A large database of rhinoceros DNA is successfully being used to prosecute poachers and those trading rhino horns, new research has revealed.
While numbers of the southern white rhino – the only wild subspecies of white rhino in Africa – have grown to about 20,000, fewer than 5,500 black rhinos are thought to exist in the wild, and both species are affected by poaching.
The animals’ horns are traded for their use in traditional Asian medicines, and poaching is soaring – in part as a result of rumours that a former politician in Vietnam was “cured of cancer” using a rhino horn remedy. Figures for 2016 suggest that poachers killed more than 1,050 rhinos in South Africa alone.
Now researchers working on DNA-based forensic testing have shown just how powerful the technique is in fighting the illegal trade and bringing criminals to justice.
“Based on a really solid number of animals, both white and black rhinos, we can get solid match statistics to show ‘that’ horn is definitely from ‘that’ carcass,” said Dr Cindy Harper, a co-author of the study from the University of Pretoria in South Africa.
The set-up, known as the Rhinoceros DNA index system or RhODIS, was established in 2010, and currently contains more than 20,000 rhino samples from living animals, stockpiled horns and forensic cases – such as poaching.
The authors say the latest study shows just how powerful the database is in linking forensic evidence to particular animals.
Published in the journal Current Biology, the researchers describe how they selected samples from 3,085 white rhinos and 883 black rhinos from the database and examined their DNA, comparing the number of times particular patterns are repeated at certain locations in their genomes.
“It is similar to human DNA profiling for forensic cases now,” said Harper, pointing out that the team looked at repeated patterns at 23 locations in the genome.
The results not only reveal that black rhinos fall, as currently thought, into three subspecies, and wild white rhinos into one, but also sheds light on the genetic variation within different populations.
Moreover, the team were able to use the genetic data from the 3,986 rhinos to calculate the probability that a match between a forensic sample and a particular rhino could crop up by chance.
So far more than 120 criminal investigations have included genetic evidence, based on the RhODIS system, as part of a court case.
Looking at genetic data from nine of the cases, the team found while the probability of a chance match varies for each case, it is about one in several million for white rhinos and is even more remote for black rhinos, due to their higher genetic variability. “In a population of 20,000 [white rhinos], that is a pretty good match that you can be pretty certain of,” said Harper.
That, she added, is vital for a prosecution. “That’s what we need to show, because one of the defence’s arguments [in court] could be ‘yeah, but it could have been another rhino that matched,’” she said.
One criminal case in which a genetic match led to a prosecution was that of a Kenyan individual who in 2017 was sentenced to 11 years in jail after blood on a carpet was matched to the horn of a black rhinoceros.
The team are continuing to work to increase the number of rhinos in the database and analyse the data for all samples currently collected, to improve the statistics even further. And after South Africa lifted its ban on domestic rhino horn trading last year, Harper says the forensic technique is more important than ever to prevent “blood horns” leaking onto the market.
Dr Tanya Wyatt, an expert in the illegal wildlife trade from Northumbria University said conservation work was also vital. “This is helpful maybe for deterrents and prosecutions, [but] it shouldn’t be taken on its own,” she said. “We really still need to make a lot of effort in protecting the rhinoceros from being poached in the first place.”