Editing Chameleon (section)

==Change of color==
{{Further|Animal coloration|Signaling theory}}
Some chameleon species are able to change their [[animal coloration|skin coloration]]. Different chameleon species are able to vary their colouration and [[patterns in nature|pattern]] through combinations of pink, blue, red, orange, green, black, brown, light blue, yellow, turquoise, and purple.<ref name="NatGeog">{{cite web |archive-url=https://web.archive.org/web/20080820084937/http://magma.nationalgeographic.com/ngexplorer/0210/articles/mainarticle.html |author=Sharon Katz Cooper|title=Chameleons |publisher=National Geographic Explorer |url=http://magma.nationalgeographic.com/ngexplorer/0210/articles/mainarticle.html |archive-date=20 Aug 2008}}</ref> Chameleon skin has a superficial layer which contains pigments, and under the layer are cells with very small (nanoscale) [[guanine]] crystals. Chameleons change colour by "actively tuning the photonic response of a lattice of small guanine nanocrystals in the s-iridophores".<ref name=" Teyssier Saenko van der Marel Milinkovitch 2015"/> This tuning, by an unknown molecular mechanism, changes the wavelength of light reflected off the crystals which changes the colour of the skin. The colour change was duplicated ''[[ex vivo]]'' by modifying the [[osmolarity]] of pieces of white skin.<ref name="Teyssier Saenko van der Marel Milinkovitch 2015">{{cite journal |last1=Teyssier |first1=Jérémie |last2=Saenko |first2=Suzanne V. |last3=van der Marel |first3=Dirk |last4=Milinkovitch |first4=Michel C. |title=Photonic crystals cause active colour change in chameleons |journal=Nature Communications |volume=6 |issue=1 |date=10 March 2015 |issn=2041-1723 |doi=10.1038/ncomms7368 |pages=1–7<!--pagination maybe just for the offprint?-->|pmid=25757068 |pmc=4366488 |bibcode=2015NatCo...6.6368T }}</ref>

[[File:Colour change and iridophore types in panther chameleons.png|thumb|left|upright=2.2|Colour change and iridophore types in [[panther chameleon]]s: 
<br/>(a) Reversible colour change is shown for two males (m1 and m2): during excitation (white arrows), background skin shifts from the baseline state (green) to yellow/orange, and both vertical bars and horizontal mid-body stripe shift from blue to whitish (m1). Some animals (m2) have their blue vertical bars covered by red pigment cells.
<br/>(b) Red dots: time evolution in the CIE chromaticity chart of a third male with green skin in a high-resolution video; dashed white line: optical response in numerical simulations using a face-centered cubic (FCC) lattice of guanine crystals with lattice parameter indicated with black arrows.
<br/>(c) Haematoxylin and eosin staining of a cross-section of white skin showing the epidermis (ep) and the two thick layers of iridophores.
<br/>(d) TEM images of guanine nanocrystals in S-iridophores in the excited state and three-dimensional model of an FCC lattice (shown in two orientations).
<br/>(e) TEM image of guanine nanocrystals in D-iridophores.
<br/>Scale bars, 20&nbsp;mm ( c); 200&nbsp;nm (d,e).<ref name="Teyssier Saenko van der Marel Milinkovitch 2015"/>]]

Colour change in chameleons has functions in [[camouflage]], but most commonly in social signaling and in reactions to temperature and other conditions. The relative importance of these functions varies with the circumstances, as well as the species. Colour change signals a chameleon's physiological condition and intentions to other chameleons.<ref>{{cite journal |last1=Stuart-Fox |first1=D. |last2=Moussalli |first2=A. |doi=10.1371/journal.pbio.0060025 |title=Selection for Social Signalling Drives the Evolution of Chameleon Colour Change |journal=PLOS Biology |volume=6 |issue=1 |pages=e25 |year=2008 |pmid=18232740 |pmc=2214820 |doi-access=free }}</ref><ref>{{cite web |url=http://science.howstuffworks.com/animal-camouflage2.htm |title=How Animal Camouflage Works |publisher=How Stuff Works |first=Tom |last=Harris |date=18 May 2001 |access-date=2006-11-13}}</ref> Because chameleons are [[ectotherm]]ic, another reason why they change colour is to regulate their body temperatures, either to a darker colour to absorb light and heat to raise their temperature, or to a lighter colour to reflect light and heat, thereby either stabilizing or lowering their body temperature.<ref name="Walton Bennett 1993">{{cite journal | last1=Walton | first1=B. Michael | last2=Bennett | first2=Albert F. | title=Temperature-Dependent Color Change in Kenyan Chameleons | journal=Physiological Zoology | publisher=University of Chicago Press | volume=66 | issue=2 | year=1993 | issn=0031-935X | doi=10.1086/physzool.66.2.30163690 | pages=270–287| s2cid=80673490 }}</ref><ref>{{cite web |last1=Cook |first1=Maria |title=The Adaptations of Chameleons |url= https://sciencing.com/adaptations-chameleons-8771909.html |website=Sciencing |date=17 April 2018 |access-date=15 June 2020}}</ref> Chameleons tend to show brighter colours when displaying aggression to other chameleons,<ref>{{cite journal |last1=Ligon |first1=Russell A. |last2=McGraw |first2=Kevin J. |doi=10.1098/rsbl.2013.0892 |title=Chameleons communicate with complex colour changes during contests: different body regions convey different information |journal=Biology Letters |volume=9 |issue=6 |pages=20130892 |year=2013 |pmid=24335271 |pmc=3871380}}</ref> and darker colours when they submit or "give up".<ref>{{cite journal |last1=Ligon |first1=Russell A |doi=10.1007/s00265-014-1713-z |title=Defeated chameleons darken dynamically during dyadic disputes to decrease danger from dominants |journal=Behavioral Ecology and Sociobiology |volume=68 |issue=6 |pages=1007–1017 |year=2014|s2cid=18606633 }}</ref> Most chameleon genera (exceptions are ''Chamaeleo'', ''Rhampholeon'' and ''Rieppeleon'') have blue [[fluorescence]] in a species specific pattern in their skull [[tubercle]]s and in ''Brookesia'' there is also some in tubercles on the body. The fluorescence is derived from bones that only are covered in very thin skin and it possibly serves a signaling role, especially in shaded habitats.<ref name="Prötzel et al 2018"/>

Some species, such as [[Smith's dwarf chameleon]] and several others in the genus ''[[Bradypodion]]'', adjust their colours for camouflage depending on the vision of the specific predator species (for example, bird or snake) by which they are being threatened.<ref>Young, Emma (2008) [https://www.newscientist.com/article/dn13944-chameleons-finetune-camouflage-to-predators-vision.html Chameleons fine-tune camouflage to predator's vision]. ''[[New Scientist]]''</ref><ref name=StuartFox2009>{{cite journal| last1=Stuart-Fox | first1=D. | last2=Moussalli | first2=A. | year=2009 | title=Camouflage, communication and thermoregulation: lessons from colour changing organisms | journal=Philos Trans R Soc Lond B Biol Sci | volume=364 | issue=1516 | pages=463–470 | doi=10.1098/rstb.2008.0254 | pmid=19000973 | pmc=2674084 }}</ref> In the introduced Hawaiian population of [[Jackson's chameleon]], conspicuous colour changes that are used for communication between chameleons have increased whereas anti-predator camouflage colour changes have decreased relative to the native source population in Kenya where there are more predators.<ref name=Whiting2022>{{cite journal| last1=Whiting | first1=M.J. | last2=Holland | first2=B.S. | last3=Keogh | first3=J.S. | last4=Noble | first4=D.W.A. | last5=Rankin | first5=K.J. | last6=Stuart-Fox | first6=D. | year=2022 | title=Invasive chameleons released from predation display more conspicuous colors | journal=Science Advances | volume=8 | issue=19 | pages=eabn2415 | doi=10.1126/sciadv.abn2415 | doi-access=free | pmid=35544573 | pmc=9094656 | bibcode=2022SciA....8N2415W }}</ref>

Chameleons have two superimposed layers within their skin that control their colour and thermoregulation. The top layer contains a lattice of guanine nanocrystals, and by exciting this lattice the spacing between the nanocrystals can be manipulated, which in turn affects which wavelengths of light are reflected and which are absorbed. Exciting the lattice increases the distance between the nanocrystals, and the skin reflects longer wavelengths of light. Thus, in a relaxed state the crystals reflect blue and green, but in an excited state the longer wavelengths such as yellow, orange, green, and red are reflected.<ref>{{cite web |publisher=National Geographic Society |year=2015 |url=http://ngm.nationalgeographic.com/2015/09/chameleons/edmonds-text |title=The colourful Language of Chameleons |archive-url=https://web.archive.org/web/20160311023144/http://ngm.nationalgeographic.com/2015/09/chameleons/edmonds-text |archive-date=11 Mar 2016 |author=Patricia Edmonds}}</ref>

The skin of a chameleon also contains some yellow pigments, which combined with the blue reflected by a relaxed crystal lattice results in the characteristic green colour which is common of many chameleons in their relaxed state. Chameleon colour palettes have evolved through evolution and the environment. Chameleons living in the forest have a more defined and colourful palette compared to those living in the desert or savanna, which have more of a basic, brown, and charred palette.<ref>{{cite journal |last1=Stuart-Fox |first1=Devi |last2=Moussalli |first2=Adnan |date=2008-01-29 |title=Selection for Social Signalling Drives the Evolution of Chameleon Colour Change |journal=PLOS Biology |volume=6 |issue=1 |pages=e25 |doi=10.1371/journal.pbio.0060025 |issn=1545-7885 |pmc=2214820 |pmid=18232740 |doi-access=free }}</ref>