Lizards can develop new 'love language' to suit their setting

Animal chemical cues can rapidly and flexibly change to suit new circumstances

Lizards A male Podarcis erhardii, the Aegean wall lizard | Colin Donihue

Male lizards are known to flash bright colours on their skin as sexual signalling to attract females and intimidate rival males. Sometimes a male lizard may dance around a female for a while before moving on to bite her on the neck as a prelude to sex.

Since chemical signals between animals are less obvious to humans and more technically complex to analyse, much of the existing studies on these signals have focused on insect pheromones relevant to certain agricultural applications.

Animal are found to shift their chemical signalling at a slow pace and it may take up to four generations to get a new one. However, animals can adapt very fast and change their communication in a new situation, according to a new research from Washington University in St. Louis.

"What we've discovered is that within species there is important variation in chemical signals depending on your context: Who's trying to eat you, who wants to mate with you and who you're trying to compete with," said Colin Donihue, a postdoctoral fellow in biology in Arts & Sciences at Washington University in St. Louis and lead author of a new study published on April 21 in the Journal of Animal Ecology.

Both lizards and snakes collect chemical cues from their surroundings by flicking out their slender forked tongues, then process those cues using a well-developed sensory organ in the roof of their mouths.

Lizards deposit their chemical messages encoded in secretions from specialized glands located on their inner thighs. The secretions are a waxy cocktail of lipid compounds that contains detailed information about the individual lizard that produced them.

In this study, researchers relocated groups of eight male and 12 female Aegean wall lizards (Podarcis erhardii) from a single source population in Naxos, Greece, to five small islets that lacked predators. Under normal conditions, these lizards would have to contend with a number of native and non-native predators—including snakes, birds and cats. Free from predators on the small islets, the lizard populations grew rapidly and competition for resources was fierce.

Over the next four years, when the scientists revisited the lizards, what they found was striking: On each of the predator-free islands, lizards rapidly and repeatedly developed a new chemical "mix" that was distinct from that of lizards in the source population. The changes were apparent after only four generations.

For the first time, researchers believe that they have demonstrated solid evidence that lizards can "put on a new cologne" to suit their setting.

"Signals to attract mates are often conspicuous to predators," said Simon Baeckens, a postdoctoral fellow at the University of Antwerp in Belgium and co-author of the new paper. "As such, sexual signals present a compromise between attractiveness and avoidance of detection. However, on these islets, there is no constraint on the evolution of highly conspicuous and attractive signals.

"Animals have spent over a billion years developing a complex chemical communication library. But we only invented the technology to identify many of those chemicals a century ago, and the experiments for understanding what those chemicals mean for the animals in nature have only just begun,” said Donihue.

"We found that animal chemical cues can rapidly and flexibly change to suit new settings, but this is only the beginning for understanding what the lizards are saying to each other."

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