Date of Award
Great Lakes Institute for Environmental Research
Biological sciences, Gene dispersal, Gene flow, Population divergence, Speciation
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Understanding how species persist and how they arise are among the most fundamental objectives of ecology and evolutionary biology. Genetic markers coupled with population genetic theory are frequently employed in the study of animal dispersal and gene flow, two parameters central to understanding the genetic structure underlying natural populations.
This thesis presents novel examples of the temporally-stabilizing effect of low to moderate levels of gene flow (Chapter 2), population admixture or evidence of sympatric divergence (Chapter 3), a lack of genetic structure among phenotypes with no reproductive barriers (Chapter 4), river effects on genetic structure of endemic populations (Chapter 5), and parallelism in ecological diversification (Chapter 6).
Throughout this thesis, dispersal also plays a fundamental role in the observed genetic structure, taking on a number of forms given the life history of the species under study. For homing salmonids, straying from natal spawning sites is dispersal. In Chapter 2, I argue that low levels of gene flow can elevate effective population sizes and preserve genetic variability highlighting the importance of considering gene flow acting to temporally stabilize populations. The genetic data presented here overwhelmingly suggests that dispersing individuals are likely reproductively successful members of the populations into which they stray (Chapter 2). For the Malili Sailfin silversides, larval dispersal most likely accounts for the sympatric population structure of an endemic fish in Lake Matano (Chapter 3, 4). Population genetic structure in the presence of substantial dispersal provides a unique perspective on the evolution of reproductive isolation. Genetic analyses using novel microsatellite markers revealed significant population-level structure consisting of 4-6 sympatric clusters resolving the apparent paradox of population genetic structure coupled with frequent dispersal.
Despite an ontogenetic predisposition to dispersal, geographic and other environmental factors also encourage or retard dispersal. Rivers act to facilitate the movement of individuals between lacustrine populations but biasing one lake as a new exporter of migrants (Chapter 5), or they can completely block passage leading to isolation and the independent evolution of similar feeding strategies (Chapter 6). In all these cases, dispersal (or a lack of) influences the underlying population genetic structure.
Walter, Ryan P., "Gene flow & dispersal as factors mediating population divergence, admixture and speciation in fishes" (2009). Electronic Theses and Dissertations. 7909.