Ferocious Whole Genome Sequencing

Tiger (Panthera tigris) is a ferocious, but at the same time a majestic wildlife species which is found in habitats ranging from Siberian temperate forest to subtropical and tropical forests of South and South-East Asia. Although there were earlier nine subspecies of tigers, currently, there are six subspecies, i.e. Bengal, Indochinese, Malayan, South-china, Siberian, and Sumatran. Three subspecies of the tiger (Bali, Caspian, and Java) have already been extinct mainly due to poaching and habitat loss.  Although there are about 150 individuals of South-China tiger in captivity, they have already been extinct from the wild habitat. Tiger is listed as an endangered species because of its rapid decline in populations as a result of loss of habitats, hunting and poaching. Currently, the global tiger population is estimated to be in between 3000 and 4000 individuals.

Scientists have debated about the exact number of existing tiger subspecies; some say two (Asian Mainland tiger and Greater Sunda Island tiger), and others claim six (Bengal, Indochinese, Malayan, South-china, Siberian, and Sumatran). To resolve this dispute, scientists decided to use the genomic approach. They sequenced whole-genome of 32 individual tigers representing all its geographic regions. When the cluster analysis of the whole-genome sequence data was performed, the 32 individuals grouped into six separate clusters. This confirmed that there are six subspecies of tigers as opposed to two. The genomic data also revealed that there is almost no gene flow among tiger populations suggesting that all these six subspecies of tigers have unique evolutionary history. In the same study, scientists also found indications of natural selection in the genome of the Sumatran tiger in the ADH7 gene, which is responsible for body size. Because the Sumatran tiger is smaller in body size than other, scientists suggested that this tiger may have responded the evolutionary pressure by praying small animals such as wild pigs, muntjac, and small deer available in the island. The genomic data is not only useful to resolve the phylogenetic issue, but also to plan an appropriate conservation and management strategy for this magnificent species.