What numbers do not reveal about tiger conservation

• India is now reporting increased tiger numbers, and a recent International Union for Conservation of Nature (IUCN) assessment suggests that tiger numbers have increased by 40% since 2005.

Relations between distribution and genetic variation

• Research suggests that numbers are critical to avoid extinction.
• Populations that are smaller than 100 breeding individuals have a high probability of extinction.
• Individuals in small populations are more likely to be related, leading to inbreeding.
• This exposes the many slightly disadvantageous genetic variants that are present in all genomes.
• When expressed together, these detrimental genetic variants cause inbreeding depression, and reduced survival and reproduction of inbred individuals.
• A closer look at the distribution of tigers across their range shows that most tiger ‘populations’ are smaller than 100.

Research findings about movement of tigers

• Tigers can be genetically sampled using their excreta/scat, hair and other biological samples from different tiger reserves and analysed in a laboratory.
• Genetic variants in tiger DNA can be identified and analysed and compared across tiger reserves.
• Sets of tiger reserves that share less genetic variation must have barriers or landscapes that impede movement and connectivity.
• However, the presence of built-up areas and high traffic roads greatly impeded tiger movement.
• Extinction could be avoided if corridors were safeguarded.

Genetic changes in isolated tiger population

• Black tigers were found only in the Similipal tiger reserve in Odisha.
• Results of the research pointed to genetic drift, or random events that have lead to this genetic variant that causes pseudo melanistic coat colour becoming common only in Similipal.
• In Rajasthan, genome sequences from wild tigers reveal that individuals in the Ranthambore tiger reserve show inbreeding.

Way forward

• Focus on connectivity: While we celebrate the recovery of tiger populations only by looking at numbers, we must not lose sight of other factors that are critical to their continued survival, such as connectivity.
• Special attention is needed for populations that are becoming isolated and facing the genetic consequences of such isolation.
• The future of such populations may depend on genetic rescue or even the introduction of novel genetic variants.

Conclusion

• We are fortunate that novel genome sequencing technology provides an opportunity to understand tigers much better in the context of their conservation.
• The future of tigers will require a ‘dialogue’ between such data and management strategies in order to ensure their survival.