Color Vision

Misnomer

Human Color blindness- color vision deficiency (CVD)

CVD affects how many men and women (%)

8% of men; 0.5% of women

Trichromats

Individuals with 3 cone types

Anamalous trichromacy

very closely spaces peaks for L and M cones; difficult to distinguish between red and green on color wavelength spectrum

Dichromats

Have 2 functional cone types; 2 types

Protanope

An individual who suffers from color blindness that is due to the absence of L-cones (~580 nm)

Duetranope

Lack M cone (~530 nm)

Tritanope

An individual who suffers from color blindness that is due to the absence of S-cones (~420 nm)

Monochromacy (Achromatopsia)

No functional cones

How common is monochromacy

very rare; 1/33,000

Remember

Rods and cones form mosaic on OUTSIDE of retinas surface

Most Mammals S cone:

Widely spaced and less common than other cone types (~10%)
NO S cones in foveal centre

Most mammals L and M:

Normally variated, random distribution from individual to individual (~90%)

Human Color Pathways

1. Red/green opponent
2. Blue/yellow opponent

red-green opponent

In fovea: no summation of P cell pathway
Each P GC gets input from L OR M cone (only one)-direct signals
Input to brain from central P cells color-coded
used to determine relative excitations of 3 cones

blue-yellow opponent

HAVE SPECIAL GC: small bistratisfied GC
SBGC receive on signals from S cone and off signals from M/L cone
used to determine relative excitations of 3 cones

Additive color mixing

Mixing of different wavelengths
=white

Subtractive color mixing

Mixing of pigments (removal of white light)
=black

Tetrachromacy

4 cone photopigments; common in non-mammals

Most mammals (placental)

Dichromats; LCA had 2 cone types (usually 1 M/L and 1 UV)

Some mammals

monochromats (no S cone)

Tarsiers and Lemuriformes are:

dichromats

Some FEMALE Lemuriformes are ___ and their activity pattern is ___

polymorphic trichromats; diurnal

Lorisiformes

Monochromats

Catarrhines

ALL are routine trichromats
Old World Monkeys, Apes, Humans

Platyrrhines

MOST are polymorhpic trichromats

Which Platyrrhine is the exception to routine trichromacy and what is it?

Howler Monkey: routine trichromacy

Which ANTHROPOID (platy and cata) is the exception to trichromacy and what is it?

Aeolus (owl monkey); monochromat

What happened to the Aeolus to become monochromatic?

Pseudogene

What is the VERY RARE condition some human females have?

tetrachromacy-4 cone types

Polymorphic trichromacy has evolved how many times minimum?

3

How many times in LEMURS and PLATYRRHINES?

2x lemur; 1x platyrrhines

What is the ancestral condition for S cone photopigment in mammals? Which chromosome is it found on?

1 gene for S cone photopigment; chromosome 7

What is the ancestral condition for M/L cone photopigment in mammals? Which chromosome is it found on? Why does it make it more likely for males to be colorblind?

1 gene for M/L photopigment; found on X chromosome; because they only get one X-if defective no color vision

What color vision do most CATHEMERAL Marsupials have?

routine trichromacy

What finding found that vision can be adaptive with nocturnality?

Many nocturnal primates show GENETIC evidence of selection to maintain DICHROMACY

Why trichromacy?

Color based visual signals in catarrhines are SOCIAL communication

What type of social communication for trichromatic catarrhine?

Sexual selection
Dominance (color intensity)

Hypotheses of color vision evolution

1. Fugivory (old)
2. Folivory (new)

Fugivory Hypothesis dealt with?

Fruits of many colors can be hard to distinguish amongst each other; hard to distinguish NO MATTER WHAT COLOR against LEAVES (green)
need the cones to distinguish fruits from one another and against green
Dichromats distinguish red and orange from purple and blue-NOT green (probably why it is less popular)

Folivory Hypothesis deals with?

Red flush in YOUNG leaves; they taste good and so it nice to be able to distinguish

What is the red flush pigment produces in young leaves-what could it be good for?

anthocyanin pigment
-bug camo
-sunscreen

Why do young leaves taste better?

Increased protein
Decreased cellulose and tannins (make leaf tough) AND less toxin
easier to eat

Proof for Folivory?

Howler monkeys...?
Lemurs:
Verraux's sifaka (lemurs) lose 10-20% (A LOT) of body mass in dry season w/o leaves
BUT: lemurs with polymorphic trichromatic females are 5% fatter than others

Evolution Picture: LCA OF VERTS

LCA of ANIMALS lives 360 mya: GOOD color vision
primitive vertebrates had tetrachromacy (4 cones incl. UV)

What is the nocturnal bottleneck and when did it occur for placental mammals and what did it cause?

LCA of placental mammals lived in Mesozoic Era (252-60mya)-because of heavy predation pressure these mammals shifted to nocturnality
EFFECT: became dichromatic

After dinosaur extinction what happened to mammals?

Mammal diversity INCREASED
ecological RELEASE on MASSIVE scale

What did the crappy eyesight of mesozoic era leave mammals with? What did some do?

diminished eyesight; some evolved adaptions to restore functions lost in bottleneck

Now: diurnal and cathemeral primates have

expanded vision abilities
POLY and ROUTINE trichromacy