Ecologists find missing link in lizard tail-shedding puzzle
Animals have different defence mechanisms. Porcupines spread their sharp quills, Malaysian ants internally combust and sloths curl up into tight balls to resemble tree nests. But one of the strangest defence mechanisms is caudal autotomy, or what is commonly known as tail shedding, in lizards. New research published in the journal Evolution sheds light on what determines a lizard's ability to shed its tail when predators attack. According to the Greek-US research team that conducted the study, the key factor is venom. Observed in many lizards, caudal autotomy occurs when the vertebrae at the joint between the tail and the pelvis are weakened and easily broken. The lizard tightly contracts the muscles at the posterior of the pelvis, breaking the vertebrae and triggering the tail's break. By breaking off the tail, the lizard hopes the predator will focus on the tail giving the reptile enough time to get away. Over the years, experts have postulated that predator pressure controls how easily lizards drop their tails. The larger the number of lizard-eating predators, the stronger the need to make sure tail shedding works. Despite the advantages of tail shedding, there is a downside as well. Impaired mobility, slower growth rates and even lower social status can impact the lizards' lives. The experts have said, however, that the tail-shedding ability should be maintained if predators are lurking in the area. Led by ecologists from the University of Michigan in the US, the research team used a combination of laboratory tests and field measurements undertaken in mainland Greece and a number of Greek islands in the Aegean Sea, which are inhabited by different combinations of predators. Over 200 insect-eating lizards from 15 species were tested in the study; distinctions can be made between lizards that have dropped their tails and those that have retained their original tails (e.g. a regenerated tail is usually deformed). The ecologists targeted correlations between autotomy rates and the presence or absence of different types of lizard predators at the study's 10 collecting sites. The autotomy rate measures the ease with which lizards drop their tails. According to the researchers, tail shedding becomes easier as the rate increases. The researchers found that while evidence of the predator-pressure theory exists, predators are not created equal. 'The only predators that truly matter are vipers,' explained co-author Professor Johannes Foufopoulos of the University of Michigan's School of Natural Resources and Environment, and the Department of Ecology and Evolutionary Biology. 'In the Aegean, vipers are specialised lizard predators,' he added. 'So it makes sense, in retrospect, that the lizards' primary defence would be aimed against their main enemy, the viper. But no one had made this connection, until now.' According to Professor Foufopoulos, the peculiarities of viper attacks play a key role. Tail shedding comes in handy during non-venomous attacks only when the tail is firmly grasped by the predator, the researcher said. The ability to drop a tail as quickly as possible becomes especially important when a viper bares its fangs and strikes. He added that even a glancing contact with the lizard's tail can inject a lethal dose of venom. 'You lose your tail, but you come away with your life,' Professor Foufopoulos underlined. 'And you can always grow another tail.' Also participating in the study were the University of Athens and the Natural History Museum of Crete in Greece and Yale University in the US.
Countries
Greece, United States