Najin, one of only two female northern white rhinos left in the world, walks in the pen where she is kept for observation at the Ol Pejeta Conservancy in Laikipia county in Kenya.
SCIENTISTS, for the first time, have created hybrid embryos with DNA from the nearly extinct northern white rhinoceros, an advance that could ultimately lead to the first resurrection of a mega-mammal.

But while this could provide a new way to produce future generations of endangered or extinct animals, applying this approach to the white rhino does not meet with universal approval among conservationists.

The international team of researchers, led by Professor Thomas Hildebrandt from the Leibniz Institute for Zoo and Wildlife Research, have used an existing assisted reproduction technology developed for horses, and applied it to the white rhino.

Eggs and sperm from northern white rhino are in short supply, owing to the rarity of the subspecies. So the team also used material from southern white rhino, successfully fertilising southern eggs with sperm from both northern and southern subspecies, proving that the process works.

Only seven out of 314 fertilised eggs developed into embryos - a roughly 2% success rate - but the research demonstrated three important steps.

First, that rhino eggs can be captured from live females.

Second, that they can be fertilised using IVF and developed to the “blastocyst” early embryonic stage (ready for transfer to a surrogate female) - and that this can be done as a hybrid of southern and northern rhino.

And third, that the resulting embryos can be frozen without damage.

This process is technically challenging. A special device was developed to enable the operators to extract oocytes (unfertilised eggs) from the ovaries of anaesthetised female southern white rhino from a number of European zoos. This is a three-person job requiring a steady hand that can guide a needle of just over 1mm in diameter and almost 1m in length into the reproductive system via the rectum to capture the eggs.

The next step will be to transfer three of the embryos that have been frozen to the uterus of surrogate southern white rhino for gestation and birth.

This final step towards the birth of a calf containing northern white rhino DNA is no small step, as artificial insemination in rhino has rarely been attempted. San Diego Zoo is evaluating six surrogacy candidates, and has successfully artificially inseminated one with southern white rhino sperm. The four other embryos produced were used to evaluate the potential for creating sperm and eggs from the genetic material of northern white rhino whose sex cells are not already available.

While this only worked for southern white rhino embryos and not the hybrids, it did demonstrate the method could be successful. As the first demonstration of this process working for the rhino, the research is significant, impressive and exciting.

It offers a possibility to rescue the genes of a subspecies that, after the death of the last male northern white rhino earlier this year, is now represented by just two elderly females.

And if the method works for the rhino, it should be possible to extend it to other endangered large mammals.

The key question of whether scientists can produce pure northern white rhino embryos using this technique remains unanswered.

But even if it is possible, what would be the point?

Ultimately, to be useful these manipulative techniques need to increase the chance of survival of endangered (wild) animal populations. Otherwise, artificially engineered fertilisation and the management of genes has little value for nature conservation.

To my mind, the time to save the northern white rhino has passed. If we could not save it when it was here (the last wild northern white rhino is thought to have disappeared around 2006), it seems unlikely we could conserve a resurrected wild population now or in the foreseeable future.

The purpose of simply preserving the subspecies’ genes in a new hybrid rhino (in captivity), and whether it would be worth all the effort, is unclear.

Recent research by Dr Tate Tunstall of the San Diego Zoo Institute for Conservation Research and colleagues indicates that there may be enough genetic diversity in the frozen northern white rhino material (from only 12 individuals) to provide a suitably diverse founder population for resurrection.

They also showed that the genetic differences between the northern and southern subspecies may be the result of evolutionary adaptations to different habitats.

An alternative strategy to resurrection would be to secure a safe habitat in the former northern white rhino’s range of central East Africa, populate it with southern white rhino and let natural selection run its course.

The introduced rhino population would be expected to evolve over generations to adapt to their new environment and fill the ecological role left vacant by the northern white rhino.

There are already southern white rhino living and breeding in Uganda at the Ziwa Sanctuary.

Restoration ecologists have similarly replaced extinct giant tortoises with related species in a process called taxon substitution.

Taxon substitution using the southern white rhino would be simpler and more cost-effective than manipulating genes and introducing manufactured hybrids, and would likely have a higher probability of success. - The Conversation

Gilchrist is an ecologist at Edinburgh Napier University.