The release of captive bred Arabian leopards carefully selected for their genes could make a significant contribution to the successful recovery of the Critically Endangered wild population and avert extinction, according to new research involving UCL.
An international team of scientists, from the University of Kent, University of East Anglia, UCL, Nottingham-Trent University and the Diwan of Royal Court in Oman, surveyed the remote Dhofar mountain range of southern Oman to determine how many of Arabia's last big cat survive.
By deploying camera traps to identify individual leopards and performing DNA analyses from wild leopard scat alongside samples from the captive population, the team estimates there could be only 51 wild leopards remaining in Oman, distributed between three isolated, genetically impoverished but distinct subpopulations.
Despite revealing extremely low levels of genetic diversity in the wild leopard population in Oman, the team discovered higher levels of genetic diversity in captive leopards across the region, in particular among several individuals originating from neighbouring Yemen that helped found today's captive-breeding population. This important genetic resource has the potential for a major role in successful recovery of the Arabian leopard.
The team's research, published in Evolutionary Applications, showed that the dwindling regional wild population could most effectively be recovered thorough 'genetic rescue', namely, the introduction of offspring from captive-bred leopards - which harbour the greatest amount of genetic diversity - into the wild population. However, their predictions indicate that for genetic rescue to establish the most viable populations through leopard reintroductions, the benefit that new genes can bring needs to be carefully assessed, in particular because captive leopards may already be in-bred.
The study used conservation genetic analysis, cutting-edge computer simulations, and extensive fieldwork in Oman to closely examine Arabian leopard DNA and assess the risk of future extinction, as well as forecasting how genetic rescue can secure the leopard's viability. The authors say their findings could help other threatened species.
Co-author Dr Jim Labisko (UCL Centre for Biodiversity and Environment Research, UCL Biosciences) said: "Combining multiple methods of surveying, monitoring, and sampling leopard populations has been crucial for us to now determine that genetic rescue could now be an achievable means by which to help recover the Arabian leopard.
"Camera trapping meant we could both count and individually identify wild leopards, analyses of droppings from wild leopards and sampling material from captive animals provided insight as to the current levels of genetic diversity within the extant population, and the use of material from crucially important museum collections indicates that significant levels of genetic diversity were already lost by the end of the 20th century, due primarily to the targeted killing of leopards.
"Our combined modelling of these data puts us in a considerably better-informed position to determine next steps in the long-term recovery of the iconic Arabian leopard, the region's last remaining big cat."
Professor Jim Groombridge, who led the research at the University of Kent's Durrell Institute of Conservation and Ecology, explained how the genetic analysis was carried out: "In collaboration with the Diwan of Royal Court in Oman, we surveyed and collected leopard scats from across the Dhofar mountain range, and extracted DNA from them which we analysed using microsatellite DNA markers to quantify genetic diversity."
First author Dr Hadi Al Hikmani, Arabian leopard Conservation Lead at the Royal Commission for AlUla in Saudi Arabia, described the motivation for this study: "The Arabian leopard is one of the world's rarest carnivores and is extraordinarily elusive. The only way to monitor these leopards in the wild is to deploy camera traps high up across the mountain ranges where the leopards live, and to collect the scats they leave behind on the mountain passes, for DNA analysis."
Professor Cock van Oosterhout, of the School of Environmental Sciences at UEA, added: "The problem is that all individuals are somehow related to each other. They are the descendants of the few ancestors that managed to survive a major population crash. Hence, it becomes virtually impossible to stop inbreeding, and this exposes 'bad' mutations, what we call genetic load. In turn, this can increase the mortality rate, causing further population collapse.
"The genetic load poses a severe threat, but it can be alleviated by genetic rescue, and our study has projected the best way to do this. The wild population needs 'genetic rescue' from more genetically diverse leopards bred in captivity.
"However, there is a risk that we could introduce other bad mutations from the captive population into the wild, so we will need a careful balance."
