FROZEN ZOO

An alarming worldwide extinction of animal species is taking place as a result of the activities of the increasing global human population. But more commonly the threat is wholesale damage to the entire ecosystems than it to a single species Threat to an individual species may prove easier to control, because effort and resources can be directed solely towards that species, whereas threat to an ecosystem requires intervention to preserve the entire environment. So the concept of ex-situ genetic management of small captive population of endangered species with a view to re-introducing them into the wild is attracting increasing interest. Modern reproductive techniques will play an important role in such programmes, and it is likely that an increasing number of veterinarians become involved. 

                 There are species like that where captive breeding technologies and breeding is crucial. But captive breeding is not always easy. Many animals are disoriented by living in the wrong climate or social system, or being squeezed into small habitats in the presence of humans. 

MAJOR DRAWBACKS OF CAPTIVE BREEDING AND SUBSEQUENT REINTRODUCTION OF ANIMAL TO WILD: 

  •   A small group of animals in the captivity is adapted only to captive environment so the success of reintroducing them into the wild becomes unsatisfactory.

  •   Reproduction within small population results inbreeding. At each fertilization event, only a single copy of each gene is transmitted from each parent to the offspring. Thus, for genes for which the parents are heterozygous, there is genetic loss during reproduction. This genetic loss results in a rapid, irreversible loss of potentially valuable alleles from the population and a progress towards a state in which individuals are homozygous.

  •  Inbreeding in the Dama Gazelle has adverse effect on sperm motility, cryptorchidism in puma, sperm pleomorphism in lions etc.

  • Inbreeding results in loss of genetic variability in the MHC which produces particular problems to the endangered species reintroduced to the constantly changing repertory of potential pathogen present in the wild.

  • Problems such as behavioral adaptation to captivity, the adverse effect of captivity or anaesthesia related stress, risk of disease transmission etc.

  • Financial cost and physical space for the maintenance of large captive population.

  • Fraction of the genetic diversity of one generation is invariably lost in the population of next. To avoid this we have to produce more progeny in the next generation (i.e., number of young ones from one generation should be increased) or population should be directly produced from the founder animals. The population of wild animals becomes smaller in near future with increase in the human activities and there will be drastic lost in genetic material due to rapid inbreeding in these smaller groups. By preserving the genetic material and gametes of the present population we can reintroduce it into the future generation even after several decades.

  • Since there is the loss of genetic material during the production of gametes it has been suggested that increasing the intervals at which chromatin undergo meiosis would reduce the rate of inbreeding. This entails extending the generation time of the captive population which may be achieved by breeding from older animals, but problem with older animal is that fertility will be low. A better option is to preserve embryos and gametes for long period before thawing them to generate new individuals.

  • To avoid inbreeding in captivity scientist try to help animals bred naturally, but often researchers do not even know how normal mating takes place.

  • In each geographical area wild animal survived as smaller population and the bloodline becomes more inbred. Transport of a representative number of animals between each group (it may be intercontinental or between countries) will introduce a new genetic diversity in that population. But this is very tedious process and has the risk of disease transmission. But transport of gamete or embryo is less expensive with low risk of disease transmission.

  • The genetic variability of the founder population used to initiate captive breeding programme is increasingly viewed as the fundamental resource that must be preserved during the periods of captivity, since it will allow species to be reintroduced successfully into the wild and to adapt to subsequent changes in their habitat. Genetic variability is probably a better predictor of the success of captive breeding schemes than the number of animals generated, and hence endangered populations might best be regarded as a gene pool rather than as a collection of individuals. The preservation of genetic variability in small relict populations should the primary aim of captive breeding programmes. Central to such reproductive management is the concept of the genetic resource bank or FROZEN ZOO.

      Frozen zoo can be generally defined as a collection of animal genes in the form of frozen semen and embryos maintained in a state of constant interaction with the live population by the use of reproductive technology. But it stock files biological materials such as tissue samples, serum and oocytes (even though it is not freeze very well) from a wide variety of rare and critically endangered species. It represents a genetic bank vault, an archive of irreplaceable genetic information that can be preserved for perhaps hundred of years. Generation of such a virulent frozen population have many potential benefits for the management of small population. 

       The laboratory set up in the Zoological Society of San Diego's Center for Reproduction of Endangered Species (CRES) in 1976 dealt with cytogenetics. This lab immediately began growing fibroblast (skin) cell cultures from various exotic species for chromosomal studies. These cells were frozen in liquid nitrogen at -195 degrees Celsius. Today the lab, called the Frozen Zoo, is housed in 4 storage tanks, which hold viable cell lines from more than 3,200 individual mammals, representing 355 species and subspecies.            

      The first so called frozen zoo was created by Kurt Benirschke in 1975 at the San Diego Zoo. San Diego Zoo studying gene pools and genetic diseases made prevalent by inbreeding. Today in zoos around the world, their deep freeze tank acts as a high-tech Ark, housing cells from the planet’s most endangered animals including chimps, cheetahs, pandas, California condors and hundred more. Now there are less than a dozen frozen zoo worldwide. The world first inter species transfer using an embryo that had been frozen and thawed was produced in 1999 at Audubon center for research of endangered species Jass an African wild cat kitten was born to his surrogate mother.

Jazz, an African wildcat kitten, is the result of the first successful interspecies transfer of a frozen embryo. Mother Cayenne is a domestic tabby cat    

               If the animal near extinction, the samples can be thawed and used to produce offspring through assisted reproductive technologies such as Artificial Insemination, Embryo Transfer, In Vitro Fertilization, embryo splitting, production of transgenic animals, cloning etc with the goal of repopulating them in their original habitat. By banking cryogenically preserved genetic material for future use, they create a safety net against the extinction of species. The genetic material can be collected from animals in the wild preserved in the liquid nitrogen and used to increase the number of individuals of captive species with the goal of repopulating them in their original habitat. 

              Although the success rate of modern reproductive technologies are very low as compared to natural breeding, these technique make it possible to collect genetic material from dead animal or animals which are unable to mate or carry offspring to term owing to debility. In Vitro maturation of immature oocytes, collection of semen from epididymis makes these dead animals becoming parents from grave.

             Future application of frozen zoo technology will be the provision of biological materials for basic and applied research in the area of molecular genetics, disease research and new reproductive technology. In the new area of molecular genetics, using DNA collected from the frozen tissue and cell lines researchers will be able to determine how closely related the individual animals that are currently housed by many zoos and will be able to prevent inbreeding. Researchers studying the evolution of a species will now have the access to a large population sample without having to go into the field to collect the samples from many species.

                There is an urgent need to protect and conserve endangered wild life in the world. The inevitable environmental changes and other circumstances have driven man into a situation where it is impossible to stop the destruction of many species without special conservation programme. These programmes have traditionally included breeding animal in captive surrounding, which again often is very difficult and limits the number of individuals thus restricting the genetic basis. A decrease in the genetic variation in a population results finally in failure in reproduction and vitality. But modern reproductive technologies have potential contribution to reduce inbreeding and genetic adaptation to captivity, which depends on the constant dynamic interaction between captive populations and cryopreserved genetic resource bank

 

Courtesy: Dr. Ratheesh Babu M (1997 Batch)

MVSc Scholar,

Dept. of Animal Reproduction,

COVAS

 
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