The genetics of ghosts
Scientists are mapping the family trees of tigers they have never seen. In the Western Ghats of India, a sprawling biodiversity hotspot, researchers walk the same paths as tigers, collecting a unique source of data: their scat. These fecal samples are a genetic goldmine, allowing teams from institutions like the National Centre for Biological Sciences (NCBS) to extract the DNA of individual animals. This non-invasive technique helps scientists understand the lives of the elusive Bengal tiger, Panthera tigris tigris.
The studies focus on the vast Nilgiri Biosphere Reserve, a landscape that connects several protected areas, including Nagarhole National Park, Bandipur Tiger Reserve, and Mudumalai Tiger Reserve. By analyzing repeating segments of the genome called microsatellites, scientists can create a unique genetic fingerprint for each tiger. One study collected genetic data from 115 individual tigers across a 30,000 square kilometer area. This allows them to identify individuals, determine their sex, and, most importantly, uncover how they are related. The data reveals which tigers are mating, how far their offspring disperse, and how different populations are connected.
A river of genes
The genetic evidence shows a remarkable story of connection. Tigers in this region are part of a single, large population linked by corridors of forest that allow them to move, mate, and exchange genes. This "gene flow" is essential for the population, preventing the genetic isolation and inbreeding that can lead to health defects and local extinction. The Western Ghats hosts the world's largest contiguous tiger population, and this genetic connectivity is the reason for its relative stability.
However, this connection is fragile. Studies correlating genetic distance with landscape features show that human activity is the primary barrier to tiger movement. Roads, settlements, and agriculture fragment the forest, creating obstacles that can isolate tiger populations. Genetic analysis shows that even small breaks in a corridor can sever the flow of genes. In other parts of India, tiger populations are already showing signs of genetic isolation, which reduces their long-term chances of survival. The scat, therefore, shows: for tigers to survive, the landscape must remain connected.