Biology Reference
In-Depth Information
the difference in energy demand for migration is quite likely the major
factor in selection for differences among populations.
Life history features have also been modified in shad (
Alosa sapidis-
sima
), another anadromous fish. Shad were introduced to rivers in the
Pacific Northwest from the mid-Atlantic coast in the late 1800s (Carroll
and Dingle 1996). In these Pacific rivers, shad now show an increased fre-
quency of repeat spawning and greater numbers of eggs than do fish from
their mid-Atlantic origin. In these characteristics, they are more like shad
from more northern areas of the Atlantic coast.
Similar evolutionary responses have been noted in freshwater fish. In
Norway, Koskinen et al. (2002) documented rapid evolutionary change in
grayling (
Thymallus thymallus
) introduced to lakes 80-100 yr ago. These
fish, introduced first to Lake Lesjaskogsvatn in 1880, were then translo-
cated from there to two smaller lakes in 1910. From these lakes, they col-
onized a fourth lake in 1920 by natural dispersal.Thus, only an estimated
11.8-22.0 generations separate these four populations from a common
ancestor. Several life history traits now differ significantly among the four
populations. In addition, the magnitude of the differences is incompatible
with their origin by genetic drift, so selection for adaptation to local lake
conditions seems to be responsible. The lakes differ substantially in pre-
vailing water temperature, and experimental studies (Koskinen et al. 2002)
found that fish from cold, intermediate, and warm lakes showed the high-
est survival rates in water of corresponding temperature.
The western mosquitofish (
Gambusia affinis
), native to North America,
has shown rapid evolutionary change in several locations to which it has
been introduced (Stearns 1983a; Stockwell and Weeks 1999). Stearns
noted adaptive genetic changes in life history characteristics of mosqui-
tofish introduced to Hawaii over a period of about 70 generations. Stock-
well and Weeks (1999) found genetic change in body fat content and size
at maturity in populations of mosquitofish introduced to thermal springs
in Nevada. In this case, the changes probably occurred over about
110-165 generations (Table 8.1). Meffe et al. (1996) observed selection
for increased temperature tolerance in populations of a related species
(
Gambusia holbrooki
) over 60-90 generations in a power plant cooling
pond in South Carolina.
Some alien birds also have shown rapid evolutionary adjustments to
the habitat conditions and resource availability patterns of their new envi-
ronments. The house sparrow (
Passer domesticus
), for example, has been
introduced to North America and many other temperate regions from its
home in Europe. It now occupies a broad range of climates from deserts
