Oliver A Ryder,
Center for Reproduction of Endangered Species, Zoological Society of San Diego, PO Box 120551, San Diego, CA 92112–0551, USA |
Available online 2 May 2002.
Although controversy surrounds cloning efforts, the cloning of animals to assist efforts to preserve genetic variation in support of endangered speciesconservation efforts has attracted serious interest. A recent report by Loi et al. describing the cloning of a mouflon (a species of wild sheep) in a domestic sheep surrogate points to potential conservation opportunities and additional challenges in the evaluation of appropriate technologies for present and future efforts to conserve gene pools of endangered species.
Keywords: cloning; endangered species;Mouflon, nuclear transfer; oocytes
Keywords: Biotechnology; Cell biology; Development; Genetics
* Successful cloning of an endangered sheep
* Defects in cloned animals
* Cloning as a tool for assisting in conservation of gene pools
* Cell banking and research should top the current agenda
* Planning for the future
Each major report about cloning involving somatic nuclei brings new insights and new debates. As the controversy around human cloning expands [1.] and [2.] there is a diversity of opinion regarding the potential of cloning for the conservation of endangered species [3.] , 4. and 5.. It is important to evaluate separately the issues surrounding human cloning and those of animal cloning.With respect to predictions for loss of species, technologies for assisted reproduction, such as artificial insemination, embryo transfer and cloning from somatic cells, have been advocated as technologies that could contribute to conservation of biological diversity .
Successful cloning of an endangered sheep
Discussion of the application of cloning technology to conservation efforts forendangered species  was an immediate result from Ian Wilmut's 1997 report of the cloning of Dolly . Although reports of embryo development [8.] and [9.] and newborn animals have appeared as a result of cloning technology, the recent report of surprising success in cloning mouflon (a species of wild sheep)  is notable for several reasons. The success rate was much greater than when thedomestic sheep, Dolly, was cloned. A higher proportion of embryos (constructed by nuclear transfer to enucleated domestic sheep ova) developed in vitro to blastocysts and, subsequently, to pregnancies and live birth in surrogate dams than previously reported [7.] and [11.] . It is also noteworthy that the donor nuclei were obtained from dead donor mouflon. These rather unexpected findings might serveas the basis for additional studies to help identify factors contributing to the rate of success. Studies of telomere length were not reported and future work in this area will be of interest.
From a theoretical perspective, there is reason to believe that cloning can assist in the preservation of genetic diversity in precariously small populations. The cloned animals, as individuals, might serveas conduits for the retention of genetic variation otherwise lost. There are many vulnerable and endangered forms of sheep (including forms of argali, urial, desert bighorn and Marco Polo and snow sheep) for which this technology could be considered in defined programs of gene pool preservation.
Objections to the use of cloning technology for conservation focus on inefficiencies of the currentprocess, impracticalities involved in applying these techniques to non-domestic ova donors and surrogate dams, and the lack of fitness for survival of cloned animals in the natural environment. Fitness concerns are heightened owing to the use of domestic surrogates that fail to impart appropriate behavioral attributes for cloned offspring that will interact with others of their species raised by...