After the sad passing of Sudan the northern white rhino earlier this year, there are just two of his kind left in the world. Both are female.
It is safe to say that bar a miracle conception, Najin and Fatu will not be having any children. However, thanks to some exciting new research, there may be hope in the form of IVF treatment. That is because the northern white rhino (Ceratotherium simum cottoni) is much more closely related to its cousin, the southern white rhino (Ceratotherium simum simum) than we previously thought.
We already knew that the two sub-species diverged from a common ancestor sometime around 1 million years ago. Now, a paper published in the journal Proceedings of the Royal Society of London B has found that the northern and southern white rhinos were interbreeding (successfully) as recently as 14,000 years ago. This is good news for wildlife conservationists – It improves the odds of successful in vitro fertilization (IVF) with northern and a southern white rhino parents.
"Despite the fact that they started to diverge one million years ago, we show that they have been exchanging genes during that period, possibly as recently as the last ice age, when the African savannah expanded and reconnected the two populations," Michael Bruford, lead researcher and molecular ecologist at Cardiff University, told BBC News.
"So, if they have been exchanging genes recently, this may imply that they could do so now."
Bruford and his team came to this conclusion after analyzing and comparing DNA samples from 232 individual rhinos (217 southern and 15 northern), some living and others from museum sources. The results revealed a divergence between the two lineages approximately 1 million years ago (with a ±500,000-year confidence limit) and more recently, post-divergence secondary contact and gene-flow.
This interspecies intermingling, they say, was facilitated by the expansion of savannah grassland following the Eemian interglacial (115,000 – 130,000 years ago), which allowed the distribution of both to expand and merge during the last glacial period of the late Pleistocene (14,000 – 106,000 years ago) and as recently as the last glacial maximum (14,000 – 26,000 years ago).
Right now, locked up at the Leibniz Institute for Zoo and Wildlife Research, Berlin, is a cryogenic tank containing 300 milliliters of Sudan's sperm, stored in liquid nitrogen at -196°C. The plan is to use this precious resource to bring the northern white rhino back from the brink of extinction, potentially using eggs from Najin and Fatu and a southern white rhino surrogate.
This study opens up another possibility – create hybrid embryos using Sudan's sperm and eggs from southern white rhinos, the only rhino species not currently listed as vulnerable or endangered. A team already fertilized eggs from southern white rhinos using the sperm back in July and this research ups the odds of a successful birth, even if it's not a sure-fire guarantee.
"It is difficult to predict what might happen if we cross the two subspecies but given the current options for the northern white rhino it becomes a more viable option, should other approaches fail," Bruford told the BBC.
[H/T: BBC News]