Transcript 25.Vision

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
all-trans-retinal
11-cis-retinal
Diagram modified from Terakita(2005)
Light Perception:
Opsins I
The Chromophore:
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
Rhabdomeric
Photoreceptor
(depolarizing/
“on” receptor)
= Dark-to-light
detector
Ciliary
Photoreceptor
(hyperpolarizing/
“off” receptor)
= Light-to-dark
detector
Diagram modified from Nilsson and Arendt(2008)
Light Perception:
Signal Transduction
Opsins in a selection of metazoans
Species
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
From Marlow and Speiser et al(in prep).
Oral disk flexion
Tentacle flexion
Response
Tentacle retraction
Wavelength (nm)
From Clark and Kimmeldorf (1977).
Building an Eye
COMPONENTS:
Depolarizing photoreceptor
("on" receptor)
Pigment layer
Hyperpolarizing photoreceptor
("off" receptor)
Mirror
Lens
Light path
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 Eyes:
Lens optics
Camera eye w/ depolarizing photoreceptors
and a lens (ex. squid and octopi)
Camera eye w/ hyperpolarizing photoreceptors
and a lens (ex. fish)
Diagrams by Dan Speiser
Camera Eyes:
Corneal optics
Camera eye w/ depolarizing photoreceptors
and corneal optics (ex. land spiders)
Camera eye w/ hyperpolarizing photoreceptors
and corneal optics (ex. land vertebrates)
Diagrams by Dan Speiser
Big Concept 2:
Trade-offs (part 1)
Optical resolution ≈
Inter-receptor angle (ΔΦ) = s/f
Optical sensitivity (S) ∝
D2Δρ2 (where Δρ = d/f)
D
f
s
f
d
Compound Eyes
Basic compound eye w/ depolarizing photoreceptors
at the base of pigment tubes (ex. many inverts)
Diagrams by Dan Speiser
Compound Eyes II:
Trade-offs (Part II)
Apposition compound eye w/ depolarizing
photoreceptors and lenses (ex. diurnal insects)
Diagrams by Dan Speiser
Compound Eyes III
Reflecting superposition eye with depolarizing
photoreceptors (ex. decapod shrimp and lobsters)
Diagrams by Dan Speiser
Big Concept 2:
Trade-offs (part 2)
Ɵi
f
d
An eye gathers light from an area
with an angular size of, say, 10°
A naked photoreceptor gathers light
from an entire hemisphere
All else being equal, a naked photoreceptor will be 130x
more sensitive than an eye with an angular resolution of 10°.
= 10 μm
Lens
Big concept 1:
Convergence (part 2)
Big Concept 2:
Trade-offs (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 fastermoving objects.
Back to eye diversity . . .
“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
Scallop (Aequipecten)
?
File shell (Lima scabra)
+
Turkey wing (Arca zebra)
?
Giant Clam (Tridacna)
?
Lantern Shell
?
Cockle (Dinocardium)
DAPI
Anti-tubulin
Autoflourescence
= 100 μm
Lens
Distal retina
Proximal retina
Mirror
The optical resolution of a selection of animal eyes
Name
Optical resolution (degrees)
Eagle
0.004
Human
0.007
Octopus
0.01
Human (legally blind)
0.07
Rat
0.5
Honey bee
1.0
Scallop
1.6
Wolf spider
1.8
Fruit fly
5
Nautilus
8
Cephalopod mollusk
Giant clam
16.5
Bivalve mollusk
Ark clam
20 – 40
Bivalve mollusk
Cephalopod mollusk
Bivalve mollusk
Table modified from Land and Nilsson (2002).
DAPI
Anti-tubulin
Autoflourescence
= 100 μm
Optical resolution ≈
Inter-receptor angle (ΔΦ) = s/f
Receptor spacing (s) = the distance
between adjacent receptors
Focal length (f) of a concave spherical mirror
= 0.5 x the radius of the mirror
Mirror
optical resolution (in degrees)
5
distal retina
4
proximal retina
3
2
1
0
A. balloti,
100 cm/s
P. magellenicus A. irradians ,
,
68 cm/s
≈50 cm/s
C. hastata,
≈35 cm/s
C. rubida,
≈35 cm/s
Scallop species,
max. swimming speed
C. gigantea,
0 cm/s
S. americanus,
0 cm/s
Optics concept 2:
Spherical aberration
An camera eye with a lens that
causes spherical aberration
A camera eye with a lens that
does not cause spherical aberration
(due to, for instance, having
a graded refractive index)
Optics concept 2:
Spherical aberration (in the scallop eye)
A spherical mirror w/ no lens
= more spherical aberration
A spherical mirror w/ correcting lens
= less spherical aberration
Optics concept 3:
Chromatic aberration (prism)
Optics concept 3:
Chromatic aberration
Chromatic aberration in a camera eye
Chromatic aberration in a scallop eye