Not two, only one species of hoolock gibbon in India: study

Fourteen years after reports noting that India has two separate species of the gibbon – the hoolock gibbon and the eastern hoolock gibbon – a latest genetic analysis has now proved that there is only one species of ape in India.

Hoolock gibbon (Hoolock hoolock) is the only gibbon (apes in the family Hylobatidae) found in India, according to the analysis. Earlier, northeastern India was said to be home to two species: eastern (Hoolock leuconedys) and western hoolock (Hoolock hoolock) gibbons. A study led by Centre for Cellular and Molecular Biology (CCMB), Hyderabad scientists states that there is no separate species of eastern hoolock gibbon in northeast India, debunking earlier research that had suggested a separate species (the assumed eastern hoolock gibbon) based on coat colour.

The CCMB research team was led by G. Umapathy; the other members of the team were Mihir Trivedi, Shivakumara Manu, Sanjaay Balakrishnan, Jihosuo Biswas, and N. V. K. Asharaf.

“These two populations are kept separately in the zoos and not allowed to breed, now they can be allowed to breed as they belong to single species. Further, a slight coat colour change in any species does not make a separate species. One has to examine genetic characteristics before describing a species,” G. Umapathy, Group Leader, Laboratory for the Conservation of Endangered Species (LaCONES), CSIR-Centre for Cellular and Molecular Biology, told Mongabay-India.

“We estimate that gibbon divergence from a common ancestor occurred 8.38 million years ago and that the split between H. hoolock and H. leuconedys occurred 1.49 million years ago,” the authors said.

Hoolock gibbon was described first in 1834, in the erstwhile kingdom of Assam by American naturalist R. Harlan. Previously eastern and western hoolocks were considered as sub-species but were later classified as species in 2005. The first distribution record of eastern hoolock gibbons in India was published in 2006.

Western hoolock gibbon is distributed all over northeast India, south and east of Brahmaputra river; along with Bangladesh and Myanmar. The eastern hoolock gibbon (termed as Mishmi hills hoolock in the paper) is distributed between Nao-Dehing, Lohit and Dibang rivers in Arunachal Pradesh. IUCN states that the presence of H. leuconedys in India is uncertain. In 2013, primatologist Anwaruddin Choudhury proposed H. hoolock mishmiensis, a sub-species of western hoolock gibbon found in the Mishmi hills.

Study co-author Jihosuo Biswas said the genetic analysis was necessary to clear the confusion between two physically different hoolock gibbon populations. The scientists collected blood, tissue, and faecal samples from various populations of H. hoolock and the Mishmi Hills gibbons in the wild, zoos, and rescue centers in northeast India. The study could not find any genetic differences between H. hoolock and the assumed eastern hoolock gibbon population in the region between the Lohit and Dibang rivers in northeast India.

The study suggests that the Mishmi hills hoolock is not a subspecies of H. hoolock but a population that was recently separated from the main H. hoolock population by the Barak river. The population of gibbons in Southern Assam, Mizoram and Bangladesh constitutes a “meta-population”. Metapopulations are populations of subpopulations within some defined area, in which dispersal from one local population (subpopulation) to at least some other habitat patches is possible.

“Our findings will help establish the species identity of the gibbons and can be used to create an effective gibbon conservation breeding program that will be undertaken by many Indian zoos and also aid translocation programmes,” Biswas of Primate Research Centre Northeast India, Guwahati told Mongabay-India.

Known for their vigorous vocal displays, gibbons are unique small apes, with 20 species, all of them endemic to south and southeast Asia. Gibbons play an important role in seed dispersal, which contributes to maintaining the health of the forests they call home, and benefit the communities that also use forest resources, states the International Union for Conservation of Nature, adding that globally, gibbons are one of the most threatened families of primates.

Gibbons are pair-living, usually with a monogamous mating system, and the adult male and female of a group sing prolonged duets. Hoolock gibbon adults exhibit distinct sexual dimorphism in pelage colouration, the males are black overall and the female becomes varying shades of brown and fawn at maturity, the study states. Both H. hoolock and H. leuconedys infants are born with a pale brown natal coat (infants are nearly white) similar in colouration to that of adult females. Infants of both sexes turn black.

Scientists say the identification of species and their distributions is crucial for successful conservation and understanding speciation. Phylogenetics plays an important role in recognising species and understanding their relationships with other taxa. Although new species have been declared based on distribution and morphology, phylogenetic studies are an integral part of describing and delineating a species through integrative taxonomy. In addition to assisting in situ conservation efforts by assessing the phylogenetic diversity of a taxon, phylogenetics is also useful for conservation breeding and captive management strategies and directly affects decisions regarding which individuals to breed, to prevent hybridisation and to maintain genetic diversity.

Primatologist Dilip Chetry who is not associated with the study said there is scope for more research in this direction by taking the samples from higher altitudes from Mishmi hills as well as from plain areas of Sadiya, Wakro, Kamlang and other areas from the north bank of Noadehing river.

Divya Vasudev, a senior scientist with Conservation Initiatives who is not associated with the study said, “The paper is critical for our understanding of the evolution, ecology and conservation status of both the eastern and western hoolock gibbon. We know now that there are populations of the western hoolock gibbon – a highly endangered species – and habitat for the species in Arunachal as well.” Divya has worked in Garo Hills in Meghalaya on gibbons.

“This also emphasises how important community-based conservation is for the western hoolock gibbon. The threats to the species remain though, and this understanding will only support on-ground conservation efforts for gibbons” she added.

Read more: Communities join hands to keep alive the hoolock gibbon’s song

Banner image: A female hoolock gibbon. Photo by J. Biswas.