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| naebad... |
 Posted: Thu Nov 05, 2009 6:56 am |
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Many plants rely on insects to polenate so they can reproduce. How can
this come about by evolution?
Do the insects evolve first (then they may have nothing to feed on) or
the plants - which cannot reproduce.
Is there a clear understanding of the process. Even a primitive plant
would need an insect unless it reproduced anotehr way first and then
changed over time. In which case what was the original way for a plant
to reproduce and why did evolution not keep that method? Surely
relying on insects is risky. |
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| Graham Jones... |
| Posted: Fri Nov 06, 2009 7:37 am |
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"naebad" <naebad at (no spam) yahoo.com> wrote in message
news:hcv039$29vj$1 at (no spam) darwin.ediacara.org...
[quote]Many plants rely on insects to polenate so they can reproduce. How can
this come about by evolution?
Do the insects evolve first (then they may have nothing to feed on) or
the plants - which cannot reproduce.
Is there a clear understanding of the process. Even a primitive plant
would need an insect unless it reproduced anotehr way first and then
changed over time. In which case what was the original way for a plant
to reproduce and why did evolution not keep that method? Surely
relying on insects is risky.
[/quote]
Lots of plants (still) reproduce without insects. See
http://www.biology4kids.com/files/plants_reproduction.html
Graham |
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| Lorentz... |
| Posted: Fri Nov 06, 2009 7:37 am |
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On Nov 5, 11:56=A0am, naebad <nae... at (no spam) yahoo.com> wrote:
[quote]Many plants rely on insects to polenate so they can reproduce. How can
this come about by evolution?
Most of the plants that get fertilized by insects are[/quote]
angiosperms, or flowering plants.
[quote]Do the insects evolve first (then they may have nothing to feed on) or
the plants - which cannot reproduce.
Some of the animals that fertilize flowers are not obligated to[/quote]
get their food from the flowering plants. Some flowers are fertilized
by carrion eating flies. The flowers smell like rotting meat to
attract the flies. Many flowers are fertilized by beetles. The beetles
can eat meat. Some orchids are pollinated by wasps that try to mate
with a part of the orchid that looks like a female wasp. Some wasps
eat nectar and pollinate flowers. However, these wasps also eat meat
and other plants.
Nor is there an obligation on the flowers part to be pollinate
only by animals. Grass has flowers that disperse their pollen by wind.
If some insect tries to eat a grass flower and picks up pollen, then
fertilizing another grass flower, than that is fortunate for the
flowers involved. However, there is no required "fine tuning"
necessary for an animal to fertilize flowers.
My point is that the specificity of flower with pollinator is the
result of evolution. The first pollinators were probably not specific
to any one food source. The first flowers were probably not specific
to any one animal.
The first pollen fossils, and the first flower fossils, seem to
come from the same time as dinosaurs. This is well before the first
bees or wasps evolved. The first moths seem to have developed at this
time. However, beetles seem to have evolved a long time before the
flowers.The theory is that the first pollinators were beetles.
In the modern world, pollinators and flower species are often
specific to each other. However, that is the result of an "arms race"
between flower and insect. Flowers that attract the wrong type of
pollinator are at a disadvantage with other flowers, even if they
attract the right type of flower. So flowers develop ways to
discourage insects that aren't exactly right for them. Insects that
crawl to the wrong type of flower are at a disadvantage compared to
other insects. So they learn ways to find the right type of flower.
However, if they didn't evolve that way there would be less
competition.
[quote]Is there a clear understanding of the process. Even a primitive plant
would need an insect unless it reproduced anotehr way first and then
changed over time. In which case what was the original way for a plant
to reproduce and why did evolution not keep that method? Surely
relying on insects is risky.
Risky compared to what? It depends on the environment that the[/quote]
early flowers evolved in.
In the days of the dinosaurs, there were a lot of plants that got
fertilized by means other than animals. Some of these plants are still
with us today, far smaller in size and in far smaller in numbers.
Conifers are fertilized by wind. They are not fertilized by insects.
Ferns are fertilized by splashing water. There is a big list. However,
there are environments where these methods don't work well.
Conifers are at a disadvantage in places where there is little
wind. If the wind is small, then a few conifers would reproduce.
However, in places of little wind the flowering trees push out the
conifers. The competition favors flowering trees in places of no wind.
Conifers attract lightening more than flowering plants. It is no
coincidence that conifers are the first trees to grow up after a
forest fire. The forest fire kills most of the animals, including
insects. So a flowering plant does not get fertilized as easily.
However, eventually the insects come back. And so do the flowering
plants.
Similarly, ferns have this strange two stage cycle. One stage is
sexually reproducing. However, the sperm and eggs of fern require
water. They are also very small. The seeds if ferns were once thought
to be invisible. They are almost too small to be called seeds.
However, in the days of the dinosaurs a fern could grow to be the size
of a tree. This no longer happens, because of competition with the
flowering plants.
Ferns are fertilized when splashing water carries the eggs or
sperm to each other. Since the sperm and eggs are so small, water
droplets carry them easily. Obviously, ferns can't reproduce far from
water. A flowering plant can live very far from splashing water.
There are other limitations to ferns. This method is limited in
range. Water can't carry these things too far. So ferns tend to be
highly inbred. They often reproduce by self fertilization. However,
they don't need insects. So after a forest fire, guess what type of
plant wins out? Ferns again. After a forest fire, or other disaster,
there aren't that many animals around. So in those areas that are
close to water, after a disaster, the ferns outdo the flowering
plants. However, eventually the insects and the flowers return.
Note that all these methods can and are facilitated by insects.
Insects can carry conifer or fern spores. However, they aren't
especially needed by ferns or conifers. Flowers specialize in
attracting insects. There are always a few plants that are fertilized
in more than one way. |
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| Lorentz... |
| Posted: Tue Nov 10, 2009 6:38 am |
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On Nov 5, 11:56=A0am, naebad <nae... at (no spam) yahoo.com> wrote:
There is no obligation on the part of insects or flowers to
restrict their activities to the other. Some insects can eat both
nectar and other insects. Some flowers can attract insects and spread
their pollen by the wind. Grasses are flowering plants that seldom use
insects to spread their pollen. They usually use wind. However, they
do have flowers.
You didn't directly ask your real question. Why should insects and
flowers become dependent on each other. Some flowers can only be
fertilized by one species of insect. And some insects can be
fertilized by only one species of flower.
Flowers that spread by use of insects have problems because the
insects are too "greedy." If an insect eats all the pollen, it
obviously won't be useful to the insect. So the flower has to
discourage insects that eat all the pollen. It helps the flower to
limit the appetite of the insect it attracts. Even if the insect eats
some pollen, it won;t be too useful to the flower. If an insect drinks
too much nectar, that can also damage the flower. So once a flower is
using a insect, it evolves methods to frustrate the appetites of
insects. It may eventually develop a flower that is exactly as long as
the insects probiscus. Or it may develop a scent that repels all
insects but the exact type insect with a limited appetite.
Insects that use flowers for food have problems because the flower
has developed these methods to frustrate it. So insects develop
methods to get around the defenses of the flower. A wasp could get at
the pollen by tunnelling through the flow near the bottom. A butterfly
could develop a longer probiscus to get more nectar.
Hence, their is a chain reaction. The insects evolve to prefer to
flowers which they can exploit, and the flower evolves to attract
insects they can exploit. The general name of this type of chain
reaction is "coevolution." Some scientists humerously refer to this as
an "arms race," using the metaphor of the cold war. Charles Darwin
briefly described such coevolution, although we now know a lot more
than he did.
It may help you to realize that flowers were not common in the
days of the dinosaurs, and were entirely absent in the years before
the dinosaurs. There were no flowering trees in the days of the
dinosaurs. There were fern trees, conifers, horsetails, and a few
other nonflowering trees. Most plants did not flower. The smaller
plants were mostly nonflowering. Flower fossils from the Mesozoic are
rare. There also were no bees. There were no butterflies, although a
few moths are found late in the dinosaur age. Flowers become the most
common plants soon after the dinosaurs died (along with almost
everything else). It isn't until the end of the Mesozoic that fruit
trees (i.e., flowering trees) arrive and flowering plants become
common. Before the Mesozoic, there were no flowers, bees, or
butterflies. There were beetles.
It may also help to realize that some flowers are now almost
entirely fertilized by wind. The grasses are almost always fertilized
by wind, even though they have flowers.Conifers are also fertilized by
wind, still.
Also, flower petals evolved from leaves. Petals and sepals are
leaves. One of the earliest "flowering plants" have no recognizable
petals. It had anthers, ovaries, and leaves. Sepals have clearly a
leaf character. Petals, though now different from leaves, have
developmental similarity. So petals didn't come from "nowhere" before
there were insects to be attracted.
Keywords: flowers, coevolution, insects. |
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