Striped lizards have always fascinated scientists, who are curious as to how these creatures escape predators when their bright lines can give them away.
Now, researchers from the Indian Institute of Science Education and Research in Thiruvananthapuram have shown how the stripes can help lizards. The stripes — termed as ‘motion dazzle’ patterns — cause a predator to misjudge the speed of the lizard’s movement.
The researchers developed a computer game wherein volunteers were asked to “catch” (that is, touch) moving prey (a patterned rectangle), both with and without stripes, on a touch screen.
Motion dazzle
“We noticed that most of the time the volunteers touched the tail-end of the prey. They perceived the prey to be moving slower [than what it was]. This shows the power of motion dazzle. The stripes help the lizard to redirect the attack to its tail and save its head. Sometimes it even detaches the tail and runs away,” explains Gopal Murali, PhD scholar at the institute and corresponding author of the study. The experiment also showed that lizards with stripes were attacked less than those with blotched patterns.
Their recent work, published in the journal Behavioural Ecology, compares the body size of the lizard to motion dazzle stripes. The scientists found that smaller lizards benefited more. Natural selection might have favoured striped colouration in smaller species, which have high speed and greater manoeuvrability.
Smaller the better
Having a small body with a relatively long tail increases the chances of survival as the lizard is likely to be hit only on the tail. In some lizard species, longitudinal stripes are present only in juveniles, which disappear as they grow up.
Many studies carried out on snakes have also shown that longitudinal stripes were present in shorter snakes. They have stripes that run the full length of the body and motion dazzle may help them avoid being captured.
Out of about 6,000 species of lizards, only few have detachable tails. The researchers are planning further studies to understand the relationship between motion dazzle and detachable tails.
Clinching evidence
“Animals have evolved a breathtaking array of colour patterns, many of which have been thought to protect against predation. But these ideas have remained untested because experiments with real predators attacking live prey are very difficult to design, and in many cases also raise ethical concerns,” explains Ullasa Kodandaramaiah, scientist at IISER-TVM and a co-author of the paper.
“Researchers now have been able to explain the presence of many kinds of colour patterns in animals through experiments where humans attack ‘virtual’ prey. We have adopted such an approach to ask the question ‘Why do so many lizards have conspicuous stripes, which could make them more easily detected by predators?’. Our results add to a growing body of knowledge indicating that some striking colour patterns can be very effective [in enabling survival] despite enhancing [the risk of] detection.”
