Kind: captions
Language: en
[Applause]
there is a misconception about
chameleons that they change their color
in order to blend in with their
environment that is actually not the
case when a chameleon is calm it is
green and so it naturally Blends in with
its leafy surroundings but male
chameleons change color when they become
excited in the presence of a female or a
rival male as shown here I'll put the
first frame in the bottom right for
comparison as you can see as he becomes
more excited his color changes to be
more yellow orange and red so instead of
blending in this chameleon will now
stand out but how do chameleons actually
change their color for years we thought
that there was a simple well-established
mechanism for this color change in their
skin chameleons have different cells
containing colored pigments some are
yellow others are red and some contain
the dark melanin pigment many animals
including chameleons are known to turn a
darker shade by causing the melanin to
spread out along the fingery extensions
of the cell they turn lighter Again by
condensing the pigment back into one
spot it was assumed that chameleons must
turn yellow orange and red in the same
way by causing those pigments to spread
out in those cells but new research from
collaborating groups of physicists and
biologists at the University of Geneva
shows that this is incorrect now the
first clue should come from the fact
that there is actually no green pigment
in a chameleon the green color is
actually created by two distinct
mechanisms pigment color and structural
color beneath the yellow pigment cells
there are cells containing tiny 130
nanometer crystals regularly arranged in
a lattice now light defract off these
crystals and due to the spacing between
them blue light constructively
interferes and is therefore strongly
reflected whereas the other colors are
not reflected this is very similar to
how a morpho butterfly wing creates an
iridescent blue the there is no blue
pigment just the periodic nanoscale
structure that acts as a strong
reflector for only one color so a
chameleon looks green due to the
combination of the yellow light from the
pigment plus the blue light reflected
off the crystal structure beneath it so
how do chameleons Chang this green into
yellow orange and red well previously it
was assumed that the color change was
achieved by dispersing pigments in the
colored cells but now scientists have
found it's actually the crystals
underneath which are changing by
increasing the spacing between the
crystals the chameleons can change which
color is selectively reflected bigger
gaps between the crystals are better at
reflecting longer wavelengths so as the
spacing increases the color changes from
blue to green to yellow and then orange
and red scientists compared skin samples
from calm green chameleons and excited
yellow chameleons and found that indeed
in the excited chameleon the crystal
spacing was much further apart here you
can see a single cell enlarged and the
color it reflects changing from blue to
green to yellow orange and red plus a
computer simulation of the light
reflected off crystals while their
spacing is decreasing also provides
excellent agreement with these
observations furthermore applying
physical pressure to the skin causes the
crystals to compress and so they reflect
more blue light when that pressure is
removed the crystals EXP expand again
reflecting more green light the
structure of a chameleon skin gets even
more fascinating as there's another
layer of cells underneath which also
contain crystals but these crystals are
larger more spaced out and more
disorganized this means they reflect
longer wavelengths in the infrared part
of the spectrum and they reflect a
broader range of these wavelengths it's
thought that the function of this layer
could be to reflect heat from the Sun
since these chameleons live in bright
full sun habitats so male chameleons
don't change their color Hue by
spreading out red and yellow pigments
instead they do something much more
remarkable they actively tune the
spacing between nanoscale crystals in
order to create structural colors that
span the whole length of the visible
spectrum now what I find amazing is that
in this day and age we thought we had
the answer to how chameleons change
color but it actually took the combined
expertise of physicists and biologists
working together to figure out what's
really going
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