Biology Reference
In-Depth Information
is native to coastal areas of northern Queensland, Australia. This form
apparently spread into more temperate waters near Brisbane, Australia,
from which it was taken to aquarium culture in Monaco.
Thus, adaptation to colder waters has occurred in
Caulerpa taxifolia
,
enabling its success in the Mediterranean (Meusnier et al. 2002). These
colder water strains are more robust in growth form than those in north-
ern Queensland. Furthermore, distinct coastal and reef ecotypes of
Caulerpa taxifolia
have been recognized.This species appears to be a com-
plex of genetically differentiating forms that probably represent sibling
species.
Speciation in Animals
Polyploidy is frequent in animal species of arctic environments that have
been recolonized since the last glacial retreat. Polyploid species of the
cladocerans
Daphnia
and
Bosmina
are confined to the arctic, where they
reproduce parthenogenetically (Beeton and Hebert 1988). During peri-
ods of maximum glacial advance, populations of these species may have
been confined to isolated refugia south of the glacial front. As these pop-
ulations expanded during glacial retreat, secondary contacts between
them may have led to allopolyploidy. Polyploidy may be advantageous in
the arctic because of developmental advantages (Adamowicz et al. 2002).
The polyploid forms of these species, many of which are likely of recent
origin, are genetically isolated from their diploid ancestors.
Recent speciation has been documented for animals, as well, includ-
ing many instances involving alien species. Native animals may undergo
sympatric speciation when alien plants provide suitable resources and a
mechanism for reproductive separation of portions of a parental popula-
tion (Via 2001). Often this appears to occur because the alien plants have
a different reproductive phenology than that of native plants. Perhaps the
best-documented example involves the maggot flies (
Rhagoletis
spp.)
described in chapter 13. Biotypes of these flies on introduced apple and
cherry trees are almost completely isolated from their ancestral forms on
native trees, thus representing incipient species. Two-spotted spider mites
(
Tetranychus urticae
) also tend to form genetically distinct host races
adapted to the secondary chemistry or defensive morphology of the host
plants (Agrawal et al. 2002b), as we noted in chapter 9. Adaptation to dif-
ferent hosts often involves fitness tradeoffs, that is, adaptation to a new
host results in reduced fitness on the old host.
Another well-documented example of this sort involves the pea aphid
