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.
"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."
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