Persistence of Trachypithecus geei (Mammalia: Primates: Cercopithecidae) in a rubber plantation in Assam, India

Non-human primates are highly threatened as a result of habitat destruction, agricultural expansion, industrial development, large-scale build-ups and wildlife trafficking. Nearly 60% of all primates are threatened and many are found in habitats with some form of human modifications (e.g., croplands and plantations). The adaptability of primates to survive in human-modified habitats is thus a key to determine their persistence in anthropogenic landscapes. In this study, we examined the population number and age-sex composition of the ‘Endangered’ Golden Langur Trachypithecus geei in a rubber plantation in the Kokrajhar District in Assam, India in 2016, and compared with past data of the langur population and demographics from the same location to better understand the population dynamics, demographic characters and persistence of the Golden Langurs in the rubber plantation. In 2016, we recorded six groups of Golden Langurs totaling 78 individuals with a mean group size of 13.00±4.00SD. Of the total population, 10.29% were adult males, 41.18% were adult females, 32.35% were juveniles and 16.18% were infants. The overall population growth from 1997 to 2016 was estimated to be 5.54% per year. Habitat matrices of rubber plantations with natural forest patches are important in the fragmented landscape for the persistence of Golden Langur populations. They may also act as a corridor for the langurs to move between the fragments and as food resources, highlighting the importance of such matrices for the langurs outside protected areas. Population monitoring and ecological studies in such matrices would therefore be needed for the successful implementation of targeted management strategies for the conservation of these threatened langurs.

The convoluted evolutionary history of the capped-golden langur lineage (Cercopithecidae: Colobinae) – concatenation versus coalescent analyses

Evolutionary studies have traditionally relied on concatenation based methods to reconstruct relationships from multiple markers. However, due to limitations of concatenation analyses, recent studies have proposed coalescent based methods to address evolutionary questions. Results from these methods tend to diverge from each other under situations where there is incomplete lineage sorting or hybridization. Here we used concatenation as well as multispecies coalescent (MSC) methods to understand the evolutionary origin of capped and golden langur (CG) lineage. Previous molecular studies have retrieved conflicting phylogenies, with mitochondrial tree grouping CG lineage with a largely Indian genus Semnopithecus, while nuclear markers support their affinities with a Southeast Asian genus, Trachypithecus. However, as pointed by others, the use of nuclear copies of mitochondrial DNA in the above studies might have generated the discordance. Because of this discordance, the phylogenetic position of CG lineage has been much debated in recent times. In this study, we have used nine nuclear and eight mitochondrial markers. Concatenated nuclear as well as the mitochondrial dataset recovered congruent relationships where CG lineage was sister to Trachypithecus. However nuclear species tree estimated using different MSC methods were incongruent with the above result, suggesting presence of incomplete lineage sorting (ILS)/hybridisation. Furthermore, CG lineage is morphologically intermediate between Semnopithecus and Trachypithecus. Based on this evidence, we argue that CG lineage evolved through hybridisation between Semnopithecus and Trachypithecus. Finally, we reason that both concatenation as well as coalescent methods should be used in conjunction for better understanding of various evolutionary hypotheses.