Lizards continue to evolve and lose resistance to snake venom in the reptile war

In Australia and snake-infested parts of Indonesia, it pays to be resistant to snake venom, even, or perhaps especially, if you are part of the same zoological order as snakes. A study into how large and medium-sized lizards deal with the problem of their cousins’ toxins has revealed an unprecedented evolutionary progression that the discoverers liken to Russian dolls.

Some large lizards like to feed on snakes, which makes sense because the squamates often live in similar territory, but this comes with its own dangers. Many years ago, Professor Bryan Fry of the University of Queensland discovered that venom is much more common in lizards than previously thought, but few produce anything nearly as potent as their legless counterparts.

However, such a diet carries risks, because the snakes do not like to be eaten. Smaller lizards can in turn fall prey to snakes, which use the venom to suppress their dinners. In either case, some resistance to the poison can be the difference between life and death. Fry and PhD student Uthpala Chandrasekara set out to investigate how the lizards cope with the poison, studied 27 species of varanid lizards (25 of them Australian) and discovered a much more complex story than they had imagined.

For starters, lizards have evolved two very different methods of poison resistance. Komodo dragons and the Perentie rely on armor that would be the envy of a medieval knight. “Their thick, bone-filled scales are enough to protect them from snake bites, while their large teeth are used to quickly dismember the fettuccini-like snakes,” Fry said in a statement to IFLScience.

Bryan Fry admires the snake-repelling scales of a Komodo dragon.

Bryan Fry admires the snake-repelling scales of a Komodo dragon, the future of humanity.

Image credit: Bryan Fry

Smaller lizards can’t carry as much weight, so they evolved biochemical defense mechanisms instead. Using synthetic nerves that Fry helped invent and which allow scientists to study nervous behavior without having to use live animals, the team found that some lizards have developed nerves that are less sensitive to the local snakes’ neurotoxins.

“Every biological application carries a burden,” Fry told IFLScience. In the case of neurotoxin resistance, this is a slower nerve response time – a problem for both primates and lizards. So while the large lizards remain armored, they quickly lose their resistance when their smaller counterparts are in places where snakes are not common. This may be the result of moving out of reach of the snakes, or of seeking out the trees, where some lizards have found safety.

Every time the lizards get too close to snakes for comfort, they develop new resistance. However, Fry told IFLScience that each time this happens, it is with a slightly different mutation. Consequently, zoologists can trace the lizards’ history by observing all the genetic changes that have caused them to evolve over and over again and lose resistance genes.

“This complex dance of adaptation has resulted in a Russian doll-like nesting of gains and losses over time and suggests that the evolutionary battle is not always in one direction,” says Chandrasekara.

Obviously the snakes don’t accept the resistance… okay, they certainly lie, but that doesn’t mean they just accept it. Instead, they continually develop new toxins that bypass the lizards’ resistance, creating a biological arms race that only stops if the two don’t overlap much.

Although Fry recently made headlines when he led the celebrity-backed discovery of the world’s largest snake, venom is his main specialty. Most of his discoveries are accompanied by suggestions that the work could lead to better antivenoms or have potential for medicine, following in the footsteps of captopril derived from Brazilian viper venom.

In this case, however, he told IFLScience there is “zero practical use”. That said, he sees the appeal of genetically modifying humans to have snake-repelling scales, and acknowledges a connection to the mad scientist in a Spiderman cartoon who says he doesn’t want to cure cancer, he “wants to[s] to turn people into dinosaurs.”

The study has been published in the International Journal of Molecular Sciences.

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