The secret of the saws: historical DNA analysis reveals global genetic diversity loss in a highly threatened species

Abstract

Abstract Genetic diversity is critical to long-term survival of species but can be eroded by population declines driven by human pressures. Temporal genetic monitoring of threatened species can reveal changes in genetic diversity over time, providing key data for conservation. Specimens from natural history collections were used to assess changes in genetic diversity in the Critically Endangered largetooth sawfish (Pristis pristis). Historically, P. pristis had a circumtropical range, but following massive declines it is now primarily found in Australia, with limited depleted populations elsewhere. Genetic data (815-bp of the mitochondrial control region) from 87 specimens from across its historical range revealed significant population structure, with the Indo-West Pacific and the Atlantic/Eastern Pacific comprising distinct lineages. Comparisons between historical (approx. 1878–2000) and contemporary populations (2001–2014) revealed genetic diversity loss, with only six of 35 historical haplotypes represented in contemporary populations. Most of the lost haplotypes were from the Atlantic/Eastern Pacific, which is at risk of further genetic erosion. Genetic diversity in Australia appears stable since the 1960s, while Brazil showed a marked loss, despite contemporary estimates similar to those in Australia. These findings highlight the need to conserve remaining genetic diversity in P. pristis, emphasizing the importance of securing a stronghold in the Atlantic/Eastern Pacific.