New Delhi, July 28: An endangered monkey in Arunachal Pradesh that withstood the ice age about 20,000 years ago has experienced a population decline that began around the time the first humans arrived in the state about 1,500 years ago, a genetic study has suggested.
Biologists in Bangalore, who used tools of genetics to peer deep into the population history of the Arunachal macaque, or Macaca munzala, have found that its numbers have plummeted nearly 30-fold over this time period.
The study, just published in the journal PLOS One, suggests the population decline of the Arunachal macaque began roughly at the same time central Arunachal Pradesh was being peopled by what could have been the ancestors of the communities that continue to hunt wildlife even in the present day.
Ethnographic and genetic studies suggest ancestral tribal populations arrived in the state about 1,500 years ago.
There is no evidence to suggest that the decline was indeed caused by hunting. But the researchers, led by Anindya Sinha, a primatologist and dean of academic affairs at the National Institute of Advanced Studies, Bangalore, say their findings raise a question whether ancestral populations were able to always exploit natural resources in a prudent manner to establish a sustainable relationship between the hunters and the hunted.
The Arunachal macaque was reported from western Arunachal Pradesh — and labelled a new species, previously unknown to science — only about a decade ago. A study in 2006 had counted about 570 individuals in the Tawang district of western Arunachal Pradesh.
“Our field investigations indicate that the primate could be threatened in parts of Arunachal Pradesh due to hunting for food and, occasionally, retaliatory killing by members of the local communities during crop-raiding by the macaques,” Sinha told The Telegraph.
Sinha and his colleagues had initially assumed that the population may have started declining only over the past 300 years after human populations increased dramatically and people acquired more lethal hunting weapons than traditional ones. The population of tigers, for example, has declined dramatically only over the past two centuries.
“What was a big surprise was that modern genetic techniques could trace the origin of the decline to coincide with the peopling of the region more than a thousand years ago,” said Debapriyo Chakraborty, a research associate at the Laboratory for Conservation of Endangered Species at the Centre for Cellular Molecular Biology, Hyderabad, and the first author of the study.
The researchers, under the supervision of Uma Ramakrishnan of the National Centre for Biological Sciences in Bangalore, used a sequence of 544 genetic alphabets found in the mitochondrial DNA — genetic material handed down only by mothers to offspring — and a set of 22 other genetic markers to piece together how the population of the Arunachal macaque have changed over the past 20,000 years.
They extracted genetic material from dried skin samples from Arunachal macaques killed and preserved as hunting trophies in 14 villages across the districts of Tawang, Upper Subansiri, and West Siang.
Their study suggests that the population of Arunachal macaques remained stable through the last glacial maximum — the coldest phase of the ice age — about 20,000 years ago. Then, as temperatures rose and ice sheets withdrew, the Arunachal macaque population expanded dramatically — a population boom — about 15,000 years ago. But the population has declined steadily over the past 1,500 years.
“The strength of the study lies in the genetic analysis,” said M.D. Madhusudan, a wildlife biologist with the Nature Conservation Foundation, Mysore, who was not associated with the study but was among the team that first reported the Arunachal macaque in 2005.
“The genetic analysis tells us how and when the population increased and decreased — but it doesn't tell us anything about why it changed. Suggestions that hunting may have contributed to the decline are purely speculative, just conjecture.”