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- According to a study published in the journal Current Biology, uncertainty about the number of tiger subspecies in the world has thwarted efforts to conserve the rest of the world's tiger population.
- A research team led by Yue-Chen Liu of Beijing Chinese University analyzed the complete genomes of 32 specimens of tigers, chosen to be representative of the six potential subspecies, to confirm that the tigers are divided into six genetically distinct groups.
- The researchers also used their genome-wide survey to look for evidence that different groups of tigers were adapted to distinct environments in their geographic regions through the natural selection process. They say that their genomic research shows that very little gene flow has occurred between tiger populations, but also that, despite the low genetic diversity of the big cat, each subspecies has a unique evolutionary history.
While there were perhaps 1,000,000 tigers in the world a century ago, scientists claim that there are fewer than 4,000 today, occupying less than 10 % of their historical range. The thirteen tiger range countries responded to this steep decline in 2010 with an ambitious plan to double the global population of endangered big cats by 2022, and Nepal in particular has managed to reverse the decline. tiger.
In order to save a species from extinction, however, it is helpful to understand this species as best as possible. However, there are ongoing debates in the scientific community as to whether there are two subspecies of Panthera tigrisas suggested by some morphological and ecological analyzes, or five or six subspecies, for which there is molecular genetic evidence.
According to a study published in the journal Current Biology, this uncertainty about such a fundamental feature of the species has thwarted efforts to conserve the rest of the world's tiger population. "The lack of consensus on the number of subspecies of tigers has partially hindered the global effort to restore the endangered species, as both captive breeding and landscape intervention of wild populations increasingly require an explicit delineation of conservation management units. "The authors of the study, a research team led by Yue-Chen Liu of Peking University in China, write.
Liu and his team analyzed the complete genomes of 32 specimens of tigers, selected to be representative of all potential subspecies, to confirm that the tigers actually divide into six genetically distinct groups.
"This study is the first to reveal the tiger's natural history from a genomic perspective," said study co-author Shu-Jin Luo of Peking University in a statement. "It provides robust evidence, at the genome scale, of the origin and evolution of this species of charismatic megafauna."
The six subspecies confirmed by the research are the Love Tiger or the Siberian Tiger (Panthera tigris altaica) in the far east of Siberia and in northeastern China; the Bengal tiger (Panthera tigris tigris) Bangladesh, Bhutan, India and Nepal; the South China tiger (Panthera tigris amoyensis), which is thought extinct in the wild; the Sumatran tiger (Panthera tigris sumatrae), the last of the tiger populations of the Indonesian islands, itself seriously threatened with extinction; the Indochinese tiger (Panthera tigris corbetti), which exists in Myanmar, Thailand and Laos, but has not been reported in Vietnam for more than two decades; and the Malaysian tiger (Panthera tigris jacksoni), which was only recognized for the first time in 2004 and is also in danger of disappearing.
The research also confirmed that there were once three other subspecies of tigers already extirpated: the Javan Tiger (Panthera tigris sondaica), the Bali tiger (Panthera tigris balica) and the Caspian Sea tiger (Panthera tigris virgata).
The researchers concluded that the six existing subspecies descended from a common ancestor 110,000 years ago. "In mainland Asia, the Bengal tigers formed the oldest divergence, while the tigers of Love formed the last," they write in the study. "The Indochinese tiger is the brother taxon of the Malayan tiger, indicating a recent differentiation, albeit substantial."
The researchers used their genome-wide survey to look for evidence that different groups of tigers were adapted to distinct environments in their geographic areas through the natural selection process. They say that their genomic research shows that very little gene flow has occurred between tiger populations, but also that, despite the low genetic diversity of the big cat, each subspecies has a unique evolutionary history.
"In the end, we were quite surprised that by performing a step-by-step analysis of the genome, seven regions, including 14 genes, turned out to be potential breeding regions," Luo said.
Of course, some differences between subspecies of tigers are obvious, depending on their distinct physical characteristics. The Amur tigers, for example, are large and have pale orange fur and brownish bands, while Sumatran tigers are smaller and have darker fur with thick black bands. The researchers found that the most powerful signal of natural selection was that of the Sumatran tiger and its ADH7 gene, linked to the size of its body. Liu and his team believe that the Sumatran tiger, which stands out from all subspecies of continental tigers, has adapted its smaller size to reduce its energy demand and allow the survival of smaller prey species. Sunda Island, like wild pigs and a small deer called the muntjac.
These findings present strong genetic evidence for the delineation of the subspecies in tigers, said Luo: "Tigers are not all the same. Russian tigers are evolutionary distinct from those of India. Even tigers from Malaysia and Indonesia are different. "
The results can also help inform tiger conservation management and planning, write the authors. "As with many endangered species, tigers have been classified into subspecies – geographically separated natural populations – for recognition and conservation purposes. … As many tiger conservation policies and measures, including coordinated captive breeding programs and legislation in several tiger range countries, are based on "taxonomy of subspecies", a Proper description of this subspecies is vitally important. "
The researchers added that the results of their genome-wide study "correspond precisely to the previously named" geographical subspecies ". "Understanding the natural history of the tiger from a genomic point of view provides a data-based basis for subspecies recognition, strategic conservation planning, and management measures. Our overall objectives are to reverse the decline of the species by maximizing efforts to preserve the genetic diversity, uniqueness of evolution, and the potential of Panthera tigris. "
QUOTES
• Goodrich, J., Lynam, A., D. Miquelle, H. Wibisono, K., K. Kawanishi, A., Pattanavibool, S., Htun, T., T., Karki, Y. Jhala. & Karanth, U. 2015. Panthera tigris. IUCN Red List of Threatened Species 2015: e.T15955A50659951. doi: 10.2305 / IUCN.UK.2015-2.RLTS.T15955A50659951.en. Downloaded 25 October 2018.
• Liu et al. (2018). Evolution-scale genome-wide analysis of natural history and adaptation of the world's tigers. Current Biology 28, 1-10. doi: 10.1016 / j.cub.2018.09.019
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