http://www.eurekalert.org/pub_releases/2007-03/uocp-nbs031607.php
New bird species found in Idaho
Public release date: 16-Mar-2007
New finch species demonstrates the co-evolutionary arms race
One does not expect to discover a bird species new to science while
wandering around the continental United States. Nor does one expect
that such a species would provide much insight into how coevolutionary
arms races promote speciation. On both fronts a paper to appear in The
American Naturalist proves otherwise. Julie Smith, now at Pacific
Lutheran University, and her former graduate advisor, Craig Benkman at
the University of Wyoming, have uncovered strong evidence that
coevolution has led to the formation of a species of bird new to
science in the continental United States. Benkman discovered in 1996
what appears to be a new species restricted to two small mountain
ranges in southern Idaho (the South Hills and Albion Mountains). This
species is a morphologically and vocally distinct "call type" of red
crossbill (Loxia curvirostra complex), which is a group of seed-eating
finches specialized for extracting seeds from conifer cones. Fieldwork
by Smith has revealed some of the mechanisms that have contributed to
the nearly complete cessation of interbreeding between this crossbill
and other call types that move into the South Hills every year. Perhaps
most remarkable is that this new crossbill evolved because of a
coevolutionary arms race between crossbills and lodgepole pine (Pinus
contorta) in the last five to seven thousands years.
As South Hills crossbills exerted selection on lodgepole pine for
increased seed defenses, lodgepole pine in turn exerted selection on
crossbills for larger bills to deal with these increased seed defenses.
This coevolution has caused these crossbills to diverge substantially
in bill morphology from other crossbills. Because the South Hills
crossbill is adapted to remove seeds from the well-defended cones
there, it is a superior competitor and thereby limits the less well
adapted and nomadic call types to breeding at very low frequencies in
the South Hills. Such ecological differences lead to premating (i.e.,
before mating) reproductive isolation, which is nearly completed by
strong assortative pairing among the different call types (>99% of
South Hills crossbills pair with another South Hills crossbill). "This
indicates that levels of reproductive isolation characteristic of
recognized species can evolve rapidly even in the continued face of
potential gene flow" says Benkman. It also shows that coevolution can
be a potent force for rapidly generating biodiversity.
###
Julie W. Smith and Craig W. Benkman, "A coevolutionary arms race
causes ecological speciation in crossbills" American Naturalist. 2007.
169:455-465.
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