Washington, November 25 : Deploying robotic lizards in a Puerto Rico forest, UC Davis researchers have confirmed that animals can use body language to alert their neighbours before conveying any message, when the environment around them is noisy.
Research associate Terry Ord and professor emerita Judy Stamps, both with the Department of Evolution and Ecology, have found that Puerto Rican anole lizards perform eye-catching push-ups before beginning head-bobbing displays that advertise their territory and status.
Published in the Proceedings of the National Academy of Sciences (PNAS), this is the first time that any study has shown that animals in noisy environments can use visual displays to grab their neighbours' attention before initiating a more information-rich performance.
"What's really interesting is that the anoles are in some way assessing the environmental variables that are likely to affect the detection of their signals, and they are tailoring their behaviour accordingly," Ord said.
With this study, the research team have confirmed a nearly 30-year-old hypothesis that when the environment is noisy, animals may use conspicuous signals or "alerts", to let neighbours know that a message is forthcoming.
"It's a real formidable task for animals to be communicating out in the real world. Not only is there a lot of acoustic noise, but there's visual noise, as well. The trouble for an animal that tries to send an information-rich signal under low-light conditions or when the wind is blowing branches and leaves around is that the signal will not transmit very far. To solve that conundrum, the theory goes, you start the communication with a conspicuous component to attract the attention of your receivers," said Ord, who also holds a postdoctoral fellowship at Harvard University's Museum of Comparative Zoology.
For studying body language in yellow-chinned anoles (Anolis gundlachi) living in Puerto Rico's shaded forests, Ord designed realistic models that could dip, bend, and unfurl flaps of skin on their chins, known as dewlaps. His hand-painted latex constructions were so realistic they fooled humans and anoles alike.
The battery-powered motors could precisely imitate the typical four-legged pushups and head-bobbing displays performed by anoles.
The researcher planted the robots in the forest and observed how neighbouring anoles responded to the various displays.
Ord and Stamps viewed and analysed over 300 responses, and came to the conclusion that push-ups were an alert that the lizards mostly used only when necessary, such as when their neighbours were far away or when the light was dim.
The researchers also observed that both the push-ups and rapid dewlap extensions prompted neighbouring lizards to orient themselves more quickly to the displaying robots than when head bobs were performed without these alerts.
According to them, the fact that the lizards responded to the atypical, but eye-catching, dewlap extensions confirmed the hypothesis that any high-speed movement at the onset of a display could function as an effective alert.
Ord said that by adding animals that use visual alerts to the roster of species already suspected of using audible alerts, the case can be made that alert signals represent a significant example of evolutionary convergence.
"This is interesting because it's an example of very different species converging on a similar strategy," he said.