02893nas a2200421   4500000000100000000000100001008004100002260001200043653001300055653001000068653001500078653001900093653001400112653002400126100001600150700002300166700001900189700001900208700002100227700002300248700001800271700002600289700002000315700001800335700001600353700002400369700001700393700001800410700001800428700001800446700002000464700002100484245009100505856005200596490000800648520179000656020002502446       2021                            d  c09/202110agenetics10adrift10ainbreeding10apseudomelanism10aselection10aAnnualReport2021-221 aVinay Sagar1 aChristopher Kaelin1 aMeghana Natesh1 aAnuradha Reddy1 aRajesh Mohapatra1 aHimanshu Chhattani1 aPrachi Thatte1 aSrinivas Vaidyanathan1 aSuvankar Biswas1 aSupriya Bhatt1 aShashi Paul1 aYadavendradev Jhala1 aMayank Verma1 aBivash Pandav1 aSamrat Mondol1 aGregory Barsh1 aDebabrata Swain1 aUma Ramakrishnan00aHigh frequency of an otherwise rare phenotype in a small and isolated tiger population  uhttps://www.pnas.org/content/118/39/e20252731180 v1183 aMost endangered species exist today in small populations, many of which are isolated. Evolution in such populations is largely governed by genetic drift. Empirical evidence for drift affecting striking phenotypes based on substantial genetic data are rare. Approximately 37% of tigers (Panthera tigris) in the Similipal Tiger Reserve (in eastern India) are pseudomelanistic, characterized by wide, merged stripes. Camera trap data across the tiger range revealed the presence of pseudomelanistic tigers only in Similipal. We investigated the genetic basis for pseudomelanism and examined the role of drift in driving this phenotype's frequency. Whole-genome data and pedigree-based association analyses from captive tigers revealed that pseudomelanism cosegregates with a conserved and functionally important coding alteration in Transmembrane Aminopeptidase Q (Taqpep), a gene responsible for similar traits in other felid species. Noninvasive sampling of tigers revealed a high frequency of the Taqpep p.H454Y mutation in Similipal (12 individuals, allele frequency = 0.58) and absence from all other tiger populations (395 individuals). Population genetic analyses confirmed few (minimal number) tigers in Similipal, and its genetic isolation, with poor geneflow. Pairwise FST (0.33) at the mutation site was high but not an outlier. Similipal tigers had low diversity at 81 single nucleotide polymorphisms (mean heterozygosity = 0.28, SD = 0.27). Simulations were consistent with founding events and drift as possible drivers for the observed stark difference of allele frequency. Our results highlight the role of stochastic processes in the evolution of rare phenotypes. We highlight an unusual evolutionary trajectory in a small and isolated population of an endangered species.  a0027-8424, 1091-6490