Source of unrelated individuals for genetic augmentation
The individuals chosen for introduction to inbred populations, for
recovery of fitness and genetic diversity, may be either outbred (if available),
or inbred but genetically differentiated from the population to which they are being introduced. An example of the latter situation is provided by Australian wallabies (Table 13.1).
The black-footed rock wallaby has several inbred island populations that could be combined
to increase genetic diversity and improve reproductive fitness.
The combined
genetic material from all the island populations contains most of
the microsatellite alleles found within the mainland populations.
There are 66 alleles at 10 microsatellite loci in mainland populations
and 47 in the pool of six island populations (Eldridge et al. 1999).
Mainland populations are threatened by fox predation. In the future, it
may be necessary to use crosses among island populations to reconstitute
a new population for reintroduction to mainland localities once
foxes are eliminated. This approach is not yet being used in practice.
Where no unrelated individuals of the same taxon are available,
individuals from another sub-species can be used to alleviate inbreeding
depression. This has been done for the Florida panther (Box 16.1) and
the Norfolk Island boobook owl (Example 10.4).
If an endangered species exists as only a single population, then the
onlypossiblesourceofadditionalgeneticmaterial isfromarelated,interfertile
species. American chestnuts have been crossed to the Chinese
chestnut to introduce genetic variation for resistance to blight that
severely depleted the American species. China is the source of the blight
disease and the Chinese chestnut possesses resistance (Hebard 1994).