Tiger, lion and leopard genomes compared

An international team led by South Korea’s Personal Genomics Institute and BGI unraveled the first whole genome of a 9-year-old male Amur tiger (Panthera tigris altaica), and compared it with the genomes of other big cats including the white Bengal tiger, lions, and snow leopards. The genomic data from this study provides an invaluable resource for the future studies of big cats and their whole family’s conservation. The latest study was published online in Nature Communications.

Despite big cats’ reputation for ferocity, these majestic species face more danger than they pose: All are endangered, mainly due to habitat loss, poaching, and dwindling food supplies. As the largest felid species on earth, tiger has become one of the world’s most endangered species. Understanding of tiger’s genetic diversity and demography has been very limited without the whole-genome sequence of tiger, or any of the Panthera species.

In this study, researchers sequenced the whole genome of an Amur tiger, also known as the Siberian tiger, and assembled it using BGI self-developed software SOAPdenovo. The Amur tiger genome was predicted to contain 20,226 protein-coding genes and 2,935 non-coding RNAs, and was enriched in olfactory receptor sensitivity, amino-acid transport, and metabolic-related genes, among others. Additionally, researchers found that the Amur tiger genome showed more than 95 percent similarity to the genome of domestic cat.

Researchers also sequenced the genomes of other Panthera-a white Bengal tiger, an African lion, a white African lion, and a snow leopard-using next-gen sequencing technology, and aligned them using the genome sequences of tiger and domestic cat. They discovered a number of Panthera lineage-specific and felid-specific amino acid changes that may affect the metabolism pathways. These signals of amino-acid metabolism have been associated with an obligatory carnivorous diet.

Furthermore, the team revealed the evidence that the genes related to muscle strength as well as energy metabolism and sensory nerves, including olfactory receptor activity and visual perception, appeared to be undergoing rapid evolution in the tiger.

Previous studies showed that the human loci EGLN1 (Egl nine homologue 1) and EPAS1 (endothelial PAS domain-containing protein 1) are two key factors for mediating high-altitude adaptation. In this study, the team found that the snow leopard had unique amino-acid changes in both genes that may have contributed to snow leopard's acquisition of an alpine, high altitude ecological niche.

In addition, researchers found that white lions contain a variant in the TYR gene. Variants in TYR were previously reported to be related with white coat color in domestic cats as well as with a form of albinism in people. The white lion variant appeared to lead to an amino acid change that seems to affect the charge of the resulting protein.

When observing the species’ genetic diversity, researchers found the genetic diversity of tiger and lion were similar to that of human. Interestingly, the diversity of snow leopard genome was nearly half that of the other Panthera species and slightly lower than that of the Tasmanian devil.

The Amur tiger genome is the first reference genome sequenced from the Panthera lineage and the second from the Felidae species. The data from tigers, lions and snow leopards provides a rich and diverse genome resource that could be used in future studies of conservation and population genomics. Genetics underpins the local adaptation and potential inbreeding and/or outbreeding in wild and captive populations can be illuminated and thereby help ensure the future survival of these majestic species.