OPTICAL MIMICRY AND COMMUNICATION IN CEPHALOPODS ENGN/BIOL 267, Fall

Master of Camouflage

Where’s Waldo…err, the octopus?

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 + =

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

Chromatophores in Action

Iridophores: Reflectors * Stacks of protein plates (reflectins) in cytoplasm * They are, by themselves, colorless * Located beneath chromatophores Cooper, um Cytoplasm Protein plates

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

What is measured and how? Tissue prep: Thin slice of squid skin Photo Multiplier Tube: Collects light and amplifies Reflected from squid skin Light source with chromatic filter (and polarizer) To computer for data acq. and analysis--.e.g, the reflectance spectra! 1.Choose color of incident light and measure input intensity I inc 2.Measure intensity of reflected light I ref, then compute: R = I ref /I inc

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

Biomimicry in Cephalopods: Part Deux 1um

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

Traveling Waves Wavenumber k = 2  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  n o o = n i i = n c c I c o

Wavelength changes depending on material/medium air cytoplasm iridophore

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

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

Describing a sine wave with phasors 5

How does the octopus or squid stack up?  We found the color that is most visible. But are other colors (wavelengths) visible too?  How does the number of plates affect how the octopus optics…why not have just one protein plate?

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

Bio-inspired Engineering Block- copolymers photonic gels (Kang, 2007) Solvents modulate de/swelling = 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

Viewing angle matters: part I Mathger and Hanlon, 2007 Mathger, 2001 Viewing angle

Does viewing angle matter?  = 10 deg  = 50 deg 10 o 50 o 10 o 50 o YES! X 2  Cross section of cephalopod  = angle of incidence  = angle of refraction = 4nd cos 

Non-zero angle of incidence Image credit: n2n2 n1n1 d2d2 L r

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:  Dan Russel, Penn State: t/wave-x-t.htmlhttp:// t/wave-x-t.html  KM Copper, RT Hanlon, BU Budelmann. Cell Tissue Res (1990) 259:  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: