Abstract
The largetooth sawfish Pristis pristis (Linnaeus, 1758) is a highly threatened euryha- line elasmobranch that in recent times has undergone a significant range contraction. It now only remains in a few areas, with northern Australia being the main stronghold. Previous work using a single mitochondrial gene approach suggested the existence of regional barriers to gene flow in northern Australia. In this study, whole mitochondrial sequences of 92 P. pristis from 7 river drainages across northern Australia were used to refine the population structure. This approach revealed barriers to gene flow at a scale as fine as between adjacent river drainages. Except for those flowing into the Gulf of Carpentaria, all river drainages appeared to host a genetically dis- tinct population. The apparent genetic homogeneity in the Gulf is probably due to freshwater con- nectivity between river drainages, either during the last glaciation event when the Gulf was a freshwater lake or through contemporary wet season flooding. These results suggest that each river drainage across the species' range should be considered a discrete management unit unless there is evidence of freshwater connectivity. More broadly, the improved resolution of population structure obtained with whole mitogenome analysis compared to single mitochondrial gene approaches suggests that female reproductive philopatry may have been overlooked in previous studies of some elasmobranch species.
Highlights
The largetooth sawfish Pristis pristis (Linnaeus, 1758) was once widespread, but is listed as Critically Endangered on the IUCN Red List of Threatened Species, due to population declinesPublisher: Inter-Research · www.int-res.comMar Ecol Prog Ser 533: 237–244, 2015Morgan et al 2011, Kyne et al 2013, Dulvy et al 2014, Moore 2014)
While Phillips et al (2011) demonstrated the existence of population structure among Pristis pristis at a regional scale, with samples from the west coast (WA) appearing to belong to a different population than samples from the north coast and the Gulf of Carpentaria (NT/QLD), the present study showed that genetic heterogeneity can occur at a scale as fine as between 2 adjacent river drainages
While the use of the same control region (CR) portion as Phillips et al (2011) along with additional samples from the NT uncovered some new barriers to gene flow, it was the use of the whole mitogenome data which was necessary to uncover all barriers reported in this study (Table 2)
Summary
The largetooth (or freshwater) sawfish Pristis pristis (Linnaeus, 1758) was once widespread, but is listed as Critically Endangered on the IUCN Red List of Threatened Species, due to population declinesPublisher: Inter-Research · www.int-res.comMar Ecol Prog Ser 533: 237–244, 2015Morgan et al 2011, Kyne et al 2013, Dulvy et al 2014, Moore 2014). P. pristis reaches at least 6.5 m total length (TL) (Compagno & Last 1999), has a late age at maturity (8−10 yr) (Thorson 1982, Peverell 2008), is estimated to live to 44 yr (Tanaka 1991) and have 1−13 young every 1 or 2 yr (Thorson 1976, Peverell 2008) These life history traits limit productivity and restrict the ability of this species to recover from depletion (Dulvy et al 2014). P. pristis is protected in many countries (Dulvy et al 2014), including across its Australian range, where it is listed as Vulnerable in Australia’s Environment Protection and Biodiversity Conservation Act. Northern Australia is a key remaining population centre of global significance for P. pristis (Peverell 2005, Morgan et al 2011, Kyne et al 2013, Dulvy et al 2014). Much of northern Australia remains remote and sparsely inhabited, pressure is mounting to develop the region (The Parliament of the Commonwealth of Australia 2014), which has the potential to degrade natural systems, including key P. pristis habitats (Chin et al 2012)
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