: Native American elms and evolution against diseases

How interesting! I am inspired by your comments. For American Chestnut tree: have nature another strategy? That is, there may be one small group of trees, that is beyond our ability to locate, which has the resistance to CB. Then, their seedlings will be able to expand into an environment with no competition from the same species. As a result, these trees can expand very rapidly.

I heard that there are artificial solutions. For example, one strategy is to select blight-resistance genes during the back crossing, while preserving the more wild-type traits of American Chestnut as the dominant phenotype. By this approach, it has produced 15/16 (fifteen over sixteen) or higher true American Chestnut with CB resistance.


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RE: Native American elms and evolution against diseases

Yeah it should take a lot less than a million years...it could happen in as little as 100. The peppered moth situation is a good example of rapid evolution. The main problem in my area is that all of the american elms were cut down...now I have only slippery elm growing around me. What we need to do is plant back all of the american elms first. I think that if you plant all of the resistant cultivars (princeton, valley forge, columbia, etc.) in one area they would be able to recover sooner and spread around via seed. The seed itself should contain a higher percentage of resistance than if you plant a grove of just regular american elms that don't have resistance. My guess is that resistance is a recessive trait, if two plants have the trait then the progeny should contain this trait as well. So what I am trying to say is that its best to plant a diverse mix of resistant cultivars than just planting any american elm if the species is going to recover in a given area.


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RE: Native American elms and evolution against diseases

Something we could try is to mail seeds around. If each of us that is able, plants a resistant cultivar, then lets that pollinate local elms or more resistant cultivars, some of that seed will be resistant????We could mail a spoonfull of seed to each person who has room to grow them out. A spoonfull of elm seeds makes a lot of trees. I'm in a province that forbids importing elms, but not their seeds, so I can recieve and mail out the seed. Anybody else in an area where mailing seeds is allowed? gene flow would be easy that way, and the good stuff could spread faster. Mature elms that are still alive are at least possibly resistant....could we save seed there too, and mail those? I have been looking for large elms and forestry has asked for seeds from what I find. they have kindly mailed seeds to me from mature survivors...some of which are just not exposed, but some who may be resistant. Could we do the same, informally? Is anybody interested?

Jocelyn


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RE: Native American elms and evolution against diseases

We have scattered American Elm growing in Texas. DED has not had much effect down here. Assume the hot and dry climate are the big factors, but perhaps genetics come into play also. The Cedar Elm is planted more often than American Elm here.


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RE: Native American elms and evolution against diseases

I suspect that we should send and recieve seeds in large areas, but not the whole of the continent. Say, southern US, northern Us, southern Canada, northern Canada???? Assisted migration might work better if we picked an area to send seeds into/out of that was not too large. Thoughts? Might be that Texas hasn't too many bark beetles? I am guessing only. If there is a good seed crop here, I have promised seed already to Forestry, but there might be lots, so i would have some to send...don't know yet....Forestry wants a litre.


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RE: Native American elms and evolution against diseases

jocelyn pei, you are talking about a social activity, while my interests lie in biology and natural science.


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RE: Native American elms and evolution against diseases

A friend of mine nearby cut several Elms down on his family farm because they died of DED. But he has one tree that didn't seem to be affected. I've been planning to visit him during the spring, if it ever arrives and take a look at the tree.

vince


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RE: Native American elms and evolution against diseases

Jujujojo, I don't think the two have to be mutually exclusive. Think of the elm research institute, asking the public to flag their attention to local survivor elms. Remember that the princeton elm was a chance discovery. Vince, if your buddy's tree is still alive in the spring, it may be exposed and resistant , or just lucky and not exposed. In either case, it would be worth while to gather seeds and or take cuttings. Cuttings exactly reproduce the original tree, and if it's resistant, cuttings from that tree can be planted with cuttings from other possibly resistant trees so they can make seeds together. Some trees flush so early that they are past the vulnerable stage when the beatles come out that spread DED. Some, like Liberty, have small diameter phloem vessels that allow them to more easily wall off the fungus the beetles carry, and still others produce nasty compounds that discourage either the beetles or the fungus. (i don't know which it is) If one can plant lots of different tollerant or resistant trees and their seeds together, they can swap genes at pollination. Think of a tree with all possible types of resistance, grin. Vince, I'd love some seeds off your buddy's elm, if you get some. Want some from here too?


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RE: Native American elms and evolution against diseases

They've just mapped the genome of DED. Likely the solution will come this way rather than 3-4-500 years of random growth in a city that may or may not get cut down in that time.


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RE: Native American elms and evolution against diseases

Hi Jocelyn,

I will make a point to talk to him more about the tree and get some seeds from him when I see him. He's a tree nut like the rest of us, just lucky to still live on his own family's original farm.

I wish I had room to grow a few elms here, but all the room is taken. There used to be many elms in town.

vince


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RE: Native American elms and evolution against diseases

Was not aware of that WxDano. Thanks for that tidbit, I'm going to have to go look that stuff up now. ;-)

Arktrees


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RE: Native American elms and evolution against diseases

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RE: Native American elms and evolution against diseases

  • Posted by beng z6b western MD (My Page) on
    Tue, Mar 26, 13 at 11:00

Slippery elms are ubiquitous around here, but invariably get infected & die. However, they live long enough (~10-20 yrs) to reproduce. Perhaps it may be permanently relegated to this status. And maybe this is how some trees get naturally "demoted" to a short-lived shrub/small tree status.


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RE: Native American elms and evolution against diseases

As mentioned earlier, there is already some resistance present in the American elm population. Several resistant trees have been identified (showing various degrees of resistance), and there are surely more growing in the wild that have not been identified.

Evolution is defined as the change over time in the genetic variation in a population. If some heritable phenotype (characteristic) becomes more or less prevalent in a population, evolution has occurred. In the case of elm trees, resistance to DED has certainly become more prevalent, since such a large percentage of susceptible trees have died. So, evolution has occurred. In this case, it does not take very long, since the genetic variation for resistance was already present in the population. Several resistant cultivars are available, and they are being planted by homeowners and parks all over the place. Pollen from these trees will surely speed up the distribution of DED resistance into the wild populations.

You are correct that susceptible trees reach reproductive age before they succumb to DED. It is possible that new mutations which confer resistance will arise in that segment of the population, but there is no telling how long that will take. Such an estimate would require a lot of information that is just not available. In any case, I suspect this path wil be much slower than the one facilitated by the widespread planting of the various resistant cultivars.

WRT to the DED genome project, I suspect that is more likely to lead to treatments for susceptible trees, rather than the development of DED resistant trees.

An interesting quote from the link above: "it’s only a matter of time before most the elm trees are gone". I've got some news for you.....most of the elms are already gone!

Alex


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RE: Native American elms and evolution against diseases

Much appreciated Dano.

Arktrees


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RE: Native American elms and evolution against diseases

jocelyn pei,

I think you have a very good point there. Every task is a comprehensive task in the real world.

For the task of revitalizing American Elm, we need to consider not just disease resistance, but also social reactions, psychological reactions, inter-personal relations, economics, politics, ... everything.


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RE: Native American elms and evolution against diseases

It can be FUN too, not just work. Remember that people have been gardening and herding for a LONG, LONG, LONG time, before much science had built up. I don't think it has to be all that hard, does it matter whether 2000 people each grow an elm or two, or a bigger operation grows two to 4000 seedlings? As long as the seeds get mailed around, it becomes one big population to select from. As long as they are planted outside, nature will exercise mass selction on them all.

For those interested in cuttings, this is how some folks do it. For dormant cuttings do this: Cut some twigs, about 6 inches long and an inch below the last bud. Scrape the bark just enough to expose a strip of the green layer under it. Dip in water and roll in rooting hormone, IBA in talc, 5000 ppm. Pot in clean soil and pop the whole thing in a plastic bag. Take a match and light it, then blow it out and use the hot match head to burn a few holes in the plastic for air. Place in a sunny window. Wait, wait some more...it takes 5 or 6 weeks, although they may bud at 7 to 10 days. They will need more holes in the plastic as the leaves grow, to prevent mould from the moisture the leaves give off. After they are growing well, open the bag a little to harden them off.
I haven't tried green wood or semi hardwood cuttings yet, but I hear they are done the same way.


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RE: Native American elms and evolution against diseases

I have watched all the large elms die over the years. I have two large ones that haven't caught the disease although they should have because large ones have died all around them. I'll see about collecting seeds from them.
Another note, the woods are full of smaller american elm trees. This is in Missouri.


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RE: Native American elms and evolution against diseases

  • Posted by lkz5ia z5 west iowa (My Page) on
    Sun, Mar 31, 13 at 10:02

I have a couple large red elms that I want to clone. The final large American elm I had died last decade. Elms resistant to DED can die in old age from it, so can always be good to clone the old ones.
But on the overall, I view those two species as weeds and mostly kill them now, room for other things that are not perpetually dying over and over again.


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RE: Native American elms and evolution against diseases

If you want to clone your red elm, you can try cuttings. I have heard, but not tried, taking a piece of root will work too. Dig up a short piece of root, pot it right side up and wait till it grows shoots at the upper end. You can thin the shoots to a single stem when they first start to get woody.

For elm seed saving, this is what the seed bank in New Brunswick does.....they said it's OK to pass along the directions.

gather elm seeds and spread them out to dry for 2 to 4 days, depending on the weather. If you are going to mail them the slight drying prevents heating in the mail. If you want to sow them right now, go ahead. If you want to keep them for later, place them in a small jar after having dried them those few days. Seal the lid of the jar with electric tape so they don't dry out any more. Pop in the back of the fridge and plant within two years. If you need to keep them longer than that, dry them an extra day before putting them in the jar and sealing them up, then drop them in the freezer, the deep freeze. they keep for years and years frozen.

So who lives withing 2 degrees latitude of the seeds in I_James's place? Those might be real good seeds to grow out.


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RE: Native American elms and evolution against diseases

If I can collect some seeds from these this spring I'll post it.
One is a old tree that I'm suprised hasn't sucumbed to the disease. It has a few smaller bur oaks around it that would replace it if nit ndied but it shows no sign of sickness. The other tree is in the forest on a ridge.
I was at Daniel Boones home site a few years ago and the tree that he held court under to settle disputes between the Indians and settlers was a large American Elm. It had died and the dead tree was still laying on the ground at the site.


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