Evolutionary biology of the exploited cephalopod, Nautilus pompilius

Williams, Rachel Clare and Sinclair, Billy (2015) Evolutionary biology of the exploited cephalopod, Nautilus pompilius. PhD thesis, Lancaster University.

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Abstract

Commercial species worldwide are experiencing significant population declines. Marine research is needed to understand species biology in an attempt to sufficiently manage levels of exploitation. Nautilus pompilius is unsustainably fished for the ornamental shell trade and large-scale population losses in the Philippines have been reported. We generated data that are intended to inform legislation to protect N. pompilius from overexploitation. Specifically, we investigated the evolutionary divergence and genetic structure between populations sampled from across the Indo-Pacific. In addition to research into the genetic structure of N. pompilius populations we also addressed the pharmacological responses of neurotransmitters widely used across the animal kingdom. We collected data from the mitochondrial locus cytochrome c oxidase sub unit I (COI) and a novel microsatellite-enriched genomic library to describe the relatedness of N. pompilius populations sampled from across their range. Gene flow between west Australia and the Philippines was modelled using approximate Bayesian computation (ABC) analysis. Initial experiments to determine phylogenetically taxon specific usage of widely used neurotransmitters were conducted by testing for the presence and absence of targeted receptors using specific drugs. Demonstrating sufficient responses to these drugs will confirm the scope for further research into the physiological role played by receptors in N. pompilius, thus allowing us to determine taxonomic relationships at this fundamental level. Finding relatively high protein sequence homologies in cross species comparisons would be informative both on the evolution of nautiloids, and the functional role of receptors across taxa.Results of maximum likelihood phylogenetic analyses show that N. pompilius is divided into three distinct clades, with additional subdivision occurring within two of these clades. Genetic structure is high between Great Barrier Reef individuals, and those of Osprey Reef and Shark Reef in the Coral Sea (FST=0.312, 0.229 respectively). Interestingly, low genetic structure was shown between west Australia and the Philippines (FST=0.015), despite the large geographic scale from which these samples were collected. Further analyses of genetic data collected from west Australia and Philippine samples using ABC indicate that the observed genetic similarity is not the result of current gene flow and that individuals sampled from these regions are indeed genetically isolated. This similarity is explained by large effective population sizes over time suggesting a minor role for genetic drift. The population structure of east Australia and the west Pacific reflects oceanic topographic features. Recorded drug/tissue responses warrant further exploration into this area of their evolution, enabling us to compare biological signalling pathways among taxa and understand the unique nature of Nautilus at this fundamental level.Our data demonstrate widespread substructure and isolation among populations of N. pompilius. Furthermore, we show that local extinction of N. pompilius in the Philippines is possible due to their low levels of migration. These findings reduce gaps in our knowledge of N. pompilius biology that currently inhibit their conservation classification. Results support the case to gain CITES protection for N. pompilius.