Most of the time, the toad-headed agama looks like any other desert lizard. Tan and fleet-footed, the reptile calls the arid regions of Central Asia and north-west China home. But in an instant, it can unfold special skin flaps bracketing the corners of its wide mouth, creating a pair of bright pink, spiny shields.
New research suggests the impressive display is used to startle predators.
żěè¶ĚĘÓƵs have long been aware of toad-headed agamas (Phrynocephalus mystaceus) and their colourful cheek flaps, but the precise purpose of the dramatic display was unknown. It was thought possible that the unexpected facial unfurling could frighten predators. But other uses were also considered – for instance, the flaps could be useful in courtship or territorial disputes.
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To understand the display’s purpose, at the Chinese Academy of Sciences in Chengdu and his colleagues studied the agamas in China’s Tukai desert, capturing the lizards and placing them in small outdoor arenas.
They tested if the cheek flaps were used in competition for mates, by recording the agamas’ behaviours in 14 male-male and 17 female-female pairs. Not a single lizard flared its flaps, but many flicked their curled tails around, suggesting the species may employ other physical cues in social interactions.
Next, in a 2.4-metre by 2.4-metre arena, the team presented 38 agamas with an image of a flying falcon printed on a laminated board, held overhead on a stick. Most of the lizards reacted to the “predator” by running away, and only 3 per cent flared their cheek flaps. When the researchers replicated this test with free-ranging lizards, only 12 per cent displayed their cheeks.
But when the agamas were surprised by an ambush attack – ensnared by a dental floss lasso – 84 per cent of them unleashed the flamboyant flaps.
The display may be a startle response, Qi and his team argue, meant to alarm an attacker when it draws near or has the agama pinned, and so aid the lizard’s escape.
This may be why the lizards mostly reserved their cheek flares for when they were brought to bay. Such displays are most effective at close range. The team’s analysis of light wavelengths reflecting off the pink flaps predicts that the colourful features would be quite noticeable to both bird and snake eyes.
at Carleton University in Canada lauds the researchers for their work. He adds that Australia’s frilled lizards (Chlamydosaurus kingii) use their giant collars for both discouraging predators and mating purposes, but blue-tongued skinks (Tiliqua sp.) show off their colourful maws only as a defence.
at the University of Missouri says the findings are valuable for scientists’ understanding of startle displays, which have received less empirical testing compared with animals’ social signals.
“In contrast, startle displays almost entirely rely on anecdotal evidence and have historically been glossed over,” he says.
Perez-Martinez points out that further research on the predator’s response to the agama’s display is necessary.
“The flip side of the coin remains to be tested,” he says. “Whether the displays are effective in eliciting a pause or retreat by a predator is unknown.”
Biological Journal of the Linnean Society
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