Biology Reference
In-Depth Information
Yellow starthistle (
Centaurea solsticialis
) is an example of a self-incom-
patible annual weed that shows high genetic variability as measured by
allozyme analysis (Sun 1997). For 22 populations in Washington, Idaho,
and California, allozyme analysis showed that 43% of loci were polymor-
phic and that 38% of individual plants were heterozygous for polymor-
phic loci. Little genetic divergence has yet occurred among populations,
however, with the exception of a small, outlying population in San Diego
County, California, which shows reduced variability.
Slender wild oat (
Avena barbata
), on the other hand, is a primarily self-
fertilizing grass that maintains levels of allozyme variability in California
comparable to those existing in Old World populations (Clegg and Allard
1972).The high variability of this grass is apparently due to its introduc-
tion on numerous occasions.
Leafy spurge (
Euphorbia esula
) is one of the most serious plant invaders
of rangeland in western North America. As a sexually reproducing, out-
crossing species, a fairly high genetic variability was not unexpected.
Analyses of cpDNA by RFLP and RAPD techniques showed that vari-
ability of maternally inherited patterns was very high (Rowe et al. 1997).
This indicates that a number of introductions from different sources in the
Old World probably occurred.
In North America, bulbous bluegrass (
Poa bulbosa
) presents an interest-
ing example of high variability in spite of the fact that it reproduces
almost entirely by the asexual production of bulblets (Novak and Welfley
1997). Like cheatgrass, bulbous bluegrass is continent-wide in distribu-
tion, occurring in 40 U.S. states. One would expect this reproductive
strategy to be associated with low genetic diversity, especially if a genetic
bottleneck occurred at the time of introduction. Allozyme analysis
showed that bulbous bluegrass has an unexpectedly high level of variabil-
ity, with about 47% of loci being polymorphic. Heterozygosity was also
high, and many individuals showed three alleles at each locus, a conse-
quence of the North American populations apparently being autopoly-
ploids. Multiple introductions have probably contributed to the high
genetic variation.
Genetic Variability Among Alien Animals
Analyses of the genetic variability of alien animals also reveal very diverse
patterns. Many alien aquatic invertebrates show high levels of genetic
variability, suggesting that the founding populations consisted of numer-
ous individuals or involved multiple introduction events. Many of these
