Genomic evidence for low genetic diversity but purging of strong deleterious variants in snow leopards

Long-term persistence of species with low genetic diversity is the focus of widespread attention in conservation biology. The snow leopard, Panthera uncia, is a big cat from high-alpine regions of Asia. However, its subspecies taxonomy, evolutionary history, evolutionary potential, and survival strategy remain unclear, which greatly hampers their conservation. We sequence a high-quality chromosome-level genome of the snow leopard and the genomes of 52 wild snow leopards. Population genomics reveal the existence of two large genetic lineages in global snow leopards, the northern and southern lineages, supported by the biogeography. The Last Glacial Maximum drove the divergence of two lineages. Microclimate differences and large rivers between the western and central Himalayas likely maintain the differentiation of two lineages. EPAS1 is positively selected in the southern lineage with almost fixed amino acid substitutions and shows an increased allele frequency with elevation. Compared to the southern lineage, the northern lineage exhibits a lower level of genomic diversity and higher levels of inbreeding and genetic load, consistent with its recent population decline. We find that snow leopards have extremely low genomic diversity and higher inbreeding than other Carnivora species; however, strong deleterious mutations have been effectively purged in snow leopards by historical population bottlenecks and inbreeding, which may be a vital genetic mechanism for their population survival and viability. Our findings reveal the survival strategy of a species with low genetic diversity and highlight the importance of unveiling both genetic diversity and genetic burden for the conservation of threatened species.