Editing Zebra (section)

===Stripes===
{{Redirect|Zebra stripes||Zebra stripes (disambiguation)}}
[[File:Zebra species (ENG).png|thumb|left|alt=An illustration showing the three living zebra species |Comparative illustration of living zebra species]]
Zebras are easily recognised by their bold black-and-white striping patterns. The [[Animal coat|coat]] appears to be white with black stripes, as indicated by the belly and legs when unstriped, but the skin is black.<ref name="Bard1977" /><ref>{{cite web |author=Langley|first=  Liz |date=4 March 2017 |title=Do Zebras Have Stripes On Their Skin? |work=National Geographic |access-date=2 June 2020 |url=https://www.nationalgeographic.com/news/2017/03/animals-skin-colors-zebras-big-cats/|archive-url=https://web.archive.org/web/20200801013454/https://www.nationalgeographic.com/news/2017/03/animals-skin-colors-zebras-big-cats/|url-status=dead|archive-date=1 August 2020}}</ref>{{sfn|Caro|2016|pp=14–15}} Young or [[foal]]s are born with brown and white coats, and the brown darkens with age.<ref name="Grub 1981" /><ref name="Churcher 1993" /> A [[Anatomical terms of location#Dorsal and ventral|dorsal]] line acts as the backbone for vertical stripes along the sides, from the head to the rump. On the snout they curve toward the nostrils, while the stripes above the front legs split into two branches. On the rump, they develop into species-specific patterns. The stripes on the legs, ears and tail are separate and horizontal.<ref name="Bard1977" />

Striping patterns are unique to an individual and heritable.{{sfn|Caro|2016|pp=7, 19}} During [[embryonic development]], the stripes appear at eight months, but the patterns may be determined at three to five weeks. For each species there is a point in embryonic development where the stripes are perpendicular to the dorsal line and spaced {{convert|0.4|mm|in|abbr=on}} apart. However, this happens at three weeks of development for the plains zebra, four weeks for the mountain zebra, and five for Grévy's zebra. The difference in timing is thought to be responsible for the differences in the striping patterns of the different species.<ref name="Bard1977">{{cite journal |author=Bard|first=  J. |year=1977 |title=A unity underlying the different zebra patterns |journal=[[Journal of Zoology]] |volume=183 |issue=4 |pages=527–539 |doi=10.1111/j.1469-7998.1977.tb04204.x}}</ref>

Various abnormalities of the patterns have been documented in plains zebras. In "[[melanistic]]" zebras, dark stripes are highly concentrated on the torso but the legs are whiter. "Spotted" individuals have broken up black stripes around the dorsal area.<ref name=Larison2020>{{cite journal|last1=Larison|first1=Brenda|last2=Kaelin|first2=Christopher B.|last3=Harrigan|first3=Ryan|display-authors=etal|year=2020|title=Population structure, inbreeding and stripe pattern abnormalities in plains zebras|journal=Molecular Ecology|volume=30|issue=2|pages=379–390|doi=10.1111/mec.15728|pmid=33174253|s2cid=226305574}}</ref> There have even been [[Polymorphism (biology)|morphs]] with white spots on dark backgrounds.{{sfn|Caro|2016|p=20}} Striping abnormalities have been linked to [[inbreeding]].<ref name=Larison2020/> [[Albino]] zebras have been recorded in the forests of [[Mount Kenya]], with the dark stripes being blonde.<ref>{{cite web |url=https://www.nationalgeographic.com/animals/2019/03/rare-partially-albino-zebra-spotted-in-serengeti/ |archive-url=https://web.archive.org/web/20190329161519/https://www.nationalgeographic.com/animals/2019/03/rare-partially-albino-zebra-spotted-in-serengeti/ |url-status=dead |archive-date=29 March 2019 |title=Extremely Rare 'Blonde' Zebra Photographed |publisher=[[National Geographic]] |date=29 March 2019 |access-date=25 May 2020}}</ref> The quagga had brown and white stripes on the head and neck, brown upper parts and a white belly, tail and legs.<ref name="Walker">{{cite book |last=Nowak |first=R. M. |year=1999 |title=Walker's Mammals of the World |volume=1 |publisher=[[Johns Hopkins University Press]] |pages=1024–1025 |isbn=978-0-8018-5789-8}}</ref>

====Function====
The function of stripes in zebras has been discussed among biologists since at least the 19th century.{{sfn|Caro|2016|p=1}} Popular hypotheses include the following:
* The '''[[crypsis]] hypothesis''' suggests that the stripes allow the animal to blend in with its environment or [[disruptive coloration|break up its outline]]. This was the earliest hypothesis and proponents argued that the stripes were particularly suited for camouflage in tall grassland and woodland habitat. [[Alfred Wallace]] also wrote in 1896 that stripes make zebras less noticeable at night. Biologist [[Tim Caro]] notes that zebras graze in open habitat and do not behave cryptically, being noisy, fast, and social and do not freeze when a predator is near. In addition, the camouflaging stripes of woodland living ungulates like [[Bongo (antelope)|bongos]] and [[Cape bushbuck|bushbucks]] are much less vivid with less contrast with the background colour.{{sfn|Caro|2016|pp=2–3, 23, 48, 50}} A 1987 [[Fourier analysis]] study concluded that the [[spatial frequencies]] of zebra stripes do not line up with their environment,<ref>{{cite journal |last1=Godfrey|first1=  D. |last2=Lythgoe|first2=  J. N. |last3=Rumball|first3=  D. A. |year=1987 |title=Zebra stripes and tiger stripes: the spatial frequency distribution of the pattern compared to that of the background is significant in display and crypsis |journal=[[Biological Journal of the Linnean Society]] |volume=32 |issue=4 |pages=427–433 |doi=10.1111/j.1095-8312.1987.tb00442.x}}</ref> while a 2014 study of wild equine species and subspecies could not find any correlations between striping patterns and woodland habitats.<ref name="Caro" /> Melin and colleagues (2016) found that [[lion]]s and hyenas do not appear to perceive the stripes when they are a certain distance away at daytime or nighttime, thus making the stripes useless in blending in except when the predators are close enough by which they could smell or hear their target. They also found that the stripes do not make the zebra less noticeable than solidly coloured herbivores on the open plains. They suggested that stripes may give zebras an advantage in woodlands, as the dark stripes could line up with the outlines of tree branches and other vegetation.<ref>{{cite journal|last1=Melin|first1=A. D.|last2=Kline|first2=D. W.|last3=Hiramatsu|first3=C|last4=Caro|first4=T|year=2016|title=Zebra stripes through the eyes of their predators, zebras, and humans|journal=PLOS ONE|volume=11|issue=1|page=e0145679|doi=10.1371/journal.pone.0145679|doi-access=free|pmid=26799935 |pmc=4723339|bibcode=2016PLoSO..1145679M }}</ref>
[[File:Mountain zebra stripes.jpg|thumb|right|alt=Closeup shot of mountain zebra stripes |Closeup of mountain zebra stripes]]
* The '''confusion hypothesis''' states that the stripes confuse predators, be it by: making it harder to distinguish individuals in a group as well as determining the number of zebras in a group; making it difficult to determine an individual's outline when the group runs away; reducing a predator's ability to keep track of a target during a chase; [[dazzle camouflage|dazzling]] an assailant so they have difficulty making contact; or making it difficult for a predator to deduce the zebra's size, speed and direction via [[motion dazzle]]. This theory has been proposed by several biologists since at least the 1970s.{{sfn|Caro|2016|pp=72–81, 86}} A 2014 computer study of zebra stripes found that they may create a [[wagon-wheel effect]] and/or [[barber pole illusion]] when in motion. The researchers concluded that this could be used against mammalian predators or biting flies.<ref name="How2014">{{cite journal |author=How|first1=  M. J. |last2=Zanker|first2=  J. M. |year=2014 |title=Motion camouflage induced by zebra stripes |journal=Zoology |volume=117 |issue=3 |pages=163–170 |doi=10.1016/j.zool.2013.10.004|pmid= 24368147 |bibcode= 2014Zool..117..163H }}</ref> The use of the stripes for confusing mammalian predators has been questioned. Caro suggests that the stripes of zebras could make groups seem smaller, and thus more likely to be attacked. Zebras also tend to scatter when fleeing from attackers and thus the stripes could not break up an individual's outline. Lions, in particular, appear to have no difficulty targeting and catching zebras when they get close and take them by ambush.{{sfn|Caro|2016|pp=80, 92}} In addition, no correlations have been found between the number of stripes and populations of mammal predators.<ref name="Caro" /> Hughes and colleagues (2021) disputed the idea of motion dazzle and concluded that moving objects that are solidly grey or have less contrasted patterns are actually more likely to escape being caught.<ref>{{cite journal|last1=Hughes|first1=A. E.|last2=Griffiths|first2=D|last3=Troscianko|first3=J|last4=Kelley|first4=L. A.|year=2021|title=The evolution of patterning during movement in a large-scale citizen science game|journal=Proceedings of the Royal Society B: Biological Sciences|volume=288|issue=1942 |page=20202823|doi=10.1098/rspb.2020.2823|pmid=33434457 |pmc=7892415 }}</ref> 
* The '''[[Aposematism|aposematic]] hypothesis''' suggests that the stripes serve as warning colouration. This hypothesis was first suggested by Wallace in 1867 and discussed in more detail by [[Edward Bagnall Poulton]] in 1890. As with known aposematic mammals, zebras are recognizable up close, live in more open environments, have a high risk of predation and do not hide or act inconspicuous. However, Caro notes that stripes do not work on lions because they frequently prey on zebras, though they may work on smaller predators, and zebras are not slow-moving enough to need to ward off threats. In addition, zebras do not possess adequate defenses to back up the warning pattern.{{sfn|Caro|2016|pp=55, 57–58, 68}}
* The '''social function hypothesis''' states that stripes serve a role in intraspecific or individual recognition, social bonding, mutual grooming or a signal of [[Fitness (biology)|fitness]]. [[Charles Darwin]] wrote in 1871{{efn|The cited source cites the 1896 edition of Darwin's 1871 book ''[[The Descent of Man, and Selection in Relation to Sex]]''.}} that "a female zebra would not admit the addresses of a male ass until he was painted so as to resemble a zebra" while Wallace stated in 1871 that: "The stripes therefore may be of use by enabling stragglers to distinguish their fellows at a distance". Regarding species and individual identification, Caro notes that zebra species have limited range overlap with each other and horses can recognise each other using visual communication.{{sfn|Caro|2016|pp=6–7, 139–148, 150}} In addition, no correlation has been found between striping and social behaviour or group numbers among equines,<ref name="Caro" /> and no link has been found between fitness and striping.{{sfn|Caro|2016|p=150}}
* The '''[[thermoregulation|thermoregulatory]] hypothesis''' suggests that stripes help to control a zebra's body temperature. In 1971, biologist H. A. Baldwin noted that heat would be absorbed by the black stripes and reflected by the white ones and in 1990, zoologist [[Desmond Morris]] suggested that the stripes create cooling [[convection current]]s.{{sfn|Caro|2016|p=7}} A 2019 study supported this, finding that where the faster air currents of the warmer black stripes meet those of the white, [[Vortex|air swirl]]s form. The researchers also concluded that during the hottest times of the day, zebras [[Hackles|erect]] their black hair to release heat from the skin and flatten it again when it gets cooler.<ref>{{cite journal |last1=Cobb|first1=  A. |last2=Cobb|first2=  S. |year=2019 |title=Do zebra stripes influence thermoregulation? |journal=[[Journal of Natural History]] |volume=53 |issue=13–14 |pages=863–879 |doi=10.1080/00222933.2019.1607600|bibcode= 2019JNatH..53..863C |s2cid= 196657566 }}</ref> Larison and colleagues (2015) determined that environmental temperature is a strong predictor for zebra striping patterns.<ref>{{cite journal |last1=Larison |first1=Brenda |last2=Harrigan |first2=Ryan J. |last3=Thomassen |first3=Henri A. |last4=Rubenstein |first4=Daniel I. |last5=Chan-Golston |first5=Alec M. |last6=Li |first6=Elizabeth |last7=Smith |first7=Thomas B. |year=2015 |title=How the zebra got its stripes: a problem with too many solutions |url=http://rsos.royalsocietypublishing.org/content/2/1/140452tempa |journal=[[Royal Society Open Science]] |volume=2 |issue=1 |page=140452 |doi=10.1098/rsos.140452 |pmid=26064590 |pmc=4448797|bibcode=2015RSOS....240452L }}</ref> Others have found no evidence that zebras have lower body temperatures than other ungulates whose habitat they share, or that striping correlates with temperature.{{sfn|Caro|2016|pp=158–161}}<ref name="Caro" /> A 2018 experimental study which dressed water-filled metal barrels in horse, zebra and cattle hides concluded that the zebra stripes had no effect on thermoregulation.<ref>{{cite journal|last1=Horváth |first1=Gábor |last2=Pereszlényi |first2=Ádám |last3=Száz |first3= Dénes|last4=Barta |first4= András |last5= Jánosi |first5= Imre M. |last6=Gerics |first6= Balázs |last7=Åkesson |first7=Susanne|year=2018|title=Experimental evidence that stripes do not cool zebras|journal=Scientific Reports|volume=8|issue=1|page=9351|doi=10.1038/s41598-018-27637-1|pmid=29921931 |pmc=6008466 |bibcode=2018NatSR...8.9351H |doi-access=free }}</ref>
[[File:Journal.pone.0210831.g001.png|thumb|right|alt=Comparison of horse fly flight patterns on horses and zebras |Comparison of flight patterns and contact/landings of horse flies around domestic horses (a-c) and plains zebras (d-f).<ref name="Caro2" />]]
* The '''fly protection hypothesis''' holds that the stripes deter [[blood-sucking]] flies. [[Horse fly|Horse flies]], in particular, spread diseases that are lethal to equines such as [[African horse sickness]], [[equine influenza]], [[equine infectious anemia]] and [[trypanosomiasis]]. In addition, zebra hair is about as long as the mouthparts of these flies.<ref name="Caro" /> This hypothesis is the most strongly supported by the evidence.<ref name="Caro2" /><ref name=Tombak2022/> It was found that flies preferred landing on solidly coloured surfaces over those with black-and-white striped patterns in 1930 by biologist R. Harris,{{sfn|Caro|2016|p=5}} and this was proposed to have been a function of zebra stripes in a 1981 study.<ref>{{cite journal|last1=Waage|first1=J. K.|year=1981|title=How the zebra got its stripes - biting flies as selective agents in the evolution of zebra coloration|journal=Journal of the Entomological Society of Southern Africa|volume=44|issue=2|pages=351–358|hdl=10520/AJA00128789_3800}}</ref> A 2014 study found a correlation between striping and overlap with horse and [[tsetse fly]] populations and activity.<ref name="Caro">{{cite journal |last1=Caro|first1=  T. |last2=Izzo|first2=  A. |last3=Reiner|first3=  R. C. |last4=Walker|first4=  H. |last5=Stankowich|first5=  T. |year=2014 |title=The function of zebra stripes |journal=[[Nature Communications]] |volume=5 |page=3535 |bibcode= 2014NatCo...5.3535C|doi=10.1038/ncomms4535 |pmid=24691390 |doi-access=free}}</ref> Other studies have found that zebras are rarely targeted by these insect species.{{sfn|Caro|2016|pp=196–197}} Caro and colleagues (2019) studied captive zebras and horses and observed that neither could deter flies from a distance, but zebra stripes kept flies from landing, both on zebras and horses dressed in zebra [[Animal print|print]] coats.<ref name="Caro2">{{cite journal |author=Caro|first1= T. |last2=Argueta|first2= Y. |last3=Briolat|first3= E. S. |last4=Bruggink|first4= J. |last5=Kasprowsky|first5= M. |last6=Lake|first6= J. |last7=Mitchell|first7= M. |last8=Richardson|first8= S. |last9=How|first9= M. |year=2019 |title=Benefits of zebra stripes: behaviour of tabanid flies around zebras and horses |journal=PLOS ONE |volume=14 |issue=2 |page=e0210831 |doi=10.1371/journal.pone.0210831 |pmid= 30785882 |pmc= 6382098 |bibcode= 2019PLoSO..1410831C |doi-access=free}}</ref> There does not appear to be any difference in the effectiveness of repelling flies between the different zebra species; thus the difference in striping patterns may have evolved for other reasons.<ref name=Tombak2022>{{cite journal|last1=Tombak|first1=K. J.|last2=Gersick|first2=A. S.|last3=Reisinger|first3=L. V.|last4=Larison|first4=B|last5=Rubenstein|first5=D. I.|year=2022|title=Zebras of all stripes repel biting flies at close range|journal=Scientific Reports |volume=22|issue=18617|page=18617 |doi=10.1038/s41598-022-22333-7|pmid=36329147 |pmc=9633588 |bibcode=2022NatSR..1218617T }}</ref> White or light stripes painted on dark bodies have also been found to reduce fly irritations in both cattle and humans.<ref>{{cite journal |last1=Kojima|first1= T. |last2=Oishi|first2= K. |last3=Matsubara|first3= Y. |last4=Uchiyama|first4= Y. |last5=Fukushima|first5= Y. |year=2020 |title=Cows painted with zebra-like striping can avoid biting fly attack |journal=PLOS ONE |volume=15 |issue=3 |page=e0231183 |doi=10.1371/journal.pone.0231183 |pmid= 32214400 |pmc= 7098620 |doi-access=free}}</ref><ref>{{cite journal |last1=Horváth|first1= G. |last2=Pereszlényi|first2= Á. |last3=Åkesson|first3= S. |last4=Kriska|first4= G. |year=2019 |title=Striped bodypainting protects against horseflies |journal=Royal Society Open Science |volume=6 |issue=1 |page= 181325 |doi=10.1098/rsos.181325 |pmid= 30800379 |pmc= 6366178 |bibcode= 2019RSOS....681325H |doi-access=free}}</ref> The effect even extends to pelts, with zebra pelts being less attractive to flies than unstriped [[impala]] pelts. How the stripes repel flies is less clear.<ref name=Tombak2022/> A 2012 study concluded that they disrupt the [[Polarization (physics)|polarised]] light patterns these insects use to locate water and habitat,<ref>{{cite journal |last1=Egri |first1=Ádám |last2=Blahó |first2=Miklós |last3=Kriska |first3=György |last4=Farkas |first4=Róbert |last5=Gyurkovszky |first5=Mónika |last6=Åkesson |first6=Susanne |last7=Horváth |first7=Gábor |year=2012 |title=Polarotactic tabanids find striped patterns with brightness and/or polarization modulation least attractive: an advantage of zebra stripes |journal=[[Journal of Experimental Biology]] |volume=215 |issue=5 |pages=736–745 |doi=10.1242/jeb.065540 |pmid=22323196 |doi-access=free|bibcode=2012JExpB.215..736E }}</ref> though subsequent studies have refuted this.<ref name=Caro2023/><ref name=Takács2022/><ref>{{cite journal|last1=Britten|first1=K. H.|last2=Thatcher|first2=T. D.|last3=Caro|first3=T|year=2016|title=Zebras and biting flies: quantitative analysis of reflected light from zebra coats in Their natural habitat|journal=PLOS ONE|volume=11|issue=5|page=e0154504|doi=10.1371/journal.pone.0154504|pmid=27223616 |pmc=4880349 |bibcode=2016PLoSO..1154504B |doi-access=free }}</ref> Stripes do not appear to work like a barber pole against flies since [[Check (pattern)|checkered pattern]]s also repel them.<ref name=Caro2023/><ref>{{cite journal|last1=How|first1=M. J.|last2=Gonzales|first2=D.|last3=Irwin|first3=A.|last4=Caro|first4=T.|year=2020|title=Zebra stripes, tabanid biting flies and the aperture effect|journal=Proceedings of the Royal Society B: Biological Sciences|volume=287|issue=1933|doi=10.1098/rspb.2020.1521|pmid=32811316|pmc=7482270}}</ref> There is also little evidence that zebra stripes confuse the insects via visual distortion or [[aliasing]].<ref name=Caro2023/> Takács and colleagues (2022) suggest that, when the animal is in sunlight, temperature gradients between the warmer dark stripes and cooler white stripes prevent horseflies from detecting the warm blood vessels underneath.<ref name=Takács2022>{{cite journal|last1=Takács|first1=P|last2=Száz|first2=D|last3=Vincze|first3=M|last4=Slíz-Balogh|first4=J|last5=Horváth|first5=G|year=2022|title=Sunlit zebra stripes may confuse the thermal perception of blood vessels causing the visual unattractiveness of zebras to horseflies|journal=Scientific Reports|volume=12|issue=10871|page=10871|doi=10.1038/s41598-022-14619-7|pmid=35927437|pmc=9352684|bibcode=2022NatSR..1210871T}}</ref> Caro and colleagues (2023) conclude that the insects are disoriented by the high colour contrast and relative thinness of the patterns.<ref name=Caro2023>{{cite journal|last1=Caro|first1=T|last2=Fogg|first2=E|last3=Stephens-Collins|first3=T|last4=Santon|first4=M|last5=How|first5=M. J.|year=2023|title=Why don't horseflies land on zebras?|journal=Journal of Experimental Biology|volume=226|issue=4|page=jeb244778|doi=10.1242/jeb.244778|pmid=36700395|pmc=10088525|bibcode=2023JExpB.226B4778C|s2cid=256273744}}</ref>