Written by Ximena Nelson
The author of this article, Jimenez Nelson, is a lecturer in animal behavior at the University of Canterbury, New Zealand. Her research focuses on animal communication and cognition, with a focus on jumping spiders and birds.
Translator: Chen Xuexin
In the animal kingdom, "liars" are everywhere. There are many classic examples in books describing mimesis (one species simulating another species during evolution), such as the king snake imitating the coral snake, and the aphid-eating fly camouflaging bees. One may not be familiar with the mimicry of one of the genus Arachnids, the genus, but in some ways, the mimicry of the genus is even more fascinating: they disguise themselves to look exactly like ants.
Ant spiders have a smooth body and an "extended version" of their body, which makes them look more ant, and is also clearly divided into three parts - head, chest and abdomen, but in fact they have only two parts like all spiders. To perfect the camouflage, the ant spiders walk with their three pairs of hind feet and lift the fourth pair of feet above their heads, swinging around to mimic the ant's antennae. They even use the fast, drifting, non-stop movement mode characteristic of ants to replace the stop-and-go motion mode that spiders usually have. It's an Oscar-caliber performance and a recipe for the species' success – today, more than 200 species of ant-spiders around the world thrive in the rainforests of Africa, Asia, Australia and the Americas.
The abundance of species diversity makes mimetic ants the most prevalent form of mimeticism, but little is known about it. New research is revealing incredible complexities when it comes to ant spiders mimicting ants.
Ant spiders gain a survival advantage by making themselves look like other species (i.e., poisonous ants), because predators avoid this ant as well as similar species. But ant spiders also pay a price: in order to make the camouflage more realistic, they must expose themselves to considerable danger. They must avoid predators and avoid becoming prey to ants.
To fake the real
The classical theory of mimesis was proposed by the British naturalist Henry Walter Bates. Bates argues that if a prey-eatable species is disguised as an unpalatable or completely toxic species, potential predators will be tricked into ignoring them, giving the pretender a survival advantage. In Bates' theory, predators, after preying on species that are difficult to swallow, learn from this unpleasant experience and try to avoid those that are poisonous, and thus avoid those who are harmless in themselves. This "parasitic" disguise is known as "Bayesian mimicry," in which one species utilizes another species' avoidance mechanisms.
But the mimic process is not as simple as Bates describes. For example, some species disguise themselves as another species not to deceive their predators to avoid predation, but to deceive their prey, to lure their prey by sending false signals, and thus to achieve a full meal – this is called "attack mimesis". There are many reasons why animals use mimesis, and spiders that mimic ants are perhaps the best example to help scientists elucidate the complexity of mimetic behavior and the evolutionary roots of this behavior.
The price of "cheaters"
In tropical rainforests, ants have more biomass than all vertebrates combined. As powerful environmental shapers, ants can have a huge impact on other "residents" in the environment. Therefore, they are the first choice to be imitated.
Ant spiders "steal" the ants' feared reputation by defending their nests by biting or stinging. In cases where an intruder can pose a lethal threat to an ant colony, such ants can usually rally the entire colony for defense, so predators would wisely choose to avoid eating prey from any such ant. But for ant spiders that want to deceive predators, they have to face some real dangers. For example, they need to live next to ants to avoid predators from feeling that they don't look like ants. If they are found to be "liars", they can only serve as a "lunch" for ants.
Living under the roof of an enemy is not the only price these ant-imitating spiders pay. Predators who specialize in eating ants— including other species of jumping spiders — attack them as prey, and the risk of this predation is exacerbated by fierce competition between males to get closer to females. However, cunning mimetics are able to proactively protect themselves from these threats. The spider's performance begins when an ant-eating jumping spider intends to approach it: its forefoot changes from a normal antennae posture to a raised state, perpendicular to its head, staring at the other jumping spider motionless. This "performance" seems to convey the signal that it is a spider, or at least not exactly an ant. Similarly, when a scientist (or other potential predator) tries to catch an ant spider attached to a plant, the ant spider will stop imitating the ant, jump off the plant, and hang on a silk thread to escape.
Imitation is derived from genes
To fully understand how mimetic behavior evolved and why animals simulate specific forms, scientists first need to know what factors make predators avoid mimetics. As early as the 19th century, Bates believed that predators must first suffer the loss of a certain creature before they would "remember" and actively avoid the creature or the simulater of the creature. But the behavior of ant spiders once again challenges the conventional wisdom that most jumping spiders instinctively avoid eating ants and ant spiders, not learning from their failed experiences.
In other words, the forces of evolution have "branded" this act of avoidance in the "bones" of predators. This is probably because predators who don't like to approach ants are more likely to survive and reproduce, and their genes are passed down from generation to generation, and eventually individuals who are born with ant-averse make up the majority of the population, while individuals who lack this trait are quickly eliminated in the evolutionary process.
Explore the mimetic world
Scientists have found that the complexity of ant spider mimicry has a warning effect. From the example of ant spiders, they learned that multiple predators created an mimetic species. In the case of ant spiders, studies have shown that in addition to the common jumping spiders and praying mantises, birds, lizards and frogs may also have an effect on ant spiders. Studies of other organisms also suggest that mimesis may involve both smell and hearing.
Scientists can now take related techniques to study the sensory experiences of various animals. For example, a high-frequency recorder can be used to visualize sounds that humans cannot hear; mass spectrometry techniques can be used to understand the hydrocarbon composition of ants and their mimetics, and thus to gain a deeper understanding of the biochemical processes in animals. Predators and prey are eternal rivals, and the use of these techniques to study mimesis and other natural phenomena will undoubtedly reveal the extraordinary game strategies that these animals have developed over the course of evolution.
This article is contributed by Global Science (Scientific American, Chinese edition) with edits.
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