CHAPEL HILL — A new study by a UNC-Chapel Hill biology professor and a graduate student has raised questions about the nature of evolution and whether North Carolina's rarest venomous snake is now almost gone.
The study by David Pfennig, who specializes in evolution, and student Chris Akcali appears in the June edition of the online journal Biology Letters. Among other things, it asserts that the eastern coral snake is now either extinct or "functionally extinct" in the Sandhills region of the state, where many science books have long shown the snake to live.
This was the farthest north that heat-loving eastern coral snakes had been found. Like many species they were uncommon at the edge of their range.
But that's not the main point of the study. It actually focuses on a different serpent, the nonvenomous scarlet kingsnake, which has long been thought by many scientists to mimic the coral snake, taking advantage of similarities to persuade predators that it's dangerous, too.
Both feature bands of red, yellow and black, but in different order, leading to various versions of the rhyme "red on yellow, kill a fellow; red on black, friend of Jack's."
An earlier study that Pfennig performed with another student, William Harcombe, found that predators in areas without coral snakes were significantly more likely to attack decoys made of modeling clay in the proper ring pattern for scarlet kingsnakes.
That study required them to make more than 1,000 soft clay snakes, place them in areas with and without coral snakes, and meticulously tally the beak, claw and fang marks the decoys received from attackers. Predators of the snakes include bears, foxes, raccoons and various birds of prey.
In the new study, the researchers decided to test the evolutionary theory that if an animal was copying another that had vanished that the mimic would no longer continue to improve its disguise, because there would be no apparent benefit.
In falling short of proving it, they may have captured something interesting: a snapshot of a short period in which evolution was just coasting along.
The coral outlier
The coral snake is the biggest outlier in North Carolina's array of venomous serpents. It's a relative of the cobra and carries a particularly toxic venom that attacks the nervous system. It's slender, cylindrical and clad in bright colors.
The other venomous snakes in the state - the copperhead, water moccasin and a handful of rattlers - are all pit vipers, with a venom that attacks the blood and cardiovascular system. They generally have heavy bodies, arrowhead-shaped heads and favor earth tones.
The eastern coral snake is extraordinarily shy, living nearly its entire life out of sight in rodent burrows or under leaf litter or other cover. Its range is believed to include an arc across North Carolina's Sandhills and southeastern coastal plains.
But that doesn't seem to be true any longer, given that no one has positively identified a coral snake in the Sandhills since 1960.
Either it's extinct there or, for any practical purposes such as the effect on kingsnake coloration, it is so rare that it might as well be gone, Pfennig said.
For the study, Akcali located more than two dozen specimens of scarlet kingsnakes that had been collected since 1960. He chased these down in various museums, including the Smithsonian in Washington, and carefully made digital images of them.
The researchers measured the width of the various bands and found that even after the apparent extinction of the eastern coral snake in the Sandhills, scarlet kingsnakes continued to develop wider black bands and shrink their red and yellow ones, coming ever closer to the heavy proportion of black found on the coral snakes.
The shift, Pfenning said, was so clear that it was obvious to the naked eye.
The researchers also deployed more model snakes, retrieving the latest batch a month ago. The results show that predators are still wary of good mimics, Pfennig said.
That, and the evolving of the kingsnakes' bands, are sure to end eventually, Pfennig said. But for now both effects seem to be operating on momentum.
"We believe this is another example of how we can actually observe evolution over a short period, actually over a human's lifetime," he said.
The study has created a stir among the state's small circle of snake researchers.
"I don't want to completely dismiss it, but there are a lot of people asking questions about it," said Jeffrey C. Beane, collections manager for herpetology at the N.C. State Museum of Natural Sciences.
Beane said he wondered whether the scarlet kingsnake was actually mimicking the coral snake, whether evolution can occur that quickly and whether coral snakes are truly gone from the Sandhills.
The one place in the state where everyone seems certain that eastern coral snakes still live is in and around Carolina Beach State Park, south of Wilmington. Four were found there last year, Beane said, including one he saw himself. Single specimens have been positively identified in Bladen County in 1984, western Pender County in 1995 and Robeson County in 2009.
Otherwise, there have been few or no confirmed records, he said.
Also, while no coral snake has been found in the Sandhills for more than 50 years, not even as roadkill, it was hard to say for sure that a species as rare and secretive has truly vanished.
"These are all debatable issues," he said.
Michael Dorcas, a professor of biology at Davidson College and author of "A Guide to the Snakes of North Carolina," agreed that it would be hard to say coral snakes were extinct in the Sandhills, but he isn't willing to disagree with it, either.
Snake experts have done a huge amount of field work there in recent decades without seeing any, Dorcas said.
"I've read the paper, and I don't have any problem with the way it's worded," he said. "It's pretty interesting stuff they've found."