Tiger population around the world is sparse and despite several efforts to boost the population of tigers, the species’ future is uncertain primarily due to habitat fragmentation, human-wildlife conflict and poaching.
Scientists have been looking at global tiger populations decline for quite a few years now, but clarity over the animals’ dwindling numbers and impact on their genetic level wasn’t high. To find out, researchers at Stanford University, the National Centre for Biological Sciences, India, and various zoological parks and NGOs sequenced 65 genomes from four of the surviving tiger subspecies. Their findings confirmed that strong genetic differences exist between different tiger subspecies but showed, surprisingly, that these differences emerged relatively recently, as Earth underwent a major climatic shift and our own species grew increasingly dominant.
The research, detailed in a new paper published this week in the journal Molecular Biology and Evolution, shows how genomics can help guide conservation efforts toward wild tigers and other species, said study co-leader Elizabeth Hadly, the Paul S. and Billie Achilles Professor in Environmental Biology in the School of Humanities and Sciences.
The study reveals that the world’s existing tiger subspecies began exhibiting signs of dramatic and recent contractions starting only around 20,000 years ago – a period that coincided with both the global transition out of the Pleistocene Ice Age and the rise of human dominance in Asia. Each subspecies of tiger the team studied showed unique genomic signatures as a consequence of their increasing isolation from one another.
For example, local environmental genomic adaptation to cold temperatures was found in the Siberian (or Amur) tigers, the northernmost tigers found in the Russian Far East. These adaptations were absent in the other tiger subpopulations studied. Tigers from Sumatra, meanwhile, showed evidence of adaptations for body size regulation, which could help explain their overall smaller size. Despite these adaptations, tigers from these populations have low genetic diversity, suggesting that if populations continue to decline, genetic rescue may need to be considered.
One form that rescue might take is through the mating of different tiger subspecies together as a way of increasing their genetic diversity and protecting against the ill effects of inbreeding. Inbreeding occurs when populations are so small and isolated from other populations that related individuals breed with each other. Over time, this leads to lower genomic diversity and to the emergence of recessive diseases, physical deformities and fertility problems that often result in behavioral, health and population declines. Although increasing genetic diversity is one goal, another might be to select for inherited traits that confer higher survival in a changing world.
Even Bengal tigers from India, which comprise about 70 percent of the world’s wild tigers and exhibit relatively high genomic diversity compared to other subspecies, showed signs of inbreeding in some populations, the study concluded.