1. Light: The EM Spectrum

2. Light: Solar Radiation Spectrum

3. Light Perception: The Chromophore
all-trans-retinal
11-cis-retinal
Diagram modified from Terakita(2005)

4. Light Perception: Opsins I
The Chromophore:
Diagram modified from Terakita(2005)

5. Light Perception: Opsins II
Diagram modified from Terakita(2005)

6. Light Perception: Photoreceptors I
Diagram modified from Nilsson and Arendt(2008)

7. 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)

8. Light Perception: Signal Transduction

9. From Marlow and Speiser et al(in prep).
Opsins in a selection of metazoans
Species
Phylum
# of opsins
Eyes?
Nematostella
Cnidarian 14 No
Hydra
2 – 63 (?)
Cladonema
18 (?)
Yes
Capitella
Polychaete 3
Lottia
Mollusk 5
Drosophila
Arthropod 7
Apis
Papilio
Stomatopods
6 - 15
Strongylocentrotus
Echinoderm 6
Amphioxus
Chordate
Homo (human)
Danio (zebrafish)
Gallus (chick)
Mus (mouse)
Figure 1: Phylogenetic relationship of metazoan opsins. This consensus tree was constructed using a Bayesian inference orthology of bilaterian and cnidarian opsins and five million generations under the Blosum62 model of evolution. Posterior probability branch supports are shown in black. Opsins from Nematostella vectensis (orange) form three distinct groups nested within previously known clades of metazoan opsins. Cnidarian representatives of clade I (Go-coupled opsins and RGRs) include CnidOps 1a, which contains genes from Medusazoans, and CnidOps 1b, which contains genes from Anthozoans. CnidOps Groups 2 and 3 fall out as sister clades to clade I opsins. Outgroups include members of the rhodopsin-alpha family of GPCRs, as well as cnidarian non-opsin GPCR outgroups. "Gprtn" refers to the class of G-protein with which the opsins of a group are known to associate. "Phtrcptr" refers to whether a group of opsins is expressed in photoreceptors that are rhabdomeric (R), ciliary (C), or of an unknown or unspecialized morphological type (U). "O/XO" refers to whether an opsin is known to be expressed in ocular (O) or extraocular (XO) tissue. A complete tree with expanded nodes and a full listing of taxa used in the analysis are found in Supplementary Figure 1. `
From Marlow and Speiser et al(in prep). 9

10. From Clark and Kimmeldorf (1977).
Tentacle retraction
Oral disk flexion
Tentacle flexion
Response
Wavelength (nm)
From Clark and Kimmeldorf (1977).

11. Diagrams by Dan Speiser
Building an Eye
Components:
Depolarizing photoreceptor
("on" receptor)
Pigment layer
Hyperpolarizing photoreceptor
("off" receptor)
Mirror
Lens
Light path
Diagrams by Dan Speiser

12. 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.

13. 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

14. 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

15. 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 f s d

16. Diagrams by Dan Speiser
Compound Eyes
Basic compound eye w/ depolarizing photoreceptors at the base of pigment tubes (ex. many inverts)
Diagrams by Dan Speiser

17. Compound Eyes II: Trade-offs (Part II)
Apposition compound eye w/ depolarizing photoreceptors and lenses (ex. diurnal insects)
Diagrams by Dan Speiser

18. Diagrams by Dan Speiser
Compound Eyes III
Reflecting superposition eye with depolarizing photoreceptors (ex. decapod shrimp and lobsters)
Diagrams by Dan Speiser

19. Big Concept 2: Trade-offs (part 2)
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°.

20. Big concept 1: Convergence (part 2)
= 10 μm
Lens
Big concept 1: Convergence (part 2)

21. 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 faster-moving objects.

22. 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

23. Scallop (Aequipecten)

24. File shell (Lima scabra)?
File shell (Lima scabra)

25. Turkey wing (Arca zebra)+
Turkey wing (Arca zebra)

26. ?
Giant Clam (Tridacna)

27. ?
Lantern Shell

28. ?
Cockle (Dinocardium)

29. Lens DAPI Anti-tubulin = 100 μm Autoflourescence Distal retina
Differences between retinas
Distal retina
Proximal retina
Mirror 29

30. Table modified from Land and Nilsson (2002).
The optical resolution of a selection of animal eyes
Name
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
Giant clam
16.5
Ark clam
20 – 40
It is known that scallops see relatively well for any metazoan, let alone a bivalve. I’ll be discussing inter-receptor angle in this talk. It is a measure of optical resolution. A lower number represents better optical resolution. Note that a two –fold difference is functionally significant. 20/200 is legally blind (10x difference)
Table modified from Land and Nilsson (2002). 30

31. Inter-receptor angle (ΔΦ) = s/f
DAPI
Anti-tubulin
Autoflourescence
= 100 μm
Optical resolution ≈
Inter-receptor angle (ΔΦ) = s/f
Differences between retinas
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 31

33. 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)

34. 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

35. Optics concept 3: Chromatic aberration (prism)

36. Optics concept 3: Chromatic aberration
Chromatic aberration in a camera eye
Chromatic aberration in a scallop eye