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Dumber than Fungus?
Dumber than Fungus?
Date: 6/2/2007 5:26:07 PM ( 17 y ) ... viewed 2450 times Could we be dumber than fungus?
I have my suspicions.
While we seem to have trouble with relationships between two sexes,
mushrooms regularly juggle far more. In fact, only the most primitive fungi
are two-gendered. On the other hand, the wood-rotting variety,
Schizophyllum commune, has more than 28,000 sexes. And it's not even the
sexiest.
But there are no Men are from Mars; Women are from Venus; Gender Z is from
Neptune books in the mushroom library. In fact, there's no sign of a war of
the sexes at all.
This multiplicity of genders, rather than turning every meeting of
Mushrooms Without Mates into a narrow search for that one special someone,
is instead a sexual smorgasbord.
So many genders, so little time.
Contemplating multiple genders can be like trying to understand what
physicists mean when they talk about 16-dimensional space. Having
first-hand knowledge of only three dimensions, the imagination balks at
adding a baker's dozen.
But that's just at first glance. The existence of multiple genders in fungi
is much simpler than physics. And you can leave your wild imagination at
home because there's no erotica in these exotica. There aren't even sex
organs as such, said Dr. Thomas Volk of the University of
Wisconsin-LaCrosse. Sex among the split-gill fungi is a touch-and-go event.
One brush-by and the deed is done.
It starts with a hypha. When mushrooms cast spores to the wind, any of the
dust-like grains that land on suitable terrain grow into hyphae.
Hyphae are microscopic filaments that make even hair look fat. They can be
many miles long, Dr. Volk said. But when hypha meets hypha, they mate. With
one touch, cells merge.
Eventually this meeting of the hyphae will grow into what we call a fungus,
or as mycologists like to say, the fruiting body.
"It takes a lot of hyphae to make one fruiting body,'' Dr. Volk said. "They
may have to grow for several years.''
Mushrooms, unlike plants, cannot make their own food. But unlike animals,
they digest first, ingest later. Mushrooms release enzymes to break down
bark or other preferred foods. It's as though they're spewing stomach acid
at the table.
When a well-fed fungus reaches optimal size, it will launch a new
generation by releasing spores. But life isn't easy for a proto-mushroom.
The chances of any spore landing in a good spot are slight. Overriding
those odds takes a heck of a lot of spores.
The problem is, the spore manufacturing area isn't quite big enough in a
mushroom. While elves manage cookie production in a hollow tree, the small
size of fungi limits spore baking. But not to worry. Evolution made up for
that limitation with adaptations that increase surface area. In the
split-gilled fungi, the adaptation is the gill itself. These are the folds
on the underside of the fungus. In some fungi species, such folds can
increase surface area 100 times, Dr. Volk said.
Gills have another advantage for the split-gilled fungus. Their
construction allows them to open only when the mushroom is plump with
moisture. In dry weather, the desiccated fungus closes its gills, saving
spore for the moist weather that baby mushrooms prefer.
Hmmm. Somehow we managed to get from birth to babies again without
explaining the 28,000 sexes. As you might have guessed, the genes order
that bit of engineering.
There are two separate spots on two separate chromosomes that determine
gender in fungi. But genes come in a variety of flavors. For the sake of
explanation, let's talk about an imaginary magic mushroom.
Imagine one gene on the magic mushroom determined size. We'll call it SZE.
In this instance, one arrangement of chemicals on the SZE gene makes the
mushroom larger. Another chemical arrangement on SZE makes the mushroom
small. (And for those of an age when the term "magic mushroom'' carried
significance, I should add that the genes that Mother gives you don't do
anything at all. But that would be incorrect.)
In the split-gill mushroom, there are about 300 possible chemical
arrangements that can sit on one sex-determination gene. The second
sex-determination gene has about 80 possible combinations. A little mixing
and matching, and you come up with around 28,000 potential genetic
combinations, each arrangement a new gender.
See. I told you it was simple.
So, why bother with this startling sexual diversity? It's incest protection.
This gets a little more complicated.
Fungi cannot mate with fungi with the same flavor gene on either
sex-determination site. In any mating event, offspring can have one of four
gene combinations. Any one of those four combinations will have at least
one identical gene - which bars sibling mating 75 per cent of the time. So
an individual cannot mate with three out of four siblings, but it can mate
with 27,997 other individuals. Dr. Volk says this sex-rich system appears
to work well for the split-gilled fungi. They're found all over the world,
from the tropics to Antarctica. Then again, so are humans. We've even
managed to inhabit Antarctica on a temporary basis. And all this with only
two genders.
It's really quite remarkable. Maybe we're not so dumb after all.
By the way, if you want to know just about everything there is to know
about mushrooms, you really must check out Dr. Volk's web page. The web
page address is
http://www.wisc.edu/botany/fungi/volkmyco.html.
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