Light: The EM Spectrum
http://www.antonine-education.co.uk/physics_gcse/Unit_1/Topic_5/em_spectrum.jpg
Light: Solar Radiation Spectrum
http://upload.wikimedia.org/wikipedia/commons/4/4c/Solar_Spectrum.png
Light Perception:The Chromophore
11-cis-retinalall-trans-retinal
Diagram modified from Terakita(2005)
The Chromophore:
Light Perception:Opsins I
Diagram modified from Terakita(2005)
Light Perception:Opsins II
Diagram modified from Terakita(2005)
Light Perception: Photoreceptors I
Diagram modified from Nilsson and Arendt(2008)
Light Perception: Photoreceptors II
Diagram modified from Nilsson and Arendt(2008)
RhabdomericPhotoreceptor(depolarizing/“on” receptor)
CiliaryPhotoreceptor
(hyperpolarizing/ “off” receptor)
= Dark-to-light detector
= Light-to-dark detector
Light Perception: Signal Transduction
From Marlow and Speiser et al(in prep).
Opsins in a selection of metazoansSpecies Phylum # of opsins Eyes?
Nematostella Cnidarian 14 No
Hydra Cnidarian 2 – 63 (?) No
Cladonema Cnidarian 18 (?) Yes
Capitella Polychaete 3 Yes
Lottia Mollusk 5 Yes
Drosophila Arthropod 7 Yes
Apis Arthropod 5 Yes
Papilio Arthropod 5 Yes
Stomatopods Arthropod 6 - 15 Yes
Strongylocentrotus Echinoderm 6 No
Amphioxus Chordate 6 No
Homo (human) Chordate 7 Yes
Danio (zebrafish) Chordate 6 Yes
Gallus (chick) Chordate 6 Yes
Mus (mouse) Chordate 6 Yes
Oral disk flexion Tentacle flexionTentacle retraction
From Clark and Kimmeldorf (1977).
Wavelength (nm)
Resp
onse
Building an Eye
Depolarizing photoreceptor("on" receptor)
Hyperpolarizing photoreceptor("off" receptor)
Lens
Pigment layer
Mirror
Light path
COMPONENTS:
Diagrams by Dan Speiser
Optics concept 1:Refraction
Refraction is the deflection from a straight path undergone by a wave (such as light) when it passes obliquely from one medium (such as air) into another medium (such as water) in which its velocity is different.
Camera eye w/ depolarizing photoreceptorsand a lens (ex. squid and octopi)
Camera eye w/ hyperpolarizing photoreceptors and a lens (ex. fish)
Diagrams by Dan Speiser
Camera Eyes: Lens optics
Camera eye w/ depolarizing photoreceptorsand corneal optics (ex. land spiders)
Diagrams by Dan Speiser
Camera eye w/ hyperpolarizing photoreceptors and corneal optics (ex. land vertebrates)
Camera Eyes: Corneal optics
Big Concept 2:Trade-offs (part 1)
f
s
Optical resolution ≈ Inter-receptor angle (ΔΦ) = s/f
f
d
Optical sensitivity (S) ∝ D2Δρ2 (where Δρ = d/f)
D
Diagrams by Dan Speiser
Basic compound eye w/ depolarizing photoreceptors at the base of pigment tubes (ex. many inverts)
Compound Eyes
Diagrams by Dan Speiser
Apposition compound eye w/ depolarizing photoreceptors and lenses (ex. diurnal insects)
Compound Eyes II:Trade-offs (Part II)
Diagrams by Dan Speiser
Compound Eyes III
Reflecting superposition eye with depolarizing photoreceptors (ex. decapod shrimp and lobsters)
A naked photoreceptor gathers light from an entire hemisphere
Ɵi
f
d
An eye gathers light from an area with an angular size of, say, 10°
All else being equal, a naked photoreceptor will be 130x more sensitive than an eye with an angular resolution of 10°.
Big Concept 2:Trade-offs (part 2)
= 10 μm
Lens
Big concept 1:Convergence (part 2)
• Eyes allowed chitons to distinguish 10° objects from shadows.
• However, eyes decreased optical sensitivity: we found that chitons without eyes responded to changes in illumination of 1%, while chitons with eyes only responded to changes in illumination of 5% or greater.
• Eyeless chitons also responded to faster-moving objects.
Big Concept 2:Trade-offs (part 2)
“Bivalve lineages may be aptly described as evolutionary eye factories, in the sense that they have developed eyes of many
different types, often at unusual positions of the body”
- Dan-E. Nilsson
Back to eye diversity . . .
Scallop (Aequipecten)
File shell (Lima scabra)
?
+
Turkey wing (Arca zebra)
Giant Clam (Tridacna)
?
Lantern Shell
?
?
Cockle (Dinocardium)
= 100 μm
Lens
Distal retina
Proximal retina
DAPIAnti-tubulinAutoflourescence
Mirror
The optical resolution of a selection of animal eyesName Optical resolution (degrees)
Eagle 0.004
Human 0.007
Octopus 0.01 Cephalopod mollusk
Human (legally blind) 0.07
Rat 0.5
Honey bee 1.0
Scallop 1.6 Bivalve mollusk
Wolf spider 1.8
Fruit fly 5
Nautilus 8 Cephalopod mollusk
Giant clam 16.5 Bivalve mollusk
Ark clam 20 – 40 Bivalve mollusk
Table modified from Land and Nilsson (2002).
= 100 μmDAPIAnti-tubulinAutoflourescence
Mirror
Receptor spacing (s) = the distance between adjacent receptors
Focal length (f) of a concave spherical mirror = 0.5 x the radius of the mirror
Optical resolution ≈ Inter-receptor angle (ΔΦ) = s/f
Optics concept 2:Spherical aberration
A camera eye with a lens thatdoes not cause spherical aberration
(due to, for instance, having a graded refractive index)
An camera eye with a lens thatcauses spherical aberration
A spherical mirror w/ correcting lens = less spherical aberration
A spherical mirror w/ no lens= more spherical aberration
Optics concept 2:Spherical aberration (in the scallop eye)
Optics concept 3:Chromatic aberration (prism)
Chromatic aberration in a camera eye Chromatic aberration in a scallop eye
Optics concept 3:Chromatic aberration