|
Left to right. This scarlet kingsnake could be easily
mistaken for its venomous relative (Photo credit David Pfennig) Middle. A
venomous coral snake from Florida (Florida Images/Alamy). Right. Scarlet
kingsnakes living in the North Carolina Sandhills have fine-tuned their mimicry
of coral snakes, even though — or perhaps because — coral snakes have become
extinct in the area (Photo credit Wayne Van Devender).
|
An article in
Nature News by Ewen Callway discusses North
Carolina scarlet kingsnakes evolving in North Carolina to more closely resemble
the eastern coral snake, a species no longer found in the area.
Scarlet kingsnakes are chasing an evolutionary ghost. In
North Carolina's Sandhills forest, the harmless snakes have evolved to better
resemble a poisonous species that vanished from the region more than 50 years
ago.
The scarlet kingsnake, Lampropeltis elapsoides, copies
the stripe patterns of deadly coral snakes, Micrurus fulvius, so well that
people use mnemonic rhymes to tell them apart, such as: “If red touches yellow,
you’re a dead fellow; if red touches black, you’re all right, Jack.” The
species live side by side across much of southeastern North America. The
scarlet kingsnake uses mimicry to dupe predators, such as red-tailed hawks,
keen to avoid attacking the venomous reptile.
The Sandhills, a pine and oak forest in the eastern
Carolinas, were once home to both snakes, but coral snakes disappeared from the
area in the 1960s, says Chris Akcali, an evolutionary biologist at the
University of North Carolina in Chapel Hill. He and his colleague David Pfennig
are interested in how biological mimicry evolves, and they wondered whether the
extinction of coral snakes would influence the colour patterns of scarlet
kingsnakes.
To find out, Akcali and Pfennig compared scarlet kingsnakes
from the Sandhills collected over the 40 years after coral snakes went extinct,
and compared them to kingsnakes from the Florida panhandle, where coral snakes
still slither. They expected that the Sandhills scarlet kingsnakes would have
started evolutionarily drifting and looking less and less like coral snakes.
“When I went and collected the data, I looked at it and
said, ‘This can’t be’,” Akcali says. The kingsnakes from the Sandhills that
were collected in recent years tended to more closely resemble coral snakes —
with red and black bands more similar in size — than did snakes collected in
the 1970s, which tended to have larger black bands. He and Pfennig detected no
such change in the Florida panhandle snakes over the same period. They report
their results today in Biology Letters1.
The result makes sense, Akcali says. “If you are a predator,
and you’re in an area like Florida, where coral snakes are everywhere, then you
should avoid anything that looks like a coral snake,” he says. “If you are in
North Carolina where coral snakes are really, really rare, predators can
benefit from attacking [mimics] sometimes.”
Scarlet kingsnakes in the Sandhills should eventually stop
resembling coral snakes, Akcali predicts. “Presumably, at some point predators
are going to act as if there are no coral snakes, and they should attack them
indiscriminately.“ A shortage of prey, he suggests, could provide the spark.
But Tom Sherratt, an evolutionary biologist at Carleton
University in Ottawa, is not so sure that scarlet kingsnakes’ mimicry will
become sketchier over time. “Many of the predators — especially avian ones —
are mobile and may visit locations where the model is present, which might
explain why selection for mimicry still lingers.”
Akcali, C. & Pfennig, D. W. Biol. Lett. http:/dx.doi.org/10.2098/rsbl.2014.0304
(2014).
Harper, G. R. Jr & Pfennig, D. W. Proc.
R. Soc. B 274, 1955–1961 (2007).