A new genetic study of the tiger family has uncovered a previously unknown sub-species of the big cats, researchers report in the journal Plos Biology.
Bengal tigers appear to be a valid sub-species (Image: Ullas Karanth)
Evidence suggested previous attempts to classify tigers may have been flawed.
So the team sampled DNA from 130 tigers from eastern Russia, China, India and countries in south-east Asia.
The new sub-species, Panthera tigris jacksoni, is named after tiger campaigner Peter Jackson and comes from splitting one sub-species into two.
The so-called Indochinese subspecies should be divided into two groups, representing a northern Indochinese and a peninsular-Malayan population, the scientists say.
Eight sub-species of Panthera tigris are traditionally recognised on the basis of physical characteristics and geography, three of which have recently gone extinct.
Shu-Jin Luo and colleagues from the National Cancer Institute's Laboratory of Genomic Diversity in Maryland, US, carried out the latest study to see whether these traditional groupings were reflected in genes.
But their DNA analysis suggested that just six should be recognised.
In Plos Biology, the team write that its results "will lead to the improved management and conservation of these recently isolated but distinct geographic populations of tigers".
Amur - (Panthera tigris altaica)
N. Indochinese - (P. t. corbetti)
South China - (P. t. amoyensis)
Malayan - (P. t. jacksoni)
Sumatran - (P. t. sumatrae)
Bengal - (P. t. tigris)
The big cats are critically endangered. The combined stresses of habitat loss, hunting and an illegal trade in tiger parts have left wild tiger numbers at less than 7,000.
By contrast, an estimated 100,000 wild tigers roamed much of Asia in 1900.
Analysis of the tigers' mitochondrial DNA revealed that all tigers diverged from a common ancestor that lived 72,000-108,000 years ago.
Despite their relatively recent lineage, factors such as diversity of habitats have led recognisable subdivisions to appear in tigers.
However, the researchers also explore the possibility that their recent population decline and consequent isolation may also have led to this.