1. Optical camouflage in Cephalopods
Optical camouflage in Cephalopods
ENGN/BIOL 267

2. Where’s Waldo…err, the octopus?
Video really starts at about 1:50. Probably a good one for Friday.

3. Cuttlefish Camouflage

4. How does it do it?
If you are an octopus (or squid, or whatever cephalopod), what “equipment” do you need to pull off the color changes?
Reflectors
Pigment =

5. Chromatophores: Pigment Sacks
Variable size, under muscarinic control.
Young et al, 2001
Mathger and Hanlon, 2007
Variable size/radius
Under muscarinic control
Color spectrum somewhat limited

6. Chromatophores in Action

7. Biological vs. synthetic displays
From Kreit et al 2013

8. Iridophores: Reflectors
* Stacks of protein plates (reflectins) in cytoplasm
* Single reflectins plate by itself is clear
* Located beneath chromatophores
Cytoplasm
Protein plates
1um
Cooper, 1990

9. Iridophores are active
*Spacing between layers can change.
* Changing layer spacing implies changing reflected wavelength
* Under neural and chemical control (Ach)
Cytoplasm
Protein plate
Scale bars: 250 nm
Cooper, 1990
Cooper, 1990
Mathger, 2007

10. Mechanism for optical tuning
Iridocyte (cell that contains iridophore)
Reflectins plates exchange water into cytoplasm driven by ACh
DeMartini, 2013

11. Two to Tango: Chromatophore-Iridophore Interaction
Yellow chromatophore + green iridophore = dark yellow
Yellow chromatophore + red iridophore = orange!

12. Getting under its skin
Kreit et al 2013

13. Biomimicry in Cephalopods: Part Deux
Modeling the Optics
1um

14. Application of Optics Convenient Physics model The Real Thing
Cytoplasm
Protein plate
Scale bars: 250 nm

15. Traveling Waves Frequency f Wavenumber k = 2p/l
Animation credit: Dan Russel, Penn St. :
Wavenumber k = 2p/l
How wave varies in space
Frequency f
How wave varies with time

16. Different strokes for different folks
Wavelength changes depending on medium in which it is traveling
nolo= nili = nclc lI lc lo

17. Wavelength changes depending on material/medium
cytoplasm
iridophore
air

18. Cytoplasm – Iridophore Optics
* Reflection is the superposition of reflected waves
* Take just one repeating unit for now

19. How does the octopus or squid stack up?
Color we see (wavelength most strongly reflected in ideal stack configuration:
lo = 4nIdI = 4ncdc
But are other colors (wavelengths) visible too?
Why have >1 or 2 iridophore plates?
What if the stack is non-ideal?

20. Phasors!
Sine wave can be represented by a rotating vector, called a phasor.
* Super convenient to keep track of phase differences
Animation:

21. Another great phasor animation
*2 waves can interfere constructively or destructively
*Many waves interfere in just the same way – sum them up.

22. Range observed by Ghoshal, 2013
Survey says…
More plates = better reflectance
More plates = narrower bandwidth
Range observed by Ghoshal, 2013
Figures from Land, 1972

23. Biomimicry in Cephalopods: Part Trois
Bioinspired Designs
1um

24. Bio-inspired Engineering
Block- copolymers photonic gels (Kang, 2007)
Solvents modulate de/swelling
l = 350 – nm

25. Block Copolymers in action
Decreasing
Salt concentration
Figures from Kang, 2007

26. Electrically Induced Color Change
Apply voltage to electrochemical cell
Redox Reaction
Compression/Ex pansion 
Color change
Wallish, 2009

27. The current state of the art
Wallish, 2009

28. Biomimetic Chromatophores
OFF state
ON state
Elastomer Gel
Conductive carbon grease
Rossiter 2012

29. Efficient everyday design?

30. References
RE Young, M Vecchione, KM Mangold, Tree of Life: Cephalopod Chromatophore:
LM Mathger and RT Hanlon. Cell Tissue Res (2007) 329:
LM Mathger and EJ Denton, J Exp Biol (2001) 204:
E Kreit et al., J. Royal Society Interface (2013) 10:
Dan Russel, Penn State:
KM Copper, RT Hanlon, BU Budelmann. Cell Tissue Res (1990) 259: 15-24
MF Land. Progress in Biophysics and Molecular Biology, 24: 75–106.
Y Kang et al, Nature Materials, 6:
JJ Walish et al, Advanced Materials, 21:
D DeMartini et al, Proceedings of the National Academy of Sciences, 110(7),
A Ghoshal et al, Journal of The Royal Society Interface, 10(85),
J Rossieter et al, Bioinsp.Biomim. (7)

31. Describing a sine wave with phasors
4.33
2.5 5

32. Ideal vs Non-ideal stacks
What if the stacks are non-ideal?
Non ideal means:
nidi != ncdc
Land, 1972
The tradeoff:
Less reflectance
Narrower bandwidth, better chromatic selectivity

33. Another coloration mechanism: viewing angle matters
Mathger, 2001
Viewing angle
Mathger and Hanlon, 2007

34. Does viewing angle matter?
YES! X 2
Cross section
of cephalopod
a= 10 deg
a= 50 deg
Apply Snell’s Law:
a = angle of incidence
b = angle of refraction
lo = 4nIdIcosbI = 4ncdccosbc

35. Non-zero angle of incidence
Image credit:

36. What is measured and how?
To computer for data acq.
and analysis--.e.g, the reflectance spectra!
Photo Multiplier Tube:
Collects light and amplifies
Reflected from squid skin
Light source with chromatic filter
(and polarizer)
Tissue prep:
Thin slice of squid skin
Choose color of incident light and measure input intensity Iinc
Measure intensity of reflected light Iref, then compute: R = Iref/Iinc