Okay, you didn’t plan to begin your day with this but be patient. Snake species didn’t necessarily evolve venom by a long, slow, process of natural selection acting on random mutations (Darwinism). Some get their venom from a variety of sources and sometimes they change sources (whatever works?) So unfolds a curious tale of a snake that switched suppliers: The Southeast Asian snake, one of the Rhabdophis species, gets lethal by eating poisonous toads and then unloads the venom on its own predators. But the story takes a twist…
Commonly called “keelbacks” and found primarily in southeast Asia, the snakes sport glands in their skin, sometimes just around the neck, where they store bufadienolides, a class of lethal steroids they get from toads, their toxic prey of choice.
“These snakes bend their necks in a defensive posture that surprises unlucky predators with a mouthful of toxins,” says Utah State University herpetologist Alan Savitzky, who has long studied the slithery reptiles.
“Scientists once thought these snakes produced their own toxins, but learned, instead, they obtain it from their food — namely, toads.”
In a surprising twist, Savitzky and colleagues discovered not all members of the genus derive their defensive toxin from the same source. The multi-national team, consisting of researchers from USU; Kyoto University, University of the Ryukyus and Nihon University in Japan; the Chinese Academy of Sciences and Leshan Normal University in China; the National Pingtung University of Science and Technology in Taiwan; the University of Sri Jayewardenepura in Sri Lanka; and the Vietnam Academy of Science and Technology, reports a species group of the snakes, found in western China and Japan, shifted its primary diet from frogs (including toads) to earthworms.
The earthworms don’t produce the toxins; instead, the snakes also snack on firefly larvae, which produce the same class of toxins as the toads. Their findings appear in the Feb. 24, 2020, early online issue of the Proceedings of the National Academy of Sciences.
“This is the first documented case of a vertebrate predator switching from a vertebrate prey to an invertebrate prey for the selective advantage of getting the same chemical class of defensive toxin,” says Savitzky, professor in USU’s Department of Biology and the USU Ecology Center.
Given the distant relationship between toads and fireflies, he says, the dramatic dietary shift most likely involved a chemical cue shared by the toads and fireflies; perhaps the toxins themselves.
“This represents a remarkable evolutionary example of adaptation to compensate for the absence of defensive compounds following a shift to a new class of prey,” Savitzky says.
Utah State University, “Surprising evolutionary shift in snakes” at ScienceDaily
But the moral of the tale is: Be cautious when someone offers a simple-minded Darwinian pathway to explain some feature of a life form. Evolution, as a history of life, is—like all histories—complicated. What we are told is remarkable is probably normal. It just doesn’t coincide with the claims made by Darwinians that a simple application of their theories can interpret all of life.
FYI, here’s the snake capturing a toad and its venom:
But, it appears, some snakes have found earthworms easier to manage, supplemented with poisonous firefly larvae, which deter their own predators. (We did not find vid for this just now.)