While Nola, a critically endangered northern white rhino who died Nov. 22 at the San Diego Zoo Safari Park, is still being mourned by those who worked closely with her, as well as people from around the globe, scientists at San Diego Zoo Global are focusing on how Nola’s contributions to science could eventually help save her species from extinction.
Taking a science-based approach, Oliver Ryder, Ph.D., director of genetics; Barbara Durrant, Ph.D., director of reproductive physiology; and their teams at the San Diego Zoo Institute for Conservation Research Frozen Zoo — along with collaborators at Scripps Research Institute in La Jolla and at the Institute for Zoo and Wildlife Medicine in Berlin— are working to develop and perfect assisted reproductive technology to save the northern white rhino from extinction.
“Nola’s unique story, of the incredible journey she took in her lifetime and her impact on the world, could never be re-created by any facet of science,” stated Oliver Ryder, Ph.D., director of genetics, San Diego Zoo Institute for Conservation Research. “However, the information in her DNA—the digitized sequence of her genome—and the living cells that we have saved will serve as a legacy, and a crucial tool for our efforts to bring back the northern white rhino from the brink of extinction. We hope what we can learn will also contribute to conservation of other species of rhinoceros.”
Durrant and Ryder, who both knew and worked with Nola for 26 years, obtained tissue samples collected post-mortem for banking and establishment of additional cell cultures for the Frozen Zoo. The Frozen Zoo also has genetic material from 11 other northern white rhinos. The genetic material includes frozen viable cell cultures, semen from two male northern white rhinos, but no eggs from females. As expected, due to Nola’s advanced age, no eggs were able to be collected; but her ovarian and uterine tissues were saved.
“Although Nola did not reproduce in her long lifetime, she touched the hearts of everyone who was fortunate enough to meet her. In that way, she contributed to our mission of saving the northern white rhino by demonstrating the intelligence and gentleness of her species,” stated Barbara Durrant, Ph.D., director of reproductive physiology, San Diego Zoo Institute for Conservation Research. “It is a great consolation to all who loved her that many of her tissues were collected and frozen for future research and assisted reproduction. Her passing only strengthens our commitment to develop the technology needed to realize the goal of producing an offspring from Nola’s preserved cells.”
To reach the ultimate goal of successfully producing a northern white rhino, multiple steps must be accomplished. The first step involves sequencing the genomes of the northern white rhino to clarify the extent of genetic divergence from their closest relative, the southern white rhino. Understanding these differences will assist scientists in guiding assisted reproduction efforts. The next step requires conversion of the cells preserved in the Frozen Zoo to stem cells that could develop into sperm and eggs, a process successfully begun in the laboratory of Jeanne Loring, Ph.D., of Scripps Research Institute and published in 2011.
Reproductive options might include artificial insemination, in vitro fertilization, embryo transfer, genetic engineering or a hybrid with a southern white rhino. The reproductive system of rhinos is very complex, and there is still much to be learned. San Diego Zoo Global recently opened a new Rhino Rescue Center at the San Diego Zoo Safari Park, home to six southern white rhinos that could eventually serve as surrogates.
To further Nola’s contributions to science, her body and valuable horns will be sent to the National Museum of Natural History at the Smithsonian Institution in Washington, D.C., for inclusion in the research collections, where they will be maintained in an off-exhibit area with materials from other northern white rhinos. Nola’s physical remains will be preserved so that scientists now and in the future can continue to study this magnificent species.
The 41-year-old Nola had been on around-the-clock watch since Nov. 17, when her keepers noticed signs of a reduced appetite and activity level. Her condition worsened significantly in the early hours of Sunday, Nov. 22, and the Safari Park’s animal care team made the difficult decision to euthanize her.
Nola’s death leaves three northern white rhinos remaining on Earth: a 43-year-old male, Sudan; and two females, 26-year-old Najin and 15-year-old Fatu; all living under human care at the Ol Pejeta Conservancy in Kenya. These rhinos all have reproductive issues.
Northern white rhinos have been brought to the brink of extinction due to poaching in Africa. Rhinos are poached for their horn, which is made of keratin—the same material that forms human fingernails. Rhino horn has been erroneously thought to have medicinal value and is used in traditional remedies in some Asian cultures. In addition, objects made of rhino horn have more recently become a “status symbol,” purchased to display someone’s success and wealth, because the rhino is now so rare and endangered.
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