Decoding Tiger Families Through A Strand Of Hair

by GoNews Desk 2 weeks ago Views 737
Decoding Tiger Families Through A Strand Of Hair
Tigers are elusive solitary cats often very difficult to track in the thick jungles of India. Further, understanding family relationships among tigers is even difficult difficult to observe and document. Over many decades, genetic data has emerged as an alternative tool to investigate tigers’ familial relationships. The best method to access the genetic data is sequencing the whole genome, or reading the entire genetic code for an individual tiger. While technologies to read genetic data has advanced significantly in the last decade, they usually depend on good sources of DNA, like blood and tissue, which are difficult to acquire for wild tigers. For the first time, researchers use shed hair that can be sampled from identified tigers to sequence most of their genomes. The recent study shows shed hair can be used to identify family relationships.
But why shed hair? Fecal samples have been used before to sequence a few bits of the tiger genome. While small bits of the genome (from ten independent regions) have been useful for inferring connectivity between populations, these types of data cannot accurately infer pedigree relationships and inbreeding in populations, or assist in investigating variation in specific parts of the genome, since they do not have adequate statistical power. Also, fecal samples contain lots of bacterial, fungal, and prey DNA. These contaminants make it difficult for fecal samples to be used effectively for next generation sequencing. 
Researchers at NCBS, in collaboration with the Rajasthan Forest Department and Medgenome Labs, recently showed that shed hair is the ideal non-invasive source for sequencing DNA from across the genome and acquiring millions of information bits for tigers. During the fieldwork in Ranthambhore Tiger Reserve they followed individual tigers (at safe distances) and noted the shrubs and trees the individual brushed against, or the areas the individual rested at. Searching these spots very carefully yielded shed hair of the particular tiger, which was then transported to the lab.The team tested and found that DNA sequences from shed hair are better than those from fecal samples. They also found that DNA sequences from shed hair match the ones from blood samples and yield identical results about population connectivity. Using the sequences from shed hair, they discovered two new matrilines in Ranthambhore Tiger Reserve. They also discovered that the tiger T47 might belong to the same matriline as the famous tigress Machali. T47’s ancestry was previously unknown. Shed hair from field-observed tigers can help sequence genetic material and establish previously unknown genetic links. 
The NCBS researchers present the largest collection of Indian tiger genomes to date. The paper includes the whole genome of the tigress Machali, one of the founders of the Ranthambore Tiger population (after the population recovered from a significant decline in 2005). Her genome is important as it can potentially yield insights into the ancestry of many tigers in the Ranthambhore tiger population. The study reports whole genome sequences of six Ranthambhore tigers including that of the tigers Ustad (T24), Jhumroo (T20) and Machali (T16), four of which are from shed hair and the other two from blood.
Key to this study has been the long-term data on tiger maternity collected by the Rajasthan Forest Department. In an applied context, these results will be useful in selecting founders for tiger rewilding and translocation. From a biological perspective, this data will be critical to understanding the impacts of isolation (and connectivity) on the genetic variation of particular populations, and for the study of particular individuals.

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