The common blue-tongue lizard (Tiliqua sincoides), found throughout mainland Australia, uses its tongue as a defence against being eaten, according to new research from scientists at Macquarie University in Sydney.
The lizards – or, more accurately, skinks, of the family Scincidae – are a single species with two colour forms that are often referred to by different common names, according to the Australian Museum. The smaller lizards on the east coast are called eastern blue-tongue skinks and the larger, yellower animals from northern Australia are called northern blue-tongue skinks.
The study, published in the journal Behavioral Ecology and Sociobiology, found that the animals’ characteristic blue tongue is likely evolved as a protection against predators.
“Not only are their tongues blue, but they also have a very pure ultraviolet component, and the purest or most obvious UV was also at the rear of the tongue,” says study author Martin Whiting, part of Macquarie University’s ‘Lizard Lab’.
“UV is not visible to most mammals (including humans), but is visible to lizards, birds and snakes. Given that both male and female blue tongues have UV tongues, we tested the hypothesis that the tongue colour probably evolved in response to predation pressure.”
The study notes that from camouflage to warning coloration (known technically as aposematism), anti-predator strategies are ubiquitous in nature. Some prey exhibit a specific type of behavior, such as ‘deimatic’ displays, defined as “momentary, transient, and highly conspicuous, inducing a startle response and/or overloading the senses of an attacking predator such that the predator pauses, slows, or stops the attack”.
The researchers placed northern blue tongues (T. scincoides intermedia) into a large outdoor enclosure, to test their behavioural responses to artificial predators. The lizards were presented with a model snake, bird, fox, goanna (a type of monitor lizard), and a piece of wood as a control element.
“Blue-tongue lizards have a highly conspicuous tongue,” Whiting says, “but unlike many other kinds of lizards, it’s a big tongue – the surface area is large. When blue tongues do a ‘full tongue’ display, the mouth is opened widely, and the tongue is flattened and expanded.
“At the same time, they may hiss and puff-up their body for maximum effect. This behaviour, in combination with a highly conspicuous tongue, can be quite intimidating for anyone that has got too close to a wild bluey.”
The animals showed little response to the piece of wood but reacted strongly to the model predators that would normally represent the greatest threat.
“By delaying their display until the predator was very close, and exposing the rear of the tongue, which has the most UV and which is the brightest, blueys maximise their chance of intimidating a predator and surviving another day,” says Macquarie researcher Arnaud Badiane.
The study notes that timing of this tongue display is crucial: “If performed too early, a display may break the lizard’s camouflage and attract unwanted attention by predators and increase predation risk. If performed too late, it may not deter predators.”