For years, the wildlife community has debated whether or not all of the 4,000 wild tigers left on Earth represented one species, stalemating many conservation efforts that would otherwise tailor to more specific needs of a diverse genetic pool. Now, researchers present the strongest evidence yet that suggests modern tigers fall into six genetically distinct groups.

While it may present a new opportunity to protect endangered felines around the world, the findings come too late for three subspecies that have already gone extinct: the Caspian (1970), the Bali (1937), and Javan tigers (1976, although some claim to have since spotted it). 

Publishing their work in Current Biology, the authors note their work could help save the Bengal, Amur, South China, Sumatran, Indochinese, and Malayan subspecies still alive today.

"The lack of consensus over the number of tiger subspecies has partially hindered the global effort to recover the species from the brink of extinction, as both captive breeding and landscape intervention of wild populations increasingly requires an explicit delineation of the conservation management units," said study author Shu-Jin Luo of Peking University in a statement. "This study is the first to reveal the tiger's natural history from a whole-genomic perspective. It provides robust, genome-wide evidence for the origin and evolution of this charismatic megafauna species."

Taking a “whole genome approach”, the team analyzed the complete genomes of 32 representative tiger specimens.

“We are now able to reconstruct, for the first time, the most comprehensive evolutionary pathways in modern tigers,” wrote the authors. Despite the low genetic diversity, the six subspecies have evolutionary histories unique among big cats. (Jaguars, for example, intermix across entire continents.)

While fossil evidence shows tigers date back 2 to 3 million years ago, their genomic evidence shows that all living tigers trace back to a “bottleneck” event about 110,000 years ago, which coincides with the climate cooling during the glacial Pleistocene. At this point, Panthera tigris either stayed in its home of mainland Indochina and China or expanded out, naturally evolving to meet the needs of its new environment. Sumatran tigers became darker with thick stripes on their fur and took on a gene called ADH7 (related to body-size), making the Sunda Islands residents smaller to reduce energy needs due to less sizeable island prey such as wild pigs and small deer. On the other hand, Amur tigers remained large with pale, orange fur more suitable to their Russian climate.

And studying those already extinct may help fill in the missing evolutionary pieces for living tigers.

“Understanding the tiger’s natural history from a genomic perspective provides a data-driven foundation for subspecies recognition, conservation strategic planning, and management actions,” conclude the authors.