Biology Reference
In-Depth Information
introductions have occurred by transport of attached organisms on ship
hulls or release of ballast water from transoceanic cargo ships. Asian sea
anemones (
Diadumene lineata
), which reproduce largely by clonal growth,
have apparently been introduced on several occasions, so several or many
genotypes are present in many alien populations (Ting and Geller 2000).
Introductions to the North American Great Lakes, such as those of zebra
and quagga mussels (
Dreissena polymorpha
,
D. bugensis
), typically involve
massive founding populations that carry a large fraction of the genetic
variability of source populations (Stepien et al. 2002). On the other hand,
some introduced marine mollusks appear to show reduced genetic vari-
ability (Holland 2000).
A well-documented example of high genetic variability in an alien
species is provided by the brown mussel (
Perna perna
), native to the
South Atlantic and Indian Oceans, which appeared in the Gulf of Mex-
ico in 1990. It has subsequently spread rapidly along the coast of Texas
and Mexico. Analyses of microsatellites for populations in the Gulf of
Mexico and various native localities in South America and South Africa
showed very high levels of allelic diversity in both alien and native pop-
ulations (Holland 2001).The high level of diversity in the Gulf of Mex-
ico indicates that the initial population was established by a large
founder population that carried most of the genetic variability of the
source area.
A quite different pattern is shown by several alien ant species in North
America and Hawaii.Two species of alien ants have been highly success-
ful in continental North America. Both the Argentine ant, described at
the chapter outset, and the red fire ant show genetic variability that is low
compared to populations in their native regions. Alien populations of
these species, together with those of several other invasive ants, tend to
form enormous supercolonies, which can have a severe impact on native
animals (Holway et al. 2002). In all likelihood, invading populations of
these species have experienced genetic bottlenecks during their invasion
of new geographical regions (Tsutsui et al. 2000).
In the case of the red fire ant (
Solenopsis wagneri
), two forms exist:
monogyne (“one queen”) and polygyne (“many queens”).The monog-
yne red fire ant was introduced from South America to the Gulf Coast
near Mobile, Alabama sometime between 1933 and 1945. It has spread
widely through the southern United States and has established colonies
in California. In this case, the high density achieved appears to be
the result of release from predators and parasites that exist in South
America.
