European wild horse

BREEDING

· Breeding back, a breeding effort to re-assemble extinct breed genes

· Breeding pair, bonded animals who cooperate to produce offspring

· Breeding program, a planned breeding of animals or plants

· Breeding season, the period during each year when a species reproduces

· Captive breeding, raising plants or animals in zoos or other controlled conditions

· Cooperative breeding, the raising of the young using non-parental care givers

· Crossbreeding, the process of breeding an animal with purebred parents of two different breeds, varieties, or populations

· Preservation breeding, a selection practice to preserve bloodlines

· Selective breeding, an animal selection practice to encourage chosen qualities

· Smart breeding, a plant selection practice to encourage chosen qualities

Breeding back

Heck cattle have been bred to resemble the aurochs in the 1920s. Since they are regarded as not meeting the criteria for "new aurochs", recent efforts such as theTaurOs Project attempt to get considerably closer to the wild bovine.

Konik in Haselünne, Germany.

Breeding back is a form of artificial selection by the deliberate selective breeding of domestic animals in an attempt to achieve an animal breed with aphenotype that resembles a wildtype ancestor, usually one that is extinct. Breeding back is not to be confused with dedomestication.

It must be kept in mind that a breeding-back breed may be very similar to the extinct wild type in phenotype, ecological niche, and to some extent genetics, but the initial gene pool of that wild type is lost forever with its extinction. It is not truly possible for a breeding back attempt to actually recreate an extinct wild type that is the breeding target, as an extinct wild type cannot be resurrected via selective breeding alone. Furthermore, even the outward authenticity of a bred-back type depends on the quality of the stock used as the foundation of the project. As a result, some breeds, likeHeck cattle, are at best a vague look-alike of the extinct wildtype aurochs, according to scientific literature.

Background

It is the target of breeding back to restore the wild traits that may have been preserved in domestic animals within one breeding lineage. Commonly, only the phenotype and ecological capacity are considered in breeding back projects, but a few projects, like the TaurOs Project, also consider the genetic aspect of the animals they are working with.^[2] In nature, usually only individuals suited to the natural circumstances can survive and reproduce, while humans select those with additional attractive, docile or productive characteristics. Therefore, selection criteria in nature versus those in domestic conditions are different and domesticated animals often differ significantly in phenotype, behaviour and genetics from their wild forerunners. It is the target of breeding back to re-create the wild traits that may have been preserved in domestic animals within one breeding lineage. Commonly, only the phenotype and ecological capacity are considered in breeding back projects, but single ones, like TaurOs Project also consider the genetic aspect of the animals they are working with.

In many cases, the extinct wild type ancestors of a given species are only known through skeletons and, in some cases, historical descriptions, so their phenotype is not directly accessible. Therefore, there is no certainty of success with a breeding back attempt and the results must be reviewed with caution. In order to test genetic closeness, both mitochondrial DNA and nuclear DNA have to be accessible. However, success is possible: humans only selected for superficial characters and as a rule did not change inner mechanisms such as digestion. Further, since many domestic animals show a behaviour that is derived from their wild ancestors (such as the herding instinct of cattle or the social instincts of dogs), and are fit to survive under natural circumstances, as evidenced by the many feral populations of many domestic animals, it can be presumed that back-bred animals will function like their wild ancestors.^[1] For example, food choice should be the same in domestic and wild types. Natural selection could serve as an additional tool in creating authentic robustness, behaviour and maybe also phenotype. For large herbivores, a sufficient predator population would also be necessary to support such a process, but this largely is not present in current Europe, where many breeding back projects are conducted.

There is a difference between creating a look-alike breed from domestic animals and creating a look-alike via artificial selection of individuals of a different species or subspecies that may resemble the animal that is targeted. For example, the Quagga was an independent subspecies of the plains zebra, and has no descendants which preserved its features. Thus, the Quagga Project tries to breed a look-alike out of living plains zebras which have fewer stripes than average, selecting for reduced striping. The resulting animal will bear only a superficial resemblance to the extinct Quagga.

Use

Bred-back breeds are interesting for conservation biology since they may fill an ecological gap that has been left due to the extinction of the wildtypes, in some cases due to hunting by humans. As long as food choice, behaviour, robustness, defence against predators, hunting or foraging instincts and phenotype are the same as in the wild type, it will function like it in the wilderness. Releasing such animals into the wild would fill the previously empty niche and allows a natural dynamic between the species of the ecosystem to re-evolve. However, breeding back-attempts do not always result in an animal that is closer to the wild type than other domestic breeds. For example, heck cattle bear less resemblance to the aurochs than many Iberian fighting cattle do.

Examples of breeding back

A Tamaskan Dog, bred to resemble the wolf in phenotype.

Aurochs

Ideas for creating an aurochs-like animal from domestic cattle have been around since 1835. In the 1920s, Heinz and Lutz Heck tried to breed a look-alike using central European dairy breeds and southern European cattle. The result, heck cattle, is hardy, but differs from the aurochs in many respects, although a vague resemblance in colour has been achieved.^[1] A new project to achieve a type of cattle that resembles the largest possible degree is TaurOs Project using primitive and hardy southern European breeds, Scottish Highland cattle and modern knowledge of DNA and animal breeding. These "TaurOs-ochs "are planned to be released in various European natural reserves.

European wild horse

At the beginning of the 19th century, the last horses thought to be Tarpans were donated to Polish farmers, and they were claimed to have been incorporated into domestic stock. It is, however, questionable whether the free-roaming stock of horses called "Tarpans" at the time were actually never-domesticated European wild horses, or just feral domestic horses. In any case, Tadeusz Vetulani attempted to recreate the original Tarpan type from these horses by selecting those individuals which fitted his conception of the ancestral wild horse. The resulting breed is called the Konik. The Heck brothers later on crossed Koniks withPrzewalski’s horses, Icelandic horses and Gotland ponies; the result is now called the Heck Horse.

Besides the Konik, the Exmoor Pony has also been attributed to be close to the European wild horse. It bears some resemblance to the Przewalski’s horse and to the horses in Lascaux cave paintings, and still lives in a semi-feral state in some parts of Southern England.

Wolf

Although the Wolf, the wild ancestor of domestic dogs, is not extinct, its phenotype is the target of several developmental breeds including the Northern Inuit Dog and the Tamaskan Dog. They are all crossbreeds of German Shepherds and Huskies, selected for phenotypic wolf characteristics. Therefore, these breeds are breeding-back attempts as well.

Breeding pair

Breeding pair is a pair of animals which cooperate over time to produce offspring with some form of a bond between the individuals. For example, many birds mate for a breeding season or sometimes for life. They may share some or all of the tasks involved: building a nest, incubating the eggs and feeding and protecting the young. The term is not generally used when a male has a harem (zoology) of females, such as with mountain gorillas.

True breeding pairs are usually found only in vertebrates, but there are notable exceptions, such as the Lord Howe Island stick insect. True breeding pairs are rare in amphibians or reptiles, but fairly common with fish (e.g. discus) and especially birds. Breeding pair arrangements are rare in mammals, where the prevailing patterns are either that the male and female only meet forcopulation (e.g. brown bear) or that dominant males have a harem (zoology) of females (e.g. walrus).

Breeding program

Breeding programs help animals to breed and can be good for animals as well as the agricultural economy.

A breeding program is the planned breeding of a group of animals or plants, usually involving at least several individuals and extending over several generations. There are a couple of breeding methods, such as artificial (which is man made) and natural (it occurs on its own, which is very rare).

Breeding programs are commonly employed in several fields where humans wish to completely obliterate the characteristics of their animals' offspring through careful selection of breeding partners:

· Dog and cat fanciers may coordinate a breeding program to raise the probability of an animal's litter producing a championship-caliber animal.

· Horse breeders try to produce fast racehorses through breeding programs.

· Conservationists use breeding programs to try to help the recovery of endangered species by preserving the existing gene pool and preventing inbreeding.

· There also can be breeding programs for plants. For instance, a winery owner, seeking to find a better tasting wine, could design a breeding program so that only the vines whose grapes make the very best wine are allowed to breed.

Seasonal breeder

Seasonal breeders are animal species that successfully mate only during certain times of the year. These times of year allow for the births at a time optimal for the survival of the young in terms of factors such as ambient temperature, food and water availability, and even changes in the predation behaviors of other species.^[1] Related sexual interest and behaviors are expressed and accepted only during this period. Female seasonal breeders will have one or more estrus cycles only when she is "in season" or fertile and receptive to mating. At other times of the year, they will be anestrus. Unlike reproductive cyclicity, seasonality is described in both males and females. Male seasonal breeders may exhibit changes in testosterone levels, testes weight, and fertility depending on the time of year.

Seasonal breeders are distinct from opportunistic breeders, which mate whenever the conditions of their environment become favorable, and continuous breeders like humans that mate year-round.

Breeding Season

The breeding season is the most suitable season, usually with favourable conditions and abundant food and water, for breeding. Abiotic factors such as the timing of seasonal rains and winds can also play an important role in breeding onset and success.

Many species breed in colonies or large communities which is known as communal breeding. It is common to see large congregations of these species in particular favourable locations in their breeding seasons. These breeding colonies and their location are generally protected by wildlife conservation laws to keep the species from going extinct. Some species have evolved for communal breeding in large breeding colonies and can not breed in smaller numbers or pairs alone. These species can be threatened by imminent extinction if they are hunted on their breeding grounds or if their breeding colonies are destroyed. The Passenger pigeon is a famous example of probably the most numerous land bird on the American continent which had evolved for communal breeding that went extinct due to large scale hunting in its communal breeding grounds during the breeding season and its inability to breed in smaller numbers.

Physiology

The hypothalamus is considered to be the central control for reproduction. Hence, factors that determine when a seasonal breeder will be ready for mating affect this tissue. This is achieved specifically through changes in the production of the hormone GnRH. GnRH in turn transits to the pituitary where it promotes the secretion of the gonadotropins LH and FSH, both pituitaryhormones critical for reproductive function and behavior, into the bloodstream. Changes in gonadotropin secretion initiate the end of anestrus in females.

Factors that determine time of fertility

Photoperiod

When a seasonal breeder is ready for mating is strongly regulated by length of day (photoperiod) and thus season. Photoperiod likely affects the seasonal breeder through changes in melatoninsecretion by the pineal gland that ultimately alter GnRH release by the hypothalamus.

Hence, seasonal breeders can be divided into groups based on when they are fertile. "Long day" breeders cycle when days get longer (spring) and are in anestrus in fall and winter. "Short day" breeders cycle when the length of daylight shortens (fall) and are in anestrus in spring and summer. The decreased light during the fall decreases the firing of the retinal nerves, in turn decreasing the excitation of the superior cervical ganglion, which then decreases the inhibition of the pineal gland, finally resulting in an increase in melatonin. This increase in melatonin results in an increase in GnRH and subsequently an increase in the hormones LH and FSH, which stimulate cyclicity.

Day length variations with latitude can also impact breeding. For instance, sheep and goats in tropical climes may breed throughout the year while those in more polar arctic areas may have a shortened season.

Females are generally more sensitive to changes in day length. For instance, unlike mares, stallions remain fertile year-round, suffering only some declines in sexual behavior and sperm production out of season.

Other factors

Other factors that affect breeding time include the presence of a ready and available mate. For instance, the presence of a fertile male will induce an estrus cycle in a doe shortly after introduction.

Further environmental factors can include nutrition, chemosensory and hormonal cues. Weight and age are other factors.

Partial list of seasonal breeders

Many non-mammals are seasonal breeders, such as many birds and fish. Here is partially listed those that are mammals.

Long day breedersRing-tailed lemur

Horse

Hamster

Groundhog

Mink

Short day breeders

Sheep

Goat

Fox

Deer, Red Deer

Elk

Moose

Summer breeders

Ruffed lemur (May - July)

Select species of hamster, vole and mouse

Captive breeding

Captive breeding is the process of breeding animals in human controlled environments with restricted settings, such as wildlife reserves, zoos and other conservation facilities; sometimes the process is construed to include release of individual organisms to the wild, when there is sufficient naturl habitat to support new individuals or when the threat to the species in the wild is lessened. Captive breeding programs facilitate biodiversity and may save species from extinction. However, such programs may also reduce genetic diversity and species fitness.

History

Captive breeding has been used with success for some species for some time, with probably the oldest known instances of captive breeding being attributed to menageries of European and Asian rulers, a case in point being the Pere David's Deer. This species was successfully saved through captive breeding programs after almost being hunted to extinction in China. The idea was popularized among modern conservationists independently by Peter Scott and Gerald Durrell in the 1950s and 1960s, founders of the Wildfowl and Wetlands Trust and Jersey Zoo, who demonstrated success with a wide variety of life forms in the 1970s ranging from birds (e.g. Pink Pigeon), mammals (e.g. Pygmy Hog), reptiles (e.g. Round Island Boa) and amphibians (e.g. Poison arrow frogs). Their ideas were independently validated by the success of Operation Oryx (under the auspices of the Fauna and Flora Preservation Society), which captive bred the Arabian oryx starting in 1963 for eventual reintroduction to the wild. The Przewalski's horse has recently been re-introduced to the wild in Mongolia, its native habitat.

Coordination

The breeding of endangered species is coordinated by cooperative breeding programmes containing international studbooks and coordinators, who evaluate the roles of individual animals and institutions from a global or regional perspective. There are regional programmes for the conservation of endangered species:

· Americas: Species Survival Plan SSP (Association of Zoos and Aquariums AZA, Canadian Association of Zoos and Aquariums CAZA)

· Europe: European Endangered Species Programme EEP (European Association of Zoos and Aquaria EAZA)

· Australasia: Australasian Species Management Program ASMP (Australasian Regional Association of Zoological Parks and Aquaria ARAZPA)

· Africa: African Preservation Program APP (African Association of Zoological Gardens and Aquaria PAAZAB)

· Japan: Conservation activities of Japanese Association of Zoos and Aquariums JAZA

· South Asia: Conservation activities of South Asian Zoo Association for Regional Cooperation SAZARC

· South East Asia: Conservation activities of South East Asian Zoos Association SEAZA

Challenges

Captive breeding techniques are usually difficult to implement for highly mobile species like some migratory birds (e.g. cranes) and fishes (e.g. Hilsa). Species like large cetaceans (whales, dolphins, etc.) may also have some difficulties as it would be hard to meet their biological requirements in captivity, especially the vast amount of space required to keep large populations.

Genetics

If the captive breeding population is too small, inbreeding may occur due to the reduced gene pool, which may lead to the population lacking immunity to diseases and other problems. Over a sufficient number of generations, inbred populations can regain "normal" genetic diversity.^[

For example, since the 1970s the Matschie's tree-kangaroo, an endangered species, has been bred in captivity. The Tree Kangaroo Species Survival Plan (TKSSP) was established in 1992 to help with the management of Association of Zoos and Aquariums (AZA). The mean kinship strategy (MK) is used by TKSSP to make annual breeding recommendations to preserve genetic diversity in small populations. This is done to retain their adaptive potential and avoid the negative consequences of inbreeding. Comparison of the genetic diversity of the captive breeding population to wild populations is done to evaluate how the captive breeding program is retaining the population’s genetic diversity over time. In a study done by McGreezy et al. (2010), "AZA Matschie tree kangaroo’s haplotype diversity was almost two times lower than wild Matschie tree kangaroos." This difference with allele frequencies shows the changes that can happen over time, like genetic drift and mutation, when a species is taken out of its natural habitat.

Behaviour changes

Impacts of captive breeding include behavioural problems in released animals, which are not being able to hunt or forage for food leading to starvation. This could occur because when in captivity young animals miss critical learning periods. Released animals often do not avoid predators and are not able to find ample shelter for themselves and may die as a result. Golden Lion Tamarinmothers often die in the wild before having offspring because they do not have the climbing and foraging skills they need to survive. This results in populations continuing to decline despitereintroduction because the species does not produce viable offspring. Training can improve anti-predator skills, but the effectiveness of such interventions is influenced by a number of constraints.

Domestication is another challenge that captive breeding faces. In a study done by Belyaev (1979), silver foxes were bred in captivity over several decades and many generations to display behavioral and physiological characteristics of a domesticated dog. The study found that after several generations of breeding the domesticated silver foxes picked up behavioral traits seen in domesticated dogs, such as wagging their tails, and licking the hands and faces of humans. They also showed physiological changes such as drooping ears, erect tails and two breeding periods per year. All of these characteristics are not present in wild silver foxes. The experimenters also mentioned that the domesticated foxes "eagerly seek human contact", which could be detrimental as they are hunted for their fur and are viewed as pests by poultry farmers.

Loss of habitat

Another challenge with captive breeding is the habitat loss that occurs while they are in captivity being bred (though it is occurring even before they are captured). This may make release of the species nonviable if there is no habitat left to support larger populations.

As climate change increases and more invasive species are introduced, more and more species become threatened with extinction. Just from a decrease in population size, reductions in genetic diversity occurs which leads to a decrease in the ability of populations to adapt to the changing environment. In this context, loss of genetic polymorphism, which is a difference in DNA sequence among individuals, groups or populations, is related to extinction risk. Conservation programs can now obtain measurements of genetic diversity at functionally important genes due to advances intechnology

Success

In 1971 the de Wildt Cheetah and Wildlife Centre was established. Between 1975 and 2005, 242 litters were born with a total of 785 cubs. In a study done by Bertschinger, H. J., Meltzer, D. J. A., & Van Dyk, A. (2008), the survival rate of cubs was examined. "Mean cub survival from 1 to 12 months and greater than 12 months of age was 71.3 and 66.2%, respectively." This study shows that cheetahs can be bred successfully and that their endangerment can be decreased through these breeding programs. It also indicated that failure in other breeding habitats may be due to "poor" sperm morphology.

Recently, the number of wild Tasmanian devils is declining from transmissible Devil Facial Tumor Disease. A captive insurance population program has started, but the captive breeding rates at the moment are lower than they need to be. A study done by Keeley, T. J., O, J. K., Fanson, B. G., Masters, K., and McGreevy, P. D. (2012), had a goal to "increase our understanding of theestrous cycle of the devil and elucidate potential causes of failed male-female pairings." The temporal patterns of fecal progestogen and corticosterone metabolite concentrations were examined. The majority of unsuccessful females were captive-born, suggesting that if the species' survival depended solely on captive breeding, the population would probably disappear.

In 2010, the Oregon Zoo found that Columbia Basin pygmy rabbit pairings based on familiarity and preferences resulted in a significant increase in breeding success.

Recent advances

The Major Histocompatibility Complex is a region of the genome that is being studied by researchers in the field. Scientists have found that genes that code for the major histocompatibility complex have an effect on the ability of certain species (such as Batrachochytrium dendrobatidis) to resist certain infections because the MHC has a mediating effect on the interaction between the body’s immune cells with other body cells. Measuring polymorphism at these genes can give an indirect measure of the immunological fitness of populations. It is suggested that captive breeding programs that place emphasis on selectively breeding those organisms that carry the disease resistant gene, can help in reintroducing endangered species with a better chance in the wild.

There have also been recent advances in captive breeding programs with the use of induced pluripotent stem cell (iPSC) technology. This technology has been tested on several endangered species. Scientists hope the stem cells could be used to be converted into germ cells in captive breeding programs to help diversify the gene pools of threatened species. Healthy mice have been born with this technology. It is suggested that induced pluripotent stem cells may one day be used in producing therapeutic solutions for captive animals suffering from diseases and increasing the size of endangered animal populations.

Date: 2016-04-22; view: 2002