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11/07/2000
Nervy Octopuses
The other day I was finishing my 3-mile walk when I met my
friendly school crossing guard. Even if no cars are in sight he
blows his whistle, puts up his stop sign and sees me safely to the
other side. It''s one of the few times I feel like a kid again. This
time I noticed he had a bandaged finger. A week or so before, a
concrete block had fallen on it and half the finger was hanging
by a thread. Fortunately, he was taken to the hospital quickly
and a surgeon sewed the finger back in place. Although the
nerves no longer function, he''s glad to have a whole finger.
The detached finger reminded me of a recent Nature program I
watched on PBS. It was called "The Octopus Show" and one
scene showed a crab snapping off and eating one of a small
octopus''s eight arms. We were assured that the octopus was
going to be ok since it would regrow the missing arm. There are
other animals that can rejuvenate stolen tails or other
appendages. Such creatures have been the objects of much
scientific attention in the hopes that their secrets of rejuvenation
can be extended to the human species. I''ve seen recent reports
of studies on animals that hold out promise for repair of spinal
injuries, as I recall, through the use of stem cells.
While the devoured octopus arm was interesting, what really
blew my mind were two other events that were shown on the
program. In an aquarium somewhere, a giant octopus had been
kept in a separate tank from the other marine creatures. I think
they decided to make things more realistic and put the octopus in
the same tank with the sharks and other fish. One morning the
keepers arrived to find only skeletal remains of one of the sharks.
I believe this happened more than once, so someone stayed up
one night to see what was going on. What happened was
captured on film or camcorder. As a shark swam over the
octopus, an arm whipped up to embrace the shark; then a couple
more arms joined the fray. Sure enough, the octopus ate the
shark! Typically, an octopus will eat only the "meat" of the prey,
leaving any bones behind. Because of the lack of scale, I
couldn''t tell the sizes of the shark and octopus were but it was a
weird sight to see.
The octopus is a weird beast anyway. Its head is in the middle of
its body, its arms extend out from what amounts to the back of its
head and its mouth is where most animals have their "private
parts". And its other bodily functions are performed in the
bulbous sac above its head. A search of the Web and other
sources turned up other interesting characteristics. For example,
there are over two hundred species of octopus ranging in size
from around 30 feet to just an inch. In fact, the octopus most
deadly to humans is the golf ball size blue-ringed octopus found
around Australia and the South Pacific. One bite and you''re dead
in 15 minutes! The blue-ringed octopus is a colorful guy covered
with bright blue rings highlighted in black. At least those were
the colors in the photo I saw. An octopus can change colors in
the blink of an eye to match its background and some octopuses
can also modify their shapes to blend in even better with their
surroundings. One octopus has arms that glow in the dark. The
Nature program even showed one octopus turning virtually pure
white.
Their reproductive habits are also unorthodox. The male has a
modified arm known as his hectocotylus. The hectocotylus has
groove between the two rows of suckers. During the mating act,
the male fondles the female with his hectocotylus and, after
getting her in the proper mood, slips it under her mantle. His
sperm travel down the groove and are deposited for transport to
her oviduct. At least in the case of the giant octopus, the male
may treat a half dozen females in this manner and then swim off
into deeper waters and die. The female then gets busy and over
perhaps a period of a couple weeks may lay 50,000 to 150,000
eggs. She then tends the eggs with her suckers, jetting water to
clean and ''rate them. Depending on the species, this tending of
the eggs may go on for a couple months or so. During this
period the female generally doesn''t eat anything. Finally, about
the time of hatching of the eggs, she joins her mate in octopus
heaven.
The young octopuses emerge and float to the surface, the larvae
becoming part of the plankton that serve as one of the lower
levels of the food chain. Those young octopuses that survive
sink to the bottom after a month or so as plankton and begin their
life as a bottom-dwelling octopus. Different species of octopus
apparently lay vastly differing numbers of eggs. I saw numbers
ranging from 150 to 400,000. Especially for the more prolific
egg layers, the survival rates are pitifully small. They don''t live
very long, only some 2 to 5 years, if all goes well. Once the
octopus does survive and sinks to the bottom it stays in the same
locale. However the spread of the octopus all over the world is
encouraged by the flow of currents when they''re in the plankton
stage. In the case of some species, for which the eggs are fewer
and larger, the baby octopuses never go into the plankton stage
but from the beginning are just like mini octopuses scratching
out a living on the bottom.
If you''re like I am, you may tend to get squid and octopus mixed
up but there is one distinct difference. The octopus has evolved
to lose all semblance of a bony skeletal structure. As a result, it
is very flexible and can squeeze into or "flow" through small
openings. It''s more like a sack of tissues, quite flexible and
certainly an ungainly looking creature, at least until it gathers
itself together for a fast getaway. Then with its jet propulsion,
off it goes obscured by the inky black cloud it often leaves
behind. The squid, on the other hand, is a firmer sort that hasn''t
lost its skeleton, which is shaped like a pen. The giant squid can
grow to 60 feet in length. That calamari with marinara sauce is
squid, not octopus, according to my dictionary.
I mentioned that there were two incidents in the Nature program
that blew my mind. The other one involved a place where the
octopus was kept in its tank of water while in another tank in the
same room crabs were housed until they were served to the
octopus for dinner. Well, just like the sharks, the workers would
arrive in the morning to find that there weren''t as many crabs in
their tank as the night before. Sure enough, a night watch
revealed the octopus climbing out of its tank, dragging itself
along the floor and up into the other tank for an extra snack! As
I recall, the program didn''t answer the question as to whether the
octopus was trying to fool its handlers by not remaining in the
crab tank. I think I found the answer in a comment in an article
authored by Jim Golden and Jean McCrae of the Oregon
Department of Fish and Wildlife. They say that, in its natural
habitat, the octopus typically feeds at night and takes its prey
back to its den to dine in peace and security.
The octopus is not a stupid creature and is the most intelligent of
the invertebrates. Apparently, it learns from its experiences and
once it learns how to do something, such as open a bottle to get
at its contents, it remembers the technique. In other words, it has
both long and short-term memory. Its brain has to be fairly
complex just to be able to handle and interpret the movements of
and sensations experienced by the couple thousand suckers on its
arms.
Back to my crossing guard friend and his nerve damaged finger.
This morning''s Star Ledger (November 6) has an AP article on
work reported at the Society for Neuroscience meeting now in
progress in New Orleans. Of particular interest was some work
done at the Salk Institute for Biological Studies in La Jolla
involving tissue taken from cadavers and made to grow into
different kinds of nerve cells. Not too long ago, it was thought
that these stem cells would be available only from fetal tissues.
This spawned a vigorous controversy over the ethics of using
fetuses for such work. One of the Salk workers cited in the
article was Fred Gage, one of the authors a year or two ago of a
paper that caused a sensation in the neurological world. It was
the finding that, contrary to a long held belief, the brain routinely
generates new neurons, at least in the hippocampus.
Another worker, Ira Black of the University of Medicine and
Dentistry of New Jersey (UMDNJ) reported that he and his
colleagues managed to convert 99 percent of bone marrow cells
into nerve cells. With all the progress being made in this area of
forming new nerve cells, one can hope that my crossing guard
friend could someday get back the feeling in his finger. Of
course, there are some much more important Holy Grails to be
achieved in this field, in particular, regeneration of a functioning
brain in Alzheimer''s patients or the repair of the broken
connections in spinal cord injuries.
This probably will take decades, but who knows, some major
breakthrough might occur even during the term(s) of our next
President .... (fill in the blank)?
Allen F. Bortrum
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