Gravitaxis

Gravitaxis (or geotaxis[1]) is a form of taxis characterized by the directional movement of an organism in response to gravity.[2]

There are a few different causes for gravitaxis. Many microorganisms have receptors like statocysts that allow them to sense the direction of gravity and to adjust their orientation accordingly. However, gravitaxis can result also from a purely physical mechanism so that organs for sensing the direction of gravity are not necessary. An example is given by microorganisms with a center of mass that is shifted to one end of the organism. Similar to a buoy, such mass-anisotropic microorganisms orient upwards under gravity. It has been shown that even an asymmetry in the shape of microorganisms can be sufficient to cause gravitaxis.[3]

Gravitaxis is different from gravitropism in a way that the latter is more about the growth response of an organism to gravity.

Taxis
Main article: Taxis

Taxis is a behavioral response of a cell or an organism to an external stimulus. The movement is characteristically directional. The movement may be positive or negative. A positive taxis is one in which the organism or a cell gravitates towards the source of stimulation (attraction). A negative taxis is when the organism or a cell moves away from the source of stimulation (repulsion).

Examples

It can be seen in many microorganisms including Euglena.[4] The response of planktonic larvae of Lithodes aequispinus (king crab) to gravity is another example of gravitaxis.[1] They show both positive and negative gravitaxis responses in a way that they move either upward (negative) or downward (positive). Gravitaxis can also be observed in Drosophila.[5]

Etymology

The term is coined from gravi- meaning gravity, and taxis or the movement of an organism in response to a stimulus.

See also

References
  1. Adams, C. F.; Paul, A. J. (February 1999). "Phototaxis and Geotaxis of Light-Adapted Zoeae of the Golden King Crab Lithodes aequispinus (Anomura: Lithodidae) in the Laboratory". Journal of Crustacean Biology. 19 (1): 106. doi:10.2307/1549552. JSTOR 1549552.
  2. "Gravitaxis - Biology-Online Dictionary". Retrieved 25 March 2018.
  3. ten Hagen, B.; Kümmel, F.; Wittkowski, R.; Takagi, D.; Löwen, H.; Bechinger, C. (2014). "Gravitaxis of asymmetric self-propelled colloidal particles". Nature Communications. 5 (1): 4829. arXiv:1409.6882. doi:10.1038/ncomms5829. PMID 25234416. S2CID 16768325.
  4. Häder, DP; Hemmersbach, R (2017). "Gravitaxis in Euglena". Euglena: Biochemistry, Cell and Molecular Biology. Advances in Experimental Medicine and Biology. Vol. 979. pp. 237–266. doi:10.1007/978-3-319-54910-1_12. ISBN 978-3-319-54908-8. PMID 28429325.
  5. Armstrong, JD; Texada, MJ; Munjaal, R; Baker, DA; Beckingham, KM (April 2006). "Gravitaxis in Drosophila melanogaster: a forward genetic screen". Genes, Brain and Behavior. 5 (3): 222–39. doi:10.1111/j.1601-183X.2005.00154.x. PMID 16594976.

The dictionary definition of gravitaxis at Wiktionary

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