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Dispersal, connectivity, and population genetic structure in the sea
Xuereb, A. (2018). Dispersal, connectivity, and population genetic structure in the sea. PhD Thesis. University of Toronto; Department of Ecology and Evolutionary Biology: Toronto. xiii, 178 pp.

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Document type: Dissertation

Keyword
    Marine/Coastal
Author keywords
    biophysical modeling; marine invertebrate; seascape genomics

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  • Xuereb, A.

Abstract
    The spatial distribution of genetic variation across landscapes is influenced by physical features that facilitate or restrict movement and natural selection driven by environmental heterogeneity. Many marine organisms undergo a pelagic larval stage, during which time ocean currents influence dispersal and the degree of gene flow. Furthermore, gradients in temperature, salinity, and other environmental conditions produce spatially varying selection pressures across species ranges. In the first part of my thesis, I offer a novel perspective for marine conservation that emphasizes the importance of considering both connectivity (where connectivity is maintained by dispersal) and the potential for marine populations to adapt to their environment. To do so, I highlight how genomic data can be used to infer population connectivity (i.e. based on neutral genetic variation) and environmental selection (i.e. based on putatively adaptive genetic variation) in the context of marine reserve networks. Next, using a genomic dataset derived from restriction-site associated DNA sequencing (RADseq), I investigated the impact of ocean currents and environmental variables on spatial patterns of neutral and adaptive genetic variation in the commercially harvested giant California sea cucumber (P. californicus) along the northeastern Pacific coast. The results showed evidence for population structure despite the potential for widespread gene flow, and demonstrated that accounting for directionality of ocean currents explained genetic variation better than between-site geographic distances. Strong associations between sea bottom temperature and putatively adaptive loci were identified at a broad spatial scale, as well as moderate evidence that surface salinity and bottom current velocities contribute to regional patterns of adaptive differentiation. In a study using simulations of larval dispersal coupled with demo-genetic simulations, I found that potential dispersal was spatially restricted with shorter pelagic larval duration (PLD), but there was no difference between a model of diffusive (isotropic) larval transport and oceanographic (anisotropic) transport. However, several important caveats were highlighted that should be addressed in future work. Collectively, my thesis integrates genomic, environmental, and oceanographic data to understand the role of seascape features on connectivity and adaptation, with implications for marine conservation plans that aim to connect marine populations and support adaptive responses to environmental change.

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