Genetic study on the two primate species, one from the plains of Indian peninsula, the bonnet macaque and the other from the mountainous southern edge of the Tibetan plateau, the Arunachal macaque in order to understand their relatedness, distribution, population structure and demographic histories

We did a genetic analysis of four macaque species—the bonnet macaque, Assamese macaque, Tibetan macaque and the Arunachal macaque. Our genetic study shows that the Arunachal macaque is distinct from the Assamese, Tibetan and bonnet macaques. The Arunachal macaque resembles the Assamese and Tibetan macaques in its morphology (physical features) possibly because the three species occur in similar ecological conditions. However, it is genetically distant from them, perhaps because the River Brahmaputra acts as a barrier to the mixing and dispersal of their genes. Interestingly, however, the Arunachal macaque is genetically very close to its geographically-distant cousin, the bonnet macaque although they are morphologically very different. 

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Based on genetic analyses, we compared factors that may influence the distribution pattern of populations of the Arunachal and bonnet macaques. The unique geographical location in the Tibetan Plateau, rugged topography, socio-behavioural characteristics and historic geological events has influenced the distribution of populations of Arunachal macaque. On the contrary, the bonnet macaque shows an extensive, continuous distribution of populations organised at a fine-scale. 

Arunachal macaque, an edge primate species have yielded a very complex image of how geographical features such as latitude and altitude, animal physiology and climate change in the past may have together influenced its population size historically. Populations, for instance, show a signature of expansion, right after the Last Glacial Maximum thousands of years ago. This study also underscores the possibility that a cold-tolerant species like the Arunachal macaque, which could withstand historical climate change and grow once the climate became conducive, could also be extremely vulnerable to anthropogenic exploitation, as is perhaps indicated by its more recent mid-Holocene population decline. The demographic history of the tropical bonnet macaque, however, indicates that the temperate glaciations may not have any effect on its population size; instead, the historical fluctuations in monsoon patterns in Indian subcontinent may have been an important factor that drove population size change in this species. Interestingly, we would have expected a generalist species like the bonnet macaque to be extremely adaptable to changes in its environment but found that a large-scale climate change could profoundly affect the species.