VISUAL SIGNALS Biological Science

What is vision? Light signals are detected by photoreceptors in the eye (in mammals, located on the retina at the back of the eye) Electrical signals are transmitted to the brain via nerves The brain processes these signals to form a ‘picture’

Light forms part of the electromagnetic spectrum The electromagnetic spectrum describes the spectrum of energy waves of different wavelengths

What do animals use vision for? Avoiding predators Looking for resources/food/water/prey Communication within groups Establishing dominance Avoiding conflict Mating rituals Co-operation in hunting or other tasks

Few animals have good colour vision. Most animals either see no colours, or only see the world as shades of blue and yellows. Squirrels and some primates can see red and green. Why do many organisms not require colour vision? What do they use instead? What is the significance of the colour yellow in biology?

Ultra-violet Some birds not only see more hues than we can, but they can also see ultraviolet colours, too. Insects can also see the ultra-violet part of the spectrum as well as yellow and blue light- so flowers often have markings in these wavelengths.

Infra-red Nocturnal animals have no colour vision but some of them are able to ‘see’ the part of the spectrum called the infra-red. These animals can ‘see’ a picture of warm objects. Snakes detect infra-red via special sense organs- small pits located on the head

Vision & behaviour within groups Communication Showing dominance/submission Communicating within group Courtship behaviour (plumage, changes in colour)

Why are some organisms brightly coloured, while others are not? Reasons for dull colourations Camouflage, either as predators or prey Reasons for bright colourations: To attract members of the opposite sex To show poisonous taste Batesian or Mullerian mimicry

Visual signals as a defence Camouflage Passive (permanent) Active- changes colours Illusions Disruptive patterning Appearing larger/threatening

Camouflage- predators Give 2 other examples of predators using camouflage.

Camouflage- prey Structural changes

Camouflage Also called cryptic colouration May be passive or active

Many fish have different colourings on their dorsal and ventral (top & bottom) sides, so that they are camouflaged when seen from below or above, as do penguins Prey species have paler bellies to give the appearance of being thinner

Disruptive patterning Zebras- predators (e.g. lions) are unable to distinguish individuals in the large group

Some organisms make themselves appear larger & more threatening. Many mammals erect their hairs to appear larger and more dangerous. e.g. Frill necked lizards display their frill to intimidate predators (it also helps with temperature regulation) Porcupines make their quills stand up when threatened to draw attention to them.

Visual display- mating rituals Male birds develop bright plumage and perform mating displays to attract females. Why are the females of the species generally less brightly coloured? Female baboons indicate oestrus with changes in colour/swelling Male fireflies send out flashes of light while in flight as a signal to the female fireflies. Different species of firefly use different flashing codes!

Some fish which live in deep water with very little light have light-producing organs on the sides of their bodies. The light is used to attract prey or scare away predators. Jellyfish use their transparency to avoid predators. Many jellyfish are also bioluminescent.