但凡看过文革时期一部叫做《决裂》的电影的人，都记得片中的一句经典台词：“马尾巴”的功能。查查百度，得知马尾巴的功能还真不少！
保持马奔跑的平衡；夏季驱赶蚊蝇，给马消暑降温；躲避敌害，保护自己；繁衍生息不可缺少的一部分；分清优良品种的标准和参照物。
回到正题，大家都见过斑马，你有没有想过斑马为何有斑纹？恐怕大多数人都是见怪不怪，无非认为它是一种自然现象罢了。可是，这个世界上还真有为斑马纹“较真”的人！
美国戴维斯加州大学的科学家们不仅认真研究了斑马纹的功能，而且他们得出的研究结果已于4月1日发表在《自然—通讯》杂志上，你不会认为这是愚人节开的玩笑吧？
Tim Caro, Amanda Izzo, Robert C. Reiner, Hannah Walker, Theodore Stankowich.The function of zebra stripes. Nature Communications, 2014; 5 DOI:
10.1038/ncomms4535早在120年前，华莱士与达尔文曾就斑马纹发生过争论，并提出了多种假说，包括：一种伪装形式；迷惑捕食者，避免遭到猎杀；具有社交功能；防止寄生虫（如蚊虫）偷袭。
美国科学家首先描绘出斑马、马、驴的7个种及其亚种的地理分布图，观察其体表不同部位斑纹的宽度、密度和位置。然后，将动物的地理范围与各种变量（草原面积、大型猎食动物范围、温度和蚊虫）进行比较，由此得出斑纹与变量是否重叠的结论。
最后，研究团队排除了上述5种假说中的4个，只保留一种可能：防止蚊虫叮咬！此前有人发现蚊虫总是不喜欢停留在黑白相间的区域内（
flies prefer to land on uniformly colored, not striped, surfaces）。他们此次研究发现，凡是蚊虫越猖獗的地区，斑马纹就越多。
有人会问：为什么其他有蹄类动物没有斑纹？专家的解释是：以非洲为例，斑马的体毛比其他有蹄类动物的体毛短，而蚊虫口器的长度刚好能够叮咬斑马，却不能叮咬其他有蹄类动物。
如果这种解释合理，它将为过去颇受争议的“获得性遗传”现象提供新的佐证。那么，这种环境对基因的“塑造”是利用表观遗传模式吗？是否DNA甲基化修饰？有待进一步分析。
你认为这个解释及其所依据的研究结果靠谱吗？
以下是发表在Science Daily上的原文：
Scientists solve the riddle of zebras' stripes: Those pesky bugs
Date:
April 1, 2014
Source:
University of California - Davis
Summary:
Why zebras have black and white stripes is a question that has intrigued scientists and spectators for centuries. Scientists now examined this riddle systematically.
Why zebras have black and white stripes is a question that has intrigued scientists and spectators for centuries. A research team led by the University of California, Davis, has now examined this riddle systematically. Their answer is published April 1 in the online journalNature Communications.
The scientists found that biting flies, including horseflies and tsetse flies, are the evolutionary driver for zebra's stripes. Experimental work had previously shown that such flies tend to avoid black-and-white striped surfaces, but many other hypotheses for zebra stripes have been proposed since Alfred Russel Wallace and Charles Darwin debated the problem 120 years ago.
These include: A form of camouflage;
Disrupting predatory attack by visually confusing carnivores;
A mechanism of heat management; Having a social function;
Avoiding ectoparasite attack, such as from biting flies.
The team mapped the geographic distributions of the seven different species of zebras, horses and asses, and of their subspecies, noting the thickness, locations, and intensity of their stripes on several parts of their bodies. Their next step was to compare these animals' geographic ranges with different variables, including woodland areas, ranges of large predators, temperature, and the geographic distribution of glossinid (tsetse flies) and tabanid (horseflies) biting flies. They then examined where the striped animals and these variables overlapped.
After analyzing the five hypotheses, the scientists ruled out all but one: avoiding blood-sucking flies.
"I was amazed by our results," said lead author Tim Caro, a UC Davis professor of wildlife biology. "Again and again, there was greater striping on areas of the body in those parts of the world where there was more annoyance from biting flies."
While the distribution of tsetse flies in Africa is well known, the researchers did not have maps of tabanids (horseflies, deer flies). Instead, they mapped locations of the best breeding conditions for tabanids, creating an environmental proxy for their distributions. They found that striping is highly associated with several consecutive months of ideal conditions for tabanid reproduction.
Why would zebras evolve to have stripes whereas other hooved mammals did not? The study found that, unlike other African hooved mammals living in the same areas as zebras, zebra hair is shorter than the mouthpart length of biting flies, so zebras may be particularly susceptible to annoyance by biting flies.
"No one knew why zebras have such striking coloration," Caro said. "But solving evolutionary conundrums increases our knowledge of the natural world and may spark greater commitment to conserving it."
Yet in science, one solved riddle begets another: Why do biting flies avoid striped surfaces? Caro said that now that his study has provided ecological validity to the biting fly hypothesis, the evolutionary debate can move from why zebras have stripes to what prevents biting flies from seeing striped surfaces as potential prey, and why zebras are so susceptible to biting fly annoyance.
http://www.sciencedaily.com/releases/2014/04/140401112111.htm以下是发表在Science上的焦点介绍：
ScienceShot: Why the Zebra Has Its Stripes
1 April 2014 12:30 pm
1 CommentTim Caro
Zebras’ bold striped patterns have puzzled scientists for nearly 150 years. Researchers have offered a lengthy list of possible explanations, from confusing predators by creating a distracting dazzle when a herd gallops away, to helping the animals avoid biting flies. Support for the dazzler hypothesis comes from computer tests using people, who have trouble tracking striped, moving objects on a computer; while other studies have shown that the
flies prefer to land on uniformly colored, not striped, surfaces. Now, a team of scientists reports online today in Nature Communications that it has tested these hypotheses—as well as suggestions that the stripes might cool zebras down or make them more attractive to mates—to see which one makes the most ecological sense. The winner:
those pesky, blood-sucking, disease-carrying (such as parasitic trypanosomiasis) biting flies. The team discovered that the ranges of the horse fly and tsetse fly species and the three most distinctively striped zebra species (Equus burchelli, E. zebra, and E. grevyi) overlap to a remarkable degree. They did not find a similar ecological match for any of the other hypotheses, not even those involving predators. Instead, the researchers argue that biting flies are the most likely reason that zebras, such as those shown above grazing in Tanzania’s Katavi National Park, evolved their distinctive ornamentation. The insects, they note, harass the equids almost year-round, and are known to torment domesticated horses in these areas. The zebras’ black-and-white patterns, which others have shown seem to interfere with the flies’ vision, at least give them a bit of a break. Why equids are so susceptible to the flies’ attacks remains mysterious, but, as the researchers found, the zebras’ short coats may make them particularly vulnerable, and the diseases the flies carry are often fatal.
http://news.sciencemag.org/evolution/2014/04/scienceshot-why-zebra-has-its-stripes
