The
complexity of the Squid.
For a time, humans have
been seen as the pinnacle of evolutionary success, or god ultimate creation.
Scientists now know that this is not the case, humans lack traits that could be
valuable to us and have faulty designs in our anatomy, squids for example have
useful traits that we lack and have a key similar trait that is anatomically
more efficient. No organism is perfect but, as far as invertebrates go, the
squid is as close as they get. The squid is a highly modified Mollusca
cephalopod that has a number of traits that make it very well fit in the
evolutionary sense. The squid has the ability to change colors in seconds to hide
from possible threats and ambush its prey. Squids also have a highly complex
eye for seeking out its prey that is better designed than our own. Squids even
share a very interesting symbiotic relationship with species of bacteria.
Source:
http://www.ryanphotographic.com/images/JPEGS/Squid%20from%20kaikoura%20montage%20copy.jpg
Certain species of squids, and other cephalopods,
have the ability to change their color drastically in a matter of seconds. This
sudden color change is made possible by the possession of cromatophores.
Cromatophores are tiny pigment filled sacs in their skin that contain different
pigments. The chromatophores are connected to muscles that run to the
cephalopods brain and when the brain signals for the turning on of the
chromatophores, these muscles relax and let out the pigment desired. The
chromatophores are limited in the colors they can produce so to reach even
further color change, the cephalopods have a second layer of skin armed with
iridophores. Iridophores are extremely fast acting, neuron controlled, pigments
that reflect certain wavelengths of light to achieve the desired color. The
mechanism in which iridophores work is not completely understood but
researchers understand that they modify the pigment expressed by the
chromotophores. It has also just been accepted in the scientific community that
iridophores do so by moving closer or further apart at a nanoscale level to
achieve the desired color. Of course the full mechanism has not been discovered
and there is much more research on this phenomena to be done. Another
astonishing anatomical feature of the squid is the complexity in the wiring of
its eye.
Certain
species of squids, and other cephalopods, have the ability to change their
color drastically in a matter of seconds. This sudden color change is made
possible by the possession of cromatophores. Cromatophores are tiny pigment
filled sacs in their skin that contain different pigments. The chromatophores
are connected to muscles that run to the cephalopods brain and when the brain
signals for the turning on of the chromatophores, these muscles relax and let
out the pigment desired. The chromatophores are limited in the colors they can
produce so to reach even further color change, the cephalopods have a second
layer of skin armed with iridophores. Iridophores are extremely fast acting,
neuron controlled, pigments that reflect certain wavelengths of light to
achieve the desired color. The mechanism in which iridophores work is not
completely understood but researchers understand that they modify the pigment
expressed by the chromotophores. It has also just been accepted in the
scientific community that iridophores do so by moving closer or further apart
at a nanoscale level to achieve the desired color. Of course the full mechanism
has not been discovered and there is much more research on this phenomena to be
done. Another astonishing anatomical feature of the squid is the complexity in
the wiring of its eye.
Neurally stimulated squid iridophore. (Credit: Wardill,
Gonzalez-Bellido, Crook & Hanlon, Proceedings of the Royal Society B:
Biological Sciences)
The squid has eyes that are anatomically more
sufficient than ours. A humans eye lined with neurons that take in light to
decipher the image given to us. A major problem with the wiring of these
neurons is that they are facing inwards towards our brain. This caused the light
to have to travel through our pupil twice to be processed by out neurons, and
eventually our brain. The squid has a similar intake of light mechanism in its
eye except the neurons a facing the outwards. The change in wiring, although
seemingly small, allows the squids neurons to take in the light instantly and
process the image. The wiring of a humans eye has another major malfunction
that is corrected by software in our brain, this is the presence of blood
vessels in front of our pupil. These blood vessels create blind spots in the
human eye that is filled in by our brain. The squid, on the other hand, has its
blood vessels behind its pupil making these blind spots nonexistent for them. At
this point it is easy to understand that the squid really is a magnificent
invertebrate adapted well by natural selection, but if that wasn’t enough some
squids even have an extremely beneficial symbiotic relationship that makes them
shine, literally!
Eye of
Giant Humboldt Squid Norbert Wu, Corbis Norbert Wu, Corbis
Some squids possess more color changing organs
located under the mantle cavity that are home to a species of luminous
bacteria. These organs are called the crypt and the lens. The crypt is the home
to these tiny luminescent microbes, the vibrio
fischeri, while the lens controls the brightness of the bacteria in the
crypt. The lens is composed of tiny reflecting plates piled together in a sack.
The lens comes in great use for a squid in hiding from potential predators.
Therefore
we should not view humans as the best designed organisms of evolution, squids
are just one example of high complexity that rivals our own. Although not all
traits that squids have would fit our lifestyles as terrestrial mammals, their
complexity should not be ignored. These
intelligent cephalopods are adapted well to predatory lifestyle with their own
unique modifications like their complex and well wired eye, designed better
than our own! They are also equipped with defense mechanisms such as color
change and some squids even have acquired a mutualistic symbiotic relationship
with bacteria. Squids are amazing feats of evolution and although much has been
discovered about them, there is still much more to learn.
Further studies on squids:
http://www.earthlife.net/inverts/mollusca.html
References:
Wei, S.L., and R.E. Young. 1989. Development of
symbiotic bacterial bioluminescence in a nearshore cephalopod, Euprymna
scolopes. Marine Biology 103:541-546.
Staaf, Danna. Quest. Aug 28, 2012. Squid Skin:Why
Pigment (but Not Glitter) Will Dance to the Beat. http://science.kqed.org/quest/2012/08/28/squid-skin-why-pigment-but-not-glitter-will-dance-to-the-beat/
Holt AL, Sweeney AM, Johnsen S, & Morse DE
(2011). A highly distributed Bragg stack with unique geometry
provides effective camouflage for Loliginid squid eyes. Journal of
the Royal Society, 8(63):1386-99
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