Optical camouflage in Cephalopods http://symbiol.blogspot.com/ Optical camouflage in Cephalopods ENGN/BIOL 267

Where’s Waldo…err, the octopus? http://www.ted.com/talks/david_gallo_shows_underwater_astonishments.html Video really starts at about 1:50. Probably a good one for Friday.

Cuttlefish Camouflage

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 + = http://www.toolsandleisure.co.uk/round-amber-self-adhesive-reflector-294-p.asp

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

Chromatophores in Action http://blog.backyardbrains.com/2012/08/insane-in-the-chromatophores/

Biological vs. synthetic displays From Kreit et al 2013

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

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

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

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

Getting under its skin Kreit et al 2013

Biomimicry in Cephalopods: Part Deux Modeling the Optics 1um

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

Traveling Waves Frequency f Wavenumber k = 2p/l Animation credit: Dan Russel, Penn St. : http://www.acs.psu.edu/drussell/Demos/wave-x-t/wave-x-t.html Wavenumber k = 2p/l How wave varies in space Frequency f How wave varies with time

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

Wavelength changes depending on material/medium cytoplasm iridophore air

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

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?

Phasors! Sine wave can be represented by a rotating vector, called a phasor. * Super convenient to keep track of phase differences http://edumation.org/play_file.php?file_type=animation&file_id=84 http://www.physics.udel.edu/~watson/phys208/phasor-slow.html http://en.wikipedia.org/wiki/File:Unfasor.gif Animation: http://edumation.org/play_file.php?file_type=animation&file_id=84

Another great phasor animation *2 waves can interfere constructively or destructively *Many waves interfere in just the same way – sum them up. http://resonanceswavesandfields.blogspot.com/2007/08/phasors.html#phasor-addition

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

Biomimicry in Cephalopods: Part Trois Bioinspired Designs 1um

Bio-inspired Engineering Block- copolymers photonic gels (Kang, 2007) Solvents modulate de/swelling l = 350 – 1600 nm

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

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

The current state of the art Wallish, 2009

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

Efficient everyday design?

References RE Young, M Vecchione, KM Mangold, 2001. Tree of Life: Cephalopod Chromatophore: http://tolweb.org/accessory/Cephalopod_Chromatophore?acc_id=2038 LM Mathger and RT Hanlon. Cell Tissue Res (2007) 329: 179-186 LM Mathger and EJ Denton, J Exp Biol (2001) 204: 2103-2118 E Kreit et al., J. Royal Society Interface (2013) 10:20120601 Dan Russel, Penn State: http://www.acs.psu.edu/drussell/Demos/wave-x-t/wave-x-t.html 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, 2007. Nature Materials, 6: 957-960 JJ Walish et al, 2009. Advanced Materials, 21: 3078-3081 D DeMartini et al, 2013. Proceedings of the National Academy of Sciences, 110(7), 2552- 2556. A Ghoshal et al, 2013. Journal of The Royal Society Interface, 10(85), 20130386. J Rossieter et al, 2012. Bioinsp.Biomim. (7) 036009

Describing a sine wave with phasors 4.33 2.5 5

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

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

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

Non-zero angle of incidence Image credit: http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/interf.html#c1

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