Captive breeding


Captive breeding, also known as captive propagation, is a conservation strategy aimed at preserving endangered or threatened species by breeding them in controlled environments, such as wildlife reserves, zoos, botanic gardens, and other conservation facilities. It is sometimes employed to help species that are being threatened by the effects of human activities such as climate change, habitat loss, fragmentation, overhunting or fishing, pollution, predation, disease, and parasitism.
For many species, relatively little is known about the conditions needed for successful breeding. Information about a species' reproductive biology may be critical to the success of a captive breeding program. In some cases a captive breeding program can save a species from extinction, but for success, breeders must consider many factors—including genetic, ecological, behavioral, and ethical issues. Most successful attempts involve the cooperation and coordination of many institutions. The efforts put into captive breeding can aid in education about conservation because species in captivity are closer to the public than their wild conspecifics. These accomplishments from the continued breeding of species for generations in captivity is also aided by extensive research efforts ex-situ and in-situ.

History

Captive breeding techniques began with the first human domestication of animals such as goats, and plants like wheat, at least 10,000 years ago. These practices were expanded with the rise of the first zoos, which started as royal menageries such as the one at Hierakonpolis, capital in the Predynastic Period of Egypt.
The first actual captive breeding programs were only started in the 1960s. These programs, such as the Arabian Oryx breeding program from the Phoenix Zoo in 1962, were aimed at the reintroduction of these species into the wild. These programs expanded under The Endangered Species Act of 1973 of the Nixon Administration which focused on protecting endangered species and their habitats to preserve biodiversity. Since then, research and conservation have been housed in zoos, such as the Institute for Conservation Research at the San Diego Zoo founded in 1975 and expanded in 2009, which have contributed to the successful conservation efforts of species such as the Hawaiian Crow.

Coordination

The breeding of species of conservation concern is coordinated by cooperative breeding programs containing international studbooks and coordinators, who evaluate the roles of individual animals and institutions from a global or regional perspective. These studbooks contain information on birth date, gender, location, and lineage, which helps determine survival and reproduction rates, number of founders of the population, and inbreeding coefficients. A species coordinator reviews the information in studbooks and determines a breeding strategy that would produce most advantageous offspring.
If two compatible animals are found at different zoos, the animals may be transported for mating, but this is stressful, which could in turn make mating less likely. However, this is still a popular breeding method among European zoological organizations. Artificial fertilization is another option, but male animals can experience stress during semen collection, and the same goes for females during the artificial insemination procedure. Furthermore, this approach yields lower-quality semen, because shipping requires extending the life of the sperm for the transit time.
There are regional programmes for the conservation of endangered species:

Genetics

The objective of many captive populations is to hold similar levels of genetic diversity to what is found in wild populations. As captive populations are usually small and maintained in artificial environments, genetics factors such as adaptation, inbreeding and loss of diversity can be a major concern.

Domestication adaptations

Adaptive differences between plant and animal populations arise due to variations in environmental pressures. In the case of captive breeding prior to reintroduction into the wild, it is possible for species to evolve to adapt to the captive environment, rather than their natural environment. Reintroducing a plant or animal to an environment dissimilar to the one they were originally from can cause fixation of traits that may not be suited for that environment leaving the individual disadvantaged. Selection intensity, initial genetic diversity, and effective population size can impact how much the species adapts to its captive environment. Modeling works indicate that the duration of the programs is an important determinant of reintroduction success. Success is maximized for intermediate project duration allowing the release of a sufficient number of individuals, while minimizing the number of generations undergoing relaxed selection in captivity. Can be minimized by reducing the number of generations in captivity, minimizing selection for captive adaptations by creating environment similar to natural environment and maximizing the number of immigrants from wild populations.

Genetic diversity

One consequence of small captive population size is the increased impact of genetic drift, where genes have the potential to fix or disappear completely by chance, thereby reducing genetic diversity. Other factors that can impact genetic diversity in a captive population are bottlenecks and initial population size. Bottlenecks, such as rapid decline in the population or a small initial population impacts genetic diversity. Loss can be minimized by establishing a population with a large enough number of founders to genetically represent the wild population, maximize population size, maximize ratio of effective population size to actual population size, and minimize the number of generations in captivity.

[Inbreeding]

Inbreeding is when organisms mate with closely related individuals, lowering heterozygosity in a population. Although inbreeding can be relatively common, when it results in a reduction in fitness it is known as inbreeding depression. The detrimental effects of inbreeding depression are especially prevalent in smaller populations and can therefore be extensive in captive populations. To make these populations the most viable, it is important to monitor and reduce the effects of deleterious allele expression caused by inbreeding depression and to restore genetic diversity. Comparing inbred populations against non-inbred or less-inbred populations can help determine the extent of detrimental effects if any are present. Closely monitoring the possibility of inbreeding within the captive bred population is also key to the success of reintroduction into the species' native habitat.
Outbreeding">Outbreeding depression">Outbreeding
Outbreeding is when organisms mate with unrelated individuals, increasing heterozygosity in a population. Although new diversity is often beneficial, if there are large genetic differences between the two individuals it can result in outbreeding depression. This is a reduction in fitness, similar to that of inbreeding depression, but arises from a number of different mechanisms, including taxonomic issues, chromosomal differences, sexual incompatibility, or adaptive differences between the individuals. A common cause is chromosomal ploidy differences and hybridization between individuals leading to sterility. The best example is in the orangutan, which, prior to taxonomic revisions in the 1980s would be commonly mated in captive populations producing hybrid orangutans with lower fitness. If chromosomal ploidy is ignored during reintroduction, restoration efforts would fail due to sterile hybrids in the wild. If there are large genetic differences between individuals originally from distant populations, those individuals should only be bred in circumstances where no other mates exist.

Behavior changes

Captive breeding can contribute to changes in behavior in animals that have been reintroduced to the wild. Released animals are commonly less capable of hunting or foraging for food, which leads to starvation, possibly because the young animals spent the critical learning period in captivity. Released animals often display more risk-taking behavior and fail to avoid predators. Golden lion tamarin mothers often die in the wild before having offspring because they cannot climb and forage. This leads to continuing population declines despite reintroduction as the species are unable to produce viable offspring. Training can improve anti-predator skills, but its effectiveness varies.
Salmon bred in captivity have shown similar declines in caution and are killed by predators when young. However, salmon that were reared in an enriched environment with natural prey showed less risk-taking behaviors and were more likely to survive.
A study on mice has found that after captive breeding had been in place for multiple generations and these mice were "released" to breed with wild mice, that the captive-born mice bred amongst themselves instead of with the wild mice. This suggests that captive breeding may affect mating preferences, and has implications for the success of a reintroduction program.
Human mediated recovery of species can unintentionally promote maladaptive behaviors in wild populations. In 1980 the number of wild Chatham Island Black Robins was reduced to a single mating pair. Intense management of populations helped the population recover and by 1998 there were 200 individuals. During recovery scientists observed "rim laying" an egg laying habit where individuals laid eggs on the rim of the nest instead of the center. Rim laid eggs never hatched. To combat this land managers pushed the egg to the center of the nest, which greatly increased reproduction. However, by allowing this maladaptive trait to persist, over half the population were now rim layers. Genetic studies found that this was an autosomal dominant mendelian trait that was selected for due to human intervention.
Another challenge presented to captive breeding is an attempt to establish multi-partner mating systems in captive populations. It can be difficult to replicate the circumstances surrounding multiple mate systems and allow it to occur naturally in captivity due to limited housing space and lack of information. When brought into captivity, there is no guarantee that a pair of animals will pair bond or that all the members of a population will participate in breeding. Throughout facilities, there is limited housing space so allowing for mate choice may establish genetic issues in the population. A lack of information surrounding the effects of mating systems on captive populations can also present issues when attempting to breed. These mating systems are not always fully understood and the effects captivity may have on them cannot be known until they are studied in greater capacity.