Biology Reference
In-Depth Information
reproduction.This procedure tends to select for high fecundity and small
egg size (Heath et al. 2003). Offspring from small eggs have been shown
to have lower survival than those from large eggs. In rivers that have
received heavy supplementation with fry from hatchery spawning, signif-
icant reductions in egg size have been noted in the wild population.
Few cases of hybridization between aliens and natives are known
among terrestrial vertebrates. Among mammals, hybridization occasion-
ally occurs between domestic dogs (
C. familiaris
) and other canids, such as
the gray wolf (
Canis lupus
) and the Ethiopian wolf (
Canis simiensis
) (see,
e.g., Andersone et al. 2002; Gottelli et al. 1994). Feral domestic cats (
Felis
catus
), derived from the North African race of the wildcat (
Felis sylvestris
),
have also hybridized with the Scottish race of the wildcat, which is the
last remaining wild race of the species (Beaumont et al. 2001).
More interesting is the interaction between the coyote (
C. latrans
) and
the gray wolf. In eastern North America, coyotes expanded their range
eastward and northward during the 1900s (Thurber and Peterson 1991).
Animals in the eastern areas of range expansion also tend to be larger and
heavier, especially in parts of New England.This difference is probably at
least in part genetic. We shall consider this example in more detail in
chapter 10.
Hybridization Between Alien and Native Microbial
Species
Introduced fungal parasites can also hybridize with native forms. In the
Netherlands,
Phytophthora nicotianae
, an introduced form, has hybridized
with
P. cactorum
,a native, to produce a new blight fungus that attacks plants
of the genera
Primula
and
Spathiphyllum
(Man in't Veldt et al. 1998).
In the Pacific Northwest, hybridization has occurred between the rust,
Melampsora occidentalis
, native to the black cottonwood (
Populus tri-
chocarpa
), and the introduced
M. medusae
, native to the eastern cotton-
wood (
P. deltoides
) (Newcombe et al. 2000). The original geographical
ranges of these trees and their rusts are nonoverlapping. A hybrid of the
two species of
Populus
has been produced and grown as clones in com-
mercial plantations in the Pacific Northwest.These hybrids were resistant
to
M. occidentalis
. In 1991,
M. medusae
appeared on the hybrid cotton-
woods, and since 1995, hybrid rusts (
M.
columbiana
) have been detected.
By 1997, the rust hybrid had apparently displaced its parental forms in the
Pacific Northwest. This hybrid form is capable of infecting not only the
black and eastern cottonwoods but also the three other close relatives of
×
