The critically endangered black rhino has suffered a greater decline in genetic diversity than previously thought. Scientists now say that protecting genetically distinct populations should become a priority for conservationists.
During the 20<sup>th century, black rhino populations have declined by 20-fold, until the mid-1990s. The International Union for the Conservation of Nature (IUCN) estimates that between 1970 and 1992, the Black Rhino suffered as much as a 96% reduction in numbers, with just about 2,400 animals remaining in the wild.
Conservation efforts led to a relative recovery of just over 5000 rhinos by 2014, but in the last few years, renewed poaching has threatened this fragile success. Black rhinos are hunted for their horns which in 2013 reached a price on the black market of $65,000 per kilogram.
There is a high demand for these horns in Asia, to use in traditional Chinese medicine, or in the Far East, to make dagger handles. It is now feared that the number of rhinos killed could exceed the number of rhinos being born.
For the black rhino, the situations is dire. It is now found only in five African countries – South Africa, Namibia, Kenya, Zimbabwe and Tanzania. Conservation efforts have been hampered by the fact that very little is known to date about the genetic variation among black rhinos and about their evolutionary history.
Genetic lineages have disappeared
In the study, now published in the journal Scientific Reports, researchers have investigated the genetic consequences of the black rhino population decline, in the hope of refining conservation strategies.
Using a combination of tissue and fecal samples from wild modern animals as well as skin samples from museum specimens, they have examined the genetic structure of historic and modern black rhino populations. Their sample constitutes the largest and most geographically representative sample of black rhinos ever assembled.
Mitochondrial and nuclear DNA sequencing suggests that the decline of black rhinos has gone hand in hand with a massive decline in the species' genetic diversity.
There has been a staggering loss of 69% of the species' mitochondrial genetic variation, including the most ancestral lineages, which are now absent from modern populations. In total, 44 of 64 genetic lineages no longer existing.
The scientists believe that the priority for conservationists should be to protect remaining living rhino populations from poaching. However, they a greater focus on protecting genetically distinct populations will also be needed. Improving the genetic management of these animals – to maintain genetic variability and to avoid inbreeding – will be crucial for the long-term survival of the species.