Taxis

The word taxis is also the plural form of the word taxi.

A taxis (plural taxes, pronounced "takseez") is an innate behavioral response by an organism (or cell) to a directional stimulus (a stimulus from a particular direction) whereby an organism moves (orientation movement) either towards (positive taxis) or away from (negative taxis) the stimulus. A taxis differs from a turning response or tropism in that the organism has mobility and demonstrates guided movement to or away from the stimulus (Kendeigh, 1961). For example, flagellate protozoans of the Genus Euglena move towards a light source. Here the directional stimulus is light, and the orientation movement is towards the light. This reaction or behaviour is a positive one to light and specifically termed a positive phototaxis. Phototaxis, then, is a response to a light stimulus. Many other types of taxes that have been identified, and named using one of the following prefixes to specify the stimulus eliciting a response:

baro- – pressure. See barotaxis

chemo- – chemical, See chemotaxis

galvano- – current (electricity)

geo- – gravity. See geotaxis

hydro- – moisture. See hydrotaxis

photo- – light. See phototaxis

rheo- – current (flow). See rheotaxis

thermo- – temperature. See thermotaxis

thigmo- – contact (touch). See thigmotaxis

Depending on the type of sensory organs present, taxes can be classified as klinotaxes, where an organism continuously samples the environment to determine the direction of a stimulus, tropotaxes, where bilateral sense organs are utilized to determine the stimulus direction, and telotaxes, similar to tropotaxes but a single organ suffices to establish the orientation movement.

See also: haptotaxis, durotaxis, kinesis.

Reference

Kendeigh, S. Charles. 1961. Animal Ecology. Prentice-Hall, Inc., Englewood Cliffs, N.J., 468 p.

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