Lecture #11

Lecture #11

Invertebrate visual pigments3/5/13

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Mathematical relationships

• Sensitivity ≈D2

• If D doubles sensitivity increases x4

• This is a quadratic increase - not an exponential increase

• Sensitivity ≈ exp (D) This would increase exponentially

Quadratic and exponential are both steeper than linear

Check out equation sheet for exam

Today

• Visual pigments in invertebratesBehavioral determination

• Diurnal and nocturnal color vision

Invertebrate visual pigments

Karl von Frisch• Nobel prize in

physiology, 1973• Studied the

sensory system of beesDetermined visual sensitivities from behavioral experiments

Eyes of a bee

Von Frisch bee training experimentTrained bees to come to a blue card by rewarding them with sugar water.

Sugar water

Do bees come back to blue card?

Doesn’t mean they can detect colors

Might only be sensing brightness

Bee color discrimination• “Asked” bees if they could tell blue

apart from many shades of gray• If they can discriminate blue, they will

visit only the blue card and not any gray ones

Color vision Monochromatic vision

Color discrimination

Try to train bee to different colors

If test the bees to different colors

Can see blue but confuse it with purple

Can distinguish blue from blue-green

Can see yellow but can’t tell apart from orange

Can tell blue apart from blue with UV light shining on it

UV

Questions?

• What experimental controls are needed?

• What visual pigments does a bee have?

What is the bee’s visual system??

Briscoe and Chittka 2001

/Yellow

Human visual pigments

Normal λmax = 420, 535, 565 nm

Spectral flowers

More sophisticated testing by creating flowers with narrow band light

Daumer 1956Lotto et al 2005

Set up test grid to see if can train bees to go to middle flowers

The data

Bees can correctly learn to feed at the middle flowers

Note: Some bees prefer one color

Were they trained to position or just color?

Once add 3rd color – bees choose by chance

Can they be trained to go to the corners?

Results

Conclusions

Ted talk

Bee training

Color discrimination is best if pigments overlap some but not too much

Human visual pigments

Cone pigments

Rod pigment

Color wheel

This color wheel is based on three primary colors:

R Y BThese are primaries for pigment colors.

The secondary colors are mixtures of primaries

O=R+YG=Y+BV=R+B

Bee color system

• Put bee color vision on color wheel

Green/Yellow

BlueUV

Primary

Blue-green

Bee violet

Bee purple

Secondary

Flower light reflectance

• Flowers appear yellow to us

• Often have central portion which has UV reflectance

UV Nectar guide

UV

Flowers in visible and UV light

Most diverse invertebrates are insects

• Live in many different habitatsUnder groundCaveAquaticForestField

• Live in different light conditionsDiurnal to nocturnal

Insect visual pigments

• Opsin protein bound to the chromophore• Insects have two chromophores

A1 11-cis retinal vitamin A1 carotene

A3 11-cis 3-hydroxyretinal xanthophylls

• In combination with same opsin, each chromophore makes a visual pigment which absorb at slightly different wavelengths

Compound eye = many ommatidia

Visual pigments are in rhabdoms

Photoreceptors

Rod Cone Octopus Insect

Ciliary Microvillar

Rhabdoms• Each visual cell

has a microvillar part

• The microvilli of all the visual cells project into the center to make the rhabdom

Rhabdoms• The microvilli

contain the visual pigment

• Absorption of light excites the visual cells

Bee ommatidiumUV B G

Spaethe and Briscoe 2005

Bees have compound eyes and ocelli

Ocelli are used for navigation and also contain UV opsins

Drosophila eyes

WT cinnabar

white sepia

800 ommatidia per eye

Drosophila ommatidium• There are 8

rhabdomeres that make up rhabdom6 are around center2 in center - one on top of the other

• Cells are numberedR1-6R7, R8

Drosophila visual pigments

Pigments are numbered Rh1-Rh6

Visual pigment arrangements The six outer rhabdomeres

(R1-R6) surround the two inner ones.

Inner ones are one on top of other, R7 and R8

The same visual pigment is in R1-R6

Rh1 - green

R1-R6 used for motion detection

Light

Drosophila visual pigment Rh1 is in most of rhabdomeres (R1-6)

Two combinations for R7/R8 cells

Visual pigment combinations in R7/R8

Rh2 is expressed only in ocelli

Rh2 is expressed in ocelli

R7/R8 cells are used for color vision

30% 70%

Individual ommatidia - stained for opsin

Rh1 / R1-R6

Rh4 / R7

Rh6 / R8

Three kinds of ommatidia

UV sensitive in dorsal rim

Three kinds of ommatidia

Pale

Yellow

UV

What spectral ranges are being compared?

Inverts are “usually” trichromatic

Drosophila

Many insects are trichromatic - UV, blue and green pigments

1=11-cis retinal3=11-cis 3-hydroxyretinal

Briscoe and Chittka 2001

All have UV pigments

UVblue

green

red

Present not recorded

Few dichromats - not correlated with lifestyle

UVblue

green

red

Present not recordedOwlfly diurnal

Cock roach nocturnal

A few have red or far red pigments

UVblue

green

red

Present not recorded

The phylogeny of the opsin gene sequences of insects fall into spectral groups

The spectral classes are older than the insect species

-just as vertebrate opsin classes are old

Butterflies have 8 rhabdomers like Drosophila

6 on outside are green sensitive

Two stacked rhabdomers

These can beblue/blueblue / uvuv/uv

But 9th cell below

Variation in long wavelength sensitivity of butterflies

A, alpineC, crepuscularD, desertN, nocturnalTF, trop forestTL temperate lowlands

GFV generalist flower visitor

SFV specialist flower visitor

GCF general carbohydrate forager

SP specialist predator

Evolution of red sensitivity in Lepidoptera

What is relationship of flower color with pollinator?

Bee Butterfly

Nocturnal moth

Bird

Hypotheses?

Seeing at night

Vertebrates have only one visual pigment which functions at night

One pigment can detect presence or absence of light

Land&Nilsson Table 2.1

Starlight 10-4 cd/m2

Streetlight 1 cd/m2

Sunlight 104 cd/m2

Kelber et al 2002

Hawkmoth Deilephila elphenor

Kelber et al 2002

Truly nocturnal

Feeds at darkest hours of night

Hovers in front of flower to gather nectar

Behavior experiments to test hawk moth visual capabilities

Train to feed from colored artificial flowersOffer blue or yellow and grayDecrease light intensity to see if can still distinguish color from gray

Train to blue flower

10-4 10-3 10-2 0.1 1 10-4 10-3 10-2 0.1 Light intensity (cd/m2)

Test with darker grays

Moths still pick the correct flower while humans do not

10-4 10-3 10-2 0.1 1 10-4 10-3 10-2 0.1 Light intensity (cd/m2)

Test with other colors

Humans start to confuse hues at low light intensities while moths do not. However, moths have trouble with color shade.

Can tell colors apart even in different illuminant light – color constancy

Train to green or turquoise flowers.

Invertebrate visual pigments

• Many invertebrates are trichromaticMost have UV to green sensitivitySome add red sensitivity and so could be tetrachromatic

• Many have specialized UV receptors that can detect polarized light

• Photoreceptors are very sensitive and can be used to see colors under very low light conditions