15. Modeling Problems in Conservation Genetics Using Laboratory Animals
265
Immigration
The obvious solution when small populations suffer from inbreeding depression is
to introduce immigrants. This is often costly and involves risks of introducing
disease or causing behavioral disruption. There is no clear-cut theory to predict
the benefits of introducing immigrants into partially inbred populations, and most
empirical evidence involves hybridizing all individuals, rather than introducing a
few immigrants. Spielman and Frankham (1992) evaluated the benefits of introducing a single immigrant into partially inbred populations (F = 0.5). The immigrant resulted in an approximate doubling of reproductive fitness.
Rapid Genetic Adaptation to Captivity
An inevitable consequence of maintaining populations of endangered species in
captivity is that natural selection operates to adapt populations genetically to the
captive environment. This is likely to reduce the chances of successful reintroduction into the wild. The speed of genetic adaptation can be very rapid if selection is
strong and generation interval is short (Frankham and Loebel 1992). Even under
benign captive conditions, genetic adaptation results in substantial genetic deterioration (selection of traits that facilitate survival in captivity but are deleterious in
the wild) (Woodworth 1996). Frankham and Loebel (1992) presented equations
for predicting the rate of genetic adaptation to captivity and the means for minimizing it. These predictions need to be experimentally evaluated.
Optimum Management of Populations of Endangered
Species Founded from Few Individuals
When a small number of animals is used to found a captive population, inbreeding
is inevitable and will lead to inbreeding depression. Based on theoretical considerations, research with D. mercatorum, and results of a program with Speke’s
Gazelle (Templeton and Read 1983, 1984), it was recommended that such species
be managed to adapt them to tolerate inbreeding. The recommended procedure
has been widely interpreted as an inbreeding program devised to purge deleterious
recessives (e.g., Vrijenhoek 1994), but Templeton (personal communication) attributes it primarily to positive selection for epistatic complexes. It involves an
increase in total population size, the use of inbred parents, production of inbred
offspring, and equalizing founder representation in both parents and offspring.
Although the recommended procedure has been used with endangered species, it
has not been subjected to a controlled experimental evaluation. Evaluations of
different aspects of this procedure and a purging regime have failed to yield
meaningful lowering of inbreeding depression (Loebel et al. 1992; Frankham et
al. 1993; Wright et al. 1999). Computer simulation studies (Hedrick 1994) indicated that inbreeding should be effective in purging lethals but may be deleterious
for genes of small effect. There is controversy regarding the optimum manage-
265
Immigration
The obvious solution when small populations suffer from inbreeding depression is
to introduce immigrants. This is often costly and involves risks of introducing
disease or causing behavioral disruption. There is no clear-cut theory to predict
the benefits of introducing immigrants into partially inbred populations, and most
empirical evidence involves hybridizing all individuals, rather than introducing a
few immigrants. Spielman and Frankham (1992) evaluated the benefits of introducing a single immigrant into partially inbred populations (F = 0.5). The immigrant resulted in an approximate doubling of reproductive fitness.
Rapid Genetic Adaptation to Captivity
An inevitable consequence of maintaining populations of endangered species in
captivity is that natural selection operates to adapt populations genetically to the
captive environment. This is likely to reduce the chances of successful reintroduction into the wild. The speed of genetic adaptation can be very rapid if selection is
strong and generation interval is short (Frankham and Loebel 1992). Even under
benign captive conditions, genetic adaptation results in substantial genetic deterioration (selection of traits that facilitate survival in captivity but are deleterious in
the wild) (Woodworth 1996). Frankham and Loebel (1992) presented equations
for predicting the rate of genetic adaptation to captivity and the means for minimizing it. These predictions need to be experimentally evaluated.
Optimum Management of Populations of Endangered
Species Founded from Few Individuals
When a small number of animals is used to found a captive population, inbreeding
is inevitable and will lead to inbreeding depression. Based on theoretical considerations, research with D. mercatorum, and results of a program with Speke’s
Gazelle (Templeton and Read 1983, 1984), it was recommended that such species
be managed to adapt them to tolerate inbreeding. The recommended procedure
has been widely interpreted as an inbreeding program devised to purge deleterious
recessives (e.g., Vrijenhoek 1994), but Templeton (personal communication) attributes it primarily to positive selection for epistatic complexes. It involves an
increase in total population size, the use of inbred parents, production of inbred
offspring, and equalizing founder representation in both parents and offspring.
Although the recommended procedure has been used with endangered species, it
has not been subjected to a controlled experimental evaluation. Evaluations of
different aspects of this procedure and a purging regime have failed to yield
meaningful lowering of inbreeding depression (Loebel et al. 1992; Frankham et
al. 1993; Wright et al. 1999). Computer simulation studies (Hedrick 1994) indicated that inbreeding should be effective in purging lethals but may be deleterious
for genes of small effect. There is controversy regarding the optimum manage-