Industrial robot - Wikipedia
An industrial robot is a robot system used for manufacturing. Industrial robots are automated, programmable and capable of movement on three or more axes.
phototaxis
An autonomous robot is a robot that acts without recourse to human control. The first autonomous robots environment were known as Elmer and Elsie "Elmer and Elsie (robots)"), which were constructed in the late 1940s by W. Grey Walter. They were the first robots in history that were programmed to "think" the way biological brains do and meant to have free will.[8] Elmer and Elsie were often labeled as tortoises because of how they were shaped and the manner in which they moved. They were capable of <anchor>phototaxis</anchor> which is the movement that occurs in response to light stimulus.[9]
Phototaxis - Wikipedia
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## Contents

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- (Top)

- [1Phototaxis in bacteria and archea](#Phototaxis_in_bacteria_and_archea)
- [2Phototaxis in protists](#Phototaxis_in_protists)
- [3Phototaxis in invertebrates](#Phototaxis_in_invertebrates)Toggle Phototaxis in invertebrates subsection  - [3.1Jellyfish](#Jellyfish)
  - [3.2Marine ragworm](#Marine_ragworm)
  - [3.3Insects](#Insects)
- [4Relation to magnetic fields](#Relation_to_magnetic_fields)
- [5See also](#See_also)
- [6References](#References)
- [7Further reading](#Further_reading)

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# Phototaxis

22 languages

- [العربية](https://ar.wikipedia.org/wiki/%D8%A7%D8%B3%D8%AA%D8%AC%D8%A7%D8%A8%D8%A9_%D8%B6%D9%88%D8%A6%D9%8A%D8%A9 "استجابة ضوئية – Arabic")
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From Wikipedia, the free encyclopedia

Directed movement of a motile cell or organism in response to light

[![](//upload.wikimedia.org/wikipedia/commons/thumb/8/86/Distribution_of_three-dimensional_phototaxis_in_the_tree_of_eukaryotes.jpg/440px-Distribution_of_three-dimensional_phototaxis_in_the_tree_of_eukaryotes.jpg)](/wiki/File:Distribution_of_three-dimensional_phototaxis_in_the_tree_of_eukaryotes.jpg)

**Distribution of three-dimensional phototaxis**

**in the tree of eukaryotes**[\[1\]](#cite_note-Jékely2009-1)

Red arrows indicate the likely point of origin of phototaxis in a given group. Question marks indicate uncertainties regarding independent or common origin.

**Phototaxis** is a kind of [taxis](/wiki/Taxis "Taxis"), or locomotory movement, that occurs when a whole [organism](/wiki/Organism "Organism") moves towards or away from a [stimulus](/wiki/Stimulus_(physiology) "Stimulus (physiology)") of [light](/wiki/Light "Light").[\[2\]](#cite_note-Martin1983-2) This is advantageous for [phototrophic](/wiki/Phototroph "Phototroph") organisms as they can orient themselves most efficiently to receive light for [photosynthesis](/wiki/Photosynthesis "Photosynthesis"). Phototaxis is called positive if the movement is in the direction of increasing light intensity and negative if the direction is opposite.[\[3\]](#cite_note-Menzel1979-3)

Two types of positive phototaxis are observed in [prokaryotes](/wiki/Prokaryote "Prokaryote"). The first is called **scotophobotaxis** (from the word " [scotophobia](/wiki/Scotophobia "Scotophobia")"), which is observed only under a microscope. This occurs when a bacterium swims by chance out of the area illuminated by the microscope. Entering darkness signals the cell to reverse [flagella](/wiki/Flagellum "Flagellum") rotation direction and reenter the light. The second type of phototaxis is true phototaxis, which is a directed movement up a gradient to an increasing amount of light. This is analogous to positive [chemotaxis](/wiki/Chemotaxis "Chemotaxis") except that the attractant is light rather than a chemical.

Phototactic responses are observed in many organisms such as _[Serratia marcescens](/wiki/Serratia_marcescens "Serratia marcescens")_, _[Tetrahymena](/wiki/Tetrahymena "Tetrahymena")_, and _[Euglena](/wiki/Euglena "Euglena")_. Each organism has its own specific biological cause for a phototactic response, many of which are incidental and serve no end purpose.

## Phototaxis in bacteria and archea

\[ [edit](/w/index.php?title=Phototaxis&action=edit&section=1 "Edit section: Phototaxis in bacteria and archea")\]

Part of a series onMicrobial and microbot movement[![](//upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Flagellum_from_a_gram-negative_bacterium_%28unlabelled%29.png/160px-Flagellum_from_a_gram-negative_bacterium_%28unlabelled%29.png)](/wiki/File:Flagellum_from_a_gram-negative_bacterium_(unlabelled).png)**[Microswimmers](/wiki/Microswimmer "Microswimmer")**

Taxa

- [Bacterial motility](/wiki/Bacterial_motility "Bacterial motility")


  - [run-and-tumble](/wiki/Run-and-tumble_motion "Run-and-tumble motion")
  - [twitching](/wiki/Twitching_motility "Twitching motility")
  - [gliding](/wiki/Gliding_motility "Gliding motility")

- [Protist locomotion](/wiki/Protist_locomotion "Protist locomotion")
  - [amoeboids](/wiki/Amoeboid_movement "Amoeboid movement")

[Taxis](/wiki/Taxis "Taxis")

- [Aerotaxis](/wiki/Aerotaxis "Aerotaxis") (oxygen)
- [Anemotaxis](/wiki/Anemotaxis "Anemotaxis") (wind)
- [Chemotaxis](/wiki/Chemotaxis "Chemotaxis") (chemicals)
- [Electrotaxis](/wiki/Electrotaxis "Electrotaxis")(electric current)
- [Gravitaxis](/wiki/Gravitaxis "Gravitaxis") (gravity)
- [Magnetotaxis](/wiki/Magnetotaxis "Magnetotaxis") (magnetic field)
- Phototaxis (light)
- [Rheotaxis](/wiki/Rheotaxis "Rheotaxis") (fluid flow)
- [Thermotaxis](/wiki/Thermotaxis "Thermotaxis") (temperature)

[Kinesis](/wiki/Kinesis_(biology) "Kinesis (biology)")

- [Kinesis](/wiki/Kinesis_(biology) "Kinesis (biology)")
  - [chemokinesis](/wiki/Chemokinesis "Chemokinesis")
  - [photokinesis](/wiki/Photokinesis "Photokinesis")

Microbots and particles

- [Microbotics](/wiki/Microbotics "Microbotics")
- [Nanorobotics](/wiki/Nanorobotics "Nanorobotics")
- [Nanomotors](/wiki/Nanomotors "Nanomotors")
- [DNA machine](/wiki/DNA_machine "DNA machine")
- [Microparticle](/wiki/Microparticle "Microparticle")
  - [Nanoparticle](/wiki/Nanoparticle "Nanoparticle")
  - [Janus particles](/wiki/Janus_particles "Janus particles")
  - [Self-propelled particles](/wiki/Self-propelled_particles "Self-propelled particles")
- [Swarm robotics](/wiki/Swarm_robotics "Swarm robotics")

Biohybrids

- [Biohybrid microswimmers](/wiki/Biohybrid_microswimmers "Biohybrid microswimmers")

- [bacterial biohybrids](/wiki/Biohybrid_microswimmer#Bacterial_biohybrids "Biohybrid microswimmer")
- [protist biohybrids](/wiki/Protist_locomotion#Biohybrid_microswimmers "Protist locomotion")
- [robotic sperm](/wiki/Robotic_sperm "Robotic sperm")

Collective motion

- [Active matter](/wiki/Active_matter "Active matter")
- [Bacteria collective motion](/wiki/Bacteria_collective_motion "Bacteria collective motion")
- [Collective cell migration](/wiki/Collective_cell_migration "Collective cell migration")
- [Quorum sensing](/wiki/Quorum_sensing "Quorum sensing")
- [Swarming motility](/wiki/Swarming_motility "Swarming motility")

**[Molecular motors](/wiki/Molecular_motor "Molecular motor")**

Biological motors

- [Flagellum](/wiki/Flagellum "Flagellum")
  - [archaellum](/wiki/Archaellum "Archaellum")
  - [cilium](/wiki/Cilium "Cilium")
  - [axoneme](/wiki/Axoneme "Axoneme")
  - [motor switch](/wiki/Flagellar_motor_switch "Flagellar motor switch")
  - [intraflagellar](/wiki/Intraflagellar_transport "Intraflagellar transport")
  - [evolution](/wiki/Evolution_of_flagella "Evolution of flagella")

- [Motor proteins](/wiki/Motor_protein "Motor protein")
  - [myosin](/wiki/Myosin "Myosin")
  - [kinesin](/wiki/Kinesin "Kinesin")
  - [dynein](/wiki/Dynein "Dynein")

[Synthetic motors](/wiki/Synthetic_molecular_motor "Synthetic molecular motor")

- [Synthetic molecular motor](/wiki/Synthetic_molecular_motor "Synthetic molecular motor")
- [Molecular modelling](/wiki/Molecular_modelling "Molecular modelling")
- [Molecular propeller](/wiki/Molecular_propeller "Molecular propeller")
- [molecular sensor](/wiki/Molecular_sensor "Molecular sensor")
- [molecular shuttle](/wiki/Molecular_shuttle "Molecular shuttle")
- [Molecular tweezers](/wiki/Molecular_tweezers "Molecular tweezers")

Related

- [Brownian motor](/wiki/Brownian_motor "Brownian motor")
- [Biochip](/wiki/Biochip "Biochip")

- [Endocytosis](/wiki/Endocytosis "Endocytosis")
- [Axophilic migration](/wiki/Axophilic_migration "Axophilic migration")

- [Cytoskeleton](/wiki/Cytoskeleton "Cytoskeleton")
  - [prokaryotic](/wiki/Prokaryotic_cytoskeleton "Prokaryotic cytoskeleton")

  - [eukaryotic](/wiki/Cytoskeleton#Eukaryotic_cytoskeleton "Cytoskeleton")
  - [cytoplasmic streaming](/wiki/Cytoplasmic_streaming "Cytoplasmic streaming")

- [Gray goo](/wiki/Gray_goo "Gray goo")
- [Mucilage](/wiki/Mucilage "Mucilage")
- [Molecular biophysics](/wiki/Molecular_biophysics "Molecular biophysics")
- [Molecular machine](/wiki/Molecular_machine "Molecular machine")
- [Nanoengineering](/wiki/Nanoengineering "Nanoengineering")
- [Non-motile bacteria](/wiki/Non-motile_bacteria "Non-motile bacteria")
- [Virophysics](/wiki/Virophysics "Virophysics")

- ![](//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png)[Category](/wiki/Category:Microswimmers "Category:Microswimmers")

- [v](/wiki/Template:Microbial_and_microbot_movement "Template:Microbial and microbot movement")
- [t](/w/index.php?title=Template_talk:Microbial_and_microbot_movement&action=edit&redlink=1 "Template talk:Microbial and microbot movement (page does not exist)")
- [e](/wiki/Special:EditPage/Template:Microbial_and_microbot_movement "Special:EditPage/Template:Microbial and microbot movement")

Phototaxis can be advantageous for [phototrophic](/wiki/Phototroph "Phototroph") [bacteria](/wiki/Bacteria "Bacteria") as they can orient themselves most efficiently to receive light for [photosynthesis](/wiki/Photosynthesis "Photosynthesis"). Phototaxis is called positive if the movement is in the direction of increasing light intensity and negative if the direction is opposite.[\[3\]](#cite_note-Menzel1979-3)

Two types of positive phototaxis are observed in [prokaryotes](/wiki/Prokaryote "Prokaryote") (bacteria and [archea](/wiki/Archea "Archea")). The first is called "scotophobotaxis" (from the word " [scotophobia](/wiki/Scotophobia "Scotophobia")"), which is observed only under a microscope. This occurs when a bacterium swims by chance out of the area illuminated by the microscope. Entering darkness signals the cell to reverse [flagella](/wiki/Flagellum "Flagellum") rotation direction and reenter the light. The second type of phototaxis is true phototaxis, which is a directed movement up a gradient to an increasing amount of light. This is analogous to positive [chemotaxis](/wiki/Chemotaxis "Chemotaxis") except that the attractant is light rather than a chemical.

Phototactic responses are observed in a number of bacteria and archae, such as _[Serratia marcescens](/wiki/Serratia_marcescens "Serratia marcescens")_. [Photoreceptor proteins](/wiki/Photoreceptor_protein "Photoreceptor protein") are light-sensitive proteins involved in the sensing and response to light in a variety of organisms. Some examples are [bacteriorhodopsin](/wiki/Bacteriorhodopsin "Bacteriorhodopsin") and bacteriophytochromes in some bacteria. See also: [phytochrome](/wiki/Phytochrome "Phytochrome") and [phototropism](/wiki/Phototropism "Phototropism").

Most prokaryotes (bacteria and archaea) are unable to sense the direction of light, because at such a small scale it is very difficult to make a detector that can distinguish a single light direction. Still, prokaryotes can measure light intensity and move in a light-intensity gradient. Some gliding filamentous prokaryotes can even sense light direction and make directed turns, but their phototactic movement is very slow. Some bacteria and archaea are phototactic.[\[4\]](#cite_note-4)[\[5\]](#cite_note-5)[\[1\]](#cite_note-Jékely2009-1)

In most cases the mechanism of phototaxis is a biased random walk, analogous to bacterial chemotaxis. [Halophilic](/wiki/Halophilic "Halophilic") archaea, such as _[Halobacterium salinarum](/wiki/Halobacterium_salinarum "Halobacterium salinarum")_, use sensory [rhodopsins](/wiki/Rhodopsin "Rhodopsin") (SRs) for phototaxis.[\[6\]](#cite_note-6)[\[7\]](#cite_note-7) Rhodopsins are [7 transmembrane](/wiki/7_transmembrane "7 transmembrane") proteins that bind [retinal](/wiki/Retinal "Retinal") as a [chromophore](/wiki/Chromophore "Chromophore"). Light triggers the [isomerization](/wiki/Isomerization "Isomerization") of retinal,[\[8\]](#cite_note-8) which leads to phototransductory signalling via a two-component phosphotransfer relay system. _Halobacterium salinarum_ has two SRs, [SRI](/wiki/SRI_(gene) "SRI (gene)") and SRII, which signal via the transducer proteins Htr1 and Htr2 (halobacterial transducers for SRs I and II), respectively.[\[9\]](#cite_note-9)[\[10\]](#cite_note-10) The downstream signalling in phototactic archaebacteria involves CheA, a [histidine kinase](/wiki/Histidine_kinase "Histidine kinase"), which phosphorylates the response regulator, CheY.[\[11\]](#cite_note-11) Phosphorylated CheY induces swimming reversals. The two SRs in Halobacterium have different functions. SRI acts as an attractant receptor for orange light and, through a two-photon reaction, a repellent receptor for near-UV light, while SRII is a repellent receptor for blue light. Depending on which receptor is expressed, if a cell swims up or down a steep light gradient, the probability of flagellar switch will be low. If light intensity is constant or changes in the wrong direction, a switch in the direction of flagellar rotation will reorient the cell in a new, random direction.[\[12\]](#cite_note-12) As the length of the tracks is longer when the cell follows a light gradient, cells will eventually get closer to or further away from the light source. This strategy does not allow orientation along the light vector and only works if a steep light gradient is present (i.e. not in open water).[\[1\]](#cite_note-Jékely2009-1)

Some cyanobacteria (e.g. _[Anabaena](/wiki/Anabaena "Anabaena")_, _[Synechocystis](/wiki/Synechocystis "Synechocystis")_) can slowly orient along a light vector. This orientation occurs in filaments or colonies, but only on surfaces and not in suspension.[\[13\]](#cite_note-13)[\[14\]](#cite_note-14) The [filamentous cyanobacterium](/wiki/Filamentous_cyanobacterium "Filamentous cyanobacterium") _Synechocystis_ is capable of both positive and negative two-dimensional phototactic orientation. The positive response is probably mediated by a bacteriophytochrome photoreceptor, TaxD1. This protein has two chromophore-binding GAF domains, which bind [biliverdin](/wiki/Biliverdin "Biliverdin") chromophore,[\[15\]](#cite_note-15) and a [C-terminal domain](/wiki/C-terminal_domain "C-terminal domain") typical for bacterial taxis receptors ( [MCP](/wiki/Methyl-accepting_chemotaxis_protein "Methyl-accepting chemotaxis protein") signal domain). TaxD1 also has two [N-terminal](/wiki/N-terminus "N-terminus") transmembrane segments that anchor the protein to the membrane.[\[16\]](#cite_note-16)[\[17\]](#cite_note-Light_matters:_Phototaxis_and_signa-17)[\[18\]](#cite_note-18) The photoreceptor and signalling domains are cytoplasmic and signal via a CheA/CheY-type signal transduction system to regulate motility by type IV pili.[\[19\]](#cite_note-19) TaxD1 is localized at the poles of the rod-shaped cells of _[Synechococcus elongatus](/wiki/Synechococcus_elongatus "Synechococcus elongatus")_, similarly to MCP containing chemosensory receptors in bacteria and archaea.[\[20\]](#cite_note-20) How the steering of the filaments is achieved is not known. The slow steering of these cyanobacterial filaments is the only light-direction sensing behaviour prokaryotes could evolve owing to the difficulty in detecting light direction at this small scale.[\[1\]](#cite_note-Jékely2009-1)

[![](//upload.wikimedia.org/wikipedia/commons/thumb/6/64/Types_of_photobehavior_found_in_prokaryotes.jpg/370px-Types_of_photobehavior_found_in_prokaryotes.jpg)](/wiki/File:Types_of_photobehavior_found_in_prokaryotes.jpg)

**Types of photobehavior found in prokaryotes**[\[21\]](#cite_note-Wilde2017-21)

Top: photophobic and scotophobic responses involving random tumbling or 180° motility reversals induced by sudden changes in the light environment experienced by the cells.

Middle: photokinesis involving changes in speed induced by changing light intensity. In patchy light environments, positive photokinesis results in accumulation in low light areas (and vice versa for negative photokinesis).

Bottom: true phototaxis results in movement towards or away from a light source, but is not a response to a light gradient. Direction of parallel illumination is indicated by the yellow arrows.

Spaces between the filled circles represent equal time intervals.

The ability to link light perception to control of motility is found in a very wide variety of prokaryotes, indicating that this ability must confer a range of physiological advantages.[\[22\]](#cite_note-Häder1987-22)[\[23\]](#cite_note-Armitage2003-23) Most directly, the light environment is crucial to phototrophs as their energy source. Phototrophic prokaryotes are extraordinarily diverse, with a likely role for [horizontal gene transfer](/wiki/Horizontal_gene_transfer "Horizontal gene transfer") in spreading phototrophy across multiple phyla.[\[24\]](#cite_note-24) Thus, different groups of phototrophic prokaryotes may have little in common apart from their exploitation of light as an energy source, but it should be advantageous for any phototroph to be able to relocate in search of better light environments for photosynthesis. To do this efficiently requires the ability to control motility in response to integrated information on the intensity of light, the spectral quality of light and the physiological status of the cell. A second major reason for light-controlled motility is to avoid light at damaging intensities or wavelengths: this factor is not confined to photosynthetic bacteria since light (especially in the UV region) can be dangerous to all prokaryotes, primarily because of DNA and protein damage [\[25\]](#cite_note-25) and inhibition of the translation machinery by light-generated reactive oxygen species.[\[26\]](#cite_note-26)[\[21\]](#cite_note-Wilde2017-21)

Finally, light signals potentially contain rich and complex information about the environment, and the possibility should not be excluded that bacteria make sophisticated use of this information to optimize their location and behavior. For example, plant or animal pathogens could use light information to control their location and interaction with their hosts, and in fact light signals are known to regulate development and virulence in several non-phototrophic prokaryotes.[\[27\]](#cite_note-27)[\[28\]](#cite_note-28) [Phototrophs](/wiki/Phototroph "Phototroph") could also benefit from sophisticated information processing, since their optimal environment is defined by a complex combination of factors including light intensity, light quality, day and night cycles, the availability of raw materials and alternative energy sources, other beneficial or harmful physical and chemical factors and sometimes the presence of symbiotic partners. Light quality strongly influences specialized developmental pathways in certain [filamentous cyanobacteria](/wiki/Filamentous_cyanobacteria "Filamentous cyanobacteria"), including the development of motile [hormogonia](/wiki/Hormogonia "Hormogonia") and nitrogen-fixing [heterocysts](/wiki/Heterocysts "Heterocysts").[\[29\]](#cite_note-29) Since hormogonia are important for establishing symbiotic partnerships between cyanobacteria and plants, and heterocysts are essential for nitrogen fixation in those partnerships, it is tempting to speculate that the cyanobacteria may be using light signals as one way to detect the proximity of a plant symbiotic partner. Within a complex and heterogeneous environment such as a phototrophic biofilm, many factors crucial for growth could vary dramatically even within the limited region that a single motile cell could explore.[\[30\]](#cite_note-30)[\[31\]](#cite_note-31) We should therefore expect that prokaryotes living in such environments might control their motility in response to a complex signal transduction network linking a range of environmental cues.[\[21\]](#cite_note-Wilde2017-21)

The photophobic response is a change in the direction of motility in response to a relatively sudden increase in illumination: classically, the response is to a temporal change in light intensity, which the bacterium may experience as it moves into a brightly illuminated region. The directional switch may consist of a random selection of a new direction (‘tumbling’) or it may be a simple reversal in the direction of motility. Either has the effect of repelling cells from a patch of unfavorable light. Photophobic responses have been observed in prokaryotes as diverse as _[Escherichia coli](/wiki/Escherichia_coli "Escherichia coli")_, [purple photosynthetic bacteria](/wiki/Purple_bacteria "Purple bacteria") and [haloarchaea](/wiki/Haloarchaea "Haloarchaea").[\[32\]](#cite_note-32)[\[23\]](#cite_note-Armitage2003-23)[\[21\]](#cite_note-Wilde2017-21)

The scotophobic (fear of darkness) response is the converse of the photophobic response described above: a change in direction (tumbling or reversal) is induced when the cell experiences a relatively sudden drop in light intensity. Photophobic and scotophobic responses both cause cells to accumulate in regions of specific (presumably favorable) light intensity and spectral quality. Scotophobic responses have been well documented in purple photosynthetic bacteria, starting with the classic observations of Engelmann in 1883,[\[33\]](#cite_note-33) and in cyanobacteria.[\[22\]](#cite_note-Häder1987-22) Scotophobic/photophobic responses in flagellated bacteria closely resemble the classic ‘biased random walk’ mode of bacterial chemotaxis, which links perception of temporal changes in the concentration of a chemical attractant or repellent to the frequency of tumbling.[\[34\]](#cite_note-34) The only significant distinction is that the scotophobic/photophobic responses involve perception of temporal changes in light intensity rather than the concentration of a chemical.[\[21\]](#cite_note-Wilde2017-21)

Photokinesis is a light-induced change in the speed (but not direction) of movement. Photokinesis may be negative (light-induced reduction of motility) or positive (light-induced stimulation of motility). Photokinesis can cause cells to accumulate in regions of favorable illumination: they linger in such regions or accelerate out of regions of unfavorable illumination. Photokinesis has been documented in cyanobacteria and purple photosynthetic bacteria.[\[22\]](#cite_note-Häder1987-22)[\[21\]](#cite_note-Wilde2017-21)

True phototaxis consists of directional movement which may be either towards a light source (positive phototaxis) or away from a light source (negative phototaxis). In contrast to the photophobic/scotophobic responses, true phototaxis is not a response to a temporal change in light intensity. Generally, it seems to involve direct sensing of the direction of illumination rather than a spatial gradient of light intensity. True phototaxis in prokaryotes is sometimes combined with social motility, which involves the concerted movement of an entire colony of cells towards or away from the light source. This phenomenon could also be described as community phototaxis. True phototaxis is widespread in eukaryotic [green algae](/wiki/Green_algae "Green algae"),[\[35\]](#cite_note-35) but among the prokaryotes it has been documented only in cyanobacteria,[\[22\]](#cite_note-Häder1987-22)[\[17\]](#cite_note-Light_matters:_Phototaxis_and_signa-17) and in social motility of colonies of the purple photosynthetic bacterium _[Rhodocista centenaria](/w/index.php?title=Rhodocista&action=edit&redlink=1 "Rhodocista (page does not exist)")_.[\[36\]](#cite_note-36)[\[21\]](#cite_note-Wilde2017-21)

## Phototaxis in protists

\[ [edit](/w/index.php?title=Phototaxis&action=edit&section=2 "Edit section: Phototaxis in protists")\]

[![](//upload.wikimedia.org/wikipedia/commons/thumb/4/41/Diversity_of_phototactic_protists.jpg/400px-Diversity_of_phototactic_protists.jpg)](/wiki/File:Diversity_of_phototactic_protists.jpg)

**Diversity of phototactic protists**[\[1\]](#cite_note-Jékely2009-1)

(a) [green alga](/wiki/Green_alga "Green alga") (b) [heterokont](/wiki/Heterokont "Heterokont") [zoospore](/wiki/Zoospore "Zoospore") (c) [cryptomonad](/wiki/Cryptomonad "Cryptomonad") [alga](/wiki/Alga "Alga")

(d) [dinoflagellate](/wiki/Dinoflagellate "Dinoflagellate") (e) _[Euglena](/wiki/Euglena "Euglena")_

See also: [Eyespot apparatus](/wiki/Eyespot_apparatus "Eyespot apparatus")

[![](//upload.wikimedia.org/wikipedia/commons/thumb/9/9d/Phototactic_movements_in_Volvox_rousseletii.webp/400px-Phototactic_movements_in_Volvox_rousseletii.webp.png)](/wiki/File:Phototactic_movements_in_Volvox_rousseletii.webp)

**Phototactic movements in the green algae [_Volvox rousseletii_](/wiki/Volvox "Volvox")**[\[37\]](#cite_note-37)

(a) Straight-ahead swimming in the dark

(b) A sudden dark-light switch causes the flagellar beating to reverse in the anterior hemisphere and the deceleration of the spheroid's forward movement (photophobic response)

(c) After approximately 2 seconds, only cells on the illuminated side of the anterior hemisphere of the rotating spheroid show the reversed flagellar beating direction, resulting in an acceleration of the spheroid's forward movement and turning toward the light source. Gravity assists the phototactic movements because it pulls more on the posterior hemisphere due to an anisotropic mass distribution caused by the denser daughter spheroids within the posterior hemisphere and probably also by the closer spacing of the somatic cells in the posterior hemisphere

Some [protists](/wiki/Protist "Protist") (unicellular eukaryotes) can also move toward or away from light, by coupling their locomotion strategy with a light-sensing organ.[\[38\]](#cite_note-38) [Eukaryotes](/wiki/Eukaryote "Eukaryote") evolved for the first time in the history of life the ability to follow light direction in three dimensions in open water. The strategy of eukaryotic sensory integration, sensory processing and the speed and mechanics of tactic responses is fundamentally different from that found in prokaryotes.[\[39\]](#cite_note-39)[\[1\]](#cite_note-Jékely2009-1)

Both single-celled and multi-cellular eukaryotic phototactic organisms have a fixed shape, are polarized, swim in a spiral and use cilia for swimming and phototactic steering. [Signalling](/wiki/Cell_signaling "Cell signaling") can happen via direct light-triggered [ion currents](/wiki/Ion_current "Ion current"), [adenylyl cyclases](/wiki/Adenylyl_cyclase "Adenylyl cyclase") or [trimeric](/wiki/Protein_trimer "Protein trimer") [G-proteins](/wiki/G-protein "G-protein"). The photoreceptors used can also be very different (see below). However, signalling in all cases eventually modifies the beating activity of cilia.[\[1\]](#cite_note-Jékely2009-1) The mechanics of phototactic orientation is analogous in all eukaryotes. A [photosensor](/wiki/Photosensor "Photosensor") with a restricted view angle rotates to scan the space and signals periodically to the cilia to alter their beating, which will change the direction of the [helical](/wiki/Helix "Helix") swimming trajectory. Three-dimensional phototaxis can be found in five out of the six eukaryotic major groups ( [opisthokonts](/wiki/Opisthokont "Opisthokont"), [Amoebozoa](/wiki/Amoebozoa "Amoebozoa"), [plants](/wiki/Plant "Plant"), [chromalveolates](/wiki/Chromalveolate "Chromalveolate"), [excavates](/wiki/Excavata "Excavata"), [rhizaria](/wiki/Rhizaria "Rhizaria")).[\[1\]](#cite_note-Jékely2009-1)

Pelagic phototaxis is present in [green algae](/wiki/Green_algae "Green algae") – it is not present in [glaucophyte algae](/wiki/Glaucophyte_algae "Glaucophyte algae") or [red algae](/wiki/Red_algae "Red algae").[\[1\]](#cite_note-Jékely2009-1) Green algae have a "stigma" located in the outermost portion of the [chloroplast](/wiki/Chloroplast "Chloroplast"), directly underneath the two [chloroplast membranes](/wiki/Chloroplast_membrane "Chloroplast membrane"). The stigma is made of tens to several hundreds of [lipid](/wiki/Lipid "Lipid") globules, which often form hexagonal arrays and can be arranged in one or more rows. The lipid globules contain a complex mixture of [carotenoid](/wiki/Carotenoid "Carotenoid") pigments, which provide the screening function and the orange-red colour,[\[40\]](#cite_note-40) as well as proteins that stabilize the globules.[\[41\]](#cite_note-41) The stigma is located laterally, in a fixed plane relative to the cilia, but not directly adjacent to the basal bodies.[\[42\]](#cite_note-42)[\[43\]](#cite_note-43) The fixed position is ensured by the attachment of the chloroplast to one of the ciliary roots.[\[44\]](#cite_note-44) The pigmented stigma is not to be confused with the photoreceptor. The stigma only provides directional shading for the adjacent membrane-inserted photoreceptors (the term "eyespot" is therefore misleading). Stigmata can also reflect and focus light like a concave mirror, thereby enhancing sensitivity.[\[1\]](#cite_note-Jékely2009-1)

In the best-studied green alga, _[Chlamydomonas reinhardtii](/wiki/Chlamydomonas_reinhardtii "Chlamydomonas reinhardtii")_, phototaxis is mediated by a [rhodopsin](/wiki/Rhodopsin "Rhodopsin") pigment, as first demonstrated by the restoration of normal photobehaviour in a blind mutant by analogues of the retinal [chromophore](/wiki/Chromophore "Chromophore").[\[45\]](#cite_note-45) Two archaebacterial-type rhodopsins, [channelrhodopsin](/wiki/Channelrhodopsin "Channelrhodopsin")-1 and -2,[\[46\]](#cite_note-46)[\[47\]](#cite_note-47) were identified as phototaxis receptors in _Chlamydomonas_.[\[48\]](#cite_note-Sineshchekov2002-48) Both proteins have an N-terminal 7-transmembrane portion, similar to archaebacterial rhodopsins, followed by an approximately 400 residue C-terminal membrane-associated portion. CSRA and CSRB act as light-gated cation channels and trigger depolarizing photocurrents.[\[48\]](#cite_note-Sineshchekov2002-48)[\[49\]](#cite_note-Berthold2008-49) CSRA was shown to localize to the stigma region using immunofluorescence analysis (Suzuki et al. 2003). Individual RNAi depletion of both CSRA and CSRB modified the light-induced currents and revealed that CSRA mediates a fast, high-saturating current while CSRB a slow, low-saturating one. Both currents are able to trigger photophobic responses and can have a role in phototaxis,[\[50\]](#cite_note-50)[\[49\]](#cite_note-Berthold2008-49) although the exact contribution of the two receptors is not yet clear.[\[1\]](#cite_note-Jékely2009-1)

As in all [bikonts](/wiki/Bikont "Bikont") (plants, chromalveolates, excavates, rhizaria), green algae have two cilia, which are not identical. The [anterior](/wiki/Anterior "Anterior") cilium is always younger than the [posterior](/wiki/Posterior_(anatomy) "Posterior (anatomy)") one.[\[51\]](#cite_note-51)[\[52\]](#cite_note-52) In every cell cycle, one [daughter cell](/wiki/Daughter_cell "Daughter cell") receives the anterior cilium and transforms it into a posterior one. The other daughter inherits the posterior, mature cilium. Both daughters then grow a new anterior cilium.[\[1\]](#cite_note-Jékely2009-1)

As all other ciliary swimmers, green algae always swim in a spiral. The handedness of the spiral is robust and is guaranteed by the chirality of the cilia. The two cilia of green algae have different beat patterns and functions. In Chlamydomonas, the phototransduction cascade alters the stroke pattern and beating speed of the two cilia differentially in a complex pattern.[\[53\]](#cite_note-53)[\[54\]](#cite_note-54) This results in the reorientation of the helical swimming trajectory as long as the helical swimming axis is not aligned with the light vector.[\[1\]](#cite_note-Jékely2009-1)

## Phototaxis in invertebrates

\[ [edit](/w/index.php?title=Phototaxis&action=edit&section=3 "Edit section: Phototaxis in invertebrates")\]

### Jellyfish

\[ [edit](/w/index.php?title=Phototaxis&action=edit&section=4 "Edit section: Jellyfish")\]

Positive and negative phototaxis can be found in several species of [jellyfish](/wiki/Jellyfish "Jellyfish") such as those from the genus [Polyorchis](/wiki/Polyorchis "Polyorchis"). Jellyfish use [ocelli](/wiki/Simple_eye_in_invertebrates "Simple eye in invertebrates") to detect the presence and absence of light, which is then translated into anti-predatory behaviour in the case of a shadow being cast over the ocelli, or feeding behaviour in the case of the presence of light.[\[55\]](#cite_note-55) Many tropical jellyfish have a [symbiotic](/wiki/Symbiosis "Symbiosis") relationship with [photosynthetic](/wiki/Photosynthesis "Photosynthesis") [zooxanthellae](/wiki/Zooxanthellae "Zooxanthellae") that they harbor within their cells.[\[56\]](#cite_note-56) The zooxanthellae nourish the jellyfish, while the jellyfish protects them, and moves them toward light sources such as the sun to maximize their light-exposure for efficient photosynthesis. In a shadow, the jellyfish can either remain still, or quickly move away in bursts to avoid [predation](/wiki/Predation "Predation") and also re-adjust toward a new light source.[\[57\]](#cite_note-:0-57)

This motor response to light and absence of light is facilitated by a chemical response from the ocelli, which results in a motor response causing the organism to swim toward a light source.[\[57\]](#cite_note-:0-57)

### Marine ragworm

\[ [edit](/w/index.php?title=Phototaxis&action=edit&section=5 "Edit section: Marine ragworm")\]

Phototaxis and [UV](/wiki/UV "UV")-avoidance of _[Platynereis dumerilii](/wiki/Platynereis_dumerilii "Platynereis dumerilii")_ larvae responding to UV-light (380 nm) from above See text body for further explanation.

Phototaxis has been well studied in the marine [ragworm](/wiki/Ragworm "Ragworm") _[Platynereis dumerilii](/wiki/Platynereis_dumerilii "Platynereis dumerilii")_. Both _Platynereis dumerilii_ [trochophore](/wiki/Trochophore "Trochophore") and its [metatrochophore](/wiki/Metatrochophore "Metatrochophore") larvae are positively phototactic. Phototaxis is mediated by [simple eyespots](/wiki/Simple_eye_in_invertebrates "Simple eye in invertebrates") that consists of a [pigment](/wiki/Pigment "Pigment") cell and a [photoreceptor cell](/wiki/Photoreceptor_cell "Photoreceptor cell"). The photoreceptor cell synapses directly onto [ciliated](/wiki/Ciliate "Ciliate") cells, which are used for swimming. The eyespots do not give spatial resolution, therefore the larvae are rotating to scan their environment for the direction where the light is coming from.[\[58\]](#cite_note-Jekely2008-58)

_Platynereis dumerilii_ larvae ( [nectochaete](/wiki/Nectochaete "Nectochaete")) can switch between positive and negative phototaxis. Phototaxis there is mediated by two pairs of more complex pigment cup eyes. These eyes contain more photoreceptor cells that are shaded by pigment cells forming a cup. The photoreceptor cells do not synapse directly onto ciliated cells or muscle cells but onto inter-neurons of a processing center. This way the information of all four eye cups can be compared and a low-resolution image of four pixels can be created telling the larvae where the light is coming from. This way the larva does not need to scan its environment by rotating.[\[59\]](#cite_note-Randel2014-59) This is an adaption for living on the bottom of the sea the lifestyle of the larva while scanning rotation is more suited for living in the open water column, the lifestyle of the trochophore larva. Phototaxis in the _Platynereis dumerilii_ larva has a broad spectral range which is at least covered by three [opsins](/wiki/Opsin "Opsin") that are expressed by the cup eyes:[\[60\]](#cite_note-Guehmann2015-60) Two rhabdomeric opsins[\[61\]](#cite_note-Randel2013-61) and a Go-opsin.[\[60\]](#cite_note-Guehmann2015-60)

[![](//upload.wikimedia.org/wikipedia/commons/thumb/e/e9/PlatynereisDumeriliiFemaleEpitoke.tif/lossy-page1-220px-PlatynereisDumeriliiFemaleEpitoke.tif.jpg)](/wiki/File:PlatynereisDumeriliiFemaleEpitoke.tif)

_[Platynereis dumerilii](/wiki/Platynereis_dumerilii "Platynereis dumerilii")_

However, not every behavior that looks like phototaxis is phototaxis: _Platynereis dumerilii_ nechtochate and metatrochophore larvae swim up first when they are stimulated with UV-light from above. But after a while, they change the direction and avoid the UV-light by swimming down. This looks like a change from positive to negative phototaxis (see video left), but the larvae also swim down if UV-light comes non-directionally from the side. And so they do not swim to or away from the light, but swim down,[\[62\]](#cite_note-Veraszto2018-62) this means to the center of gravity. Thus this is a UV-induced positive [gravitaxis](/wiki/Gravitaxis "Gravitaxis"). Positive phototaxis (swimming to the light from the surface) and positive gravitaxis (swimming to the center of gravity) are induced by different ranges of wavelengths and cancel out each other at a certain ratio of wavelengths.[\[62\]](#cite_note-Veraszto2018-62) Since the wavelengths compositions change in water with depth: Short (UV, violet) and long (red) wavelengths are lost first,[\[60\]](#cite_note-Guehmann2015-60) phototaxis and gravitaxis form a ratio-chromatic [depth gauge](/wiki/Depth_gauge "Depth gauge"), which allows the larvae to determine their depth by the color of the surrounding water. This has the advantage over a brightness based depth gauge that the color stays almost constant independent of the time of the day or whether it is cloudy.[\[63\]](#cite_note-Nilsson2009-63)[\[64\]](#cite_note-Nilsson2013-64)

In the diagram on the right, the larvae start swimming upwards when UV-light switched on (marked by the violet square). But later, they are swimming downward. The larval tracks are color coded: Red for upward and blue for downward swimming larvae. The video runs at double speed.[\[62\]](#cite_note-Veraszto2018-62)

- Phototaxis of _[Platynereis dumerilii](/wiki/Platynereis_dumerilii "Platynereis dumerilii")_ larvae: Some larvae show positive phototaxis by swimming towards the light. Other larvae show negative phototaxis by swimming away from the light. First, the light comes from left and then from the right side. When the light direction is switched the larvae turn. The side where the light is coming from is indicated by a white bar. The larvae display mixed phototaxis, some negatively phototactic larvae are tracked. The scale bar represents 2 mm.[\[59\]](#cite_note-Randel2014-59)

- _Phototaxis of [Platynereis dumerilii](/wiki/Platynereis_dumerilii "Platynereis dumerilii")_ larvae: The larvae turn when the light coming from the left is switched on. While the larvae turn they bend their body with their longitudinal muscles. The larvae show two dots on the head, which are the shading pigment of their adult cup eyes that mediate phototaxis. The direction where the light is coming from is indicated by white bars.[\[59\]](#cite_note-Randel2014-59)


### Insects

\[ [edit](/w/index.php?title=Phototaxis&action=edit&section=6 "Edit section: Insects")\]

[![](//upload.wikimedia.org/wikipedia/commons/thumb/6/62/Mothing_on_BukitRetakBrunei2.jpg/400px-Mothing_on_BukitRetakBrunei2.jpg)](/wiki/File:Mothing_on_BukitRetakBrunei2.jpg) Moths are positively phototactic

Positive phototaxis can be found in many flying [insects](/wiki/Insect "Insect") such as [moths](/wiki/Moth "Moth"), [grasshoppers](/wiki/Grasshopper "Grasshopper"), and [flies](/wiki/Fly "Fly"). _[Drosophila melanogaster](/wiki/Drosophila_melanogaster "Drosophila melanogaster")_ has been studied extensively for its innate positive phototactic response to light sources, using controlled experiments to help understand the connection between airborne [locomotion](/wiki/Animal_locomotion "Animal locomotion") toward a light source.[\[65\]](#cite_note-:1-65) This innate response is common among insects that fly primarily during the night utilizing [transverse orientation](/wiki/Transverse_orientation "Transverse orientation") vis-à-vis the light of the moon for orientation.[\[66\]](#cite_note-66) Artificial lighting in cities and populated areas results in a more pronounced positive response compared to that with the distant light of the moon, resulting in the organism repeatedly responding to this new [supernormal stimulus](/wiki/Supernormal_stimulus "Supernormal stimulus") and innately flying toward it.

Evidence for the innate response of positive phototaxis in _Drosophila melanogaster_ was carried out by altering the wings of several individual specimens, both physically (via removal) and genetically (via mutation). In both cases there was a noticeable lack of positive phototaxis, demonstrating that flying toward light sources is an innate response to the organisms' photoreceptors receiving a positive response.[\[65\]](#cite_note-:1-65)

Negative phototaxis can be observed in larval _drosophila melanogaster_ within the first three developmental [instar](/wiki/Instar "Instar") stages, despite adult insects displaying positive phototaxis.[\[67\]](#cite_note-:2-67) This behaviour is common among other species of insects which possess a flightless larval and adult stage in their life cycles, only switching to positive phototaxis when searching for [pupation](/wiki/Pupa "Pupa") sites. _[Tenebrio molitor](/wiki/Mealworm "Mealworm")_ by comparison is one species which carries its negative phototaxis into adulthood.[\[67\]](#cite_note-:2-67)

## Relation to magnetic fields

\[ [edit](/w/index.php?title=Phototaxis&action=edit&section=7 "Edit section: Relation to magnetic fields")\]

Under experimental conditions, organisms that use positive phototaxis have also shown a correlation with light and magnetic fields. Under [homogeneous](/wiki/Homogeneity_and_heterogeneity "Homogeneity and heterogeneity") light conditions with a shifting magnetic field, _Drosophila melanogaster_ larvae reorient themselves toward predicted directions of greater or lesser light intensities as expected by a rotating magnetic field. In complete darkness, the larvae orient randomly without any notable preference.[\[67\]](#cite_note-:2-67) This suggests the larvae can observe a visible pattern in combination with light.

## See also

\[ [edit](/w/index.php?title=Phototaxis&action=edit&section=8 "Edit section: See also")\]

![](//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png)

Wikimedia Commons has media related to [Phototaxis](https://commons.wikimedia.org/wiki/Category:Phototaxis "commons:Category:Phototaxis").

- [Photokinesis](/wiki/Photokinesis "Photokinesis")
- [Phototropism](/wiki/Phototropism "Phototropism") (more relevant to plants and fungi)

## References

\[ [edit](/w/index.php?title=Phototaxis&action=edit&section=9 "Edit section: References")\]

01. ^ [_**a**_](#cite_ref-Jékely2009_1-0) [_**b**_](#cite_ref-Jékely2009_1-1) [_**c**_](#cite_ref-Jékely2009_1-2) [_**d**_](#cite_ref-Jékely2009_1-3) [_**e**_](#cite_ref-Jékely2009_1-4) [_**f**_](#cite_ref-Jékely2009_1-5) [_**g**_](#cite_ref-Jékely2009_1-6) [_**h**_](#cite_ref-Jékely2009_1-7) [_**i**_](#cite_ref-Jékely2009_1-8) [_**j**_](#cite_ref-Jékely2009_1-9) [_**k**_](#cite_ref-Jékely2009_1-10) [_**l**_](#cite_ref-Jékely2009_1-11) [_**m**_](#cite_ref-Jékely2009_1-12)Jékely, Gáspár (2009). ["Evolution of phototaxis"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781859). _Philosophical Transactions of the Royal Society B: Biological Sciences_. **364** (1531): 2795–2808. [doi](/wiki/Doi_(identifier) "Doi (identifier)"): [10.1098/rstb.2009.0072](https://doi.org/10.1098%2Frstb.2009.0072). [PMC](/wiki/PMC_(identifier) "PMC (identifier)") [2781859](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781859). [PMID](/wiki/PMID_(identifier) "PMID (identifier)") [19720645](https://pubmed.ncbi.nlm.nih.gov/19720645).[![](//upload.wikimedia.org/wikipedia/commons/thumb/e/e1/CC_BY_icon.svg/50px-CC_BY_icon.svg.png)](/wiki/File:CC_BY_icon.svg) Material was copied from this source, which is available under a [Creative Commons Attribution 4.0 International License](https://creativecommons.org/licenses/by/4.0/).
02. **[^](#cite_ref-Martin1983_2-0)**Martin, E.A., ed. (1983), _Macmillan Dictionary of Life Sciences_ (2nd ed.), London: Macmillan Press, p. 362, [ISBN](/wiki/ISBN_(identifier) "ISBN (identifier)") [978-0-333-34867-3](/wiki/Special:BookSources/978-0-333-34867-3 "Special:BookSources/978-0-333-34867-3")
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65. ^ [_**a**_](#cite_ref-:1_65-0) [_**b**_](#cite_ref-:1_65-1)Gorostiza, E. Axel; Colomb, Julien; Brembs, Bjoern (3 August 2015). ["A decision underlies phototaxis in an insect"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5204122). _Open Biology_. **6** (12): 160229. [bioRxiv](/wiki/BioRxiv_(identifier) "BioRxiv (identifier)") [10.1101/023846](https://doi.org/10.1101%2F023846). [doi](/wiki/Doi_(identifier) "Doi (identifier)"): [10.1098/rsob.160229](https://doi.org/10.1098%2Frsob.160229). [PMC](/wiki/PMC_(identifier) "PMC (identifier)") [5204122](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5204122). [PMID](/wiki/PMID_(identifier) "PMID (identifier)") [28003472](https://pubmed.ncbi.nlm.nih.gov/28003472).
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67. ^ [_**a**_](#cite_ref-:2_67-0) [_**b**_](#cite_ref-:2_67-1) [_**c**_](#cite_ref-:2_67-2)Riveros, A.J.; Srygley, R.B. (2010), "Magnetic Compasses in Insects", _Encyclopedia of Animal Behavior_, Elsevier, pp. 305–313, [doi](/wiki/Doi_(identifier) "Doi (identifier)"): [10.1016/b978-0-08-045337-8.00075-9](https://doi.org/10.1016%2Fb978-0-08-045337-8.00075-9), [ISBN](/wiki/ISBN_(identifier) "ISBN (identifier)") [9780080453378](/wiki/Special:BookSources/9780080453378 "Special:BookSources/9780080453378"), [S2CID](/wiki/S2CID_(identifier) "S2CID (identifier)") [81357367](https://api.semanticscholar.org/CorpusID:81357367)

## Further reading

\[ [edit](/w/index.php?title=Phototaxis&action=edit&section=10 "Edit section: Further reading")\]

- Madigan, Michael T.; Martinko, John M. (2006). _Brock Biology of Microorganisms_ (11th ed.). Upper Saddle River, N.J.: Pearson/Prentice Hall. [ISBN](/wiki/ISBN_(identifier) "ISBN (identifier)") [978-0131443297](/wiki/Special:BookSources/978-0131443297 "Special:BookSources/978-0131443297").
- Jékely, G. (31 August 2009). ["Evolution of phototaxis"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781859). _Philosophical Transactions of the Royal Society B: Biological Sciences_. **364** (1531): 2795–2808. [doi](/wiki/Doi_(identifier) "Doi (identifier)"): [10.1098/rstb.2009.0072](https://doi.org/10.1098%2Frstb.2009.0072). [PMC](/wiki/PMC_(identifier) "PMC (identifier)") [2781859](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781859). [PMID](/wiki/PMID_(identifier) "PMID (identifier)") [19720645](https://pubmed.ncbi.nlm.nih.gov/19720645).
- Randel, Nadine; Jékely, Gáspár (23 November 2015). ["Phototaxis and the origin of visual eyes"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4685581). _Philosophical Transactions of the Royal Society B: Biological Sciences_. **371** (1685): 20150042. [doi](/wiki/Doi_(identifier) "Doi (identifier)"): [10.1098/rstb.2015.0042](https://doi.org/10.1098%2Frstb.2015.0042). [PMC](/wiki/PMC_(identifier) "PMC (identifier)") [4685581](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4685581). [PMID](/wiki/PMID_(identifier) "PMID (identifier)") [26598725](https://pubmed.ncbi.nlm.nih.gov/26598725).

- [v](/wiki/Template:Taxes_(biology) "Template:Taxes (biology)")
- [t](/wiki/Template_talk:Taxes_(biology) "Template talk:Taxes (biology)")
- [e](/wiki/Special:EditPage/Template:Taxes_(biology) "Special:EditPage/Template:Taxes (biology)")

Types of [taxes](/wiki/Taxis "Taxis") (directional movements in biology)

- _[Aerotaxis](/wiki/Aerotaxis "Aerotaxis")_ (stimulation by [oxygen](/wiki/Oxygen "Oxygen"))
- _Anemotaxis_ (by [wind](/wiki/Wind "Wind"))
- _Barotaxis_ (by [pressure](/wiki/Pressure "Pressure"))
- _[Chemotaxis](/wiki/Chemotaxis "Chemotaxis")_ (by [chemicals](/wiki/Chemical "Chemical"))
- _[Durotaxis](/wiki/Durotaxis "Durotaxis")_ (by [stiffness](/wiki/Stiffness "Stiffness"))
- _Electrotaxis_ or _Galvanotaxis_ (by [electric current](/wiki/Electric_current "Electric current"))
- _[Gravitaxis](/wiki/Gravitaxis "Gravitaxis")_ (by [gravity](/wiki/Gravity "Gravity"))
- _Hydrotaxis_ (by [moisture](/wiki/Moisture "Moisture"))
- _[Magnetotaxis](/wiki/Magnetotaxis "Magnetotaxis")_ (by [magnetic field](/wiki/Magnetic_field "Magnetic field"))
- _Phototaxis_ (by [light](/wiki/Light "Light"))
- _[Rheotaxis](/wiki/Rheotaxis "Rheotaxis")_ (by [fluid flow](/wiki/Fluid_flow "Fluid flow"))
- _[Thermotaxis](/wiki/Thermotaxis "Thermotaxis")_ (by changes in [temperature](/wiki/Temperature "Temperature"))
- _Thigmotaxis_ (by [physical contact](/wiki/Somatosensory_system "Somatosensory system"))

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