Studies of island bird
populations have taught us a lot about evolution, but it's hard to catch birds
in the act of naturally colonizing new islands. Instead, a new study
from The Auk: Ornithological Advances examines what's happened by
looking at the genetics of a species that arrived in Hawaii in the twentieth
century through decidedly unnatural means—us.
Japanese Bush-Warblers were
introduced to Oahu in 1929 and have since become established on all the
main islands of
Hawaii, providing a unique opportunity to follow post-invasion evolution on a
known, recent timescale. Northern Arizona University's Jeffrey Foster and his
colleagues took blood and muscle samples from 147 bush-warblers living on five
islands between 2003 and 2005. Their results indicate genetic drift is
occurring—Oahu's birds have higher genetic diversity than those on other
islands, whose populations were founded by smaller groups of individuals, just
as population genetic theory predicts. Kauai bush-warblers, however, appear to
be on a distinct genetic trajectory from those on other islands. Kauai is three
times as far from Oahu as the closest other islands, and appears to have
received a unique subset of the overall genetic diversity found elsewhere, but
it remains to be seen whether the trend on Kauai will continue in the future or
if continued dispersal of birds among islands will blur these differences.
"This study nicely showed genetic divergence for a very short period using
the artificially introduced Japanese Bush-Warblers," according to Shoji
Hamao of Japan's National Museum of Nature and Science, an expert on the
species.
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