The question of how octopuses can match their surroundings while not being able to see colours is one hell of a puzzle. Christopher Stubbs may finally have found the answer: chromatic aberration.
Maybe octopuses do see colour – not from light hitting special retinal “photoreceptors” but thanks to chromatic aberration, where different colours of light focus at different distances behind a lens.
Eyes of cephalopods are quite unlike anything seen on land: U- and W-shaped pupils backed by a lens that moves back and forth, like a camera, rather than fattening or thinning like ours. But they also have only one photoreceptor, unlike our red, green and blue ones.
Stubbs idea is the following: by adjusting the focal point of their eyes, like a photographer adjusts a lens, cephalopods might be able to detect different wavelengths – or colours – of light. This is called chromatic aberration.
To test his idea, Stubbs created a computer model of how the animals’ eyes work and see if chromatic aberration was possible.
He found not only could a shifting lens do the trick, but the cephalopods’ quirky pupils only served to maximise the effect. As Stubbs says, these creatures might exploit a ubiquitous source of image degradation in animal eyes, turning a bug into a feature.
The unusual pupils of cephalopods (from the top, a cuttlefish, squid and octopus) allow light into the eye from many directions, which spreads out the colors and [certainly] allows the creatures to determine color, even though they are technically colorblind.
As the lens moved forwards and backwards, the different wavelengths focusing on the retina at different times built up a colour picture.
It is not a proof, but the idea is definitely worth investigating !
The latest fascinating cephalopod insights come to us from a
father/son team of researchers at the University of California, Berkeley
and Harvard University, who’ve learned that weirdly-shaped pupils may
allow cephalopods to distinguish colors differently from any other
animals we know of. The discovery is published this week in the Proceedings of the National Academies of Sciences.
Boring animals like humans and birds see color using a combination of
light-receptive cone cells, each of which contains pigments that are
sensitive to a different part of the visual spectrum. It’s only by
combining information from different cone cells that colors can be
properly distinguished. Hence, when a person lacks a particular type of
cone, he’s considered colorblind.
Cephalopods only have a single type of light receptor, which means
they should not be able to distinguish color at all. And yet, many
octopuses, squids and cuttlefish have color-changing skin that’s used
for elaborate camouflage ruses and courtship rituals. Clearly, these
colorblind animals have become masters of color manipulation. How? …
All good things must come to an end, and #CephalopodWeek is no exception. But take heart! Before we close out this celebration of some of the world’s most astonishing invertebrates, we’re highlighting some of great content that this event inspired.
Our colleagues at @sciencefriday explored both the biology and psychology of octopuses (not octopi!) in this video:
Meanwhile, the @montereybayaquarium Research Institute (MBARI) assembled a remarkable highlight reel of cephalopods from around the world:
An octopus has usually a double row of circular suckers, which are strong muscular structures. When pressed against a surface, they create low pressure in the suction cup that provides grip.
Squid suckers (2-3)
Squid suckers have an inner ring of hooks and teeth, which are both stretchy and strong. They help them hang onto their prey by perforating the skin. The third picture shows for example the hooks at the end of a colossal squid’s tentacle.
The migas is said to be a huge, freshwater-dwelling octopus that comes from African folklore.
The migas dwells in swamps and deep lakes, and is said to have more tentacles than a regular octopus, ranging from twenty, to almost a hundred. Even if they dwell in such conditions, they have the ability to squeeze through the tightest of spaces, like normal octopuses, and hide in very shallow lakes.
They say that anything it will come in contact with will instantly become its target, and the migas will tear its victim to shreds.
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