| Summary: | The blue shark, Prionace glauca, a large oceanic/pelagic predator with a continuous circumglobal distribution in temperate and tropical waters, is the most abundant and widespread of all extant shark species. They are heavily exploited in targeted and incidental fisheries worldwide. Concerns have been raised over the sustainability of such exploitation as severe declines in numbers have been recently observed. Sound management of any exploited fishery requires a proper understanding of the population sub structuring and basic breeding biology of the species involved. This is lacking for this ecological and economically important inhabitant of the open seas. In this study, we have developed nuclear microsatellite and mitochondrial (mtDNA) molecular markers for blue sharks. These were used in an assessment of the global population genetic structure of the species involving over 900 specimens sampled over its distribution range. Based on micro satellite data and 21 blue shark litters (N = 578 embryos), we have characterised the mating system ofthe species. Results from the analyses of microsatellite (16 loci) and mtDNA sequence (3,1 07bp) data indicate the presence of multiple stocks on a global scale (i.e. genetic substructuring). These genetic stocks were defined by major oceanic regions, thus confirming earlier physical tagging studies, which suggest that the equator acts as a barrier to dispersal between northern and southern oceans. Analysis of data comprising 32 complete mtDNA genomes, representing the distribution range species, provides new insights into the evolutionary history of blue sharks. Microsatellite DNA profiling of blue shark litters revealed a high incidence of polyandry (80.0%) in the species. Females of multiply sired litters were larger than those of single paternity litters. Furthermore, females demonstrated a tendency to have litters sired by more males as they became older and larger. Results are discussed in light of the high energetic cost associated with the aggressive nature of copulations.
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