Biology Reference
In-Depth Information
ity, however, this behaviorally adaptable species has colonized a wide
range of habitats in North America.
On the other hand, founder populations often consist of many indi-
viduals or result from repeated introductions of individuals from different
parts of their native range. In such cases, alien populations may have high
genetic diversity. Many of these species have not only proven to be seri-
ously invasive but have also shown genetic adaptation to different envi-
ronments within their new range.
Kudzu (
Pueraria lobata
), one of the most troublesome alien plants of the
southeastern United States, exemplifies this latter category (Pappert et al.
2000). Allozyme analysis of 14 loci showed that individual populations
varied in polymorphism, some having as few as four and some as many as
12 polymorphic loci. Overall, population analyses from 20 localities
showed that 13 of the 14 loci examined were polymorphic. The high
diversity of kudzu evidently reflects its deliberate introduction on many
occasions over about 50 years. Kudzu was repeatedly introduced to the
southeastern United States as an ornamental and forage plant, as well as
for erosion control. Coupled with sexual reproduction, multiple introduc-
tions have made this species one of the most variable alien invaders of
North America.
Evolutionary adaptability is one of the key characteristics of many, if
not most, invasive alien species. In turn, adaptability reflects especially the
degree of additive and epistatic genetic variability, together with the
potential for acquiring additional variability through mutation, hybridiza-
tion, and chromosomal rearrangement. Additive genetic variation repre-
sents the component of genetic variation that consists of alleles that have
an overall quantitative effect proportional to their number (Lee 2002). In
diploid species, for example, instead of being dominant or recessive, some
alleles may have an additive effect, so when they are present on both chro-
mosomes of the pair, their effect is greater than when only one member
of the chromosome pair contains the allele. In many polyploid species, in
which the number of complete sets of chromosomes is greater than two,
the potential for accumulation of alleles with additive quantitative effects
can be high because a particular gene locus exists on more than two sets
of chromosomes. Epistasis refers to the influence of alleles at one locus on
the expression of alleles at a different locus.
Additive genetic variation is usually regarded as the material for rapid
evolutionary change, such as that seen in many alien species and native
species with which they interact. Carroll et al. (2003b), however, found
