Biology Reference
In-Depth Information
fingerprints of animals from various locations on both sides of the Atlantic
revealed that three distinct, but morphologically indistinguishable, forms
were present, two in Europe and three in North America. Each of the
three forms differed from the others by up to five mutations. The three
North American forms had evidently been considered to belong to one
species,
M. virens
. Of these three forms, as yet unnamed, two had appar-
ently been transported to European waters, probably in the ballast water
of cargo ships, in separate introduction events. One form, from the north-
ern coastline of the United States, was apparently introduced to an area
in the North Sea and has appeared along the coasts of Scotland and the
Netherlands.The second, from the southern Atlantic coast of the United
States, was apparently introduced directly into the Baltic Sea. Thus,
molecular genetic analysis revealed three cryptic species and pinpointed
the region of origin of the two alien forms that had appeared in Europe
(Bastrop et al. 1998).
In similar fashion, a jellyfish of the genus
Aurelia
appeared in a lagoon
in southwestern San Francisco Bay in 1988 (Greenberg et al. 1996). It
appeared to differ morphologically, however, from the common
A. aurita
of the outer coast of California. Allozyme analysis upheld this difference
and showed it to be similar to a form of
Aurelia
in Japan. The Japanese
Aurelia
also had been regarded as
aurita
, so the molecular genetic analysis
not only pinpointed the origin of the San Francisco Bay population, but
showed that it and the Japanese form were probably a distinct species.The
exact relationship of this yet-unnamed species to other members of the
genus
Aurelia
is still to be unraveled.
Another marine invertebrate example is provided by European crabs
of the genus
Carcinus
(Geller et al. 1997). These crabs have invaded the
east and west coasts of North America, as well as the coasts of South
Africa, Tasmanian Australia, and Japan. Presumably, these invasions were
the result of ballast water transport in cargo ships. Two similar species
occur in Europe,
C. maenas
along the Atlantic coast and
C. aestuarii
in the
Mediterranean Sea. Using mtDNA fingerprints, these species can easily
be distinguished. Analysis of specimens from the invaded regions revealed
that all
Carcinus
crabs on both the east and west coasts of North America
and in Tasmania were
maenas
. In both South Africa and Japan, where only
one species or the other previously had been detected, however, both
species were found to be present.
Uncertainties about the species status and region of origin also exist
among alien vertebrate animals, as indicated by the example at the chap-
ter outset. Another case involves swamp eels, large predatory fish of the
