Population structure and phylogeography of Octopus cyanea and Lethrinus species in the Southwestern Indian Ocean

Amy Taylor

Research output: ThesisDoctoral Thesis

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Tropical reefs such as those in the Southwestern Indian Ocean (SWIO) are the most biologically diverse of shallow water marine ecosystems. Despite this, biodiversity of the SWIO is understudied and with fishing pressure on reefs increasing there is a need to document genetic diversity of species and communities. This thesis set out to investigate intra-specific genetic diversity in four species important to subsistence and commercial fisheries: Octopus cyanea, and the emperor fish Lethrinus mahsena, L. nebulosus and L. harak. The aim was to examine factors underlying the partitioning of this genetic diversity, including historical and contemporary drivers. Population structuring and phylogeography were assessed using nuclear microsatellite genotyping and mtDNA sequencing.
Mitochondrial DNA revealed two previously unrecorded cryptic species, L. nebulosus sp. off the coast of South Africa and southern Mozambique and Lethrinus sp. A around the Seychelles, within what were previously assumed to be single stocks. The detection of cryptic species and accurate species identification is crucial for future maintenance of genetic biodiversity and management of sustainable fisheries.

High levels of genetic connectivity were observed across the majority of the SWIO in all species. Positive selection detected in a microsatellite locus of O. cyanea and mtDNA data for O. cyanea, L. harak and L. nebulosus indicated differentiation and possible emerging isolation of the Mauritian populations of these species from populations across the rest of the SWIO which may reflect local oceanographic processes. Future fisheries management of Mauritius should therefore be carefully considered as Mauritian stocks may be more vulnerable to overexploitation and environmental changes than other SWIO stocks.

Additionally, patterns of non-equilibrium conditions were reported across the studied taxa and emphasise how current neutral genetic patterns may underestimate contemporary population differentiation. Future genetic based studies may therefore benefit from adopting genomic approaches
Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • Morritt, David, Supervisor
Award date1 May 2015
Publication statusUnpublished - 2015

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