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UBC Theses and Dissertations

The evolution of swimming capacity among migratory and non-migratory populations of the threespine stickleback (Gasterosteus aculeatus) Dalziel, Anne Cecilia


Understanding how complex traits evolve is critical for understanding how animals meet environmental challenges. In my dissertation I studied the mechanisms by which prolonged swimming performance (Ucrit), a complex whole-animal performance trait, has evolved among ancestral anadromous-marine and derived non-migratory stream-resident ecotypes of threespine stickleback (Gasterosteus aculeatus). I showed that stream-resident populations from Bonsall and West Creeks have evolved a decreased Ucrit, but via different genetic mechanisms, and that three additional wild stream-resident populations also had low Ucrits. Collectively, these data are consistent with a role for natural selection in the evolution of a reduced capacity for prolonged swimming after freshwater colonization. I next determined which candidate morphological, physiological, and biochemical traits evolved in conjunction with these decreases in Ucrit capacity in Bonsall and West Creek stream- resident populations. I found that a number of traits predicted to influence Ucrit in fishes evolved as predicted in both stream-resident populations. To further assess the associations between these candidate traits and Ucrit, I compared the genetic architecture of Ucrit with the genetic architecture of candidate traits by comparing F1 hybrids to pure F1 crosses. I found that a number of candidate traits had a similar genetic architecture as Ucrit, but that many of these traits were population-specific. These data suggest that non-parallel genetic, morphological and physiological mechanisms may contribute to the evolution of similar performance capacities. To test the associations between candidate traits and Ucrit, I correlated traits with Ucrit in Bonsall Creek F2 hybrids. In F2 hybrids the complete linkage of all divergent traits in F1 crosses is partially broken apart. I found that only four candidate traits (ventricle mass, adductor mass, and adductor and abductor citrate synthase activities) significantly regressed against Ucrit in F2 hybrids, accounting for 17.9% of variation in Ucrit. These data suggest that, when dissociated from other traits, many candidate traits do not have a strong effect on Ucrit, additional unmeasured traits are likely to influence Ucrit, and that many traits are necessary to reach a high Ucrit. This dissertation provides a clear empirical example of the patterns of evolution in a complex trait and its underlying mechanisms.

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