Single species of Hoolock gibbons in India – A relief for zoos

A female Hoolock gibbon from Tinsukia, Assam

Hoolock gibbons are primates like the monkeys, langurs and chimpanzees. It is also an ape, which are the primates evolutionarily closest to humans. And it is the only ape found in India, confined to the seven states of northeast India, with Brahmaputra as the distribution boundary. They form an arboreal species, and prefer to live in canopies of the evergreen forests in the northeast India. They traverse across the canopy using their very long forelimbs hanging and jumping from branch to branch. Along with this, they are famous for their loud holou calls (that inspires their name “Hoolock”) and duets which both male and female of a group indulge in. They are thought to be territorial calls, to make their position known to other conspecific groups.

Some studies had recently claimed that northeast India is home to two, not one, species of Hoolock gibbons – Western Hoolock gibbons (Hoolock hoolock) and Eastern Hoolock gibbons (Hoolock leuconedys). A large majority of population of gibbons in India belong to the Western species. The Eastern species is primarily found in Myanmar and southern China. But few individuals were observed to possess morphological characteristics akin to the Eastern species. We called these as the Mishmi Hills gibbons. Some researchers had declared them as members of the Eastern species on the basis of morphological features. Some others opined that the Mishmi hills gibbons can also be a sub-species of Western hoolock gibbons. Nao-Dehing and Lohit rivers form the geographical boundary between the Mishmi hills and Western Hoolock gibbons. Hence, it was also suggested that there is no mating or gene flow between the Western population found in the northeast India and Mishmi hills population. But these classifications have been based only on visual observations. There was no genetic data available to validate the species identity of Mishmi hills gibbons.

This issue has also been a hindrance in captive breeding of Hoolock gibbons in the zoological parks at Itanagar and Aizawl. The two zoos have gibbons, thought to be of different species so far. It is important to breed among animals from distant locations to maintain a sufficiently varied gene pool. It is especially important now to endure climate change. But animals that are so different to form two distinct species, do not produce viable offspring upon mating.

At the Laboratory for Conservation of Endangered Species of CSIR-Centre for Cellular and Molecular Biology, we, in Dr G Umapathy’s group set to establish the genetic identity of gibbons in India. We compared the DNA of gibbons from Mishmi hills population and Itanagar zoo, the Western Hoolock gibbons from various forests and zoos in the northeast, and the Eastern Hoolock gibbon data from Myanmar. We isolated DNA from the faecal and tissue samples that we collected. We sequenced the DNA and analysed sequence similarities between them. Such an analysis, called the phylogenetics, allows us to construct genetic relationships between organisms.

Morphological differences between Western and Mishmi Hills Hoolock gibbons

Our results clearly suggest that India contains only one species of Hoolock gibbons. Our analyses showed that the all the samples from Mishmi hills Hoolock gibbons are related to the Western Hoolock gibbon samples, and not with the Eastern Hoolock gibbons from Myanmar. Also, we found evidence of recent gene flow between Western Hoolock gibbons and Mishmi hills populations despite the two rivers dividing the two regions, alluding to possible interbreeding in recent past.

This finding directly impacts the gibbon conservation measures in the country. Western Hoolock gibbons are classified ‘vulnerable’ under the IUCN Red list. They face various hazards due to forest fragmentation, mining and over-grazing. Various zoos are involved in their captive breeding to bolster their numbers. Now with our study, we know that Western Hoolock and Mishmi Hills gibbon can breed among each other. We recommend the zoological parks in the northeast India to exchange and interbreed their gibbons. It is important to make the captive bred individuals fit and resilient.

The research article can be found at https://link.springer.com/article/10.1007/s10764-021-00212-8.

About the author:

Mihir Trivedi is a PhD student at Dr G Umapathy lab in LaCONES, CSIR-Centre for Cellular and Molecular Biology, Hyderabad, working in understanding evolutionary and population genetics of primates in northeast India. He joined CCMB after post-graduating in Genetics from University of Delhi. Books, movies and travelling are his favourite escapes. You can find him at LinkedIn and Twitter.

Morphological differences between Western and Mishmi Hills Hoolock gibbons

Edited by:

Somdatta Karak, Science Communication and Public Outreach Officer at CSIR-Centre for Cellular and Molecular Biology, Hyderabad. You can find her on LinkedIn and Twitter.