suggested low population size and reduced genetic diversity across Rhinocerotidae family for an extended period of time. Detailed genetic assessment of the existing rhino populations is critical in this regard since strong historical demographic declines has led to loss of genetic variation in all rhino species (Black rhino-, White rhino-, Sumatran rhino-, Javan rhino-). As majority of the current one-horned rhino bearing areas in India and Nepal are reaching to their carrying capacities, future conservation efforts are directing towards reintroduction-based programmes. With a current population size of ~ 3700 individuals (increased from few hundred individuals in 1990s), it retains ~ 96% of the Asian rhino population. The one-horned rhino, being the only Asian species recovered from severe population decline in the past are critical for the evolutionary potential of this group. Recovery of these species in their natural habitats requires deeper understanding of demography, ecology and genetics for appropriate conservation measures. Currently the Javan and Sumatran rhinos are categorized as Critically Endangered (~ 60 Javan rhino- and < 100 Sumatran rhinos-) and one-horned rhino as Vulnerable by IUCN (~ 3700 individual, ). The one-horned rhinos faced climate-change driven habitat shrinkage in late Pleistocene. Population size of the most widely distributed Javan rhinos (during Holocene) were greatly reduced during human population expansion since 10,000 years ago, whereas the Sumatran rhino populations became fragmented and isolated (since Holocene) due to submerged Sundaland corridors (late Pleistocene). Further, the range of all Eurasian rhino species (Javan, Sumatran and One-horned rhino) were affected by a combination of natural and anthropogenic factors during Pleistocene-Holocene transition period, followed by recent events of exploitation of natural resources (during colonial era), industrialisation and poaching (since seventeenth century). Subsequently, early Holocene global warming (after Last Glacial Maxima) triggered their extinction in western Eurasia and southward movement of eastern Eurasian rhinos, leading to their distribution across Southeast Asia. By late Pleistocene, this family was reduced to only nine species (from more than 100 species) spread across Eurasia (seven species) and Africa (two species). The members of Rhinocerotidae family were once one of the most diverse and widely distributed terrestrial herbivores with complex evolutionary history. Such well-informed, multidisciplinary approach will be the only way to ensure evolutionary, ecological and demographic stability of the species across its range. With ongoing genetic isolation of the current populations, future management efforts should focus on identifying genetically variable founder animals and consider periodic supplementation events while planning future rhino reintroduction programs in India. The phylogeography and phylogenomic outcomes suggest recognition of three ‘Evolutionary Significant Units (ESUs)’ in Indian rhino. Further, the demography analyses indicated historical decline in female effective population size ~ 300–200 Kya followed by increasing trends during ~ 110–60 Kya.
Mitochondrial phylogenomics suggests one-horned rhino diverged from its recent common ancestors ~ 950 Kya and different populations (Assam, West Bengal and Uttar Pradesh/Nepal) coalesce at ~ 190–50 Kya, corroborating with the paleobiogeography history of the Indian subcontinent. The reintroduced population of Uttar Pradesh showed maternal signatures of Chitwan National Park, Nepal.
Results showed 30 haplotypes distributed as three distinct genetic clades (F st value 0.68–1) corresponding to the states of Assam (n = 28 haplotypes), West Bengal and Uttar Pradesh (both monomorphic). Further, we identified all polymorphic sites and assessed rhino phylogeography (2531 bp mtDNA, n = 111 individuals) across India. We report the first complete mitogenome from all the extant Indian wild one-horned rhino populations (n = 16 individuals). Using mitochondrial data, we investigated the phylogeography, divergence and demographic history of one-horned rhinos across its Indian range. Recent assessments recommend reintroduction-based conservation approaches for the species, and implementation of such efforts would greatly benefit from detailed genetic assessments and evolutionary history of these populations.
India currently harbours ~ 83% of the global wild one-horned rhino populations distributed across seven protected areas. The one-horned rhino is the only Asian species recovered from such conditions but most of the extant populations are reaching carrying capacity. The extant members of the Asian rhinos have experienced severe population and range declines since Pleistocene through a combination of natural and anthropogenic factors.
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