There are up to nine commonly accepted subspecies of tigers in the world, three of which are extinct. But the scientists' analysis, conducted over a course of several years, claims there are really only two tiger subspecies: one found on continental Asia and another from the Indonesian islands of Sumatra, Java and Bali.
"It's really hard to distinguish between tigers," said Andreas Wilting, the study's lead author from the Leibniz Institute for Zoo and Wildlife Research. "There has been no comprehensive approach. The taxonomies are based on data from almost a hundred years ago."
The study, described by its authors as "the most comprehensive analysis to date," looked at the mitochondrial DNA, skulls, skin markings, habitat and prey of all nine tiger subspecies. It found a high degree of overlap in these traits between the continental tigers — spanning from Russia to Southeast Asia — and between the island-dwelling "Sunda" tigers.
Nearly $50 million is spent worldwide to preserve the big cat each year, according to the Science Advances study, and there has been some progress made.
The Amur tiger, found in Russia, has been on the rise over the past decade, with as many as 540 of the tigers in the wild, up from between 423 and 502 a decade ago, according to the World Wildlife Fund. Likewise the Bengal tiger population, was reported to have increased by 30 percent since 2010, according to India’s National Tiger Conservation Authority.
The hope is that by simplifying the taxonomy, conservationists would have more flexibility in preserving the animals, such as by moving tigers from one area to the next. This is especially important for the South-China tiger, which is considered critically endangered numbers less than 100 in the wild.
"They've gotten down to such low numbers that there's really little hope for them," Wilting said.
The study reinforces evidence that tigers are perhaps the least diverse big cat in the world. It also supports a theory that there was a massive population decline after a super-eruption took place in Sumatra about 73,000 years ago, leaving only a single ancestor for all modern tigers from the South China area.
But in a field where one of the biggest goals is to preserve the diversity in tigers, convincing people that tigers aren't really that diverse can be a challenge. This is not the first time tiger taxonomy has been challenged, but earlier proposals have had trouble gaining ground due to a lack of evidence.
At the heart of the debate is a concept called "taxonomic inflation," or the massive influx of newly recognized species and subspecies. Some critics blame the trend in part on emerging methods of identifying species through ancestry and not physical traits. Others point to technology that has allowed scientists to distinguish between organisms at the molecular level.
"There are so many species concepts that you could distinguish each population separately," Wilting said. "Not everything you can distinguish should be its own species."
This concept of inflation becomes more pressing when animal habitats are destroyed. Populations affected by habitat loss often become increasingly isolated and more susceptible to genetic drift. Because there are fewer genes in the population pool, the animals change more rapidly and becomes more distinct — sometimes for the worst.
This was especially true in the case of the Florida panther in the early 1990s, when the species was reduced to fewer than 30 individuals in the wild. Rampant inbreeding left the big cat inundated with genetic defects, such as heart problems and reproductive issues.
Efforts to preserve the animal through captive breeding proved unsuccessful. Florida researchers, frantic to save the long-held state symbol, decided to take controversial action by introducing eight female Texas cougars in 1995.
The result has been considered a success, as the cougars, a close genetic relative to the panther, were able to refresh the gene pool and stave off extinction. While the Florida panther is still considered endangered, there are now somewhere between 100 and 180 in the wild.
Still, the case has sparked debate on whether the panther remains a pure subspecies. That's important because it may affect the priority placed on protecting the cat and its habitat by U.S. Fish and Wildlife Service.
"It really depends on what you define a subspecies to be," said Dave Onorato, a biologist with the Florida Fish and Wildlife Conservation Commission who worked on the panther restoration project. "Perhaps they're now more close to what they were before they became inbred."
Onorato said the Florida panther case could be held up as an example for people trying to protect big cats around the world, including the most stressed tiger populations.
Worldwide conservation efforts have been put into place to double tiger counts by 2022, but many tiger populations remain under threat by poachers, habitat loss and climate change, according to the World Wildlife Fund.