October 20, 2009
For Fish in Coral Reefs, It's Useful to Be Smart
By SEAN B. CARROLL
I have long suspected that fish are smarter than we give them credit for.
As a child, I had an aquarium with several pet goldfish. They
certainly knew it was feeding time when my hand appeared over their
tank, and they excitedly awaited their delicious fish flakes.
They also exhibited a darker, disturbing behavior. Evidently, a safe
life with abundant food was not fulfilling. From time to time, either
sheer ennui or the long gray Toledo winter got to one of the fish and
it ended its torment with a leap to my bedroom floor.
Maybe my anthropomorphizing is a bit over the top. But, really, just
how smart are fish? Can they learn?
A 10-gallon tank with a plastic sunken pirate ship is certainly not
the most stimulating habitat. But in the colorful, diverse and
dangerous world of coral reefs, fish must be able to recognize not
only food, but also to discriminate friends from foes, and mates from
rivals, and to take the best action. In such a complex and dynamic
environment, it would pay to be flexible and able to learn.
A series of studies has recently revealed that reef fish are
surprisingly adaptable. Freshly caught wild fish quickly learn new
tasks and can learn to discriminate among colors, patterns and shapes,
including those they have never encountered. These studies suggest
that learning and interpreting new stimuli play important roles in the
lives of reef fish.
To test the ability of fish to learn to discriminate shapes, a
research team led by Ulrike E. Siebeck at the University of Queensland
in Brisbane, Australia, trained damselfish to feed from a feeding tube
to which they attached a variety of visual stimuli. The latter
included a three-dimensional latex disc, a two-dimensional blue disc
painted on a plastic board, or black circles or propeller patterns on
white boards. The fish were rewarded with food when they repeatedly
tapped the stimulus — not the tube — with their snout or mouth.
The fish rapidly learned this task. The researchers then presented the
fish with the original stimulus and one alternative distracting shape
— bars versus discs, squares versus discs, or circles versus
propellers, and the fish had to nose the shape they had been trained
to tap in order to receive a reward. The fish tapped the correct shape
about 70 percent of the time in the first trial; this improved to 80
percent to 90 percent in subsequent trials.
Remarkably, the fish also learned when the food reward was delayed and
delivered far from the stimulus. The damselfish exhibited what is
called anticipatory behavior, in that they would tap the image and
then swim quickly to the other end of their tank in anticipation of
their food reward. This response is much like Pavlov's dogs who
learned to anticipate food at the sound of a bell.
In another set of experiments, Dr. Siebeck trained damselfish on
different color stimuli. She selected blue and yellow because these
are highly contrasting colors that are found on many reef fish. After
the fish quickly learned to repeatedly tap colored latex targets to
gain a food reward, they were presented with a choice between the
training target and the alternative color target. The fish were even
better at color discrimination, tapping the correct target more than
90 percent of the time.
Perhaps it is less surprising that the fish learned to discriminate
colors. After all, they live in a colorful environment. But the
question of why reef fish are typically so colorful has challenged
biologists for a very long time. It seems obvious that bright color
patterns would be effective communication signals in the shallow,
well-lighted water around coral reefs. But in that fish-eat-fish
world, bright colors would also make fish conspicuous to predators. So
how are these advantages and disadvantages balanced?
It turns out that some brightly colored fish make a living by
providing a valuable service to what may otherwise be their predators:
they clean them. In fact, cleaner fish like the cleaner wrasse form an
important part of coral reef communities. They establish small
territories as "cleaning stations," which are visited by all sorts of
"client" fish that have their parasites removed.
The cleaners' work ethic is astounding. Alexandra Grutter of the
University of Queensland found that individual cleaner wrasse
inspected as many as 2,300 fish and consumed up to 1,200 parasites a
day, which amounted to about 7 percent of their body weight.
Furthermore, Dr. Grutter found that fish on reefs without cleaner fish
had about five times the number of parasites compared with fish on
reefs with cleaners.
It would seem, then, that it would benefit potential clients to visit
cleaning stations, and for carnivorous clients not to eat their
cleaners. So, how do clients find and recognize cleaners? It appears
that certain body colors, particularly blue and yellow, signal
cleaning behavior to potential clients.
To investigate the role of color in the cleaner-client relationship,
another research team from the University of Queensland — including
Dr. Grutter, Karen Cheney, Simon Blomberg and N. Justin Marshall —
first looked at the distribution of body colors among cleaner and
noncleaner fish from the same families. They found cleaner fish were
significantly more likely to have a blue or yellow coloration.
Furthermore, they showed that these colors were the most contrasting
ones on coral backgrounds to clients like barracuda or surgeonfish and
that the contrast was enhanced against black backgrounds. In fact, all
species they examined that make their living solely from cleaning also
had a contrast-enhancing black lateral body stripe adjacent to these
colors, whereas none of the 31 noncleaner species were so marked.
To test whether potential clients paid attention to these color
schemes, the researchers painted models with various permutations of
cleaner colors in which they omitted the blue pattern or replaced it
with red, or altered the pattern, orientation and width of body
stripes. They then placed these models around reefs fringing Lizard
Island, at the northern end of the Great Barrier Reef, and observed
the frequency with which client fish visited the models. They found
that the model that most closely represented the natural blue-streak
cleaner wrasse pattern was visited more frequently than any other
model color scheme.
In a similar study performed off Sulawesi, Indonesia, the length of
the model's black body stripe also affected the frequency of client
visits. On coral reefs, it pays to advertise, even when potential
With their attention to colors, patterns and shapes and their ability
to learn about new forms, one wonders how much these creatures can
learn and what limitations they might have. They couldn't read Dr.
Seuss, of course, but they might enjoy looking at the pictures.
Sean B. Carroll, a molecular biologist and geneticist, is the author
of "Remarkable Creatures: Epic Adventures in the Search for the Origin
of Species," which has been nominated for a National Book Award.
On 10/21/09, roger malina <firstname.lastname@example.org> wrote:
> From: david mcconville <email@example.com>
> I'm responding off-list because this isn't directly related to your
> question, but I recently gave a couple of performances at CalAcademy's
> new Morrison Planetarium (50th anniversary of Vortex Performances!)
> entitled "Perceiving Home: An Ecological View of the Cosmos". I'm
> increasingly focused in my own work on how "ecology" is an apt lens
> through which to consider not only the interactions of organisms with
> their environment, but also our perceptions within those interactions.
> Getting quite positive feedback since cosmological narratives -
> especially in science center contexts - are often focused on
> communicating the quantitative nature of observations than on
> discussions of ecological principles present across scales.
> I'm continuing to tour with this performance/presentation - something
> that seems relevant to the Darwinian Theory topics...
>> Perceiving Home:
>> An Ecological View of the Cosmos
>> October 3rd, 2009
>> Presentations at 8pm and 9:30pm
>> West Coast Green After-Party at California Academy of Science Morrison
>> San Francisco, CA
>> Visions of the cosmos profoundly influence our interpretations of reality,
>> shaping the lenses through which we perceive the world. While mechanistic
>> metaphors have dominated our understanding since the scientific
>> revolution, contemporary sciences are discovering a universe that is
>> complex, dynamic, evolving, and self-organizing. The most radical findings
>> have revealed systemic interconnections across phenomena at micro and
>> macro scales that have contributed to the genesis and sustenance of life.
>> Perceiving Home visualizes some of these connections through an immersive
>> journey across vast scales of time and space within Cal Academy's new
>> state-of-the-art Morrison Planetarium. Using an interactive 3D atlas of
>> the observable universe, it explores how an emerging ecological paradigm
>> is shifting our perspectives on global and cosmic life support systems and
>> transforming perceptions of our home planet.
>> Perceiving Home will be presented by media artist David McConville, the
>> Director of Noospheric Research of The Elumenati and a Director of the
>> Buckminster Fuller Institute. Live musical accompaniment will be provided
>> by violist Christen Lien , a classically trained violist that performs
>> original compositions using guitar effects and a looping machine that are
>> a beautiful mixture of East and West, classical and postmodern, and
>> acoustic and electronic.
> david mcconville
> director, noospheric research division
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HOW TO SUBSCRIBE: click on the link to the list you wish to subscribe to. In the page that will appear ("info page"), enter e-mail address, name, and password in the fields found further down the page.
HOW TO UNSUBSCRIBE: on the info page, scroll all the way down and enter your e-mail address in the last field. Enter password if asked. Click on the unsubscribe button on the page that will appear ("options page").
HOW TO ENABLE / DISABLE DIGEST MODE: in the options page, find the "Set Digest Mode" option and set it to either on or off.