Polarisation vision

Question 1

dont say polarized light…

Answer 1

polarization of light

Question 2

define polarization vision

Answer 2

using polarization properties of light to distinguish fields of view of the same size and shape.

Question 3

what is linear polarization?

Answer 3

when the peaks and troughs of the electric and magnetic fields are aligned/in phase.
can he horizontal or vertically polarized based on orientation of electric field.

Question 4

what is circular polarization?

Answer 4

two electric waves oriented at a right angle, and out of phase, the resultant wave between them goes in a spiral.

Question 5

define angle and degree of polarisation

Answer 5

AoP - average direction that each wave is
pointed.
DoP - distribution of angles, given as a percentage. 0% if all random, non polarized.

Question 6

what 3 requirements are needed for polarization sensitivity?

Answer 6

1. visual pigment sensitive to polarization
2. photoreceptors must be aligned to provide constant and tractable information
   3 animal needs to process the information in a way which is relevant to beh. (even though humanscan see polarisation of light, it isnt beh relevant so we dont notice it).

Question 7

describe how retinol is dichroic.

Answer 7

Differential absorption of polarizations. Doesn’t absorb polrizations perpendicular to long axis of molecule.
It does absorb polarisations which are parallel to long axis. in this direction, electrons can oscillate with the electric field.

Question 8

what is the textbook explanation of polarisation absorbance?

Answer 8

proteins in membrane naturally rotate, so rhodopsin will become out of orientation with polarization direction, whereas other rhodopsin molecules will become aligned. if a flash of light bleaches rhodopsin, rotational diffusion causes recovery of absorbance.

Question 9

why might the textbook view not be correct?

Answer 9

all studies were done on rods, when actually cones are the sensitive ones to polarized light. also all studies done on Rana pipiens - frog, and there is no evidence for polarization sensitivity in this species.

Question 10

what is the evidence for polarization sensitivity?

Answer 10

1. side on illumination of the chromophore in a rod/cone, shows two different absorption spectra when illuminated parallel to rod and perpendicular to rod. the ratio of absorbances is the dichoric ratio, DR.

Question 11

what is the DR of UV cones and double cones?

Answer 11

approx 1.2

= 1:1.2

Question 12

what is the 2nd stage of detecting polarization of light

Answer 12

an ordered detector
eg regular photoreceptor mosaics in salmon and goldfish. Double cones arranged in 90 degree orientation to be able to compare angles of polarization.

Question 13

what evidence is there that cones dont undergo rotational diffusion

Answer 13

rhodopsin forms and ordered array of dimers in photoreceptors, suggesting they aren’t free to rotate.
cryo EM images show how chromophores are aligned within cones, and this alignment makes them sensitive to polarization.

Question 14

How is information regarding polarization sensitivity relayed to the brain?

Answer 14

Seen from electrophys recordings from that the optic nerve in salmon demonstrates polarization sensitivity in particular spectral channels. UV, MWS and LWS channels give highest PS values. max when polarization is vertical, least when horizontal.

Question 15

how does invert PS differ from vertebrate?

Answer 15

the microvilli are aligned, and are dichroic, and parallel to in coming light (in vertebrates, it is the chromphores which are aligned).
microvilli do not spin, due to different structure of opsins,which have a long tail and interact, not allowing them to spin. unsure if they form dimers. DR of 1.2

Question 16

which part of the insect eye is polarisation sensitive?

Answer 16

Dorsal Rim area. maps out the polarization patterns in the sky. cellular orientation change to match the overhead polarization pattern.
Many species have PS across the whole eye.

Question 17

what do insects use polarisation for?

Answer 17

orientation, to find water

Question 18

why are crustacean photoreceptors different to insect and vertebrate?

How is the info transduced?

Answer 18

they are intrinsically polarisation sensitive, as microvilli are layered at 90 degrees. gives 2 channels (1,4,5 vs 2,3,6,7) of Pol info to be compared.
each cell projects onto layers of the lamina in the brain, either epl1 or epl2. then monpolar cells M3 and M4 relay the info to the medulla.

Question 19

whats the difference betwee a cue and a signal?

Answer 19

cue - environmental eg colour of the sun. polarisation is a cue for navigation.
signal - under NS. eg use polarization for target discrimination.

Question 20

what causes polarization of light?

Answer 20

caused by raleigh scattering. angle of polarization is directly perpendicular to the sun. as the position of sun changes, band of strongest polarization changes, creating a predictable pattern which insects use to navigate.
underwater, the band of max pol surrounds the observer. sky polarization pattern enters the water through Snell’s window.

Question 21

is light polarized by reflection

Answer 21

AoP is parallel to the surface.

suggested recently that glass buildings create pol pollution to insects which use pol to identify water.

Question 22

examples of animals which use polarization to signal

Answer 22

cuttlefish

stomatopods’ maxillopods and uropods.

Question 23

when was polarisation sensitivity first seen in insects?

Answer 23

1920s, insects can only walk straight and navigate home if some blue sky is visible.
also observed by Karl von Frisch in 40s in honeybees.

Question 24

what is requires for insect polarization naviation?

Answer 24

only works if UV light is present as the DRA is UV sensitive.

Question 25

what did Rudgier Wehner discover?

Answer 25

-Saharan ants use sky polarization when navigating. join together path integration and celestial cues.
- noticed that there is sometimes a 180 degree bimodial distribution of orientation data, in a choice test, which suggests they cannot absolutely tell the position of the sun.
-

Question 26

What have more careful studies of polarisation sensitivity shown?

Answer 26

ants showed 180 degree bimodial distribution when trained under a restricted skylight pattern and tested under full sky.
can cope with only a restricted skylight pattern if it is experienced for the whole foraging trip.

Question 27

how do dung beetles travel in a straight line?

Answer 27

use a variety of celestial and visual cues to roll balls in a straight line.
sun, moon, solar polarization, intensity gradient and milky way.
Moon creates polarization pattern used by nocturnal dung beetles. Use a heirarchy of cue information, which polarization dominates in crepuscular periods.

Question 28

which animals use a time compensated compass and what is that?

Answer 28

locusts, butterflies
navigate over much longer distances, so takes longer. therefore light intensity and colour ratios are changing so must incorporate this in the map in their brain.

Question 29

how is polarization information mapped in the locust brain?

Answer 29

polarization coding network is in the locust central complex of the brain.
Protocerebral bridge encodes directions. There is unusual columnar architecture - each column is tuned to a diff polarization. v efficient. activity in the PB is correlated to the orientation of the locust

Question 30

what can be used in polarisation experiments to deliver different levels of polarization?

Answer 30

use LCD to present different stimuli, therefore minimising interference by a human and other info changing.
present pattens on a LCD with glass removed to animal and observe colour changes if the see polarization.

Question 31

can animals see all polarization?

Answer 31

no there if a threshold in the angle and degree of polarization above which they can detect changes.

Question 32

Give an example of animals which create a polarization signal

Answer 32

1. Heliconus butterflies - irridescent patterns create polarisation. Exploited in mate choice.
2. haptosquillids (stomatopods)- use pol and structural colour as a visual signal. blue signals on 1st maxillipeds. 4 species have an innate preference for horizontal pol.

Question 33

describe a habitat which has pol glare

Answer 33

mudflat, light reflecting off water gets polarized.
increases contrast of animals against bright background creating silhouettes. advantageous to fiddler crabs: early detection of preds and conspecifics. Semi transparent claws boost intensity and pol contrast.

Question 34

describe an experiment investigating whether fiddler crabs can detect targets from further away if there is pol.

Answer 34

drag a dummy crab towards a real crab protecting its burrow.
3 stage response: 1. freeze, 2. home run, 3. burrow.
observed beh through different pol filters: unpol, vertical and horizontal. Vertical gave much more contrast.
found: detection distance enhanced by pol.
important to perform experiment in the natural environment.