Vision and the role of colour Flashcards
what is meant by the term compound eye
an eye consisting of an array of numerous small visual units, as found in insects and crustaceans.
outline the structure of a compound eye
= the cornea is composed of a number of individual ommatidia (individual optical unit of the compound eye)
= each ommatidia has its own lens and nerve fibre
= all nerve fibres converge to form the optic nerve
what are the two functions of the ommatidium/compound eye
1) optical = light gathering
2) sensory = transform light into electrical energy
outline the structure of the ommatidium
- cornea
- crystalline cone
- upper iris cells
- matrix cells of cornea
- lower iris cells
- sensory cells
- rhabdom
- axons which form the optic nerve
outline the corneal lens structure
a hexagonal facet formed by a transparent cuticle which forms a lens which is usually biconvex and has a protective role
outline the crystalline cone structure
lies benath the lens and functions as a secondary lens consisting of a group of four semper cells and boarded by pigment cells
outline what retinula cells are
they are the photoreceptive part of the eye at the base of each ommatidium
= 7-9 cells arranged to leave a central core space in the centre of the ommatidium
= each projects microvilli into this space which are the light detecting parts of the cell (the rhabdomere)
outline the primary and secondary pigment cells of the eye
primary = surround the crystalline cone
secondary = surround the retinula cells
they seperate each ommatidia from the neighbouring one ensuring only light paralell to long axis of the ommatidium reaches the visual cells and triggers nerve impulses
outline adaptations to the insect eye for nocturnal vision and what these are called
sensory receptor cells of most diurnal insects end close to the lens = apposition eyes
night flying insects tend to have a clear zone between these lenses and sensory components in which pigments do not extend the entire length of the cell = super position eyes
= this means light can enter through the clear zone from neighbouring ommatidia this means less photons are needed for vision, such as at night
what is the range of wavelengths for insect photoreceptor cells
~330-640nm
= ancestral photoreceptors = UV, blue and green
visual pigments may vary in different parts of the eye
outline spectral and polarisation sensitivity in different insect spp
some insects such as lepidoptera, hymenoptera and coleoptera have 4/5 colour receptor types
= peak sensitivity in butterflies = 620-640 nm (deep red and red)
= larvae and adults use different opsins (proteins involoved in photoreception)
who is Charles henry turner and Karl von Frisch
C= first to discover bees can see both colour and pattern and used these to create memory picture, also that they were short sighted so need to hover close to an object before seeing it properly
K = discovered bees can recognise compass direction by the sun, by polarisation pattern of blue sky and by the earths magnetic field, whereby the sun is used as the main compass
outline what polarised like is
light waves vibrate at right angles to the direction of travel
polarised light = when a high proportion of these vibrations are all across one plane
plane- polarised light = all vibrations are across one plane
therefore light from blue sky is polarised and varies with sun position and can be used for navigation by hymenoptera
what are ocelli and their functions
they are simple eyes present in adult insects and larvae of hemimetabola and vary in form (usually 1-3 stuated between the compound eyes)
= they regulate daily rhythms, respond to large, sudden changes in light intensity and detect horizon or roll
outline the structure of ocelli
consist of fiver seperate parts
1) corneal lens
2) corneagen layer
3) retinal cells
4) pigment cells
5) central nervous connections
what is a stemmata
= sometimes referred to as lateral ocelli which is INACCURRATE
- found in holometabolous larvae and adults of some insect orders
= it is made up of a biconvex lens, single cluster of photoreceptor cells with a vitreous or crystalline cor
how does the perception of colour change
depends on
- illumination
- spectral reflectance of object
- spectral receptor types
- neural processing
what is meant by structureal colour
light is reflected/transmitted due to the physical nature of surface
what are pigmentary colours
insects synthesis most pigements expect flavonoids and carotenoids from their diet
- sclerotisation = black/brown of hardened cuticle
- melanin
- pterins
- omnochromes
- tetrapyrroles
- quinones
outline physiological colour change
short term and reversable
= changes in spacing between reflecting layers
= pigment movements
outline morphological colour change
= long term and formation of new pigments
- ontogenetic changes during development (aging or maturation etc)
- homochromy occurs when colour matches prodominant background colour
-
what are the significances of colour
1) predator avoidance
2) intraspecific recognition
how can colour be used for predator avoidance
- Crypsis – select background on which less conspicuous;
homochromy; countershading; disruptive colouration - Deimatic behaviour – coloured parts suddenly displayed (may
be associated with sound production); large eyespots - Deflection marks – small eyespots appear to deflect attention
from head of insect (c.f. deimatic behaviour) - Aposematic colouration – bright colouration to ‘advertise’
distastefulness due to produced/sequestered toxins - Mimicry – Batesian and Müllerian
how can colour be used for intraspecific recognition
Intraspecific recognition
* Important for many diurnal
insects
* 2 main functions:
i. Recognition of mates
ii. Recognition of conspecific
males
* Most understood in Odonata
and butterflies (Lepidoptera)
what is the significance of light production
- Principal role is sexual communication
- Two basic roles:
– Female sedentary and attracts male to herself (e.g. Lampyris)
– One sex (usually male) flies and flashes light in specific way
characteristic to species (Photuris and Photinus) - Behaviour of flashing changes after mating
- Phenogodidae may use light as defensive function
- Diptera larvae use light as lure to attract small insects into silk
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