Reduced genetic diversity in greater one-horned rhinoceros in Chitwan National Park A new challenge and opportunity for rhino conservation in Nepal

Understanding the genetic diversity of a species is vital to improve the effectiveness of conservation management interventions. The greater one-horned rhinoceros (Rhinoceros unicornis) is one of the most iconic megaherbivores in South Asia but is classified as Vulnerable by the IUCN. The species is now broadly confined to two isolated populations in Chitwan National Park (CNP), Nepal and Northeast India, which are both constrained by poaching, and the loss or degradation of habitat. Since 2016, rhino mortalities have increased in CNP for unknown reasons. To assess the impact of any current or previous mortality events, we investigated the genetic diversity in the current CNP rhino population. We collected skin samples from 67 dead rhinos found in CNP and its buffer zone between 2012 and 2019. Fragments 428 bp of mitochondrial DNA D-loop were amplified from extracted DNA using PCR and sequenced to compare with complementary sequences derived from a previous study of CNP rhinos conducted during 1986-1987. A total of six haplotypes were detected in the older sample set with a haplotype diversity (Hd) of 0.38012 compared to only four haplotypes and a Hd of 0.3374 in our cohort. This decline in haplotype diversity was unexpected as the CNP rhino population has increased by 69% over the previous 27 years. In addition, we found the haplotypes were not equally distributed across CNP, with a greater variation detected in the eastern sector (4 haplotypes) compared to the west (1 haplotype). We recommend that CNP management authorities consider translocations within the park boundaries to promote breeding between the eastern and western subpopulations to disseminate and maintain haplotype diversity throughout the population.