在自然界中，许多动物出于各种目的模仿他人。现在科学家们发现了这种奇特能力的最新例子——发现刚果巨型蟾蜍模仿有毒的加蓬蝰蛇的外表和行为，以避免被捕食者吃掉。
根据得克萨斯大学埃尔帕索分校和刚果民主共和国自然科学研究中心(刚果博士)的作者，这是世界上第一个蟾蜍假扮成蛇以逃避捕食的例子。
蟾蜍(硬化通道)——生活在中部非洲的热带雨林——相对较大，长达5.5英寸。它们可能是夜行动物，大部分时间都在森林地面觅食，尽管两栖动物在野外没有得到很好的研究。
同时，毒蛇(Bitis gabonica)——横跨中部、东部和南部非洲——是非洲大陆最大的蛇之一，身长超过5.5英尺，体重约17.5磅。它们是夜间活动的、行动缓慢的伏击食肉动物，拥有世界上最长的蛇牙，比任何其他蛇都产生更多的毒液。
为了突出它们的致命性，在以前的研究中，科学家们已经表明西非的习惯猴子——它们忽略了大多数蛇——可以从很远的地方认出加布恩毒蛇，如果它们看到了，就会变得害怕，警告它们的同伴远离它们。
根据发表在自然历史杂志作者认为，潜在的捕食者避开蟾蜍是因为两栖动物和加蓬蝰蛇在颜色、形状、大小和行为上有相似之处。
德克萨斯大学埃尔帕索分校的主要作者伊莱·格林鲍姆说，尽管相似性并不完美——许多动物模仿的例子并不完美——但这种伪装很好地满足了它的目的，因为对捕食者来说，错误(即某些死亡)的后果太高了新闻周刊。
格林鲍姆说:“与该地区绝大多数其他青蛙相比，蟾蜍相对较大，因此它们可能非常容易被一系列以青蛙为食的食肉动物捕食，包括哺乳动物、鸟类、大型蜥蜴和蛇。”。
“因为加蓬蝰蛇拥有世界上最长的獠牙，而且它咬人时能够注射大量有毒毒液，所以这些食肉动物很可能不惜一切代价避开毒蛇，”他说。
主要作者把他对最新结果的反应描述为“惊讶和惊奇”的结合。
“这是世界上第一个癞蛤蟆假装成蛇以避免被捕食的例子，所以结果既独特又重要，”他说新闻周刊。“这让我想到了我们在刚果民主共和国探索不足的森林中尚未发现的其他惊人的东西。”
研究人员在比较了野生和捕获的蟾蜍和毒蛇标本后得出了他们的结论。这些比较表明蟾蜍身体的颜色模式和形状与毒蛇头部的颜色模式和形状非常匹配。
但是蟾蜍除了这种视觉模仿外，还有另一个锦囊妙计。两栖动物在野外也会发出嘶嘶声，类似于加蓬蝰蛇和其他蛇受到干扰时发出的警告嘶嘶声。这是根据这篇论文的另一位作者，自然科学研究中心的奇夫达·库桑巴所说的。
在这项研究中，研究人员还发现，刚果巨型蟾蜍往往只出现在加布龙毒蛇也存在的地区。从生物学角度来看，这是有道理的，因为蟾蜍的伪装只会吓跑熟悉毒蛇的捕食者。事实上，作者在论文中提供了证据，表明蟾蜍和毒蛇可能共同进化，首次出现在大约同一时间——400万到500万年前——支持模仿假说。
这是从空中角度对刚果巨型蟾蜍和加蓬蝰蛇进行的并排比较，展示了它们在外观上的相似之处。
“我们的研究是基于十年的实地调查和有幸亲眼目睹蟾蜍行为的研究人员的直接观察。格林鲍姆在一份声明中说:“我们确信这是贝特西拟态的一个例子，一个无害的物种通过伪装成危险或有毒的物种来躲避捕食者。”。
“为了充分验证我们的假设，我们必须证明掠食者被成功欺骗，但这在野外很难做到，因为在野外蟾蜍很少遇到。然而，基于我们研究中提供的多种证据来源，我们相信我们的模仿假说得到了很好的支持，”他说。
格林鲍姆说，动物模仿自然界中其他动物有许多原因，但最常见的一个原因是避免被吃掉。动物王国里有无数的例子，但也许最著名的模仿物是蝴蝶，一些无毒的物种模仿其他食肉动物不可食用的物种。
许多无毒的蛇也模仿有毒的物种，而名副其实的“模仿章鱼”能够模仿剧毒的鱼。然而，最新的论文是第一篇展示两栖动物模仿毒蛇的论文。
捷克共和国布拉格查尔斯大学的研究员jindřich·布莱恰没有参与最新的研究，他将这篇论文的发现描述为“令人兴奋”,因为它展示了试图伪装自己的看似“神秘”的蝰蛇作为贝提森模型的潜力——这种动物是模仿者模仿的。
“神秘的外观通常被认为与显著性相矛盾，根据定义，显著性是贝特西模型功能所需要的，”他说。“然而，掠食者的眼睛和大脑决定了人类的显著性，而不是肉眼。"
尽管如此，布莱恰指出，在解释关于除我们之外的动物感知能力的假设的结果时，保持谨慎是很重要的。
“我们也许能够比较形态学或者模拟动物的感官输入，但是我们仍然缺乏对动物大脑如何工作的更深入的理解，”他说。“尽管我们似乎越来越清楚地普遍低估了动物的认知能力，但我们需要进一步发展我们对动物思维的洞察力。"
THIS GIANT TOAD MIMICS A DEADLY VENOMOUS VIPER WITH THE WORLD'S LONGEST SNAKE FANGS TO AVOID BEING EATEN
In nature, many animals mimic others, for a variety of purposes. Now scientists have uncovered the latest example of this peculiar ability—finding that the Congolese giant toad mimics the appearance and behavior of the venomous Gaboon viper to avoid being eaten by predators.
According to the authors from the University of Texas at El Paso and the Centre de Recherche en Sciences Naturelles, Democratic Republic of the Congo (DR Congo), this is the first example in the world of a toad pretending to be a snake to avoid predation.
The toad (Sclerophrys channingi)—which lives in the rainforests of central Africa—is relatively large, measuring up to five-and-a-half inches in length. They are probably nocturnal, spending most of their time foraging for food on the forest floor, although the amphibians are not well-studied in the wild.
Meanwhile, the viper (Bitis gabonica)—found across central, eastern and southern Africa—is among the largest of the continent's snakes, reaching lengths of more than five-and-a-half feet and weights of around 17-and-a-half pounds. They are nocturnal, slow-moving, ambush predators, have the longest snake fangs in the world and produce more venom than any other serpent.
To highlight their deadliness, in previous research, scientists have shown that habituated monkeys in West Africa—which ignore most snakes—can recognize Gaboon vipers from a great distance and will become terrified if they see one, warning their companions to stay away.
According to the latest study published in the Journal of Natural History, the authors argue that potential predators avoid the toads due to the similarities in color pattern, shape, size and behavior between the amphibians and the Gaboon viper.
Even though the similarity is not perfect—many examples of animal mimicry are imperfect—the disguise serves its purpose well enough because the consequences of being wrong (i.e. certain death) for predators is too high, lead author Eli Greenbaum, from the University of Texas at El Paso, told Newsweek.
"Because the toads are relatively large compared to the vast majority of other frogs in the region, they are likely to be very tempting prey to a suite of generalist predators that are known to eat frogs, including mammals, birds, large lizards and snakes," Greenbaum said.
"Because the Gaboon Viper has the longest fangs of any snake in the world and it is capable of injecting huge quantities of its toxic venom when it bites, many of these predators likely avoid the viper at all costs," he said.
The lead author described his reaction to the latest results as a combination of both "astonishment and wonder."
"This is the first example in the world of a toad pretending to be a snake to avoid predation, so the results are both unique and important," he told Newsweek. "It makes me speculate about other amazing things we have yet to discover in the poorly explored forests of Democratic Republic of the Congo."
The researchers came to their conclusions after comparing both wild-caught and captive specimens of the toad and viper. These comparisons showed that the color pattern and shape of the toad's body matched up well with those on the viper's head.
But the toad has another trick up its sleeve in addition to this visual mimicry. The amphibian also makes a hissing noise when found in the wild that is similar to the warning hiss that the Gaboon viper and other snakes produce when they are disturbed. That's according to another author of the paper, Chifundera Kusamba, from the Centre de Recherche en Sciences Naturelles.
In the study, the researchers also found that the Congolese giant toad tends to only be found in areas where the Gaboon viper is also present. This makes sense from a biological perspective given that the toad's disguise is only likely to scare off predators that are familiar with the viper. In fact, the authors provide evidence in the paper to suggest that the toads and vipers likely co-evolved, first appearing around the same time—between four and five million years ago—supporting the mimicry hypothesis.
This is a side-by-side comparison between a Congolese giant toad and a Gaboon viper from an aerial perspective, showing the similarities in appearance.
"Our study is based on ten years of fieldwork and on direct observation by researchers lucky enough to see the toad's behavior first-hand. We're convinced that this is an example of Batesian mimicry, where a harmless species avoids predators by pretending to be a dangerous or toxic one," Greenbaum said in a statement.
"To fully test our hypothesis, we'd have to demonstrate that predators are successfully duped, but this would be very difficult in the wild, where the toads are only encountered rarely. However, based on multiple sources of evidence provided in our study, we are confident that our mimicry hypothesis is well-supported," he said.
There are many reasons why animals mimic other animals in nature, according to Greenbaum, but the most common one is to avoid being eaten. There are countless examples in the animal kingdom, but perhaps the best-known mimics are butterflies, with some non-toxic species impersonating others that are inedible to predators.
Many non-venomous snakes also mimic venomous species, while the aptly named "mimic octopus" is capable of impersonating highly toxic fish. Nevertheless, the latest paper is the first to demonstrate an amphibian mimicking a venomous snake.
Jindřich Brejcha, a researcher from Charles University in Prague, Czech Republic, who was not involved in the latest study, described the findings of the paper as "exciting" because it demonstrates the potential for seemingly "cryptic" vipers, which try and camouflage themselves, to function as Batesian models—the animal that the mimic copies.
"The cryptic appearance is generally thought to be contradictory to conspicuousness, and it is conspicuousness that is by definition required for Batesian model functionality," he said. "However, predators' eyes and brains decide about the conspicuousness not the naked eye of humans."
Nevertheless, Brejcha notes that it is important to be cautious when interpreting results that deal with presumptions about the perceptive capacities of animals other than ourselves.
"We may be able to compare morphology or model animal sensory inputs, but we still lack a deeper understanding of how animal brains work," he said. "Even though it seems more and more clear that we generally underestimate animals' cognitive skills, we need to further develop our insights into the minds of animals."
