Galápagos shark (Carcharhinus galapagensis) is a circum-tropical distributed species that commonly occur at isolated oceanic islands (Compagno 1984). The species is currently listed by the IUCN as "near threatened" (2003 assessment; Bennett et al. 2013). A previous population genetic study of the species in the west Pacific tentatively identified two Management Units (MUs): 1) Kermadec Islands and Elizabeth-Middleton Reef, and 2) Lord Howe Island; while Norfolk Island was suggested as a stepping-stone between both MUs. Our project attempted to assess connectivity and gene flow of C. galapagensis at a bigger scale across the Pacific region using genomic approaches.
We examined the population genomic structure of Galápagos sharks using genome wide Single Nucleotide Polymorphism markers from DArTSeq. After rigorous steps of data filtering and quality control, a total of 8,218 SNPs were used for the analyses. To identify potential historical gene flow and/or sex-biased dispersal, we also sequenced the mitochondrial control region (997bp). After discarding outlier markers under potential selection, cluster analyses of neutral SNPs including STRUCTURE and NETVIEW revealed two highly distinct genetic groups, one comprising individuals from the East (Galápagos Islands, Ecuador and Revillagigedo, Mexico), the other from the Western Pacific (Hawaii, Australia and New Zealand). Phylogenetic analyses under Bayesian and Maximum Likelihood criteria using SNPs were congruent with such pattern indicating the presence of the same two major clades with high support. The sister species Carcharhinus obscurus was used as out-group. Advanced population genomics analyses will lead to detect footprints of selection and local adaptation, as well as understanding evolutionary connectivity, patterns and levels of gene flow and demographic history.
Keywords: DArTSeq, SNPs, Phylogenetics, connectivity.