When predators attempt to strike at a moving lizard, the vivid stripes on its head and trunk redirect the predator’s attention to the reptile’s tail – the expendable part. The findings are published in Royal Society Open Science this week.
There are various reasons why prey species would have conspicuous colors and patterns, even though these make them more visible to predators. Zebra stripes, for example, might serve as a form of anti-predation tactic called “motion dazzle.” During movement, highly contrasting patterns interfere with a predator’s ability to precisely estimate the speed or trajectory of the prey – which reduces the likelihood of successfully capturing a meal. Many lizards have contrastingly colored stripes that run parallel to the body and in the same direction as the animal's motion. But whether or not these so-called longitudinal stripes play an anti-predator function remained a mystery.
Gopal Murali and Ullasa Kodandaramaiah from the Indian Institute of Science Education and Research came up with a novel hypothesis: Through the motion dazzle effect, stripes along the vital anterior body parts redirect attacks towards non-vital posterior parts, such as the tail. For lizards like the skink above, the tail is less vulnerable, especially since it can be regenerated. In fact, they're known to drop their tails as an escape mechanism when threatened by predators.
To test their hypothesis, the duo recruited 155 people to “attack” virtual lizards on a touch screen computer. The rectangular prey moved across the screen at an average speed of 17 centimeters (6.7 inches) per second, and they either had black-and-white stripes or irregularly blotched white patterns on solid black.
The team found that prey with longitudinal stripes on the front half suffered fewer lethal attacks: They were hit more in the back half. Then, by employing “psychophysical” techniques, the team demonstrated that prey with striped patterning were perceived by the participants to be moving slower than they actually were – which might explain how the redirective effect works.