Biology Reference
In-Depth Information
New Orleans carried only a fraction of the genetic variability of the
native South American population.
The greatly reduced genetic variability in the California population
may be a major contributor to its pest status. In Argentina, this ant is much
less abundant than it is in California, and ants from different nests show
high levels of aggression toward each other. In California, ants from dif-
ferent nests show little or no aggression, so neighboring nests form
“supercolonies” over large areas. Individual ants, both workers and
queens, are able to move freely among these nests.This lack of aggression
seems to result in part from the genetic homogeneity of the population.
In effect, the ants do not show recognizable differences that would iden-
tify them as being from different nests.A similar pattern of low aggression
is shown by Argentine ants in central Chile, where they have also been
introduced.
In addition, following introduction of Argentine ants to North Amer-
ica, natural selection now is apparently acting against spread of genetic
variability within the continental population (Tsutsui et al. 2003). Ants
from colonies of low genetic diversity attack and kill those from more
genetically diverse colonies. This behavior tends to reinforce the super-
colony structure of the overall population.
Assessing Genetic Variability
The case history of the Argentine ant in North America demonstrates
that the degree of genetic variability of an alien species may have major
implications for its impact. In this chapter, we shall examine the patterns
of genetic variability that exist in populations of alien plants and animals.
Many techniques are now available for assessing genetic variability within
populations and determining the degree of genetic similarity among pop-
ulations (Parker et al. 1998). Thus, we are able to compare variability in
populations of introduced species to variability in their populations in
areas to which they are native. We can also evaluate how the level of
genetic variability in introduced populations influences their evolution in
the new environment.
Techniques for assessing genetic variability in samples of individuals
from populations involve analysis of variability in enzyme structure (see,
e.g., Buth and Murphy 1999) and in nuclear or organelle DNA and RNA
structure (Hillis et al. 1996; Krawczak and Schmidke 1998). These tech-
niques include allozyme analysis, various DNA fingerprinting techniques
such as DNA fragment length polymorphism analyses, microsatellite
