# tougher plants by natural selection



## spypet (Jul 27, 2007)

I'm conducting an experiment on a delicate plant and am curious what regulars think about this;
say you have a plant that does well in optimal carefully balanced conditions of light ferts Co2 etc.
but instead of giving this plant what it wants, you torment it with far less than optimal conditions.
so you *start off with a tank full of a plant, then allow it to die off till only a few plants are left*.
the theory being that those few plants may be more robust than their dead cousins. now you will
*try to grow another tank full of plants using these last few survivors,* but with less light, ferts,
and Co2 as before - think it will matter? this particular Eleocharis grass plant's morphology is to
propagate with runners to establish new daughter plants within centimeters of the mother plant.

_I'm sure many of you experienced plant keepers have neglected a tank for a while,
then cultivated the surviving plants to reestablish a newer better maintained tank.
but did you by chance notice the second generation of plant were any more robust?_


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## HeyPK (Jan 23, 2004)

You can select out the weaker plants in the population in the first selection cycle, but after that, the population won't change much unless the remaining plants can interbreed and produce new generations after each round of selection.


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## fishyerik (Oct 8, 2008)

Most aquarium plants you buy are one clone, genetically one individual, even if there's 100's of plants in the dealers tank. Reproduction in aquarium plants is almost always asexual so no effect will be achieved by "natural" selection, at all. Even if you reproduce them sexually with flowers, seeds and so on, you will be crossing the same individual with it self, and the chance for inbreeding problems will be extremely much greater then any genetic improvements.


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## spypet (Jul 27, 2007)

fishyerik - these Eleocharis was taken from a vast watershed area,
and was unlikely to have been leaked into the wild by a plant dealer

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HeyPK - if I understand you correctly, I would have to take plant samples
from two or more well separated locations in the wild so each sample could
not be daughter plants from the same mother. then I would have to
grow each sample separately into a large batch, stress them, cull out the
strongest survivors, then attempt to interbred the survivors from each
separate batch in order to get a third generation of stronger plants.

_The problem there is; Eleocharis plants breed by shooting a rigid stem
above the waterline to exchange pollen. they only do this under the
most ideal of conditions - the very conditions I'm trying to avoid having
to expose my plants to - in order to establish a more robust lineage._

so according to you, if I simply stay with the batch of plants I have,
I can only expect to toughen them up the next generation, no further.

_I suppose if the plant requirements after one generation of culling had
been reduced enough, that may be sufficient. I won't know for a few
months until the second generation of robust plants can refill my tank
while growing under less than ideal conditions._


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## fishyerik (Oct 8, 2008)

I don't even know witch species av Eleocharis it is, but most if not all Eleocharis reproduce most succesfully asexually. Chance that you have significant genetic variation in the same population is still fairly slim if you collect them from the same water body.

And, to the next point, is it general hardiness you will try to achieve? If so, I wish you the best of luck in achieving what nature has not achieved with for the last 100'000, or so, years and generations with millions and millions of plants.  

You have to focus on one treat, for example light needs, to have a real chance, even then your chances to improve hardiness genetically by selection will be extremely slim.


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## spypet (Jul 27, 2007)

true enough - I don't believe the plant can change in my lifetime on the genetic level.

I'm hoping that variations in light availability, nutrients, temperature, etc are already
built into this plant by nature given the less than optimal condition area it was taken. 
I hope at least to see it thrive in a lower light environment without stunting it's growth.

I guess I'm just wondering if the stress culling I put this plant through actually mattered.
HeyPK - seems to feel it may help, while additional stress culling may prove pointless.

_basically the mother plant that required better conditions is now dead, and the
daughters that managed to survive the culling have become the new mothers,
and will hopefully spawn daughter plants with lower environmental expectations,
all within the natural survival variation already build into this plant's genetic makeup._

_I was inspired while toying with a stem plant and found it would grow horizontally
instead of vertically when light was limited. cuttings from that stem would continue
to grow horizontal (and leaf red shift) even when light availability was increased._


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## HeyPK (Jan 23, 2004)

Populations evolve, not individuals. If the population is reproducing asexually by producing runners, for example, you can cull out the 'weaker' ones that don't survive the harsh conditions, but the remaining ones can't increase their toughness, or that of their offspring, because, through asexual reproduction, their offspring are genetically the same as their parents. On the other hand, if the population is reproducing sexually, they produce gametes (eggs or pollen) that have only one set of chromosomes (the parents have two), and when the eggs are fertilized by the pollen, you get entirely new combinations, some of which can be 'tougher' than either parent. The genes are shuffled and mixed, each generation, and the 'toughest' combinations are selected each generation. By all this gene mixing and recombining better combinations can occur.

Stress culling of asexually reproducing plants can only get you the best of the starting group. If you want to select for a very long time, hundreds or thousands of years, you might get a better one now and then by way of a random mutation. Most mutations are deleterious. A mutation that improves toughness would be very unlikely, but not impossible.


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