Biology Reference
In-Depth Information
Among terrestrial vertebrates, genetic variability in alien populations
varies greatly. The marsh frog (
Rana ridibunda
), introduced to England
from Hungary as a translocated group of only 12 adults, would have been
expected to show greatly reduced genetic variability. Rapid growth of
the new population apparently prevented a significant genetic bottle-
neck, so the resulting population in England showed a pattern of genetic
diversity similar to the source population in Hungary (Zeisset and Bee-
bee 2003).
On the other hand, some birds, such as the European starling in North
America, discussed earlier in the chapter, show low variability and evi-
dence of a genetic bottleneck associated with small numbers of colonist
individuals and a period of low initial population size. In other cases, col-
onization of new areas may be effected by only a handful of individuals,
carrying very limited genetic variability. The red fox (
Vulpes vulpes
) was
introduced to Australia in the late 1800s for rabbit control and as a game
animal. In the state of Victoria, the founding population consisted of only
a few individuals, but population growth was rapid and little loss of alle-
les by genetic drift evidently occurred (Lade et al. 1996). Foxes reached
Phillip Island, about 0.5 km from the mainland of Victoria, in 1907.The
founding population there may have been only a mated pair or a preg-
nant female. Analysis of microsatellites of island and mainland animals
showed that the current island population has much reduced genetic vari-
ability.
Many passerine birds introduced to various locations show little or
no evidence of severely reduced genetic variability (Merilä et al. 1996).
The European starling was introduced to New Zealand on 13 occa-
sions, with founding populations totaling about 653 individuals. New
Zealand starlings showed essentially equal variability with European
populations, in sharp contrast to the situation in North America. The
greenfinch (
Carduelis chloris
), with a founding population much smaller
than the 653 founder starlings when it was introduced to New
Zealand, nevertheless increased rapidly in numbers and did not expe-
rience a genetic bottleneck (Merilä et al. 1996). Common mynahs
(
Acridotheres tristis
) introduced to many locations in the Pacific and
South Africa showed an intermediate condition, with somewhat fewer
polymorphic loci and fewer alleles per locus (Baker and Moeed 1987;
Fleischer et al. 1991). The South African population showed the most
severe reduction in genetic variability, reflecting a small group of
founders (table 3.1).
