Cuttlefish camouflage: More than meets the eye
High resolution video coupled with artificial intelligence reveals that camouflaging in cuttlefish is more complex than previously thought

Date:
June 28, 2023
Source:
Okinawa Institute of Science and Technology (OIST) Graduate
University
Summary:
Researchers have shown that the way cuttlefish generate their
camouflage pattern is much more complex than previously believed.


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FULL STORY ========================================================================== Cuttlefish, along with other cephalopods like octopus and squid, are
masters of disguise, changing their skin color and texture to blend in
with their underwater surroundings.

Now, in a study published 28 June inNature, researchers at the Okinawa Institute of Science and Technology (OIST) and the Max Planck Institute
for Brain Research have shown that the way cuttlefish generate their
camouflage pattern is much more complex than previously believed.

Cuttlefish create their dazzling skin patterns by precisely controlling millions of tiny skin pigment cells, called chromatophores. Each
chromatophore is surrounded by a set of muscles, which contract and relax
under direct control of neurons in the brain. When the muscles contract,
the pigment cell is expanded and when they relax, the pigment cell is
hidden. Together, the chromatophores act like cellular pixels to generate
the overall skin pattern.

Professor Sam Reiter, who leads the Computational Neuroethology Unit at
OIST said: "Prior research suggested that cuttlefish only had a limited selection of pattern components that they would use to achieve the best
match against the environment. But our latest research has shown that
their camouflaging response is much more complicated and flexible --
we just hadn't been able to detect it as previous approaches were not
as detailed or quantitative." To make their discovery, the team used
an array of ultra high-resolution cameras to zoom into the skin of the
common European cuttlefish, Sepia officinalis. The scientists presented
the cuttlefish with a range of different backgrounds. As the cuttlefish transitioned between camouflage patterns, the cameras captured the
real-time expansion and contraction of tens to hundreds of thousands
of chromatophores.

Data from around 200,000 skin pattern images were then crunched by the supercomputer at OIST and analyzed by a type of artificial intelligence,
known as a neural network. The neural network looked holistically
at the different elements of the skin pattern images, including
roughness, brightness, structure, shape, contrast, and more complex
image features. Each pattern was then placed into a specific location in
'skin pattern space', a term the scientists coined to describe the full spectrum of skin patterns generated by the cuttlefish.

The researchers also used the same process to analyze images of the
background environment, and looked at how well the skin patterns matched
the environment.

Overall, the researchers found that the cuttlefish were able to
display a rich variety of skin patterns and could sensitively and
flexibly change their skin pattern to match both natural and artificial backgrounds. When the same animal was presented with the same background multiple times, the resulting skin patterns subtly differed in ways that
were indistinguishable to the human eye.

The path that the cuttlefish took to reach each skin pattern was
indirect. The cuttlefish transitioned through a range of different
skin patterns, pausing in between, with each pattern change improving
the camouflage until the cuttlefish stabilized on a pattern they seemed satisfied with. Such paths, even between the same two backgrounds, were
never the same, emphasizing the complexity of the cuttlefish's behavior.

"The cuttlefish would often overshoot their target skin pattern,
pause, and then come back," said Theodosia Woo, joint first author of
the study and graduate student in the Max Planck Institute for Brain
Research team. "In other words, cuttlefish don't simply detect the
background and go straight to a set pattern, instead, it is likely
that they continuously receive feedback about their skin pattern
and use it to adjust their camouflage. Exactly how they receive that
feedback -- whether they use their eyes, or whether they have a sense
of how contracted the muscles around each chromatophore are -- we don't
yet know." The researchers also examined another skin pattern display,
called blanching, which occurs when cuttlefish turn pale in response to a threat. "Unlike camouflaging, blanching was fast and direct, suggesting it
uses a different and repeatable control system," said Dr. Dominic Evans,
a postdoctoral fellow in the Max Planck Institute for Brain Research team.

When the researchers took high resolution images of the blanching display,
they realized that some elements of the previous camouflage pattern
remained, with the blanching pattern superimposed on top. Afterwards,
the cuttlefish would slowly but reliably return to displaying its
pre-blanching skin pattern.

"This suggests that information about the initial camouflage somehow
remains.

The blanching is more like a response that temporarily overrides the
camouflage signals from the brain and might be controlled by a completely different neural circuit in the brain," explained Dr. Xitong Liang,
joint first author of the study and former postdoctoral researcher in
the Max Planck Institute for Brain Research team. "The next step is
to capture neural recordings from cuttlefish brains, so we can further understand exactly how they control their unique and fascinating skin patterning abilities."
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========================================================================== Story Source: Materials provided by Okinawa_Institute_of_Science_and_Technology_(OIST)
Graduate_University. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Theodosia Woo, Xitong Liang, Dominic A. Evans, Olivier Fernandez,
Friedrich Kretschmer, Sam Reiter, Gilles Laurent. The dynamics of
pattern matching in camouflaging cuttlefish. Nature, 2023; DOI:
10.1038/s41586- 023-06259-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/06/230628130352.htm

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