Section 12 Genetics Management for Reintroduction Reintroduction is the process of releasing captive-born individuals back into the wild to re-establish or supplement existing wild populations. While reintroduction programs currently exist for many species, conditions are not suitable for reintroduction for the majority of species as native habitat is not available or threats to wild populations still exist.

Nevertheless, many captive breeding programs aim to retain sufficient levels of genetic diversity and demographic variability over the long-term to eventually if and when reintroduce animals back into the wild -- if and when the situation presents itself the situation presents itself. There are three genetic scenarios for captive populations.

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.

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.

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:

 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.

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.

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.

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.

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.

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: years/length = y/L  Number of generations in captivity (years/length = y/L) S  Selection differential in captivity (S) h 2  Additive genetic variation for reproductive fitness (h 2 ) Ne  Effective population size of the captive population (Ne) m  Proportion of the population derived from migrants (m) L  Generation length in years (L).

Rates of genetic adaptation (GA) can be predicted from: GA~(Sh 2 /L)  [1 - 1/(2Ne)] y/L (1-m i ) Where m i is the proportion of the genetic material from immigrants in the i th 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.

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.

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

Population Fragmentation as a Means for Minimizing Genetic Adaptation to Captivity 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.

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.

The sub-populations are maintained as separate populations until inbreeding builds to a level where it is of concern F ~ (F ~ ). 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.

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, NOT 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.

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 Choosing sites for reintroduction -- sites for reintroduction should maximize the chances of successful, re-establishment in the wild.

The environment should match, as closely as possible, the environment to which the population was adapted, prior to captive breeding. Reintroductions 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.

Choosing individuals for reintroduction 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.

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.

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.