Behavioral Genetics and Animal Domestication - Genetics and the Behavior of Domestic Animals - page 48

the limited genetic variability found in certain domestic populations.
For example, laboratory strains often have limited genetic polymorphism.
Animals tend to come from a limited founder population (e.g., mice ( Bonhomme
and Guenet, 1984 ) and therefore have greater genetic homogeneity. Using a
new series of crosses between animals recently caught from the wild ( Koide
et al., 2000 ) derived a series of mouse strains that exhibited much greater
polymorphism than standard laboratory strains, with several strains also
diverging in assorted behavioral assays.
Natural Selection
Although domestic animals are obviously subject to strong artificial selec-
tion, this does not mean that natural selection does not occur. Indeed,
any selection that occurs in the captive environment that is not artificial is
by definition natural ( Hale, 1969 ). Even those animals that are artificially
selected for breeding may nevertheless fail to reproduce. This can be due
to a myriad of factors, including social stress, parasitism, and in general
a failure to cope with the captive environment. Those animals that cope
best with this new environment will increase their reproductive potential.
For example, wild-caught Drosophila populations that were maintained in
captivity were found to exhibit rapid adaptation to the captive environment
over nine generations ( Frankham et al., 1999 ).
Not only that, but the artificial selection process itself, acting on certain
traits, may also lead to a reduction in reproductive potential. For example, dog
breeds have long been known to show negative fitness effects due to selected
characteristics (e.g., the ridge in ridgebacks is associated with sinus formation
( Salmon Hillbertz et al., 2007 ), hip dysplasia in alsatians ( Hedhammar et al.,
1979 )), growth is linked with decreases in reproduction in broilers ( Siegel
and Dunnington, 1985 ), and the red hair color in rabbits leads to metabolic
problems, disease susceptibility, and increased mortality ( Muntzing, 1959 ).
Generally, the extent of the occurrence of natural selection can be thought of as
determined by the extent to which the environment allows the expression of
species-typical traits ( Spurway, 1955 ). Animals with very few pre-adaptations
to this environment will therefore naturally be under greater natural selection
as they are subjected to a strong, novel environment.
Inbreeding
Inbreeding, the process whereby related individuals assortatively breed
together, leads to an increase in alleles identical by descent ( Falconer and
Mackay, 1996 ). This can be typically measured by assessing the excess
numbers of homozygotes in the population, due to substructure. In domestic
populations, inbreeding is relatively common, especially in more modern
selection practises, as fewer numbers of animals tend to get a far larger