Zebras
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Plains zebra ( Equus quagga ) |
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| CH Smith , 1841 |
The three species Grevy's zebra ( Equus grevyi ), mountain zebra ( Equus zebra ) and plains zebra ( Equus quagga ) from the genus of horses ( Equus ) are called zebras ( Hippotigris ) . They are particularly characterized by their black and white stripe pattern. All representatives of the zebras occur exclusively in Africa , where they mostly inhabit open landscapes.
Surname
When Portuguese seafarers first saw zebras on their voyages of discovery in Africa at the end of the 15th century, they were reminded of the Iberian wild horses, which they called zebros in Portugal and which also had black stripes. From then on they called these horses zebras .
features
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Zebras reach a head body length of 210 to 300 centimeters, the tail becomes 40 to 60 centimeters long and the shoulder height is 110 to 160 centimeters. The weight varies between 180 and 450 kilograms. The Grevy's zebra is the largest zebra and the largest species of wild horse. They are characterized by their typical stripes, but they differ significantly in their appearance.
Striped pattern
The developmental development of the strips has not yet been fully clarified. It is known from related animals that the melanocytes - pigment cells that color the fur dark - migrate from the neural crest on the back towards the abdomen during embryonic development . It is unclear whether the melanocytes do not migrate to the white areas of the zebra, whether they are killed in these areas or whether pigment production is simply inhibited there. How the strip-like regulation is accomplished at the genetic level is also unknown up to now.
The different number of stripes of the three zebra species is also striking: while the Grevy's zebra has around 80 stripes, the mountain zebra only has around 45 and the plains zebra only around 30. According to a hypothesis by Jonathan Bard, the stripes are around 0 in all species at the time of their development, 4 millimeters (about 20 cells) wide. However, according to Bard, this development takes place at different times in the development of the three species, and in the Grevy's zebra only later, after about 35 days, so that the embryo there is larger and there are more stripes. In the mountain zebra, on the other hand, the stripes form after 28 days, in the plains zebra after 21 days, which leads to a lower number of stripes.
There are several attempts to explain the evolutionary development of the stripes; a combination of several advantageous effects is also conceivable.
Camouflage from predators
On the one hand, Charles Darwin and Alfred Russel Wallace , among others, suspected that they could act as camouflage in tall grass or in hot, shimmering air . It is also conceivable that the outlines of the individual animals are no longer so clearly recognizable due to the striped drawing. Since zebras live in herds, this could make it more difficult for predators to pick out a single prey. However, this interpretation was largely refuted, because at a distance at which the stripe pattern would be visually recognizable, predators would have already smelled and heard the prey. There would be no optically reduced perceptibility of the contours. Tim Caro said: "We have not found any indications that the stripes convey any camouflage effect against predators ... We therefore consider the hypothesis that was already put forward by Charles Darwin and Alfred Russel Wallace to be wrong".
Protection against flies and horseflies
According to a further, experimentally verified hypothesis , the stripes formed to camouflage tsetse flies and horseflies . According to this hypothesis, these insects, which transmit sleeping sickness , can not perceive the animals with their compound eyes . In 1993, the zoologist and evolutionary biologist Josef H. Reichholf dedicated two chapters to this question in his book The Riddle of the Incarnation and refers to the tsetse fly: The trypanosome infection in horses (to which zebras belong), which corresponds to sleeping sickness, is the Nagana disease, and a Protection against this often fatal disease is a selection advantage . However, it has been shown that the tsetse flies avoid zebras because of their skin odor. This contains various aldehyde and ketone components that deter the insects. A comparable effect is known among other things with different waterbucks .
Experimentally in 2012 it was shown that striped areas are avoided by brakes. Was in 2019 - based painted replicas of human body - were further evidence that horseflies are attracted by brown models ten times more than black models with white stripes. Beige painted models attracted horseflies twice as often as black and white striped ones. The cause of these differences is evidently that the stripes lead to considerable irritation during landing when braking and therefore the landing does not occur more frequently than with non-striated targets. However, further investigations showed that this irritation probably plays a less important role, since horseflies avoid as often as striped, checkered and sometimes also spotty patterns.
Thermoregulation
The contrast between light and dark stripes, which varies depending on the habitat, correlates most strongly with the temperature of the surroundings; Which physiological mechanism is responsible for the fact that the contrast is particularly pronounced in particularly hot surroundings is not known. It is assumed, however, that the strips are used for thermoregulation . Studies on animals in Kenya have shown that the fur of the zebras heats up to different degrees during the hot phase of the day, with the surface temperature of the black stripes exceeding that of the white by 12 to 15 ° C (black stripes 44 to 56 ° C, white stripes 36 to 42 ° C). The strong temperature gradient creates locally chaotic air vortices. Since zebras, like all horses, sweat, this may increase heat dissipation through evaporation from surface water. The process can also be controlled by the fact that the hair of the black stripes can be erected, but that of the white stripes cannot.
More functions
The striped pattern may also be used to identify the individual animals with one another and thus promote group cohesion.
Distribution and way of life
Originally, the zebras were common throughout Africa . In North Africa , however, they were already exterminated in ancient times.
The plains zebra is most widespread today and occurs from southern Sudan and Ethiopia to South Africa . The Grevy's zebra inhabits a small area in East Africa ( Kenya , Uganda , Ethiopia and Somalia ). The mountain zebra inhabits southwestern Africa from southern Angola to South Africa. The Grevy's zebra prefers dry semi-deserts, the mountain zebra is also adapted to mountain regions and occurs up to 2000 meters above sea level. The plains zebra live in different habitats such as grasslands and open forests.
Social behavior is different. In the Grevy's zebra, the male animals establish mating territories that can be over 10 square kilometers - one of the largest known territorial sizes of all herbivores. Although animals sometimes form associations, there are no lasting relationships between adult animals in these species. In the mountain and plains zebra, the stallions supervise a herd of mare. In this case, larger herds with an established hierarchy can also form.
Like all horses , zebras are herbivores who mainly eat grass.
Systematics
External system
Together with the wild horse (from which the house horse was domesticated ), the African donkey (from which the house donkey is derived), the Asian donkey and the kiang, the three zebra species form the genus and family of horses (Equidae, Equus ). There are also crossbreeds within this genus: Zebroids are crossbreeds between domestic horse and zebra, zebrule or donkey between domestic donkey and zebra. However, these crosses are only fertile in the rarest of cases .
Internal system
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Internal systematics of the genus Equus according to Jónsson et al. 2014
Here both the zebras and the donkeys each form their own closed group |
The zebras form a subgenus within the genus of horses ( Equus ). This view is supported by anatomical or cranial morphological features, as well as by DNA examinations in which the striped horse representatives each form a common group. They then face the donkeys, which are grouped together in the subgenus Asinus , as a sister group . However, other genetic studies also suggest that the zebras do not form a natural taxon . In these the zebras are more strongly mixed with the different species of donkeys. According to this relationship, the characteristic stripe pattern would either have arisen convergent several times or inherited from a common ancestor and partially lost again in the related wild asses. The scientific name Hippotigris was introduced by Charles Hamilton Smith in 1841 .
The following three species are generally summarized under the term zebra , some of which are in turn divided into subspecies :
- Subgenus: Hippotigris C. H. Smith , 1841
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- Equus zebra Linnaeus , 1758 (mountain zebra); broader stripes thatrun horizontallyon the croup , on the back of the back there is a grid-like drawing.
- E. z. hartmannae Matschie , 1898
- E. z. zebra Linnaeus , 1758
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Alternative internal systematics of the genus Equus according to Orlando et al. 2009
Here the zebras are divided into different clades and mix with the donkeys |
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- Equus grevyi Oustalet , 1882 (Grevy's zebra); very narrow stripes, which alsoremain largely verticalin the rear area of the trunk , the belly is white.
- Equus quagga Boddaert , 1785 (plains zebra); variable color, often the rear half of the trunk is striped horizontally, the drawing also includes the belly and there are often lighter “shadow stripes”.
- E. q. boehmi Matschie , 1892
- E. q. borensis Lönnberg , 1921
- E. q. burchelli Gray , 1824
- E. q. chapmani Layard , 1865
- E. q. crawshayi De Winton , 1896
- E. q. quagga Boddaert , 1785
In some classifications, the Hartmann's mountain zebra ( Equus hartmannae ) is also recognized as an independent species, but it is mainly regarded as a subspecies of the mountain zebra. In systematics in which the zebras do not form a closed group, the Grevy's zebra is sometimes considered a member of the subgenus Dolichohippus .
Extinct forms, such as Equus simplicidens or the Cape zebra ( Equus capensis ), are sometimes also referred to as zebras. The latter form has turned out to be the southern subspecies of the plains zebra.
Threat and protection
In the wild, poaching and the destruction of their habitat represent the main threat. The IUCN lists the Grevy and mountain zebra as endangered and only the plains zebra as not endangered. However, several of its subspecies have become extinct, including the quagga , which was still common up to the beginning of the 19th century, but was rarely seen in the wild towards the end of this century, most recently in 1901.
In contrast to domestic horses and house donkeys , zebras have never been permanently domesticated with a few exceptions , although they are closely related to them and are even capable of reproduction ( zebroids ). There were numerous attempts by both the African pastoral peoples and later by European settlers to tame the animals, but they failed. This is mainly justified by the behavior of the zebras: They also remain shy and vicious and, in extreme cases, bite the people they want to lead until they are dead. Even in modern zoos so it comes with the keepers frequently to injury from Zebra bites than by bites of tigers . In addition, the zebras see better than other horses and therefore can not be caught with the lasso even for professional cowboys and duck away from the approaching rope. A molecular biological basis to explain the simpler domestication of horses and donkeys compared to zebras (as well as wild cattle compared to domestic cattle ) was investigated, with the hypothesis that individual areas of the genome (as "subgenome") by the process of domestication are influenced.
literature
- Ronald M. Nowak: Walker's Mammals of the World . 6th edition. Johns Hopkins University Press, Baltimore 1999, ISBN 0-8018-5789-9 (English).
- Don E. Wilson, DeeAnn M. Reeder (Eds.): Mammal Species of the World . A Taxonomic and Geographic Reference . 3. Edition. Johns Hopkins University Press, Baltimore 2005, ISBN 0-8018-8221-4 (English).
- Tim Caro: Zebra Stripes. University of Chicago Press, 2016, ISBN 978-0226411019
Web links
Individual evidence
- ↑ Zebro articles on www.sorraia.org, accessed on November 29, 2014
- ^ A b Sean B. Carroll: Evo Devo . 1st edition. Berlin University Press, 2005, ISBN 978-3-940432-15-5 , pp. 230-235 .
- ↑ a b c Amanda D. Melin, Donald W. Kline, Chihiro Hiramatsu, Tim Caro: Zebra stripes through the eyes of their predators, zebras, and humans. In: PLoS ONE. 11 (1), 2016, doi: 10.1371 / journal.pone.0145679
- ↑ Zebra crossing: Because of camouflage. On: Wissenschaft.de on January 25, 2016, accessed on September 9, 2019.
- ↑ Tim Caro, Amanda Izzo, Robert C. Reiner, Hannah Walker, Theodore Stankowich: The function of zebra stripes. In: Nature Communications. 5, 2014, p. 3535, doi: 10.1038 / ncomms4535
- ↑ Josef H. Reichholf: The Riddle of the Incarnation: The emergence of man in the interplay of nature. dtv, Munich 1993, ISBN 3-423-30341-7 , p. 96 f.
- ↑ Olabimpe Y. Olaide, David P. Tchouassi, Abdullahi A. Yusuf, Christian WW Pirk, Daniel K. Masiga, Rajinder K. Saini, Baldwyn Torto: Zebra skin odor repels the savannah tsetse fly, Glossina pallidipes (Diptera: Glossinidae). In: PLoS Neglected Tropical Diseases. 13 (6), 2019, p. E0007460, doi: 10.1371 / journal.pntd.0007460
- ↑ Ádám Egri, Miklós Blahó, György Kriska, Róbert Farkas, Mónika Gyurkovszky, Susanne Åkesson, Gábor Horváth: Polarotactic tabanids find striped patterns with brightness and / or polarization modulation least attractive: an advantage of zebra stripes. In: The Journal of Experimental Biology. 215, 2012, pp. 736-745, doi: 10.1242 / jeb.065540
- ↑ Evolution: Zebra crossing protects against bites. In: Spiegel Online , February 9, 2012
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↑ Gábor Horváth Ádám Pereszlényi, Susanne Åkesson and György Kriska: Striped body painting protects against horseflies. In: Royal Society Open Science. 6 (1), 2019, doi: 10.1098 / rsos.181325
Body-painting protects against bloodsucking insects. On: lunduniversity.lu.se on January 17, 2019 - ↑ Tim Caro, Yvette Argueta, Emmanuelle Sophie Briolat, Joren Bruggink, Maurice Kasprowsky, Jai Lake, Matthew J. Mitchell, Sarah Richardson, Martin How: Benefits of zebra stripes: Behavior of tabanid flies around zebras and horses. In: PLoS ONE. 14 (2), 2019, p. E0210831, doi: 10.1371 / journal.pone.0210831
- ↑ Miklos Blaho, Adam Egri, Lea Bahidszki, Gyorgy Kriska, Ramon Hegedus, Susanne Åkesson, Gabor Horvath: Spottier Targets Are Less Attractive to Tabanid Flies: On the Tabanid-Repellency of Spotty Fur Patterns. In: PLoS ONE. 7 (8), 2012, p. E41138, doi: 10.1371 / journal.pone.0041138
- ↑ Martin J. How, Dunia Gonzales, Alison Irwin, Tim Caro: Zebra stripes, tabanid biting flies and the aperture effect. In: Proceedings of the Roayal Society B. 287, 2020, S. 20201521, doi: 10.1098 / rspb.2020.1521
- Jump up ↑ Brenda Larison, Ryan J. Harrigan, Henri A. Thomassen, Daniel I. Rubenstein, Alec M. Chan-Golston, Elizabeth Li, Thomas B. Smith: How the zebra got its stripes: a problem with too many solutions. In: Royal Society Open Science. 2, 2015, p. 140452, doi: 10.1098 / rsos.140452
- ↑ Alison Cobb, Stephen Cobb. Do zebra stripes influence thermoregulation? In: Journal of Natural History. 53 (13-14), 2019, p. 863, doi: 10.1080 / 00222933.2019.1607600
- ↑ a b Hákon Jónsson, Mikkel Schubert, Andaine Seguin-Orlando, Aurélien Ginolhac, Lillian Petersen, Matteo Fumagallic, Anders Albrechtsen, Bent Petersen, Thorfinn S. Korneliussen, Julia T. Vilstrup, Teri Lear, Jennifer Leigh Myka, Judith Lundquist, Donald C. Miller, Ahmed H. Alfarhan, Saleh A. Alquraishi, Khaled AS Al-Rasheid, Julia Stagegaard, Günter Strauss, Mads Frost Bertelsen, Thomas Sicherheitsitz-Ponten, Douglas F. Antczak, Ernest Bailey, Rasmus Nielsen, Eske Willerslev and Ludovic Orlando: Speciation with gene flow in equids despite extensive chromosomal plasticity. In: PNAS. 111 (52), 2014, pp. 18655-18660
- ^ A b Colin P. Groves and CH Bell: New investigations on the taxonomy of the zebras genus Equus, subgenus Hippotigris. In: Mammalian Biology. 69 (3), 2004, pp. 182-196
- ↑ Julia T. Vilstrup, Andaine Seguin-Orlando, Mathias Stiller, Aurelien Ginolhac, Maanasa Raghavan, Sandra CA Nielsen, Jacobo Weinstock, Duane Froese, Sergei K. Vasiliev, Nikolai D. Ovodov, Joel Clary, Kristofer M. Helgen, Robert C. Fleischer, Alan Cooper, Beth Shapiro, and Ludovic Orlando: Mitochondrial Phylogenomics of Modern and Ancient Equids. In: Plos ONE. 8 (2), 2013, p. E55950
- ↑ a b c Ludovic Orlando, Jessica L. Metcalf, Maria T. Alberdi, Miguel Telles-Antunes, Dominique Bonjean, Marcel Otte , Fabiana Martin, Véra Eisenmann, Marjan Mashkour, Flavia Morello, Jose L. Prado, Rodolfo Salas-Gismondi, Bruce J. Shockey, Patrick J. Wrinn, Sergei K. Vasil'ev, Nikolai D. Ovodov, Michael I. Cherry Blair Hopwood, Dean Male, Jeremy J. Austin, Catherine Hänni and Alan Cooper: Revising the recent evolutionary history of equids using ancient DNA. In: PNAS. 106, 2009, pp. 21754-21759
- ↑ Samantha A. Price and Olaf RP Bininda-Emonds: A comprehensive phylogeny of extant horses, rhinos and tapirs (Perissodactyla) through data combination. In: Zoosystematics and Evolution. 85 (2), 2009, pp. 277-292
- ^ Charles Hamilton Smith: The natural history of horses. London, Dublin, 1841, pp. 1–352 (p. 321) ( [1] )
- ↑ Colin Groves and Peter Grubb: Ungulate Taxonomy. Johns Hopkins University Press, 2011, pp. 1-317 (pp. 13-17)
- ^ CS Churcher: Equus grevyi. In: Mammalian Species. 453, 1993, pp. 1-9
- ↑ Jared Diamond : Evolution, consequences and future of plant and animal domestication. In: Nature 418 (8), 2002, pp. 700-707, doi: 10.1038 / nature01019
- ↑ Valerii Glazko: An attempt at understanding the genetic basis of domestication. (PDF) In: Animal Science Papers and Reports. 21 (2), 2003, pp. 109-120