|© ScienceNOW-- 2001 (104): 2
The common raven is one of the most familiar and recognizable
species throughout the Northern Hemisphere--or so ornithologists
thought. Now a study suggests that common ravens in California
are genetically distinct from common ravens in the rest of the
world. This case of so-called "cryptic genetic variation,"
when molecules reveal a difference hidden by similar morphology,
may lead ornithologists to split the common raven into two species.
||The ebony bird that croaked "Nevermore"
over Edgar Allan Poe's chamber door is famous worldwide,
being revered by native cultures of the Pacific Northwest
and appearing in everything from biblical verse to Norse
mythology. Biologists have observed the birds just as closely,
and they have noticed slight variations in appearance and
behavior among common ravens. But they didn't suspect a
split between California birds and all the others until
they saw the results of a Northern-Hemisphere-wide survey
of raven DNA. The genetic investigation, led by evolutionary
biologist Kevin Omland of the University of Maryland, Baltimore
County, included tissue samples from ravens across North
America and Eurasia. The researchers sequenced mitochondrial
DNA and found that DNA from birds in California and neighboring
states differed by up to 5% from DNA of ravens everywhere
else, such as Alaska, Maine, France, and Mongolia. This
large a difference implies that the populations haven't
interbred for more than 2 million years, the researchers
report in the 22 December Proceedings of the Royal Society
of London Series B. They suggest that the two raven
types may have been geographically isolated, possibly by
glaciation, and are now remerging.
|Kaw! Although they all
look alike to humans, common ravens in California are genetically
different from ravens elsewhere
CREDIT: Bernd Heinrich
The study is "a superb example of how new tools
from molecular biology can reveal cryptic, unsuspected
variation in even well-known vertebrates like birds,"
says H. Lisle Gibbs of McMaster University in Hamilton,
Ontario. But birdwatchers don't have a new species to
add to their life lists yet: Most observers agree with
the study authors that further research on mating preferences,
gene flow, and behavioral and habitat differences is needed
before ornithologists split the common raven into two
Omland's home page
of the common raven
Poe's "The Raven"