Biology Reference
In-Depth Information
Genetic changes can also occur in the introduced species itself. The clearest
example is for
Anolis sagrei
, native to Cuba, the Bahamas, and the coast of northern
Central America and introduced to a variety of other localities. In Florida,
A. sagrei
was introduced at least eight separate times. These introductions were from a
variety of localities in the native range of the lizard and this resulted in genetic
diversity within Florida populations greatly exceeding that available in native
populations (Kolbe et al., 2004, 2007b). This increased genetic diversity has been
retained to a diminished extent in further populations in Grand Cayman Island,
Hawaii, Louisiana, Taiwan, and Texas founded by animals from Florida, and it is
thought to be one of the reasons for the success of
A. sagrei
in these several
invaded localities (Kolbe et al., 2004, 2007b). Similar admixture of native
genomes by multiple introductions has been shown for a number of other
Anolis
species introduced to Florida and the Dominican Republic (Kolbe et al., 2007a).
Chuckwallas (
Sauromalus
spp.) found on Alcatraz, Sonora are claimed to be a
hybrid swarm involving the three introduced species
S. ater
,
S. hispidus
, and
S. varius
(Case, 1982; Petren and Case, 1997; Mellink, 2002), although evidence
for this assertion has not been published. More often, a decrease in genetic
diversity (the so-called “founder effect”) is expected to obtain in most alien popu-
lations, reflecting their founding from very few individuals, each containing only
a limited sample of the species' total genetic diversity. Such reduced genetic vari-
ation has been observed within some populations of alien reptiles (Gorman
et al., 1978) and can also serve to set the introduced population on a different evo-
lutionary track from its parental species. So are novel genetic entities created by
the process of human introduction.
Morphological Changes
Morphological changes in head shape and body size have been documented in
two species of ranivorous Australian snakes,
Dendrelaphis punctulatus
and
Pseudechis porphyriacus
, with degree of change correlated with duration of
exposure to invasive populations of cane toads,
Bufo marinus
(Phillips and Shine,
2004). Both snakes are highly sensitive to toad toxins, and observed morphological
changes are toward reduced gape size and increased body size, in accordance
with predictions for minimizing size-dependent vulnerability to toads (Phillips
and Shine, 2006b).
The toads themselves have also changed morphologically through time, with
reduction in body size and parotoid gland size both being negatively correlated with
time since establishment of different populations (Phillips and Shine, 2005, 2006c).
These changes presumably result from the high costs of producing large bodies and
large quantities of toxin in novel environments in which they are unnecessary
(Phillips and Shine, 2005), but response to climatic and seasonal variables is also
involved (Phillips and Shine, 2006c). Furthermore, toad leg lengths have increased
with time, giving a colonization advantage to longer-legged individuals, and
