DNA capture reveals transoceanic gene flow in endangered river sharks

Abstract

For over a hundred years, the "river sharks" of the genus Glyphis were only known from the type specimens of species that had been collected in the 19th century. They were widely considered extinct until populations of Glyphis-like sharks were rediscovered in remote regions of Borneo and Northern Australia at the end of the 20th century. However, the genetic affinities between the newly discovered Glyphis-like populations and the poorly preserved, original museum-type specimens have never been established. Here, we present the first (to our knowledge) fully resolved, complete phylogeny of Glyphis that includes both archival-type specimens and modern material. We used a sensitive DNA hybridization capture method to obtain complete mitochondrial genomes from all of our samples and show that three of the five described river shark species are probably conspecific and widely distributed in Southeast Asia. Furthermore we show that there has been recent gene flow between locations that are separated by large oceanic expanses. Our data strongly suggest marine dispersal in these species, overturning the widely held notion that river sharks are restricted to freshwater. It seems that species in the genus Glyphis are euryhaline with an ecology similar to the bull shark, in which adult individuals live in the ocean while the young grow up in river habitats with reduced predation pressure. Finally, we discovered a previously unidentified species within the genus Glyphis that is deeply divergent from all other lineages, underscoring the current lack of knowledge about the biodiversity and ecology of these mysterious sharks.freshwater sharks | DNA | museum specimens

Inferring contemporary and historical genetic connectivity from juveniles

“…The Speartooth Shark, Glyphis glyphis (Carcharhinidae), belongs to a poorly known and highly threatened group of river sharks, whose taxonomy, distributions, population structure and conservation status are only now beginning to be resolved (Pillans et al 2010;Feutry et al 2014;Li et al 2015;White et al 2015). Glyphis glyphis is of high conservation concern and is classified as critically endangered on the Australian Environment Protection and Biodiversity Conservation Act 1999.…”

A rare contemporary record of the Critically Endangered Ganges shark Glyphis gangeticus

“…remain a critical knowledge gap, studies from Australia and Papua New Guinea indicate that adults can occur outside of rivers in coastal marine environments (Pillans et al ., ; White et al ., ). In fact, it is possible that adults may travel long distances with recent molecular data indicating contemporary gene flow between the populations of G. gangeticus in Myanmar (= G. siamensis ), Borneo (= G. fowlerae ) and those of India and Pakistan, suggesting marine dispersal of several thousand km (Li et al ., ).…”

“…Prior to taxonomic resolution by Li et al . (), there were thought to be five species in the genus Glyphis . However, molecular data confirmed that the Borneo river shark Glyphis fowlerae Compagno, White & Cavanagh 2010 from the Kinabatangan River, Sabah, Malaysian Borneo and the Irrawaddy river shark Glyphis siamensis (Steindachner 1896) from the Irrawaddy River, Myanmar, are junior synonyms of the Ganges shark Glyphis gangeticus (Müller & Henle 1839).…”

“…Records of G. gangeticus are patchy, mostly historical and are often based on jaw material only (Compagno et al, 2010;Li et al, 2015). In the Arabian Sea, the western extent of the species' range, there are records based on jaws prior to 2005, but the present status of the species in this region is virtually unknown.…”

“…remain a critical knowledge gap, studies from Australia and Papua New Guinea indicate that adults can occur outside of rivers in coastal marine environments (Pillans et al, 2010;White et al, 2015). In fact, it is possible that adults may travel long distances with recent molecular data indicating contemporary gene flow between the populations of G. gangeticus in Myanmar (= G. siamensis), Borneo (= G. fowlerae) and those of India and Pakistan, suggesting marine dispersal of several thousand km (Li et al, 2015). The historical population size of G. gangeticus within the region is unknown, but the population has probably been severely depleted due to a long history of fisheries and other threats in the northern Arabian Sea (Jabado et al, 2017).…”