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11/17/2004
Relating to a Sponge Named Bob
Kudos to our granddaughter, Dale. Her solo piano recital on
Sunday was no less brilliant and stirred the emotions no less than
the two performances by Lang Lang and Yefim Bronfman that I
mentioned in recent columns. As a self-appointed music critic, I
feel I can offer these opinions without a grandfatherly bias. Not
only was her performance great but the next day she passed her
driver’s test on her 17th birthday. But I must not ignore her
brother, Doug, our 11-year old grandson, who first introduced
me to a sponge named Bob last summer. I watched this fellow
on TV for a few minutes and thought how ridiculous to make a
cartoon character out of a sponge.
Now I find that Bob is featured in a movie appropriately titled
“The SpongeBob Squarepants Movie”. For those of you who are
unfamiliar with this unlikely cartoon character, SpongeBob is a
rectangular-shaped sponge of the size and shape of the kitchen
sponges we buy at Trader Joe’s. Unlike our sponges, this
character has a face and arms and legs and is so popular that
there was a feature on SpongeBob on the Sunday Morning TV
show this week. If I remember correctly, it was stated that the
SpongeBob TV program draws some 57 million viewers, about a
third of them adults!
After watching Sunday Morning, I was still puzzled that both
children and adults could relate to a sponge. Then I came across
an article, “This is Your Ancestor”, by Jack McClintock in the
November issue of Discover magazine and realized that we all
should feel close to Bob. The article discusses the work of
Mitchell Sogin, an evolutionary biologist at the Marine Biology
Laboratory in Woods Hole, Massachusetts. Last week we
discussed evolution and hobbit-sized humans living alongside us
modern humans as recently as 12 to 18 thousand years ago.
Sogin’s interests extend much more distantly in our past. Two
decades ago, he set out to answer the question, “What was the
first animal?” We’ve discussed before how single-cell bacteria
and such organisms formed billions of years ago and how it was
much later that more complex life evolved. You’ve probably
guessed, if you didn’t know already, that Sogin’s work has led to
a completely unexpected conclusion – the first animal was
SpongeBob! OK, we should call that animal SpongeAdam and it
certainly wasn’t the rectangular Trader Joe’s sponge, which I
suspect might be a synthetic product.
It’s tempting to think of the sponge as a plant, as I did when I
first stumbled across a sponge washed up on a beach. Indeed,
biologists early on did classify it as a plant. After all, except for
Bob, it doesn’t have arms or legs, organs, tissues or a brain. One
feature of most plants, and the sponge, is that they tend to anchor
themselves in place and don’t move around. However, in 1986,
biologist Calhoun Bond at the University of North Carolina used
time-lapse photography and filmed some sponges in glass tanks.
Both saltwater and freshwater sponges actually did move around,
even going so far as to climb up the walls of their tanks. One of
the speedier sponges traveled at all of four millimeters (less than
inch) a day!
Sponges come in thousands of varieties and range in size from a
fraction of an inch to as large as 8 feet tall and are flourish in
both hot tropical and cold Arctic waters. Unlike Bob, real
sponges exhibit a range of much more loosely structured forms
resembling bushy cauliflowers, cups, fans tubes, piecrusts, etc.
The sponge eats by filtering the water surrounding it through a
multitude of tiny pores into a central chamber; the water exiting
through an opening called the osculum. An ocean-dwelling
sponge may have to filter a ton of seawater to obtain just an
ounce of food. Most sponges are hermaphrodites, spewing out
both sperm and egg cells.
How did Sogin arrive at the conclusion that the sponge was the
first animal to arrive on the scene about half a billion years ago?
We’ve talked in past columns about DNA and its coding in
chains of four compounds abbreviated by the “letters” C, G, A
and T. We’ve also talked about genes, sequences of the DNA
that code for producing proteins, and how our complete set of
DNA is currently thought to contain roughly 20,000 genes.
When Sogin started on his quest this work 20 years ago, to
sequence a single gene was a major task.
What Sogin did was to pick one particular sequence for a gene
that had a specific function common to all animals. He picked a
gene that is used by cells to make a certain protein. Sogin’s gene
sequence has about 2,000 of the C, G, A and T “letters” (the
complete human genome has 3 billion). What Sogin did was to
determine the sequences for this gene in different organisms,
looking for differences in the sequences that would show how
the gene, and the corresponding organism had evolved away
from another organism. He started by looking at various kinds of
marine organisms, including sponges, algae, jellyfish, etc. You
have to admire this guy’s perseverance. It took him a year just to
sequence one gene from a red sponge, the most common sponge!
Fortunately, as gene technology advanced, Sogin’s output
increased and soon he was producing 10 to 15 gene sequences a
year. To show how far genetic sequencing has progressed, with
today’s automated sequencing he can sequence a thousand genes
overnight! By comparing his selected gene in marine animals
with the same gene in insects, birds, worms, fish and mammals,
Sogin came up with an evolutionary tree. This tree led him back
to the sponge as the first animal. The sponge’s blueprint would
serve as the jumping off place for the other animals to follow.
No wonder we feel a kinship with SpongeBob.
But Sogin didn’t stop there. What came before the sponge?
There were the “choanoflagellates”. These were single-celled
organisms characterized by having a tiny filament called a
flagellum and a collar of teensy hairs known as microvilli. They
were close to being animals but not quite. Well, sponges contain
only a few types of cells, one being a “choanocyte” (note the
name’s similarity to choanoflagellate). Sure enough, the
choanocyte cell has a flagellum and a collar of microvilli.
In a sponge, there’s another type of cell, the “archaeocyte”,
which can change its shape and its function when necessary to
absorb food, make new skin or reproduce. It seems a good bet
that this cell and a flagellate-type cell got together and decided it
was to their mutual benefit to hang out together in the form of a
sponge. But Sogin wasn’t finished yet. We’ve got even older
“relatives” – fungi! His gene sequencing has shown that fungi
are quite different from plants and actually are more closely
related to animals. He says that this doesn’t mean that we
humans are just highly evolved mushrooms but rather that we
share with fungi a common group of ancestors that split off into
separate groups which would become fungi and animals.
This finding may not seem relevant to our everyday life today,
but wait. There’s another cartoon character you may have seen
on TV commercials and it’s not as appealing as SpongeBob. I’m
referring to that little critter that pries up your toenail and sets up
shop underneath it with his fungi cohorts in a thriving fungal
community. (I admit to having just such a colony under my own
big toes – yuck!) This type of infection, and similar fungal
annoyances such as athlete’s foot, don’t represent life-
threatening situations. However, other fungal infections such as
endocarditis, an inflammation of the heart muscle (caused by
either a fungus or a bacteria), can be more serious. There’s also
an organism that has killed thousands of HIV patients. Sogin
and coworkers have shown that organism to be related to a
fungus, not to malaria as previously thought.
Why do these fungal organisms have such an easy time infecting
us? Sogin and colleagues say that it’s because we and the fungi
are so much alike, sharing the same family tree in the far distant
past. Accordingly, our immune systems find it difficult to see a
fungus as an intruder. The treatments used to combat these
infections should be ones that target fungi and to come up with
such treatments we would do well to cultivate more fungi in the
lab and test our drugs against them.
Finally, a grammatical note. I started this column with the word
“kudos”. I looked up the word in my dictionary and was shocked
to find that “kudos” is not the plural of a word “kudo”. Dale,
you deserve more than one kudos.
Allen F. Bortrum
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