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Entomology > Vision and the role of colour > Flashcards

Vision and the role of colour Flashcards

1
Q

Compound eyes

A
  • cornea composed of no. of individual ommatidia
  • each ommatidium has own lens + nerve fibre
  • all nerve fibres converge to form optic nerve
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2
Q

Corneal lens

A

hexagonal facet formed by transparent cuticle that forms lens = biconvex

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3
Q

Crystalline cone

A

beneath lens + functions as secondary lens

consists of group of 4 ‘Semper cells’

bordered by pigment cells

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4
Q

Retinula cells

A

photoreceptive part of eye at the base of each ommatidium

retinula cells (7-9) arranged to leave central core space in centre of ommatidium

each retinula cell projects series of microvilli into space

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5
Q

what are microvilli in retinula cells

A

light detecting part of cells = rhabdomere

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6
Q

what do Rhabdomeres collectively form?

A

Rhabdom

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7
Q

what is stored at Rhabdom?

A

light-sensitive pigments e.g. rhodopsin

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8
Q

Pigment cells - primary and secondary

A
  • primary pigment cells = surround crystalline cone
  • secondary pigment cells = surround retinula cells
  • separate each ommatidia from neighbour
  • ensure only light parallel to long axis of ommatidium reaches visual cells + triggers nerve impulses
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9
Q

What happens when light enters ommatidium?

A

(what occurs down the ommatidium) light enters -> focused + directed -> focused and directed -> contain photopigments that respond to light with chemical cascade -> electrical impulses carried to insect brain

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10
Q

What doe pigment cells do?

A

isolate ommatidia from each other + prevent light passing between them

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11
Q

How many classes of retinula cells? how do they differ?

A

up to 5 classes of retinula cell differ in their spectral sensitivities (λ), including UV

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12
Q

Opsins

A

proteins that bind to light-reactive chemicals to underlie vision, phototaxis, circadian rhythms, and other light-mediated responses of organisms.

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13
Q

What direction do light waves vibrate at in relation to direction of travel?

A

light waves vibrate at right angles to direction of travel

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14
Q

polarised light

A

high proportion of vibrations in one plane

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15
Q

Plane-polarised

A

all vibrations in one plane

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16
Q

what is polarised light from sky detected by?

A

detected by straight rhabdomeres of few ommatidia

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17
Q

Ocelli

A

Present in adult insects + larvae of hemimetabola

vary in form - usually 1-3 situated between compound eyes

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18
Q

Function of Ocelli

A
  • regulate daily rhythms
  • respond to large, sudden changes in light intensity
  • detect horizon (Odonata) or roll (locusts)
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19
Q

Ocelli parts?

A

5 separate parts
1. Corneal lens
2. Corneagen layer
3. Retinal cells
4. Pigment cells
5. central nervous connections

20
Q

Stemmata (sing. Stemma)

A

found on holometabolous larvae + adults of some insect orders, e.g. Siphonaptera, Zygentoma, Strepsiptera

Biconvex lens, single cluster of photoreceptor cells (retinula), w/ vitreous or crystalline core

may represent simplified compound eyes

21
Q

Visual signals - colours result from? Observed light depends on? Perceived colour depends on?

A

can generate variety of light and colour signals

caused by physical structures + pigments

observed light depend on interaction of pigments + signals controlling generation of patterns during development

position of colour-producing molecules in relation to other structures may change colour perceived

some insects exhibit fluorescence + bioluminescence

22
Q

Perception of colour depends on?

A
  • illumination
  • spectral reflectance of object
  • spectral receptor types
  • neutral processing
23
Q

Colour ‘created’? (colour of insect)

A

white light falls on insect -> some wavelengths absorbed, remainder scattered -> colour

24
Q

all reflected

A

white

25
Q

all absorbed

A

black

26
Q

pigmentary

A

absorb/reflect due to molecular structure

27
Q

structural

A

reflect / transmit due to physical nature of surface

28
Q

what is light scattered by?

A

granules/irregularities on/in surface -> matt/pearly white

29
Q

interference colours produced by?

A

reflection in multi-layers

some colours reflected/transmitted -> green, blue, UV, iridescence, metallic colours (gold, silver, bronze)

30
Q

‘phototonic crystals’ (3D structures) produce?

A

coherent scattering -> additive colour mixing

31
Q

What pigments do insects not synthesise?

A

flavonoids (white/yellow) + carotenoids (blue, red, yellow) - from diet

32
Q

Pigmentary colours - Sclerotisation

A

black/brown of hardened cuticle

33
Q

Pigmentary colours - Melanin

A

black/brown; involved in immune response

34
Q

Pigmentary colours - Pterins

A

white/yellow/orange; often occur with omnochromes

35
Q

Pigmentary colours - Omnochromes

A

yellow/red/brown; absorb UV; visual screening pigments

36
Q

Pigmentary colours - Tetrapyrroles

A

bilins = blue/green; porphyrin = incl. haem

37
Q

Quinones

A

anthraquinones = violet/blue/green; aphins = red/purple

38
Q

Colour change - Physiological

A

short-term, reversible

  • changes in spacing between reflecting layers
  • pigment movements (night, temp)
39
Q

Colour change - morphological

A

long-term, formation of new pigments

  • ontogenetic changes during development (aging or maturation in Hemimetabola, e.g. Odonata)
  • Homochromy occurs when colour matches predominant background colour (fire, λ + intensity of incident light)
  • temp/humidity/crowding
40
Q

Significance of colour
1. Predator avoidance

A
  • crypsis
  • deimatic beh
  • deflection marks
  • aposematic colouration
  • mimicry
41
Q
  1. predator avoidance - crypsis
A

select background on which less conspicuous; homochromy; countershading; disruptive colouration

42
Q
  1. predator avoidance - Deimatic behaviour
A

coloured parts suddenly displayed (may be associated w/ sound production); large eyespots

43
Q
  1. predator avoidance - deflection marks
A

small eyespots appear to deflect attention from head of insect (c.f. deimatic beh)

44
Q
  1. predator avoidance - aposematic colouration
A

bright colouration to ‘advertise’ distastefulness due to produced/sequestered toxins

45
Q
  1. predator avoidance - mimicry
A

Batesian and Mullerian

46
Q

Significance of colour
2. Intraspecific recognition

A
  • important for many diurnal insects
  • 2 main functions: recognition of mates, recognition of conspecific males
  • most understood in Odonata and butterflies (Lepidoptera)
47
Q

Significance of light production

A

principal role = sexual communication

beh of flashing after mating

Entomology (12 decks)

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