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Biological Orientation Responses

Taxes and Kineses

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Taxes and kineses are simple orientation responses which can maintain an organism in a favorable environment.

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Taxes

• Taxes are movements by an animal towards or away from an environmental stimulus.

• Movement towards a stimulus is a positive taxis, and movement away from a stimulus is a negative taxis.

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Types of Taxes

The type of the stimulus is shown by prefixes:

• Photo • Geo• Hydro• Chemo• Thigmo• Thermo

• Light• Gravity• Water• Chemicals• Touch• Heat

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Examples of Taxes

•A maggot placed on a sheet of paper will move randomly on the paper if the light source is uniform.

•If a light is switched on coming from one direction only, the maggot will move away from the light. This is a negative phototaxis.

•The advantage of this taxis to the maggot (and many other small invertebrates) is that moving away from light will take the maggot to a place of shelter where predators will not be able to get at them.

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•The female silk moth releases a pheromone called bombykol. A male silk moth is able to detect single molecules of this substance and fly in the direction of the female in order to mate with her. He does this by having two antennae sensitive to the chemical on either side of his head. He will turn to whichever antennae detects the most bombykol.

• This is an example of positive chemotaxis.

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Positive Chemotaxis

White blood cells move towards the chemicals released by inflamed and damaged tissues.

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If the behaviour is movement in the direction of the stimulus or away from the stimulus then it is most likely a taxis.

How do I recognise a taxis?

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Kinesis

• A kinesis is a random movement response to an environmental stimulus that is not oriented toward or away from a stimulus. It is non-directional. (Like nastic responses in plants).

• The rate of movement of an animal varies with the intensity of the stimulus.

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Examples of Kinesis

Woodlice will move rapidly when in a dry environment, but will slow down or stop when the environment is damp. The rate of movement is directly proportional to the humidity (stimulus).

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Woodlice – orthokinesis and klineokinesis

Orthokinesis in woodlice is when the speed of woodlice movement. It is related to the intensity of the stimulus. The more intense the stimulus, the faster the woodlice move. For example if the humidity decreases in the environment the woodlice will move faster in order to find more favorable conditions (otherwise they risk drying out).

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Klineokinesis

• Klineokinesis in woodlice is when the amount of random turning is related to the intensity of the stimulation. The drier conditions become, the greater the rate of turning in woodlice.

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http://www.faunanet.gov.au/wos/activities/lifecycle/activity.cfm?groupid=16

2.      The larvae of sea squirts move deeper into the sea water as light intensity increases. They move until a shady spot is found. This is an example of ____________________. The larvae avoid UV damage from the sun by exhibiting this behaviour.

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How do I recognise a kinesis?

Does the stimulus vary in intensity or concentration? Is the animal altering its rate of movement?

If there is no obvious direction of the stimulus then the behaviour is likely to be a kinesis.