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DNA Capture Reveals Transoceanic Gene Flow in Endangered River Sharks

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DNA Capture Reveals Transoceanic Gene Flow in Endangered River Sharks DNA capture reveals transoceanic gene flow in endangered river sharks Chenhong Lia,b, Shannon Corriganb, Lei Yangb, Nicolas Straubeb, Mark Harrisc, Michael Hofreiterd, William T. Whitee, and Gavin J. P. Naylorb,1 aKey Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Shanghai Ocean University, Ministry of Education, Shanghai 201306, China; bHollings Marine Laboratory, College of Charleston, Charleston, SC 29412; cFlorida Fisheries Consultants Elasmobranch Studies, New Port Richey, FL 34655; dInstitute of Biochemistry and Biology, Faculty of Mathematics and Natural Sciences, University of Potsdam, 14476 Potsdam, Germany; and eWealth from Oceans Flagship, Commonwealth Scientific and Industrial Research Organisation Marine and Atmospheric Research, Hobart, TAS 7001, Australia Edited by David M. Hillis, The University of Texas at Austin, Austin, TX, and approved September 16, 2015 (received for review May 4, 2015) For over a hundred years, the “river sharks” of the genus Glyphis shark specimens from northern Australia and Borneo. These in- were only known from the type specimens of species that had been cluded additional specimens from the Kinabatangan River, two collected in the 19th century. They were widely considered extinct specimens of uncertain affinity from Mukah in Sarawak, a 2-m until populations of Glyphis-like sharks were rediscovered in remote specimen from Sampit in the southernmost part of Kalimantan, regions of Borneo and Northern Australia at the end of the 20th Indonesian Borneo, and specimens from the Alligator, Adelaide, century. However, the genetic affinities between the newly discov- and Wenlock Rivers in northern Australia. The Australian spec- ered Glyphis-like populations and the poorly preserved, original imens were examined and compared with reference material from museum-type specimens have never been established. Here, we Australia and Papua New Guinea. Two species were identified. present the first (to our knowledge) fully resolved, complete phy- One was considered to be conspecific with the speartooth shark logeny of Glyphis that includes both archival-type specimens and G. glyphis, whereas the other was considered new to science and modern material. We used a sensitive DNA hybridization capture was formally named and described as Glyphis garricki Compagno, method to obtain complete mitochondrial genomes from all of White, and Last, 2008 (4). our samples and show that three of the five described river shark Initial analyses of DNA sequences derived from several of the species are probably conspecific and widely distributed in Southeast specimens sampled in Borneo showed the two specimens from Asia. Furthermore we show that there has been recent gene flow Mukah to be genetically similar to each other but highly divergent between locations that are separated by large oceanic expanses. from the G. fowlerae specimens from the Kinabatangan River (5). Our data strongly suggest marine dispersal in these species, over- Unfortunately, it was not possible to assess the genetic affinity of turning the widely held notion that river sharks are restricted to the Sampit specimen as no tissue was taken. Morphological mea- Glyphis freshwater. It seems that species in the genus are euryhaline surements, however, suggest that it too is distinct from G. fowlerae. with an ecology similar to the bull shark, in which adult individuals live It is not known whether the Sampit specimen differs from the in the ocean while the young grow up in river habitats with reduced specimens taken in Mukah, as the Mukah specimens are no longer predation pressure. Finally, we discovered a previously unidentified Glyphis available for comparison. Thus, it is entirely possible that three species within the genus that is deeply divergent from all other different species of Glyphis exist in Borneo: G. fowlerae,the lineages, underscoring the current lack of knowledge about the bio- “Sampit” Glyphis,andthe“Mukah” Glyphis. This would potentially diversity and ecology of these mysterious sharks. bring the total number of species of Glyphis to seven: three from freshwater sharks | DNA | museum specimens Significance lthough little is known about many shark species, the river The river sharks of the genus Glyphis, widely feared as man- sharks of the genus Glyphis are an especially enigmatic group. A eaters throughout India, remain very poorly known to science. Three different species of river sharks were recognized through- The group constitutes five described species, all of which are out most of the 20th century: the notorious Ganges man-eater considered highly endangered and restricted to freshwater sys- Glyphis gangeticus (Müller and Henle, 1839) (1), represented by tems in Australasia and Southeast Asia. DNA sequence data de- one dried skin lectotype and one alcohol-preserved paralectotype; rived from 19th-century dried museum material augmented with the speartooth shark Glyphis glyphis (Müller and Henle, 1839) contemporary samples indicates that only three of the five cur- (1) of unknown geographic origin represented by a single rently described species are valid; that there is a genetically dis- dried skin holotype, two small, poorly preserved specimens, tinct, but as-yet-undescribed, species recorded in Bangladesh and and a handful of dried jaws; and the Irrawaddy shark Glyphis Sarawak in Malaysian Borneo; and that these iconic and myste- siamensis (Steindachner, 1896) (2), which originated from the rious sharks are not restricted to freshwater at all but rather mouth of the Irrawaddy River in Myanmar and is known only appear to be adapted to both marine and freshwater habitats. from its alcohol-preserved holotype. All three Glyphis species were believed to be extremely rare or Author contributions: C.L., S.C., and G.J.P.N. designed research; C.L., S.C., L.Y., N.S., M. Harris, extinct. In 1984, Compagno reported that additional, as-yet- and W.T.W. performed research; C.L., M. Hofreiter, and G.J.P.N. contributed new reagents/ analytic tools; C.L., S.C., L.Y., M. Harris, W.T.W., and G.J.P.N. analyzed data; and C.L., S.C., undescribed, species of Glyphis likely existed in Borneo, M. Hofreiter, W.T.W., and G.J.P.N. wrote the paper. northern Australia, and Papua New Guinea. In 1996, researchers The authors declare no conflict of interest. encountered and collected several juvenile “Glyphis-like” sharks at This article is a PNAS Direct Submission. Kampong Abai in the lower reaches of the Kinabatangan River in northeastern Malaysian Borneo. The Kinabatangan river shark was Freely available online through the PNAS open access option. Data deposition: The mitochondrial sequences reported in this paper have been depos- subsequently described as a new species, Glyphis fowlerae Com- ited in the GenBank database (accession nos. KT698039–KT698063). The nuclear dataset pagno, White, and Cavanagh, 2010 (3). The discovery fueled op- reported in this paper has been deposited in the TreeBASE database (study ID S18221). timism that other undiscovered populations of Glyphis might exist 1To whom correspondence should be addressed. Email: [email protected]. in remote regions of the world, prompting a series of expeditions This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. from the late 1990s to 2010 that resulted in the collection of river 1073/pnas.1508735112/-/DCSupplemental. 13302–13307 | PNAS | October 27, 2015 | vol. 112 | no. 43 www.pnas.org/cgi/doi/10.1073/pnas.1508735112 Downloaded by guest on September 24, 2021 Borneo; G. garricki and G. glyphis from Australia and Papua New Guinea; and G. gangeticus and G. siamensis from the In- dian subcontinent and Myanmar. Although there has been progress in characterizing the taxonomic diversity within Glyphis, we understand neither the relationships among the various newly discovered Glyphis populations in Australia and Borneo, nor the affinities of these populations to the type specimens of G. glyphis, G. gangeticus,andG. siamensis,northe processes that have influenced present day species distributions. Resolving these questions with certainty requires obtaining refer- ence DNA sequence data from the museum type material. Al- though it is increasingly recognized that genetic comparisons of contemporary and historical reference specimens are critically im- portant for understanding global biodiversity, obtaining reliable DNA sequence data from museum specimens is challenging because the quality of DNA derived from historical (>100-y-old) museum specimens is usually poor (6). DNA hybridization capture (7) is a powerful method that can be used to recover large amounts of se- quence data while requiring very small amounts of input DNA. Although this approach has successfully been used to assemble complete mitochondrial genomes from highly degraded ancient Fig. 1. Sampling localities used in this study. Colors correspond to taxo- DNA (8, 9), only a few studies have so far reported full mitochon- nomic status assigned at time of collection. Red, Glyphis gangeticus; green, drial genomes being obtained from museum specimens, and to our G. sp. 1; blue, G. siamensis;white,G. fowlerae; pink, G. sp. 2; black, G. glyphis; knowledge, none of these investigated archival fish specimens (10). yellow, G. garricki. Solid symbol outlines indicate samples with detailed locality information. Dashed outlines indicate samples for which detailed locality in- Fishes account for more than one-half of the diversity of the ver- formation is not available. tebrate tree of life
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