15- Evolution of Colour

Question 1

How does colour vision work:
Why do we not perceive colour under scotopic (dark) conditions?

Answer 1

In retina we have rods (sensitive to light used in scotopic condition) and cones (needing a lot of photons to get them active in light conditions).
There are much less photons at night, only those reflected by the moon surface. Low intensity of the light drives us to use our rod photoreceptors which does not allow us to discriminate colour.

Question 2

How does colour vision work:

At scotopic light levels only which photoreceptors function?
What is the single photopigment called?

Answer 2

rod, rhodopsin

Question 3

At scotopic light levels only rod photoreceptors function. The single photopigment (rhodopsin) responds to lights of different wavelengths, but some of which can elicit the same photoreceptor response.

what is the term used to describe this process?
The different wavelength-intensity combinations can produce identical responses (unclear on which colour it actually is might be blue or yellow) which is known as?

Answer 3

Univaraince

• Thus a single photoreceptor type (e.g. rods) is not adequate for signaling differences in wavelength

Question 4

Which photoreceptor cannot support wavelength discrimination in scpotic settings due to the different wavelength-intensity combinations producing identical responses (univaraince)?

Answer 4

rods

Question 5

Here is a diagram of a 3 pigment system (triomatic system) in humans.

Why do we need more than a single receptor type to mediate colour discrimination?

Answer 5

There is more than one receptor type, each with different spectral absorbances avoid problems of univariance.

Lots of cones distributed, and get bigger/ lower responses from different S/M/L cones

Different wavelengths of light now produce different patterns of activity across the receptor population.

Question 6

Most light humans look at is combined with different wavelengths (colours). Most objects we look at are composed of a range of wavelengths.

Example: sunlight excites all S/M/L cones
medium wavelengths produce a signal we call green
long wavelengths produce a signal we call red

Red light will produce a smaller response in M cone but bigger response in L cones (so this overlaps)

Two wavelengths (a) elicit combined activity equal to that produced by single wavelength (b)

If two sets of lights produce same combined response, they are termed as?

Answer 6

‘metamers’

indistinguishable from which actual colour it is, cant discriminate from things that are physically different

Question 7

What are will appear identical: mixture of red and green indistinguishable from yellow light
Physical light not altered; their combination results in the same neural response ?

More photpigments you add, the fewer … you will experience.

Answer 7

‘metamers’

Question 8

Finish the sentence:

Sunlight excites short medium and long wavelength cones. When light shines on a piece of paper, it reflects a particular pigment.

We see via reflective light, photons are emitted from a source and bounce into our eyes.

The perceived colour of objects is result of wavelengths in the … and …?

Answer 8

luminance,
Reflectance properties of objects surface (surface reflection)

Question 9

Changes in either which 2 properties can result in a change in colour appearance of an object?

Answer 9

luminance,
Reflectance properties of objects surface (surface reflection)

Spectral content of light reaching eye determined by:
the surface reflectance multiplied by the illuminant

Question 10

What is the purkinje shift in colour?

Answer 10

sunlight is fluid and not static meaning it effects how we see colours early in the morning compared to closer to dusk.

Question 11

The visual system’s retinal ganglion cells form colour opponent pathways:

Name the main 3

Answer 11

1- take output from M and L wavelength sensitive cones and sum + them (Achromatic)
2- Red/Green pathway is L-M cones
3- Blue/Yellow pathway S-L+M cones

this gives us different axis in colour

Question 12

Which colour pathway in the retinal ganglion cells is key in telling us about the intensity of light in our environment?

Answer 12

Achromatic L+M pathway

Question 13

Which colour system does this belong to
[L+M] ?

Answer 13

Achromatic

Question 14

What is the selective absorption of electromagnetic radiation (photons) using cone photoreceptors containing unique photopigment.

Answer 14

Detection

Question 15

What is the relative activity across different cone types necessary to discriminate between lights of different wavelength. Single receptor type is not sufficient we need multiple,?

Answer 15

Discrimination

Question 16

What is the recombination of colour signals from retinal photoreceptors to create colour-opponent mechanisms?

Answer 16

Colour appearance

Question 17

Herrings idea of opponent colours.
All colours in the inner circle can be represented by the two pairs of opposing colours (red/green & blue/yellow).

Answer 17

Question 18

what is colour vision useful for?

Answer 18

for staying out of sight camouflage

brightness cue
colour cue
textual cue

These all match to the animals surroundings

eating,
foriging
having sex/ mate selection

Question 19

Colour vision - the case for eating and having sex

The fact that colour vision has evolved in so many different species suggests that it bestows a selection advantage.

Examples include animals that forage for food, which are known as?

Answer 19

Frugivores

-Fruit is much easier to identify if you have a well developed colour system (evolutionary advantage)
-The strawberry is much easier to identify when colour information is present. It is also easier to judge the ripeness of fruit, i.e. it suitability for consumption, using colour information

Question 20

what are the 3 basic stages to colour vision?

Answer 20

Detection
Discrimination
Colour appearance

Question 21

True of false:
Colour is used in some bird mating rituals?

Answer 21

True

-Their bright and vibrant colours are taken as an indicator of genetic health
-Need good colour vision to see displays (evolved eyes)

Question 22

Variations in colour perception:
Name the colour systems these animals have

Answer 22

monochromatic, dichromatic, trichromatic

Question 23

whales, seals, and dolphins are all…

Answer 23

monochromatic

Question 24

dogs, cats and cows are all…

Answer 24

dichromatic

Question 25

gorillas, macaques, baboons, and humans are all...

Answer 25

trichromatic

Question 26

Spectral sensitivity of cone photopigments varies between species The stomatopod crustaceans (e.g. mantis shrimp) has the record of how many different photopigments?

Answer 26

15

Question 27

Variations in colour perception: Bees have photopigments that extend into which type of range?

Answer 27

ultraviolet range

Question 28

Variations in colour perception: Why do bees have photopigments that extend into ultraviolet light range?

Answer 28

Photo B which is under Ultraviolet light shows this colour perception offers a visual advantage to the bee, displaying the flowers larger central target to collect pollen quicker.

Question 29

Variations in colour perception: What are the 2 main uses of colour photopigments?

Answer 29

Tells you about the type of wavelengths in the environment (different colours) and To initiate certain types of behaviour from the animal (eg. Cabbage white butterfly)

Question 30

Variations in colour perception: Important to distinguish between wavelength discrimination and wavelength specific behaviour e.g. when shining light on a cabbage white butterfly which 3 behaviours are produced: - ... response triggered by wavelengths around 350nm - ... response triggered by wavelengths around 460 & 600nm - ... laying triggered by wavelengths around 540nm

Answer 30

- flight response triggered by wavelengths around 350nm - feeding response triggered by wavelengths around 460 & 600nm - egg laying triggered by wavelengths around 540nm

Question 31

it is possible to use a single photopigment to create more than one type of functional cone by placing what in the light path of the receptor?

Answer 31

coloured oil droplet (filter) Some birds/ reptiles use this approach but there is a debate whether it creates functionally distinct receptor types or simply sharpens spectral sensitivity (i.e. reduced bandwidth of wavelengths) of the receptor

Question 32

Evolution of colour vision in primates: Colour visions shows diversity within the primate lineage ~100 million years ago Africa and South America split due to movement of tectonic plates this created a new evolutionary path for new world (South American) and old world primates To go from dichromatic (most Teresian mammals) to trichromatic (primates/ humans) what are the 3 things we need?

Answer 32

1) To acquire a new photopigment with unique spectral sensitvity 2) Express photopigment in class of cones 3) Develop neural mechanism that compares the output to other types of cones (this is missing in birds)

Question 33

What are the 5 distinct families of visual pigments in vertebrates?

Answer 33

LWS, MWS (RH2), SWS2, SWS1 and RH1 we have a modified opsin giving us better colour vision

Question 34

Fill in the sentence: Wavelength discrimination cannot be achieved using a ... photopigment or cone class, since wavelength and intensity are confounded (...).

Answer 34

single, univariance

Question 35

Fill in the sentence: Relative activity across different classes of ...photoreceptors determines colour perception.

Answer 35

cone

Question 36

Fill in the sentence: ... may have changed very little in the transition from a dichromatic to trichromatic colour system.

Answer 36

Retinal circuity

Question 36

Fill in the sentence: Many animal species have some form of colour vision and it is offers selective advantages in ..., ..., and ....

Answer 36

food foraging, predator detection a mate selection

Question 37

Fill in the sentence: Change from dichromatic to trichromatic vision in OW primates was mediated by ... linked gene duplication in the OW primate lineage.

Answer 37

X-linked

Question 38

Fill in the sentence: New World monkeys have taken a different route to trichromacy: ... gain trichromacy as a result of X-chromosome inactivation (or polymorphism).

Answer 38

heterozygous females

Question 39

Fill in the sentence: ... can institute ... vision in adult dichromatic primates. Rapid onset of trichromatic vision suggests pre-existing, requisite neural mechanisms.

Answer 39

Gene therapy, trichromatic

Question 40

Evolution of colour vision in primates:

Answer 40

The colour vision of man and Old World monkeys depends on two subsystems that remain parallel and independent at early stages of the visual pathway. 1. The primordial or ancient subsystem, which is shared with most mammals, depends on a comparison of the rates of photon catch in the short (S)- and middle (M)-wave cones; this system exists almost exclusively for colour vision. Humans and OW Primates [S-[L+M)] 2. The second subsystem depends on a comparison of the rates of photon catch in the long (L)- and middle (M)-wave receptors. At the early stages of the visual pathway, this chromatic information is carried by a channel that is also sensitive to spatial contrast. Humans and OW Primates (L-M). Its an old circuit readily available for usage. We cannot have the optic nerve too big because it stops the eye from moving and creates a hole in your visual field

Question 41

Retinal circuits that support trichromatic vision in humans have changed very little. Only significant evolutionary event was the acquisition of a new cone type which is the?

Answer 41

long wavelelength photopigment This arose from the phylogenetically recent duplication of a gene on the X-chromosome,

Question 42

New world primates: Do new world primates have trichromatic vision? The gene for expressing photopigment is on which chromosome?

Answer 42

X chromosome The gene on female mammals is XX

Question 43

New world primates - only females have trichromatic vision (2/3 of population) have a single gene, but it is polymorphic. What does this mean?

Answer 43

It has 3 alleles that generate a single photopigment generated at peak sensitivity of either (can be expressed) 535, 550 & 563nm.

Question 44

Female mammals are genetic mosiacs. What happens during embryonic development to avoid over expression of genes in female mammals?

Answer 44

selectively inactivate one of the two genes on the x-chromosome (lionisation) New World monkeys have taken a different route to trichromacy: heterozygous females gain trichromacy as a result of X-chromosome inactivation, which ensures that different photopigments are expressed in two subsets of retinal photoreceptor.

Question 45

Evolutionary sequence for colour vision:

Answer 45

Question 46

Monkeys were given the missing opsin photopigment and they could now see trichomatic colours immediately. True of false?

Answer 46

True