UBC Theses and Dissertations
Intraguild predation is a mechanism of divergent selection in the threespine stickleback Miller, Sara Elizabeth
Biotic interactions among species are thought to be important for the generation of phenotypic diversity. Intraguild predation is a common ecological interaction that occurs when a species preys upon another species with which it competes. This interaction is potentially a mechanism of divergence between intraguild prey populations, but it is unknown if cases of character shifts in intraguild prey are phenotypically plastic or an evolutionary response. I collected threespine stickleback (Gasterosteus aculeatus) from lakes with and without prickly sculpin (Cottus asper) and identified trait differences in armour and behaviour among populations in the wild. Differences in behavioural and morphological traits among freshwater populations persisted in a common garden, suggesting that adaptation to intraguild predation has a genetic basis. To date, the evolutionary effect that biotic selection has upon an organisms’ genome remains largely unknown in natural populations. I used whole genome re-sequencing to investigate the extent of genetic differentiation between stickleback from populations with and without sculpin. The main axis of genetic variation in these populations is strongly associated with the presence or absence of sculpin. I identified the regions of the genome that have differentiated in parallel between lakes with and without sculpin, and measured the strength of this divergence. The presence or absence of sculpin corresponds to widespread differentiation that is unevenly distributed across the stickleback genome. Adaptation to intraguild predation may involve hundreds of genes with diverse functions. Observations of extensive phenotypic and genetic differentiation between stickleback from lakes with and without sculpin provide indirect evidence that sculpin are the cause of trait differences. Pelvic morphology is one of the most conspicuously varying traits among freshwater stickleback populations. This variation has been hypothesized to be the result of predation by fish and/or insect predators. I conducted a selection experiment to test if sculpin were an agent of selection for pelvic spine length. The results were combined with other experimental selection studies and used in a meta-analysis. Fish predators are an agent of selection for longer pelvic spines, but the role of insect predators is still unclear. Intraguild predation is a mechanism of divergent selection in threespine stickleback.
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