Genetic bottlenecks in Pristis sawfishes in northern Australian waters

Nm Phillips,Dl Morgan,A Fearing

doi:10.3354/esr00815

Nm Phillips, Dl Morgan + Show 1 more

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https://doi.org/10.3354/esr00815

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Abstract

Northern Australia has been identified as the last stronghold for the dwarf sawfish Pristis clavata, green sawfish P. zijsron, and largetooth sawfish P. pristis, making these populations key in global conservation efforts for each species. This research assesses the levels of genetic diversity in these 3 sawfishes in Australian waters, testing for the presence of population bottlenecks using data at microsatellite loci. Levels of observed heterozygosity in each species from the west coast of Australia and the north-eastern Gulf of Carpentaria were generally high. M ratio tests suggest that assemblages of P. zijsron and P. pristis on the west coast and P. clavata and P. zijsron in the Gulf of Carpentaria may have experienced population bottlenecks. The bottlenecks are especially pronounced in P. zijsron populations and in P. clavata from the Gulf of Carpentaria. Demographic analyses, based on mtDNA data, indicate relatively recent (evolutionarily) range expansions in Pristis sawfishes in northern Australian waters, which could account for the population bottlenecks. A more recent range expansion in each of P. clavata and P. zijsron, as evidenced by more recent population divergence and more recent/higher rates of historic maternal gene flow, could account for the more pronounced bottlenecks in these species when compared to P. pristis. Given that Pristis sawfishes in Australian waters have experienced population bottlenecks, whether they be historic, contemporary or both, the preservation of remaining genetic diversity should be a high conservation priority.

Highlights

Over the last century, sawfishes have faced vast declines in both range and abundance, resulting in an increased threat of their global extinction (Dulvy et al 2016)
In the midst of these large global declines, Australia is regarded as the last stronghold for each of 3 Pristis sawfishes: the dwarf sawfish P. clavata, green sawfish P. zijsron, and the largetooth sawfish P. pristis (Pogonoski et al 2002, Phillips et al 2011)
Genetic data were generated from tissue biopsies or skin taken from contemporary dry rostra from the dwarf sawfish Pristis clavata, green sawfish P. zijsron, and largetooth sawfish P. pristis from sites across northern Australia, as described by Phillips et al (2011, 2017)

Summary

Introduction

Sawfishes have faced vast declines in both range and abundance, resulting in an increased threat of their global extinction (Dulvy et al 2016). While it is generally agreed that Pristis sawfishes have suffered from declines in range and abundance in Australian waters, the severity of these declines and the impact on the health of extant populations is largely unknown. This is because the evidence for the declines is largely anecdotal, with limited reliable estimates of abundance or population trend data (Kyne et al 2013). Assemblages of each of P. clavata, P. zijsron, and P. pristis on the west coast and Gulf of Carpentaria in Australia have low to moderate levels of genetic diversity, based on data from the mitochondrial (mtDNA) control region (Phillips et al 2011). The current research, aims to assess genetic diversity in Pristis sawfishes in Australian waters using nuclear DNA (nDNA) markers (microsatellite loci), and to test whether these populations have undergone population bottlenecks, providing valuable information on the genetic ‘health’ of these sawfish populations

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