A majestic and charismatic mega-herbivore, the one-horned rhino (Rhinoceros unicornis) now numbers around 4,034 individuals found only in the grasslands of India and Nepal.
Due to significant human-induced pressures like hunting, encroachment and habitat degradation, the species had severely declined during the 1900s. However, the efforts of the governments of India and Nepal and other stakeholders, along with the enforcement of conservation laws have helped the rhino population recover.
The one-horned rhino was once distributed widely in the Brahmaputra-Ganges-Indus plains, and also extended further up to the Himalayan foothills, but currently, it is found only in 11 locations across India and Nepal over a cumulative area of about 4000 square kilometres.
Four of these 11 residential populations were reintroduced in recent years through translocations after the species went locally extinct in some areas of India and Nepal. This indicates translocation is a successful and relatively safe conservation tool for rhino population restoration.
Even though the population is being re-introduced to increase its rangeland, the distribution is highly skewed. Out of the total global one-horned rhino population, about 65% is confined to Kaziranga National Park in India and 17% to Chitwan national park in Nepal.
Even though the numbers indicate a successful conservation story for the species, the rhino’s growing population might potentially reach the carrying capacity in some of the protected areas where they are found. This highlights the need for proper research to develop research-based management plans.
From the success achieved to date, it can be advocated that translocation can play a pivotal role for this species. In such a case, understanding the genetic status of the current rhino populations in both countries will be crucial for the long-term survival of the species. The National Rhino Conservation Strategy adopted by India in 2019 aims to increase the rhino distribution by 5% by 2030.
The rhino and its evolution in India
The DNA of the rhino population in India is being studied under the RhoDIS (Rhino DNA Index System) India programme implemented by the Ministry of Environment, Forest and Climate Change along with the Wildlife Institute of India, WWF India and the states bearing rhinos in India.
In a recent study, the authors of this article, attempted to shed light on the importance of the evolutionary history and genetic variations of the one-horned rhino while making conservation plans in the Indian context. Since mitochondrial DNA is maternally inherited in most species, we used that to help give us an insight into the distribution pattern and history of genetic lineages of this species.
The study was conducted across the rhinos’ distribution range in India using data collected from 111 individuals.
The findings showed that the population of the Indian rhinos has three “evolutionary significant units” corresponding to the populations of Assam, West Bengal and Uttar Pradesh. This conclusion is based on whole mitochondrial genome data analysis which corroborates with the paleobiogeography history of the Indian subcontinent documented in scientific manuscripts by Rajeev Patnaik and in the book Indicus.
The study also revealed that the most recent ancestor of the species entered India approximately one million years ago through northeast India. This was followed by their inland movement along the Siwalik range approximately 5,00,000 years ago, coinciding with a drop in sea levels that possibly facilitated the movement of multiple genera (like elephants, barking deer, other rhinoceros species like the Javan rhino, etc.) through the Siva-Malayan route.
Finally, this movement concluded around the Holocene climate period (approximately 19,000-5,000 years ago). This period was also when grasslands emerged and dominated the plains of the north and northeastern part of India, most likely due to the intensification of monsoon.
The rhino population then established itself in Nepal as well as the northwestern parts of India. It gradually got restricted to the grassland regions along the Ganga, Indus and Brahmaputra flood plains as well as in the terai grasslands in the foothills of the Himalayas.
Generic variation
In the study on rhino evolution, we also looked into the genetic variation within each of the three genetically significant units and found that except for the Assam population which has high mitochondrial diversity, the population in the other two states (West Bengal and Uttar Pradesh) are genetically poor.
Building on this, we also analysed the genetic structure of the two reintroduced populations in India – the Dudhwa population reintroduced during the 1984-85 period and the Manas population which was translocated under the Indian Rhino Vision 2020 program beginning in 2008.
The existing Manas population was also enhanced by the rhinos under this program. A study of their mitochondrial DNA showed that the Manas rhinos contained the genetic signatures of both the source populations – Kaziranga NP and Pobitora WLS. But the Dudhwa rhinos, had a single genetic signature – that of the Nepal population.
The present rhino populations are all scattered and isolated with little opportunity for genetic exchange across the populations as there is no habitat connectivity in most cases. This could be detrimental since rhinos are not known to be long-ranging, unlike elephants or tigers that cover long distances to move across habitats.
At present, only the rhino populations in Kaziranga, Orang and Pobitora, all within Assam, have connectivity along the river Brahmaputra. Studies have shown that rhinos, along with many other species, have been using these wildlife corridors to move from one habitat to the other.
The Assam government has also begun to declare critical areas to provide a safe corridor for wildlife movement along the river Brahmaputra, in addition to existing protected areas like Kaziranga and Orang. This is a very positive and futuristic decision for wildlife conservation, especially in the face of multiple anthropogenic pressures.
Similarly, there is a lot of opportunity to secure rhino movement between the rhino populations of Nepal and India in the Terai belt through multiple wildlife corridors especially in the near future with the agreement for cooperation in the field of biodiversity conservation between the governments of the two countries.
In regards to the genetic health of the two reintroduced populations in Dudhwa and Manas, we have seen that the Manas population has a higher diversity and this can be related to sourcing both males and females from two rhino source populations as well as due to the supplementation of the rhinos over a period of time instead of putting all the rhinos in the area during a short period of time and then the demography getting affected due to deaths in the population.
In the case of Dudhwa, the reintroduction took place first from Pobitora in Assam. When a couple of individuals died post-translocation, a few rhinos were further translocated from Nepal and thereafter, the population has been kept inside an enclosure. This confinement has prevented the rhinos from moving freely and has provided no opportunity for gene exchange.
The genetic makeup of the Dudhwa rhinos was quite poor due to the fact that the main breeding females in the Dudhwa population were sourced from Chitwan National Park in Nepal and the dominant male for a long time was an individual from Pobitora Wildlife Sanctuary of Assam.
Since mitochondrial DNA is only maternally inherited, the observed skewed genetic signature in Dudhwa can be attributed to the founder population composition. This can be taken as learning for planning future translocations to set up new rhino populations, especially in the context of the greater one-horned rhino.
Amit Sharma is a researcher at WWF India. Samrat Mondol and Tista Ghosh are researchers at the Wildlife Institute of India, Dehradun.
This article was first published on Mongabay.