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UV in Lizard’s Blue Tongue Evolved to Scare Predators

A new study by researchers at Macquarie University has shed light on why blue-tongued lizards have such an outrageously coloured tongue. The study, published in Behavioral Ecology and Sociobiology (https://goo.gl/UxeiRq), found that the lizard’s blue tongue likely evolved from the pink tongue of most lizards in order to scare off predators.

“Not only are their tongues blue, but they also have a very pure UV component, and the purest or most obvious UV was also at the rear of the tongue,” said study author A/Prof Martin Whiting. “UV is not visible to most mammals (and therefore 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.”

Some animals use a highly conspicuous display in an attempt to warn off a potential predator. “Blue-tongue lizards have a highly conspicuous tongue 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,” Whiting said.

The researchers placed blue-tongues in a large outdoor enclosure where they held them briefly in order to test their behavioural responses to a model snake, bird, fox, goanna, and a control element (a piece of wood) in order to establish if they use their full-tongue display as a means to intimidate a predator.

“Blueys did not respond much to the piece of wood, but they showed a strong response to the model predators that would normally represent the greatest threat,” said Arnaud Badiane, a PhD student on the research team. “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.”

Current research involves the use of a robotic blue-tongued lizard with interchangeable tongues of different colours to test intimidation of predators.