Biology Reference
In-Depth Information
appeared on the North American east coast in the early 1800s, apparently
introduced by ships from Europe. Much later, in the 1940s, it colonized
the west coast of North America from California to Alaska. Analysis of
microsatellite alleles showed that
Botryllus
populations on the New Eng-
land and California coasts were quite distinct, making it unlikely that west
coast populations were introduced from the North American east coast
(Stoner et al. 2002). Thus, it appears that the populations on the North
American west coast are derived by an independent introduction from
Europe or from Asian localities to which the species has been introduced
from Europe. Although genetic analyses have not yet been conducted to
test these alternatives, ascidian colonies from Japan and California are so
similar genetically that they will grow together into a single colony.
Numerous other alien marine invertebrates have been introduced to Cal-
ifornia from Japan.
In some cases, the locale of origin has turned out to be quite unsus-
pected. Two of these cases involve crustaceans. The Chinese mitten crab
(
Eriocheir sinensis
), native to eastern Asia, has recently become established
on the Pacific coast of the United States. The volume of trans-Pacific
shipping would suggest that the most likely source was directly from Asia
in ballast water. Analysis of mtDNA samples, however, showed that this
population was derived from a source in Europe, where the species was
introduced more than 100 years ago (Hänfling et al. 2002).
Another cladoceran that has recently appeared in North America,
Daphnia lumholtzi
, is widespread in Australia and India, with populations
in several locations in Africa. Although Australia might seem the most
likely source for this species, allozyme and mtDNA analyses indicated that
alien populations were most similar to those of India and Africa (Havel et
al. 2000). This, combined with other evidence, suggests that
Daphnia
lumholtzi
was accidentally introduced from East Africa with fish that were
brought to North America for aquaculture.
Among terrestrial animals, useful information on the sites of origin of
alien pests has also been revealed. Studies of the genetics of native and
introduced populations of the Argentine ant (
Linepithema humile
) using
mtDNA fingerprinting and microsatellite analysis have pinpointed the
source area of this alien in both North America and Europe (Tsutsui et
al. 2001).When North American populations were compared to popula-
tions from 12 sites in Brazil and Argentina, they were found to be most
similar to those from Rosario, Argentina, a major port city located on the
Parana River northwest of Buenos Aires. Argentine ants from colonies
established in South Africa and near Rome, Italy, however, may have come
