The Frozen Zoo ® (San Diego Zoo Global), a repository of biomaterials established in 1975, contains fibroblast cell lines from 12 NWR individuals, eight of which are unrelated, and of which five never reproduced. The key to applying these new techniques to endangered species is to have viable cellular material available. In 2015, we met with colleagues worldwide to outline a plan to save the NWR from extinction through the use of cellular and assisted reproduction techniques. However, as technology advances, we may have other options. Even if these animals could reproduce, they are unlikely to sustain a viable population. The NWR is now functionally extinct, with only two nonreproductive females remaining, a mother-daughter pair, living under armed guard on a preserve in Kenya, Ol Pejeta. Unfortunately, the NWR was unable to rebound being exposed to civil war, extreme poaching, and habitat loss and fragmentation, which prevented the species from recovering. The SWR population recovered, growing to ∼18,000 individuals, and is now the most abundant form of rhinoceros, although still considered near threatened by the IUCN due to continued poaching. Both forms survived severe bottlenecks during the 20th century SWR dwindled to fewer than 100 in the early part of the century and only about 15 NWR remained by the 1980s. The northern white rhinoceros ( Ceratotherium simum cottoni: NWR) and southern white rhinoceros ( Ceratotherium simum: SWR) are considered to be either separate species or subspecies, and each was hunted to near extinction in the last century. Rhinoceros horn is seen as a status symbol and erroneously believed to have medicinal value in several cultures, which has continued to drive the illegal trade. Between 20, more than 1,000 rhinoceros were poached each year in South Africa alone for the illegal trade in their horn poaching has diminished recently, but still continues. Technological advances in stem cell research may allow us to augment these more traditional conservation efforts through the generation of in vitro gametes from cryopreserved cell lines.Īll five rhinoceros species and their subspecies are listed on the International Union for Conservation of Species (IUCN) Red List ( Supplementary Table S1), with poaching and habitat loss the most destructive to these species. ![]() However, for species with small population sizes and low genetic diversity this may not be enough to maintain a stable population. Attempts to save species through habitat conservation, captive breeding, and education programs have helped some species such as the giant panda ( Ailuropoda melanoleuca) and the California condor ( Gymnogyps californianus). The earth is currently experiencing global wide extinction levels that are higher than any previously experienced, termed “the sixth extinction”, which has ultimately been caused by human activities. ![]() Advances in iPSC differentiation may enable generation of gametes in vitro from deceased and nonreproductive individuals that could be used to repopulate the species. This work is the first step of a long-term interdisciplinary plan to apply assisted reproduction techniques to the conservation of this highly endangered species. ![]() We used a nonintegrating Sendai virus reprogramming method and developed analyses to confirm the cells' pluripotency and differentiation potential. We generated iPSCs from fibroblasts cryopreserved in the Frozen Zoo ®: nine genetically diverse individuals of the functionally extinct northern white rhinoceros ( Ceratotherium simum cottoni) and two from the closely related southern white rhinoceros ( Ceratotherium simum simum). Generation of a set of iPSCs from multiple members of a species can capture some of the dwindling genetic diversity of a disappearing species. ![]() Future conservation efforts may be aided by the generation of induced pluripotent stem cells (iPSCs) from highly endangered species. Extinction rates are rising, and current conservation technologies may not be adequate for reducing species losses.
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