Resolution of the identity crisis of Hanuman langurs
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Hanuman langur is now four different species!
Discovering a new species is undoubtedly a great moment for science, but what follows afterwards is even more challenging and thrilling of them all. Taxonomy is a branch of Science that deals with the identification, naming and systematic classification of species. Every species discovered must go through this arduous process before it is finally revealed to the world. Furthermore, resolving the taxonomy of an already known species or a species complex is unequivocally an essential component in the efforts to protect and conserve them. One such species complex is the Hanuman langurs, which is distributed across most parts of India and Sri Lanka and also found in parts of Pakistan, Nepal and Bangladesh, has researchers puzzled for almost a century. Researchers from Evolving- Phylo lab at the Centre for Ecological Sciences (CES), IISc headed by Professor Praveen Karanth have recently put together the final piece of this puzzle, early taxonomic studies of which were initiated by Dr Karanth for his Phd, 25 years ago! Let’s read on to know more about this common, yet deceptively unknown primate species.
Hanuman langurs show extensive variation in physical characteristics such as coat colour, across its range. Based on this, Hanuman langur classification has been subjected to multiple changes over the past century. Recent studies incorporating ecological, morphological and molecular data together, have confirmed that Hanuman langur is a complex that consists a minimum of three species- Semnopithecus priam and Semnopithecus hypoleucus both found south of the Tapti- Godavari rivers and Semnopithecus entellus which is found across the northern plains of India. In Northern type langurs, the tails are forward facing while in the Southern type category, the tails are looping backwards away from the head.
Until 2019, langurs were mainly divided into northern and southern types (Blue line represents the border line between northern-southern types, across rivers Tapti-Godavari) and 3 species of Hanuman langurs were recognised from India. Pic credits: Prof. Praveen Karanth and Chetan Nag. Map modified from Ashalakshmi et al 2015.
However, the taxonomy of the northern type langurs, inhabiting the colder, temperate like conditions of the Himalayas is still unresolved. Historically, the species status of Himalayan langur has been ambiguous, with researchers proposing multiple classification schemes, thereby creating a convoluted taxonomic history. Himalayan langurs were either considered a single species with multiple subspecies, they were split into multiple species or even placed across multiple subspecies, all based on their physical characteristics like coat colour and tail. It was this confusion that had to be solved, for the completion of the Hanuman langur species complex.
Langurs from Himalayas, however, still remained a puzzle. Were they same species as the langurs of northern plains? Pic credit: Prof Praveen Karanth. Map modified from Ashalakshmi et al 2015.
To this end, Kunal Arekar from CES (IISc, Bangalore) used molecular and ecological data in addition to data on their physical characteristics. Their main aim was to study if the northern plains langur and the Himalayan langur were genetically distinct from one another, if there was any overlap in the habitats occupied by the two, whether Himalayan population comprised of multiple species/subspecies and determine their distribution range.
Kunal busy collecting fresh faecal samples in the Himalayas. Photo credit: Field assistant Bhanu Singh
Based on previous records of distribution, four states were chosen to conduct field surveys, namely Jammu and Kashmir, Himachal Pradesh, Uttarakhand and Sikkim. With a camera in one hand and a binocular in the other, Kunal set out to the snow-covered valleys of the Himalayas. Consequently, data pertaining to physical characteristics were obtained by photographing the langurs, fresh faecal samples were collected by following them for molecular studies, locations were mapped on a map and habitat was studied to understand their ecology.
Back in the lab at IISc, DNA sequences extracted from the faecal samples of both the Northern plain langurs and the Himalayan langurs were carefully analyzed for any similarities. Photographs were viewed to identify distinguishing features and langur distribution ranges were visualized and mapped.
An integrative approach involving genetics, morphology (physical characteristics), ecology and distribution is extremely crucial while answering complex taxonomy questions. Map from Arekar et al 2020
Information obtained from three lines of evidences point that Himalayan langurs are a distinct species and occupy unique habitats with little or no overlap with the northern plain langurs. Habitat analysis showed that Himalayan langurs prefer areas with high rainfall and moderate temperatures. On the contrary, northern plain langurs prefer areas with lower precipitation.
If you happen to come across a group of Himalayan langurs and northern plain langurs, separately of course, and you wish to identify them, look at their tail and fur colour on the head and body. In Himalayan langurs the tail tip ends above the base of the tail and loops behind the back whereas in the plain population the tail loops over the back and the tip hangs at right angles to the ground as seen in the figures below. Furthermore, Himalayan langurs show a great distinction in the head and body colour - head, as white as the snow and body, grey in colour while the langurs from the plains coat a more or less uniform colour throughout their body.
In addition to this, genetic and ecological data have confirmed that Himalayan langurs are distinct from those found in the northern plains and are a separately evolving lineage with disjunct geographical regions.
Since, the molecular analysis did not provide any evidence for the splitting of Himalayan langurs into multiple subspecies, it has been recommended that all other subspecies previously described be included into one, as a single species and hence be recognised as Semnopithecus schistaceus.
In appearance, Himalayan langurs have a prominently different tail carriage & high contrast between the head & body as compared to the northern plain langur! Pictures from Arekar et al 2020
Distribution range of Himalayan langurs is distinct from those of plains, with no or very little overlap! Maps from Arekar et al 2020
In conclusion, the taxonomy of Himalayan langurs has been resolved and henceforth will be assigned the name Semnopithecus schistaceus and include all the subspecies previously described until further investigation. This study has shed light on the importance of using an integrated methodology to answer a simple yet an important question that had scientists puzzled for a very long time. With this, the Hanuman langur species complex is complete with four species - Semnopithecus priam in south India and Sri Lanka, S. hypoleucus distributed in southern India, S. entellus distributed in northern plains and S. schistaceus found in the Himalayas, bringing a century long conundrum to a close.
The final verdict: Hanuman langur in India has been recogised as four differet species!
Source: Arekar, K., Sathyakumar, S., and Karanth, P. K. (2020). Integrative taxonomy confirms the species status of the Himalayan langurs, Semnopithecus schistaceusHodgson, 1840.J ZoolSystEvol Res. 2020;00:1–14.
Link to original article: https://onlinelibrary.wiley.com/doi/abs/10.1111/jzs.12437
Other references: Ashalakshmi, N. C., KS Chetan Nag, and K. Praveen Karanth. "Molecules support morphology: species status of South Indian populations of the widely distributed Hanuman langur." Conservation genetics 16.1 (2015): 43-58.
Link to article: https://link.springer.com/article/10.1007%2Fs10592-014-0638-4
Article written by: Nagarathna Balakrishna, edited by Kunal Arekar and Devica Ranade