OPTICAL MIMICRY AND COMMUNICATION IN CEPHALOPODS ENGN/BIOL 267, Fall 2013

OPTICAL MIMICRY AND COMMUNICATION IN CEPHALOPODS

ENGN/BIOL 267, Fall 2013

http://symbiol.blogspot.com/

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 + =

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

Chromatophores: Pigment Sacks

Mathger and Hanlon, 2007 Young et al, 2001

• Variable size/radius• Under muscarinic control• Color spectrum somewhat limited

Chromatophores in Action

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

Iridophores: Reflectors

* Stacks of protein plates (reflectins) in cytoplasm

* They are, by themselves, colorless

* Located beneath chromatophores

Cooper, 1990

1um

CytoplasmProtein plates

Iridophores are active

*Spacing between layers can change.

•* Changing layer spacing implies changing reflected wavelength

•* Under neural and chemical control (Ach)

Cooper, 1990Scale bars: 250 nm

Cytoplasm

Protein plate

Mathger, 2007Cooper, 1990

What is measured and how?

Tissue prep:Thin slice of squid skin

Photo Multiplier Tube:Collects light and amplifiesReflected 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 Iinc

2. Measure intensity of reflected light Iref, then compute: R = Iref/Iinc

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 /p l How wave varies in space

Frequency fHow 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

air cytoplasmiridophore

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: http://edumation.org/play_file.php?file_type=animation&file_id=84

-0.2 0 0.2 0.4 0.6 0.8 1 1.2-6

-4

-2

0

2

4

6

Time (sec)

v(t)

[Vol

ts]

v(t) = 5 cos(2ft) with f = 4 Hz

4.33 2.5

0

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 reflectance

More plates = narrower bandwidth

Figures from Land, 1972

Range observe

d by Ghoshal, 2013

Bio-inspired Engineering

Block-copolymers photonic gels (Kang, 2007)

Solvents modulate de/swelling

l = 350 – 1600 nm

Block Copolymers in action

DecreasingSalt concentration

Figures from Kang, 2007

Electrically Induced Color Change

Apply voltage to electrochemical cell

Redox Reaction

Compression/Expansion

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?

a= 10 deg a= 50 deg

10o

50o 10o

50o

YES! X 2

b

Cross section of cephalopod

a = angle of incidenceb = angle of refractionl = 4nd cosb

Non-zero angle of incidence

Image credit:http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/interf.html#c1

n2

n1

d2

L

r

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

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