Biology Reference
In-Depth Information
salmon (
Salmo salar
) farmed for seven generations differed significantly in
morphology, behavior, growth, and life history features from the native
fish from which they were derived (Fleming and Einum 1997). The
changes, adaptive to the aquacultural environment, can be transmitted to
wild populations through the escape of farmed animals. Interbreeding
with wild salmon may thus reduce the fitness of wild salmon and hasten
the extinction of wild populations. In Ireland, studies suggested that inter-
breeding of farmed and native salmon would lead to an increase in age of
maturity in native populations, which might be maladaptive for salmon
runs in shallow streams (McGinnity et al. 1997).
Mammals and birds are in a few cases placed at risk of extinction
through hybridization. In Scotland, for example, sika deer (
Cervus nippon
)
introduced from Japan more than 100 yr ago are interbreeding with the
native red deer (
Cervus elaphus
).The zone of interbreeding covers an area
about 350 km from the point of introduction of the sika deer and does
not appear to have stabilized (Abernethy 1994). Thus, the Scottish red
deer population at large may be at risk from genetic introgression.
The North American ruddy duck (
Oxyura jamaicensis
) was introduced
to England in 1949 and has established a large population, which has
recently invaded continental Europe. A small population of a close rela-
tive, the white-headed duck (
O. leucocephala
), has survived in southern
Spain. Ruddy ducks have appeared in Spain, and some hybridization has
been observed (Rhymer and Simberloff 1996).The Spanish population of
the white-headed duck is small and isolated from the only other popula-
tion of the species in central Asia. In this case, hybridization is a distinct
threat to survival of the white-headed duck.
Mallards have hybridized with other members of the genus
Anas
in
Florida, Hawaii, and New Zealand to an extent that threatens the genetic
extinction of local forms (Rhymer and Simberloff 1996). In eastern
North America, hybridization between mallard (
Anas platyrhynchos
) and
black (
A. rubripes
) ducks may be contributing to the gradual decline of the
latter species. A 1991 study in New Brunswick, for example, found that
14% of pairs were of mixed composition (D'Eon et al. 1994).
The European quail (
Coturnix coturnix
) is a widespread, migratory
European bird that winters partly in southern Spain and North Africa and
partly in the sub-Saharan Sahel. Domesticated Japanese quail (
Coturnix
japonica
), selected by animal breeders for lack of migration, have been
stocked for hunting in countries around the Mediterranean Sea. These
two species easily interbreed (Deregnaucourt et al. 2002), which could
lead to detrimental genetic pollution of the migratory birds native to
