Over the next 200 years, at least 2000 terrestrial vertebrate species alone will probably go extinct unless they are bred captively (Soule et al., 1986; Tudge, 1995), and it seems very unlikely that we will have sufficient resources for such a large-scale rescue operation. Even if we could preserve all of these species in captivity, their long-term survival would still depend on whether we have retained enough suitable habitat to allow for their eventual release. In the near future we will undoubtedly see a growing number of species going extinct. Because not all species that are threatened with extinction can be maintained through captive breeding, a number of organizations are setting up genetic diversity banks.
Genetic diversity banks are designed for the long-term storage of extracted DNA, seeds, tissue, sperm and other sources of genetic material. One example of this is The Millenium Seed Bank Project at the Royal Botanical Gardens in Kew, London, which aims to preserve genotypes of over 24 000 species of seed-bearing plants from around the world through the long-term storage of their seeds. Another example, albeit on a smaller scale, can be found at the Center for Plant Conservation at the Missouri Botanical Garden, which has seeds, cuttings and other material from more than 600 endangered plant species that are native to the USA.
In a similar vein, the Frozen Ark is a last ditch attempt to preserve some of the genetic diversity of animals. This project, which is a collaboration between the London Natural History Museum, the Zoological Society of London, and Nottingham University, aims to collect, store and preserve DNA and tissue from as many endangered species as possible. Priority is given to species with a high likelihood of extinction in the near future, with the first members of the ark including the yellow seahorse (Hippocampus kuda), Scimitar horned oryx (Oryx dammah), Socorro dove (Zenaida graysoni) and the Seychelles Fregate beetle (Polposipus herculeanus). If the DNA is stored appropriately it could remain intact for tens of thousands of years, possibly longer. It is too soon to know what exactly this genetic information will be used for in the future, although it is possible that cells and sperm will also be stored in the hope that future science fiction-type cloning will allow scientists to resurrect formerly extinct species.
Other genetic diversity banks have more specific short-term applications. At the Wildlife Breeding Research Centre in South Africa, for example, vets and biologists have established a sperm bank for lions and have an ongoing programme in which they travel between prides, artificially inseminating females so as to reduce inbreeding in small, isolated populations. The social structure of this species means that if a strange male is introduced to a pride then the members of that pride will either chase him away or kill him, which would do nothing to ameliorate inbreeding. Artificial insemination therefore bypasses some of the behavioural deterrents against the genetic enhancement of lion populations. Cryopreservation of sperm and oocytes may facilitate captive breeding of other taxonomic groups (e.g. Ledda et al., 2001; Browne, Clulow and Mahoney, 2002), although detailed methods generally have to be worked out separately for each species, and the technology is therefore currently available for only a small proportion of animals.
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