Rhinos cramped in Pobitora need genetic variants, spacious habitat: Report (State of Assam, India)

Indian rhinos in Pobitora Wildlife Sanctuary. Image: Wikimedia Commons.

Ajit Patowary, The Assam Tribune | September 26, 2020

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GUWAHATI: As they are confined to an isolated life within an area of around 16 sq km, the rhinos in Pobitora Wildlife Sanctuary (WLS) are resorting to inbreeding, making them vulnerable to ‘random genetic drifts leading to lower genetic diversity or inbred populations’.

This is the finding of a study carried out by the Wildlife Institute of India, WWF-India and the State’s Environment and Forest Department under the Rhino DNA Indexing System (RhoDIS). The RhoDIS has been formulated to counter rhino poaching threat and help in the management of rhino population in India.

The report has underscored reintroduction of new genetic variants from other areas to offset the genetic bottleneck and habitat area expansion for the rhino population of Pobitora. It has also suggested an exchange programme among the rhino bearing protected areas for rhino gene exchange, after completion of the genetic study for all such protected areas.

The study report – ‘Assessment of genetic status of one-horned rhino population in Pobitora Wildlife Sanctuary, Assam through Non-invasive Approaches, July 2019’ – says the rhino population of Pobitora is showing signatures of inbreeding, which is potentially due to an isolated population of around 100 rhinos getting confined to a 16-sq-km area. This has resulted in limited movement of gene flow for these rhinos.

The report focused on the genetic signatures generated from 210 rhino dung samples collected from Pobitora WLS, by looking into the inbreeding status and genetic diversity of this population with respect to rhino populations of Dudhwa National Park of Uttar Pradesh and Manas and Kaziranga National Parks of Assam.

Inbreeding goes against the biological aim of mating, which is DNA shuffling. Evidences are there that inbreeding in any life form, particularly among the endangered animals, may result in more adverse impacts. In a small population, mating within the same animals becomes common. This is called inbreeding and this may lower the respective population’s ability to survive and reproduce.

This is called inbreeding depression. Scientists, among others, cite the example of the population of 40 adders (Vipera berus), which experienced inbreeding depression when farming activities in Sweden isolated it from other adder populations. Higher proportions of stillborn and deformed offspring were born to that isolated adder population. But, when adders from other populations were introduced to that isolated population, its members recovered and produced a higher proportion of viable offspring.

Wildlife experts here maintain that inbreeding among the Pobitora rhinos could be overcome, if some fresh rhinos are added to their population and the size of the Pobitora WLS is also expanded by adding the adjacent Raja Mayong Reserve Forest (RF) and the Government khas land to it to cater to the need of the wildlife sanctuary’s growing rhino population.

Here, it is worth mentioning that in 1987, Assam Government issued a preliminary notification for upgrading Pobitora RF into a WLS, it declared the adjacent khas land with an area of 11 sq km and the Raja Mayong Hill RF, also having a similar size, as parts of the wildlife sanctuary. In 1998, the final notification on Pobitora WLS was issued, after settling the land rights-related issues of the settled areas in its vicinity. Thus, the WLS got a size 38.81 sq km, comprising both Raja Mayong Hill RF and Pobitora RF and the khas land in question.

But, the rhinos of this WLS have remained confined to a 16-sq-km-area due to non-transfer of the Government khas land. This 11-sq-km khas land area is located in between Pobitora RF and Raja Mayong Hill RF. Non-transfer of this area has created many other problems for the WLS.