There are six subspecies of tiger—Bengal, Amur, South China, Sumatran, Indochinese and Malayan—a genetic study of the big cat has confirmed. The discovery should help put to an end a lengthy debate over just how many subspecies there are—a debate that could be hindering conservation of the endangered species, of which there are fewer than 4,000 left in the wild.
At the start of the 2000s, it was generally accepted that there were eight subspecies of tiger, three of which had gone extinct. But in 2004, Shu-Jin Luo put forward an argument for the existence of six subspecies. The Malayan tiger had been found to be distinct from the Indochinese tiger that same year.
Things got more complicated in 2015, when researchers in Europe said there were only two subspecies—the Sundra tiger, which is made up of Sumatra, Javan and Bali tigers, the latter two of which are extinct, and the continental tigers, which are made up of all the rest. Putting tigers into two categories would "make conservation easier," Volker Homes, a conservation specialist from Germany, told Science magazine at the time.
Luo and colleagues have now published research that tracks the evolution of the tiger species using genetic data from across their habitats. The team analyzed the entire genomes of 32 specimens. The findings, published in Current Biology, showed there are six subspecies, and that the genetic pattern across the subspecies is highly structured—indicating they all have their own evolutionary history. One finding, for example, was that the Sumatran tiger was smaller because of the gene ADH7. It appears this was selected because it favored smaller body size, which would help with island life where prey is smaller.
"Tigers are not all alike," Luo told Newsweek. "Tigers from Russia are evolutionarily distinct from those from India. Even tigers from Malaysia and Indonesia are different… They represent the wonder of nature derived from long-term evolution, divergence and adaptation."
Understanding the different subspecies and planning conservation strategies accordingly is of paramount importance, Luo said. The team recommends that all six are now classified and protected as separate entities.
Of the six subspecies, the South China tiger is already extinct in the wild and there are only around 150 individuals in captivity. The Indochinese tiger is also thought to be on the brink of extinction in the wild. "Small, isolated populations of an apex predator species like the tiger are under extremely high risk of stochastic extinction," Luo said.
"The reasons for the precipitous worldwide decline of tigers are multiple—habitat loss and fragmentation, poaching, inadequate protection and prey depletion. The steady depletion was driven by agricultural development, by direct human depredation, by an unchecked commercial appetite for tiger parts, and by the tiger's intrinsic requirement for substantial range areas and ample prey."
