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:
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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.
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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.
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Inbreeding
in the Dama Gazelle has adverse effect on sperm motility, cryptorchidism
in puma, sperm pleomorphism in lions etc.
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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.
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Problems such as behavioral adaptation to
captivity, the adverse effect of captivity or anaesthesia related stress,
risk of disease transmission etc.
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Financial cost and physical space for the
maintenance of large captive population.
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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.
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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.
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To avoid inbreeding in captivity scientist
try to help animals bred naturally, but often researchers do not even know
how normal mating takes place.
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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.
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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
