AD 2017 Q4

LIFE
AQUATIC
A common Caribbean octopus (Octopus vulgaris) morphs in two seconds from a conspicuous
white threat display to a mottled pattern with full expansion of its 3-D skin papillae.
NOTE: These photos of camouflaged animals were taken using available light; the use of
strobe lighting could potentially alter their behavior and our perception of their color.
NATURE’S BEST AND FASTEST CAMOUFLAGE
Text and photos by Roger Hanlon
No creature on the planet can change
its camouflage as fast and effectively
as an octopus, cuttlefish or squid.
These speed merchants of adaptive
coloration can change their skin’s
color, brightness, contrast and
pattern in as little as 200 milliseconds — one-fifth of
one second — as fast as a human eyeblink.
This is no small feat given the complexity of
backgrounds in marine environments (such as those
found on coral reefs). What’s more, an octopus
must carefully orchestrate 10 million to 20 million
chromatophore organs in its skin as well as another
million or so iridescent cells and perhaps several
thousand skin bumps (called papillae) to tailor its
camouflage pattern to every specific microhabitat it
stops in while foraging. Of course, if you can change
your appearance, you have to control it, and that
requires good vision and a large brain to process
the visual information, send signals to all those skin
elements and get the pattern deployed.
WHY AND HOW
A colleague once quipped, “Cephalopods occupy the
behavioral space of fishes,” and that is an appropriate
viewpoint from which to begin the discussion. After all,
the bony fishes (snappers, groupers, barracudas, tunas,
etc.) dominate most marine ecosystems, and they have
some of the most sophisticated visual systems known.
And they all eat cephalopods, which are essentially tasty
and nutritious hunks of protein. Cephalopods have been
found in the stomachs of a vast array of marine mammals,
diving birds and fishes — they exist in the middle of the
food chain. Therefore the soft-bodied cephalopods have
to “live by their wits” and be fast, clever and hard to find.
The keen visual systems of their predators are foremost
among the selective forces that led to the evolution of
cephalopods’ diverse and detailed camouflage
How cephalopods managed this evolution is more
difficult to uncover. A basic flaw in biological thought
during the past century is the idea that camouflage is
“looking like the background.” In retrospect, this does
not make much sense simply because there are too
many backgrounds. A typical Caribbean coral reef, for
example, has 600 to 1,000 species on it (e.g., corals,
bryozoans, tunicates, algae, seagrasses, etc.), so trying
to resemble that many backgrounds is a senseless idea.
A better approach is to study the animal group that
changes its camouflage dynamically throughout these
complex backgrounds (cephalopods) and determine
how many patterns it needs and what sorts of tricks
it has evolved to deceive multiple visual predators.
One sage put it thus: “Camouflage is the least-studied
biological subject that we think we already know
about.” Fortunately, that is changing.
SOME BASIC TRICKS
A very surprising finding came from studies of cuttlefish
camouflage. When researchers assembled thousands
of images of camouflaged cuttlefish from dives and
laboratory experiments, they found only a few basic
camouflage pattern designs. This counterintuitive
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