Evolution is part of survival. This rings true for common garter snakes that were found to have evolved to survive on toxic newts.
Researchers led by Joel McGlothlin, a Virginia Tech Global Change Center affiliate, have found that several snake species like the common garter snakes are able to prey on poisonous animals such as the rough-skinned newts thanks to a hundred million years of evolution.
The snakes' ability to fight toxins produced by the amphibians is due to only one alteration in the gene, which created a domino effect — one genetic change triggers a change in another. Over a period of time, the amino acids acting on three sodium channels present in the snakes' muscles and nerves evolved, allowing some of the snakes to counter the toxicity of the newts. However, the researchers also found that the evolution of resistant muscles can only be possible in species that have the resistant nerves, which evolved about 40 million years before.
"Garter snakes and newts are locked in a coevolutionary arms race where as the newts become more toxic, the snakes become more resistant," said McGlothlin, who is also an affiliate of Fralin Life Science Institute and a biological sciences assistant professor at the Virginia Tech College of Science. "However, without the leg-up provided by those resistant nerves, snakes wouldn't have been able to withstand enough toxin to get this whole process started."
For their study, the researchers conducted gene sequencing of three sodium channels in 82 species, including 78 snakes, two lizards, one turtle and one bird. Gene mapping revealed when the evolutionary gene started to appear. The researchers noted that the snakes gain more toxin resistance as time passed, with gene changes following a specific order — resistant nerves developing prior to the toxin resistant muscle.
"The two nerve channels outside the brain, however, have both evolved resistance to the toxin, and they've done so independently. When we compared the DNA sequences to a closely related lizard, there were changes unique to the snakes that should provide resistance to the toxin," said McGlothlin.
They also noted that some species of the birds can prey on toxic newts and still survive. To further understand the pattern, the researchers are planning to study how the birds developed the same resistance.
McGlothlin said their study is an important look at the complexity of gene adaptation.
The National Science Foundation-funded study will be published in Current Biology on June 20.
