Right now, cloning is not a viable conservation strategy. But some researchers remain optimistic that it will help threatened species in the future
James and snowmanradio, Wikimedia Commons
In 2009 the Brazilian Agricultural Research Corp. (Embrapa) and the Brasilia Zoological Garden began scavenging and freezing blood, sperm and umbilical cord cells from roadkill and other wild animals that had died, mostly in the Cerrado savannaan incredibly diverse collection of tropical forest and grassland ecosystems home to at least 10,000 plant species and more than 800 species of birds and mammals, some of which live nowhere else in the world. Specimens were collected from the bush dog, collared anteater, bison and gray brocket deer, among other species.
The idea was to preserve the genetic information of Brazil’s endangered wildlife. One day, the organizations reasoned, they might be able to use the collected DNA to clone endangered animals and bolster dwindling populations. So far the two institutions have collected at least 420 tissue samples. Now they are collaborating on a related project that will use the DNA in these specimens to improve breeding and cloning techniques. Current cloning techniques have an average success rate of less than 5 percent, even when working with familiar species; cloning wild animals is usually less than 1 percent successful.
Any animals born during Brazil’s new undertaking will live in the Brasilia Zoo, says Embrapa researcher Carlos Martins. Expanding captive populations of wild animals, he and his team hope, will discourage zoos and researchers from taking even more wild animals out of their native habitats. Martins and his colleagues have not yet decided which species they will attempt to clone but the maned wolf and jaguar are strong candidates. The International Union for Conservation of Nature classifies both animals as “near threatened” on its Red List of Threatened Species, two levels below “endangered.”
Many researchers agree that, at present, cloning is not a feasible or effective conservation strategy. First of all, some conservationists point out, cloning does not address the reasons that many animals become endangered in the first placenamely, hunting and habitat destruction. Even if cloning could theoretically help in truly desperate situations, current cloning techniques are simply too ineffective to make much of a difference. Compared with cloning domestic speciesparticularly cattle, which have been successfully cloned for years to duplicate desirable traitscloning endangered species is far more difficult for a number of reasons.
Successful cloning generally involves at least three essential components: DNA from the animal to be cloned; a viable egg to receive that DNA; and a mother to gestate the resulting embryo. Often, hundreds of embryos and attempted pregnancies are needed to produce even a few clones. Scientists usually have a poor understanding of endangered animals’ reproductive physiology, which makes it too risky to extract a sufficient number of eggs from that species or rely on females of that species to give birth to clones. Legal protections sometimes preclude threatened species from such procedures as well. To compensate, researchers fuse the DNA of an endangered species with eggs from a closely related species and select mothers from the latter. Such hybrid embryos often fail to develop properly.
Although they are keenly aware of these problems, Martins and his colleagues, as well as a few other scientists around the world, think that efforts to archive the genetic information of endangered wildlife are worthwhile. Some researchers remain optimistic that cloning will become a useful tool for conservation in the future. Optimists point to recent successes cloning wild mammals using closely related domestic species, improved techniques for preventing developmental abnormalities in a cloned embryo, better neonatal care for newborn clones and in vitro fertilization made possible by stem cells derived from frozen tissue.
The first clones In the early 1950s, at the Lankenau Hospital Research Institute in Philadelphia, Robert Briggs and Thomas King successfully cloned 27 northern leopard frogs through a process known as nuclear transfer. The nucleus, often called the command center of the cell, contains most of a vertebrate’s DNAexcept for the DNA within bean-shaped, energy-generating organelles named mitochondria. Briggs and King emptied frog eggs of their nuclei, sucked nuclei out of cells in frog embryos and injected those nuclei into the empty eggs. Many of the eggs developed into tadpoles that were genetically identical to the embryos that had donated their nuclear DNA.
In 1958 John Gurdon, then at the University of Oxford, and colleagues cloned frogs with nuclear DNA extracted from the cells of fully formed tadpoles. Unlike embryonic cells, which are genetically flexible enough to become a variety of different tissues, a tadpole’s cells are “differentiated”that is, the patterns of genes they express have changed to fit the profile of a specific cell type: a skin, eye or heart cell, for example. Gurdon demonstrated that, when transplanted into an egg, nuclear DNA from a mature cell reverts to the more versatile state characteristic of DNA in an embryo’s cells. This breakthrough encouraged scientists to try cloning far larger animals using DNA from adult cells.
Will Cloning Ever Save Endangered Animals?