142 • Technologies To Maintain Biological Diversity 



sampling and preservation of gametes or em- 

 bryos from rare breeds allow a repository of 

 genetic diversity to be maintained. 



Two caveats must be kept in mind regarding 

 the role of cryopreservation of gametes and em- 

 bryos. First, considerable development work 

 is required to extend the techniques to cover 

 the full range of endangered populations. For 

 wild animals, reliable procedures for collect- 

 ing, freezing, and using semen and embryos 

 have to be developed further and validated for 

 each species or group of species to ensure that 

 sufficient levels of genetic diversity can be 

 regenerated from the frozen store. Preservation 



technologies for embryos are well developed 

 only in certain domestic mammals. Similar 

 techniques are needed for birds, reptiles, am- 

 phibians, fish, and invertebrates. 



Second, cryopreservation of gametes and em- 

 bryos should not be an llth-hour effort to pro- 

 tect seriously endangered species. Restraining 

 wild animals to collect semen or embryos is 

 risky. Some animals die, which entails an un- 

 acceptable risk if the species is already rare. 

 Therefore, research and the collection of gametes 

 and embryos from many sources should begin 

 before the populations become endangered. 



SAMPLING STRATEGIES 



Efficient programs for offsite maintenance 

 of animal genetic diversity require a mecha- 

 nism for monitoring existing populations — to 

 identify when and if intervention is required — 

 and procedures for sampling threatened pop- 

 ulations in a way that ensures desired levels 

 of genetic diversity within the conserved pop- 

 ulation. 



Identification of Candidates 

 for Conservation 



Three criteria are generally considered when 

 selecting wild species for captive propagation 

 or preservation (35): 



1. Endangerment in the Wild: Information on 

 the status of wild animals is probably best 

 obtained from the Species Conservation 

 Monitoring Unit (SCMU) of the Interna- 

 tional Union for the Conservation of Na- 

 ture and Natural Resources at Cambridge 

 University in England. Funding con- 

 straints tend to limit the scope and timeli- 

 ness of SCMU information, however. Lo- 

 cal and regional organizations may also 

 provide useful information, but their effec- 

 tiveness varies widely. 



2. Feasibility in captivity: Lack of facilities 

 and expertise may preclude captive breed- 

 ing or cryogenic storage of some species. 



The blue whale is an example of a species 

 that cannot be maintained in captivity. 

 3. Uniqueness: Given limited facilities for 

 captive propagation, programs must try to 

 represent as much available taxonomic 

 diversity as possible. Thus, endangered 

 species that are the only representative of 

 their genus, family, or order would receive 

 high priority. 



Subspecies present a special problem. Most 

 wild species have several distinct forms or 

 races, analogous to the breeds found in domes- 

 tic animals. These subspecies usually cannot 

 all be maintained as discrete breeding popula- 

 tions. Instead, captive propagation programs 

 need to concentrate on one or two representa- 

 tive subspecies or amalgamate several of them 

 into a single interbreeding population. Cryo- 

 genic preservation of semen or embryos would 

 facilitate conservation of these identifiable sub- 

 species. 



Table 6-1 provides some general guidelines 

 for monitoring and intervention to conserve a 

 natural population. Such an approach has three 

 important advantages: 



1. a sample of the source population can be 

 obtained before substantial loss of genetic 

 diversity has occurred; 



2. conflict over capture and restraint of rare 



