| dc.description | Dispersal is one of the most ubiquitous components of life histories, determining rates of connectivity, stability and persistence of populations and species. Nonetheless, dispersal estimates for marine species remain elusive despite concerns about collapse in populations and large-scale alteration of marine communities. A review of different approaches and estimates from the published literature and a subsequent evaluation using indirect measures of dispersal indicate a significant bias in the literature towards low-latitude, low-dispersal taxa. One approach that uses genetic isolation by distance relationships appears particularly promising, especially in species with high gene flow in which assumptions of drift-dispersal equilibrium are met. Using a combination of approaches, I examined dispersal within populations of anadromous rainbow smelt (Osmerus mordax) and its ecological and evolutionary consequences for spatial structure. Across different smelt life history stages, significant behavioural contributions to dispersal were observed from hatch to estuarine larval transport to adult spawning site fidelity. Overall, patterns were consistent across life history stages in that dispersal was restricted to small spatial scales such as a single estuary. Consistent with these findings, analysis of nine microsatellite loci and otolith elemental composition indicated fine-scale structure indicative of limited movements and supporting estuarine dependence. In addition, I observed signatures indicative of historic isolation and contemporary hitch-hiking selection at a putatively non-neutral locus. Trends in gene flow suggest geography as the major determinant, though morphological variation was independent of geography and gene flow. My results suggest that rainbow smelt dramatically dampen dispersal potential through behavioural mechanisms present at each life history stage, resulting in fine-scale structure on a scale comparable to anadromous salmonids. Moreover, my results suggest that given low rates of gene flow, signatures of contemporary and historical isolating mechanisms may be visible. This work allows the identification of various behavioural contributions to dispersal trajectories and, considered in the context of historical forces, their implications for spatial structuring in marine populations. Moreover, these results suggest the potential for extremely fine-scale complexity in estuarine and marine species, even in the presence of high dispersal potential. | en_US |
