Biology Reference
In-Depth Information
Among insects, the spread of African honey bees (
Apis mellifera scutel-
lata
) in the New World following their introduction to Brazil in the late
1950s has involved hybridization between this form and domesticated
European subspecies. The African subspecies has spread through tropical
and subtropical regions as feral populations that interbreed with the Euro-
pean forms in managed apiaries (Hall and McMichael 2001). The repre-
sentation of European genetic markers declines gradually in apiary pop-
ulations, and in time, European genotypes are expected to disappear
completely (Clarke et al. 2001).
A recent concern among insects is the possibility of invasion of North
America by the Asian form of the gypsy moth (
Lymantria dispar
). In the
Asian form, the female is able to fly, rather than being flightless, as in the
case of the established European strain (Liebhold et al. 1996). The Asian
and European strains hybridize freely, and the consequences of such an
interaction are difficult to predict but could likely lead to a greatly
increased rate of spread of this destructive insect. Several incipient popu-
lations of the Asian form have been detected in North America, all of
which have either failed or been eradicated.
Examples of hybridization between aliens and natives are numerous
among fish (Leary et al. 1995). Most of this result from the deliberate
stocking of alien species for the supposed improvement of sportfishing. In
these cases, much of the conservation concern also relates to genetic
extinction of the native (see chapter 16). In addition, substantial evidence
now exists that the stocking of hatchery-reared fish into wild populations
of the same species can reduce fitness of wild populations. The hatchery
environment selects for several morphological and behavioral characteris-
tics in Atlantic salmon (
Salmo salar
) and Pacific salmon (
Oncorhynchus
spp.)
that confer reduced fitness in the wild (Fleming and Einum 1997; Reisen-
bichler and Rubin 1999).
Through hybridization between fish of hatchery and wild origin, the
fitness of some populations spawning in the wild is also reduced. In Den-
mark, using DNA microsatellite analysis, Hansen (2002) found that wild
brown trout (
Salmo trutta
) populations were in some cases highly intro-
gressed and others only weakly introgressed by heavy stocking of hatch-
ery fish. Hatchery trout appeared to be poorly adapted as anadromous
fish, as opposed to permanent residents in freshwater, so interbreeding
with wild fish may have reduced fitness of the anadromous wild popula-
tion. In British Columbia, Canada, chinook salmon (
Oncorhynchus
tshawytscha
) captured in the wild are spawned in aquacultural facilities, and
the resulting fry are released back into streams to supplement natural
