Nevertheless, many captive breeding programs aim to

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Nevertheless, many captive breeding programs aim
to retain sufficient levels of genetic diversity
and demographic variability over the long-term to
eventually reintroduce animals back into the wild
-- if and when the situation presents
itself. There are three genetic scenarios for
captive populations.
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First, the threatening process in the wild may
be controlled with relative ease, for example by
extermination of exclusion of introduced
predators or competitors from an island. In this
case, the endangered species may be
reintroduced after only a few generations of
population expansion in captivity. The only
genetic issues are representative sampling
during the foundation and avoidance of
inbreeding.
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Second, loss or degredation of habitat may be so
severe that reintroduction is not a realistic
proposition. This may be the case for some
species of large, naturally wide-ranging
mammals. Here, the genetic management may,
ultimately be domestication, deliberate
selection of passive individuals, capable of
tolerating close proximity to humans and other
animals, and easily maintained on
cheap, non-specialist diets.
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The majority of captive endangered species lie
between these extremes and constitute the third
scenario and will be the focus of the following
several lectures. These species require many
generations of captive breeding, but release
remains a viable option. Genetic Changes in
Captivity that Affect Reintroduction
Success Captive populations typically
deteriorate in ways that reduce reintroduction
success such as
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• Loss of genetic diversity
• Inbreeding depression
• Accumulation of new deleterious mutations
• Genetic adaptation to captivity.
• We previously discussed the first three of these
• components and therefore will focus on Genetic
• Adaptation to Captivity.

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While genetic adaptation to captivity has
been recognized since the time of Darwin
(domestication), it has, until recently, been
considered only a minor problem in captive
breeding. However, there is now compelling
evidence that it can be a major threat to the
success of reintroductions as all populations
adapt to their local environmental conditions.
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When we compare populations across a range of
environments, we usually observe that they have
highest fitness in their own environment and have
lower fitness in other environments. This is
due to genotype X environment interactions. Thus,
for populations maintained in captivity for
many generations, adaptation to this novel
environment may severely reduce their performance
upon return to natural environments.
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When wild populations are brought into captivity,
the forces of natural selection
change. Populations are naturally or
inadvertently selected for their ability to
reproduce in the captive environment. Selection
for tameness is favored by keepers and flighty
animals such as antelope, gazelle, wallabies, and
kangaroos may kill themselves by running
into fences. Predators are controlled, as are
most diseases pests.
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Carnivores are no longer selected for their
ability to capture prey. Further, there is
usually no competition with other species in
captivity, and limited competition for mates
within species. Natural selection on all of
these characters will be relaxed, or, if there
are trade-offs with other aspects of
reproductive fitness, they may actually be
selected against.
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• To minimize the deleterious impacts of adaptation
  to
• captivity on reintroduction success, we need to
  consider
• what factors determine the annual rate of
  adaptation
• to captivity and include
• Number of generations in captivity (years/length
  y/L)
• Selection differential in captivity (S)
• Additive genetic variation for reproductive
  fitness (h2)
• Effective population size of the captive
  population (Ne)
• Proportion of the population derived from
  migrants (m)
• Generation length in years (L).

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Rates of genetic adaptation (GA) can be predicted
from GA(Sh2/L)?1 - 1/(2Ne)y/L(1-mi) Where
mi is the proportion of the genetic material
from immigrants in the ith generation. Selection
in captivity is dependent upon the mortality rate
and upon the variance in family size. If the
captive environment is very different from
the wild, selection in captivity will be strong
and the population will evolve rapidly to adapt.
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As selection is more effective in large than
small populations, genetic adaptations to
captivity is greater in larger than smaller
populations. Immigrants introduced from the
wild, will slow the rate of genetic
adaptation. However, for many endangered
species, wild individuals are either not
available or too valuable to use in augmenting
a captive population. Species with shorter
generation lengths show faster genetic adaptation
per year than ones with longer generations.
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• Adaptation to Captivity can be Reduced By
• Minimizing the number of generations in captivity
• Minimizing selection in captivity
• Minimizing the heritability of reproductive
  fitness in
• captivity
• Minimizing the size of the captive population
• Maximizing the proportion of wild immigrants and
  the
• recency of introducing immigrants
• Maximizing generation length

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Population Fragmentation as a Means for
Minimizing Genetic Adaptation to Captivity. The
competing requirements to maintain genetic
diversity and avoid severe inbreeding depression,
but also to avoid genetic adaptation to
captivity, indicate that neither large nor small
populations are ideal for breeding in captivity,
when reintroduction to the wild is envisioned.
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Small populations suffer loss of genetic
variation and inbreeding depression, but minimize
genetic adaptation to captivity. Large
populations retain genetic variation and have
only slow accumulation of inbreeding but suffer
most from genetic adaptation to captivity. A
compromise could be achieved by maintaining
large overall population, but fragmenting it into
partially isolated sub-populations.
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The sub-populations are maintained as separate
populations until inbreeding builds to a level
where it is of concern (F 0.1 --
0.2). Immigrants are exchanged among
sub-populations at this point. The
sub-populations are then maintained as
isolated populations until inbreeding again
builds up. This structure is expected to
maintain more genetic diversity than a single
population of the same total size and to exhibit
less deleterious changes to captivity.
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If all sub-populations are combined to produce
individuals for reintroduction, the pooled
population has a lower level of inbreeding and
more genetic diversity than a single large
population. A critical requirement in the use
of this design is that none of the
sub-populations becomes extinct and
therefore, this strategy is NOT recommended for
wild populations. Captive populations are
already fragmented. Individual zoos wildlife
parks have limited capacity and endangered
species are dispersed over several
institutions to minimize the risk from
catastrophes.
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Currently, individuals are moved among
institutions to create, effectively, a single
large population. The fragmented structure will
reduce costs and the risk of injury, and reduce
disease transmission. Captive Management of
Reintroductions Choosing sites for
reintroduction -- sites for reintroduction
should maximize the chances of successful,
re-establishment in the wild.
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The environment should match, as closely as
possible, the environment to which the population
was adapted, prior to captive breeding. Reintrodu
ctions should therefore be carried out within the
previous range of the species and ideally into
prime, rather than marginal habitat. This
minimizes the adaptive evolution required in
the reintroduction site.
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Choosing individuals for reintroduction --
Individuals used for reintroduction should
maximize the chance of re-establishing a
self-sustaining population. Thus, healthy
individuals with high reproductive potential, low
inbreeding coefficients and high genetic
diversity are ideal. When an individual is
transferred to the wild, its genetic diversity is
added to the reintroduced population, but removed
from the captive population and both of
these effects need to be assessed when evaluating
individuals for reintroductions.
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Since survival in the natural habitat is expected
to be much lower than in captivity, it is
undesirable to deplete the captive population of
genetically valuable individuals to benefit the
wild population. This is particularly important
at the beginning of a reintroduction program as
mortality is frequently high. Conversely, the
reintroduced population is highly related to its
source captive population and an otherwise
ideal reintroduction candidate may be closely
related to individuals previously released and
its introduction may actually reduce genetic
diversity of reintroduced population.
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How many reintroduced populations should be
established? Where several suitable
reintroduction sites and ample excess captive
bred individuals are available, a number
of reintroduced populations should be established
to maximize the numbers of reintroduced
individuals. This minimizes the loss of genetic
diversity and will minimize inbreeding if
individuals are translocated among different
sites. Additionally, several populations reduce
the risk of extinction due to natural hazards,
disease, stochastisity.