The genetic structure of Nautilus pompilius populations surrounding Australia and the Philippines

Abstract

Understanding the distribution of genetic diversity in exploited species is fundamental to successful conservation. Genetic structure and the degree of gene flow among populations must be assessed to design appropriate strategies to prevent the loss of distinct populations. The cephalopod Nautilus pompilius is fished unsustainably in the Philippines for the ornamental shell trade and has limited legislative protection, despite the species' recent dramatic decline in the region. Here, we use 14 microsatellite markers to evaluate the population structure of N. pompilius around Australia and the Philippines. Despite their relative geographical proximity, Great Barrier Reef individuals are genetically isolated from Osprey Reef and Shark Reef in the Coral Sea (F ST =0.312, 0.229, respectively). Conversely, despite the larger geographical distances between the Philippines and west Australian reefs, samples display a small degree of genetic structure (F ST =0.015). Demographic scenarios modelled using approximate Bayesian computation analysis indicate that this limited divergence is not due to contemporary gene flow between the Philippines and west Australia. Instead, present-day genetic similarity can be explained by very limited genetic drift that has occurred due to large average effective population sizes that persisted at both locations following their separation. The lack of connectivity among populations suggests that immigrants from west Australia would not facilitate natural recolonization if Philippine populations were fished to extinction. These data help to rectify the paucity of information on the species' biology currently inhibiting their conservation classification. Understanding population structure can allow us to facilitate sustainable harvesting, thereby preserving the diversity of genetically distinct stocks.

A revisited phylogeography of Nautilus pompilius

“…Microsatellites have recently been developed for Nautilus (Williams et al. , ) but have not been employed across a wide geographical range. These powerful tools should be utilized to inform fisheries management and conservation efforts, as well as assess the validity of the currently recognized extant species.…”

“…; Williams et al. , ), the samples between locations were few and the power of these observations may be low. A larger question that remains unresolved is whether genetic studies support several named species falling into their own distinct clades.…”

“…; Williams et al. , ). Original species descriptions of Nautilus utilized few discrete characters, and many of the morphological characteristics delimiting the species may be difficult to quantify or have values that overlap broadly between multiple species (e. g. size, Table S1).…”

“…There have been an increasing number of investigations into the morphological and genetic diversity of the genus Nautilus (Saunders 1981;Saunders and Landman 1987;Saunders et al 1989;Ward and Saunders 1997;Sinclair et al 2007Sinclair et al , 2011Bonacum et al 2011;Dunstan et al 2011b;Williams et al 2015aWilliams et al , 2015b. Original species descriptions of Nautilus utilized few discrete characters, and many of the morphological characteristics delimiting the species may be difficult to quantify or have values that overlap broadly between multiple species (e. g. size, Table S1).…”

Demographic disequilibrium in living nautiloids (Nautilus and Allonautilus): Canary in the coal mines?

“…Nautiloid genetic studies do not have a long tradition, but there has been a flourish of activity in recent years [29, 30, 31, 32, 33, 34, 35, 36]. By contrast, the taxonomy of extant nautiloids spans more than two centuries, with two genera, eleven species, two subspecies and six variants having been named [10, 36].…”