Scientists Clone First Endangered Species: a Wild Sheep
Bijal P. Trivedi
for National Geographic Today
|October 29, 2001|
For the first time scientists have successfully created a viable clone
of an endangered speciesthe European mouflon, one of the smallest
wild sheep in the world.
The effort, led by Pasqualino Loi, of
the University of Teramo, Italy, trumped the work early last year of
U.S. company Advanced Cell Technology whose clone of an endangered Asian
ox died of dysentery 48 hours after birth. The apparently healthy lamb
is now about seven months old and currently living in a wildlife center
in Sardinia. The work is reported in the October issue of Nature
The European mouflon is an endangered species of sheep in its original habitat: the Mediterranean islands of Sardinia, Corsica, and Cyprus. The animal nearly died out in Europe a hundred years ago and almost disappeared from the islands that were their first home (see sidebar).
Ever since the creation of Dolly, a sheep that was the first animal to be cloned, conservationists have debated the controversial merits of cloning as a means of rescuing populations of endangered and threatened species.
Those in support of the idea, like Loi and his colleagues, suggest collecting cell samples from a variety of endangered species while their numbers are somewhat highthus ensuring that a range of genetic diversity is essentially bottled. Should the population disappear the original pool of genes can be regenerated through cloning.
Others feel that cloning gives a false sense of security that populations of endangered animals can easily be rekindled. For these groups conservation through habitat preservation is the better way to protect these species.
Betsy Dresser, director of the Audubon Center for Research of Endangered Species, in New Orleans, disagrees. "Saving habitat may not be enough," she said.
"Any tool for saving endangered species is important," said Dresser. "Cloning is just another reproductive tool, like in-vitro fertilization."
Probably the most valuable aspect of cloning is to reintroduce specific members of a species that represent a "significant slice of the gene pool pie," said geneticist Oliver Ryder, of the Center for Reproduction of Endangered Species at the San Diego Zoo in California. A key member of a species may, for example, have died in captivity before it could produce offspring.
If cloning is managed properly, said Dresser, it can even expand the genetic pool. "It may allow us to bring back genetic material from infertile animals, dead animals and even very young animals that were too immature to breed."
The mouflon lamb was cloned using "somatic cell nuclear transfer"the same technique used in 1997 to clone Dolly. The only difference is that this time two species of sheep were usedthe mouflon that was cloned and the domestic surrogate mother that carried the clone.
Cloning the mouflon lamb may be a small step scientifically, said Dresser, but it is important because it proves the value of using a common species as a surrogate mother for an endangered species.
The trick with cloning is to take the genetic material from the animal to be clonedwhich is sequestered in the nucleus of the celland transferring it into an unfertilized egg from which the nucleus had been removed. The chemicals in the egg have special properties that allow the genes in the transplanted nucleus to guide the development of a complete organism.
Loi's team recovered cells from two mouflon ewes that had died the previous day in a Sardinian pasture. Using a very fine needle Loi removed the nucleus from the unfertilized egg of a common domesticated sheep and replaced it with a single mouflon cell.
With a nucleus containing mouflon DNAthe genetic instruction manual to make a mouflon lambthe egg started to divide as if it had been fertilized. After a few days it formed a small ball of cells that was transplanted into the surrogate motherin this case, also a domesticated sheep.
Of the seven embryos that were surgically implanted into four surrogate mothers, one resulted in the birth of a clone.
Since Dolly, cattle, pigs, mice and more sheep have been cloned. While these species may appear dull material for a technique as powerful as cloning, the techniques currently available have been fine-tuned to these domestic species.
"We know a lot about the reproductive cycles of cattle and sheep that we don't know for species like the black rhino and the Sumatran tiger," said Ryder, "which makes exotic species more difficult to clone."
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