W10: Invertebrate Physiology (Physiology Of Sight: Insect Vision) [Dr. Blair]

Question 1

Cambrian explosion attributes? (3)

Answer 1

• ~530-540Mya.
• Modern day Phyla emergence.
• Arthropods: Trilobites (extinct) were one of the first animals to have complex, compound vision.

Question 2

Types of eyes that insects have? (2)

Answer 2

• Simple eyes (ocelli).
• Compound eyes.

Question 3

Ocelli attributes? (5)

Answer 3

• Simple eyes.
• Found on the heads of insects.
• Positioned in a triangular arrangement between the compound eyes (often 3 ocelli).
• Help in light detection, stabilisation & orientation.
• Narrow field of view.

Question 4

Compound eyes attributes? (4)

Answer 4

• Composed of many ommatidia, each with its own lens.
• Produce a mosaic image of the environment.
• Wide/Panoramic field of view.
• For movement detection, image formation & colour vision.

Question 5

Ommatidia attributes? (2)

Answer 5

• Functional parts for vision forming the facet.
• Function independently to each other in apposition eyes.

Question 6

Some insects have a Pseudopupil. What’s a Pseudopupil?

Answer 6

= a false pupil that is an optical illusion seen in the compound eyes of some insects like the praying mantis.

Question 7

Components of ommatidia? (3)

Answer 7

• Lens.
• Rhabdom.
• Photoreceptors.

Question 8

Lens?

Answer 8

= consists of the cornea & cone.

Question 9

Cornea?

Answer 9

= outer structure that initially focuses light.

Question 10

Cone?

Answer 10

= structure in the lens that directs lights to the photoreceptors.

Question 11

Rhabdom?

Answer 11

= structure in the ommatidia where light absorption & channeling occurs.

Question 12

Photoreceptor?

Answer 12

= structure with retinula cells that contain pigments to detect light & convert it to electrical signals.

Question 13

Insect Imaging (Compound eyes): Apposition eyes attributes? (3)

Answer 13

• Type of compound eye that is optimised for bright light environments.
• Each ommatidium works independently to provide sharp & detailed vision.
• Highly effective for diurnal insects that are active during the day.

Question 14

Insect vision attributes? (7)

Answer 14

• Insects have photoreceptor cells in ommatidium (act as different wavelengths of light).
• High/Low resolution depends on the type of insect & number of ommatidium (act like pixels).
• Types of colour vision (2) come down to pigments (rhodopsins).
• Perceive a range of colours & UV light.
• More ommatidium = high resolution.
• Larger eye = more light.
• Trade-offs.

Question 15

Trade-off when it comes to vision: If an insect wants to increase its resolution, it needs to increase its ommatidia, but it will need a bigger eye, so what then?

Answer 15

Visual adaptations.

Question 16

Visual adaptation attributes? (2)

Answer 16

• Species dependent.
• Environmental pressures.

Question 17

Eg of visual adaptations?

Answer 17

Hairs in the eyes of bees that protect their eyes when foraging in pollen.

Question 18

Why do flowers have UV light?

Answer 18

To provide nectar guides for pollinators.

Question 19

Who sees the best?

Answer 19

Diurnal fliers, particularly dragonflies.

Question 20

Why do dragonflies have the greatest/exceptional vision? (2)

Answer 20

• High resolution (30 000 ommatidia).
• Divided eyes: dorsal & ventral.

Question 21

Dorsal eyes of Dragonflies?

Answer 21

= detect prey/predators against the bright sky.

Question 22

Ventral eyes of Dragonflies?

Answer 22

= detect prey/other objects against the ground or water.

Question 23

Types of colour vision in insects? (2)

Answer 23

• Dichromatic colour vision.
• Trichromatic colour vision.

Question 24

Dichromatic colour vision attributes? (3)

Answer 24

• Most insects like stink bugs.
• 2 colour pigments.
• Unable to discriminate all colours.

Question 25

Trichromatic colour vision attributes? (3)

Answer 25

- Some insects like bees & butterflies. - 3 colour pigments. - "True colour'.

Question 26

Sexual dimorphism in flies?

Answer 26

Male flies make their field of view as wide as possible through their "love spot' to search/detect female mates (aids in reproductive success).

Question 27

Who sees the least?

Answer 27

Nocturnal insects, especially moths.

Question 28

Why do nocturnal insects/moths see the least? (4)

Answer 28

- Low resolution. - High sensitivity to light. - Increased size of ommatidia, but fewer. - Triangular cornea to further capture & trap light.

Question 29

Why do nocturnal insects increase the size of their ommatidia but have fewer of them?

Answer 29

It helps with more light capture to be able to see at night.

Question 30

Advancing vision: Diurnal insects?

Answer 30

Apposition eye.

Question 31

Advancing vision: Nocturnal insects?

Answer 31

Superposition eyes.

Question 32

Superposition eyes attributes? (2)

Answer 32

- Nocturnal or crepuscular (active at dawn/dusk) insects. - Light from multiple ommatidia converge to enable vision in low light conditions.

Question 33

Dung beetles attributes? (4)

Answer 33

- Low resolution. - High sensitivity to light. - Navigate using celestial cues stars. - 1st insects to know how to use starlight for navigation.

Question 34

Why are insects attracted to light?

Answer 34

It's because of a phenomenon called positive phototaxis, where insects instinctively move toward light sources, but several reasons exist.

Question 35

How do lights in cities affect phototaxis?

Answer 35

Lights in cities negatively influence an insect's ability to navigate due to air pollution, which blocks light & stars.

Question 36

Super summary? (3)

Answer 36

- Vision origins (cambrian explosion, modern day arthropod diversity & vision). - The compound eye (ommatidia, seeing in colour, visual trade-off). - Vision (environment, visual adaptations, diurnal vs nocturnal).