Molecular analysis of newly-discovered geographic range of the threatened river shark Glyphis glyphis reveals distinct populations

The identification of population boundaries is key to determining the appropriate spatial scale for the conservation and management of wildlife. The Speartooth Shark Glyphis glyphis is a threatened euryhaline shark of macrotidal rivers and estuaries of northern Australia and southern Papua New Guinea (PNG). The major river drainages (Wenlock River, Alligator Rivers, Adelaide River) comprising the species’ known range have been shown to be distinct genetic populations. Recent surveys have revealed a wider range than previously documented with newly-identified populations in the Daly River of the Northern Territory and the Ord River of Western Australia as well as the species’ rediscovery in PNG. Using full mitogenome sequencing and DArTseq to genotype single nucleotide polymorphisms (SNPs) we aimed to test the hypothesis that the newly identified rivers (Daly and Ord Rivers), along with the Kikori River in southern PNG, also represent distinct populations given their isolation from known populations. Across the six river systems, the haplotype network showed a non-random distribution of haplotypes. Most of the genetic differentiation was found between rivers (rather than between regions), with highly significant pairwise comparisons between all river systems. The SNP data confirmed the existence of barriers to gene flow with the Ord and Kikori Rivers representing distinct populations. Results from the Daly River also suggest that this is a distinct population, although sample size was small and power limited to infer statistical significance with the nuclear SNP data. Each river system within the range of G. glyphis should be treated as a separate management unit.