How methodological changes have influenced our understanding of population structure in threatened species: insights from tiger populations across India.

Unprecedented advances in sequencing technology in the past decade allow a better understanding of genetic variation and its partitioning in natural populations. Such inference is critical to conservation: to understand species biology and identify isolated populations. We review empirical population genetics studies of Endangered Bengal tigers within India, where 60-70% of wild tigers live. We assess how changes in marker type and sampling strategy have impacted inferences by reviewing past studies, and presenting three novel analyses including a single-nucleotide polymorphism (SNP) panel, genome-wide SNP markers, and a whole-mitochondrial genome network. At a broad spatial scale, less than 100 SNPs revealed the same patterns of population clustering as whole genomes (with the exception of one additional population sampled only in the SNP panel). Mitochondrial DNA indicates a strong structure between the northeast and other regions. Two studies with more populations sampled revealed further substructure within Central India. Overall, the comparison of studies with varied marker types and sample sets allows more rigorous inference of population structure. Yet sampling of some populations is limited across all studies, and these should be the focus of future sampling efforts. We discuss challenges in our understanding of population structure, and how to further address relevant questions in conservation genetics. This article is part of the theme issue 'Celebrating 50 years since Lewontin's apportionment of human diversity'.