What’s behind the genetic threat to the rhino?
‘This is quite a staggering loss for any species to endure’, says Sarah Wild
Poaching is doing more damage than reducing the world’s black rhino population; it is eroding the genetic diversity of the iconic animal.
Recent research published in the prestigious journal Scientific Reports has found that the black rhinoceros has lost about 70% of its genetic diversity in the past 200 years.
"This is quite a staggering loss for any species to endure," says Prof Yoshan Moodley, lead author on the paper and head of the molecular ecology group at the University of Venda’s zoology department.
Species often go extinct when their genetic diversity is low, because they are less resilient to change or threats. With high diversity, some members of the population may survive when hit by a change in environment or a disease.
Black rhino are scarcer than their white counterparts, with five remaining populations in SA, Zimbabwe, Kenya, Namibia and Tanzania. But 200 years ago, they were spread across sub-Saharan Africa. "The loss of diversity, usually blamed entirely on the ravages starting in the 1980s, actually started over a century earlier with the start of colonial sport hunting."
The black rhino population is thought to have plummeted from 100,000 in the 1960s to about 2,200 in the mid-1980s. Today, there are about 5,000 black rhino. White rhino have bounced back, with numbers sitting at about 20,000, according to conservation group Save the Rhino.
Moodley’s research — which included collaborators in SA, the UK, Austria, Denmark, Kenya, Sweden and the Czech Republic — spanned several years and involved collecting genetic samples from black rhino specimens in museums.
"Imagine, a Swede came to Cape Town in the 1770s and shot his rhino in the Western Cape," Moodley says. "We extracted DNA using the same technique they use for fossils, such as Neanderthal DNA, sequenced it and analysed the data."
The researchers found that ancient rivers like the Shari, Zambezi and Nile separated genetically distinct populations.
"We found that the diversity was structured into nine genetic groups.... Of the nine, two are definitely already extinct, two are probably extinct and a further group exists only in low numbers," Moodley says.
The major problem facing the black rhino today is that conservation strategies are flawed.
"Our results are completely at odds with how the black rhino is being managed by the co-ordinating authority, the International Union for Conservation of Nature’s African rhino specialist group," Moodley says.
The genes of the remaining black rhino populations have been and are being mixed, to their detriment. "Mixing genetic groups invariably means that the diversity of one or other group is lost or, worse, that the two are genetically incompatible."
While rhino conservation experts welcome the research, they disagree with the paper’s recommendation on how rhinos need to be managed.
"The paper is good and important for understanding the complexities of historical gene flow and genetic diversity in the once panmictic African black rhino population," says Dr Mike Knight, chairman of the African rhino specialist group and general manager for planning and development at SANParks.
Knight, who is also a research associate at Nelson Mandela Metropolitan University, "strongly disagrees" with what he calls the paper’s "purist" notion. "Through focused conservation efforts such as efficient protection, good conservation management and biological management we have — in primarily four countries, SA, Namibia, Zimbabwe and Kenya — been able to double the recovery of the population in 30 years in this large, slow-reproducing species," he says. "That is a conservation success."
The loss of genetic diversity through poaching or inbreeding in isolated small populations poses much more of a threat, Knight says. "The problem with being a purist and keeping genetically different subpopulations forever separate in silos is that genetic diversity can fail, reducing evolutionary potential of the population to adapt to current and future new challenges."
Gayle Pedersen, a doctoral candidate at the University of Pretoria who was not involved in Moodley’s research, says that she interprets the paper’s findings differently: "That we could have and should have done things differently a few decades ago, had we been aware at the time of the detailed genetic history, in order to preserve evolutionary distinct lineages.
"With all the incredible advances in conservation genetics in the last 20 years, we still based our interpretation of acceptable levels of genetic diversity on fairly recent research using DNA from living or recently deceased animals.
"Previous studies into black rhino genetic diversity suggested levels were acceptable despite historic population crashes, but they did not have the historical data to be able to compare the past with the present," she says.
Moodley and his group at the University of Venda plan to do more research, piecing together the genetic histories of endangered species. He is working on similar studies with antelope.
"Now that we have shown the value of museum specimens for endangered species conservation, there will likely be a whole host of similar studies in the next couple of years on wild, lion, sable, roan, riverine rabbit, etc," he says.
Despite their differences on conservation strategies, geneticists and conservationists agree that more research is needed and that poaching continues to threaten rhino numbers and their genetic diversity.