UC San Diego

Frequently the source of selection driving divergence of putatively adaptive traits is unknown. Even in cases where traits or genes have been studied for decades, we often don’t know what agents of selection are involved. Manipulative experiments provide an opportunity to link phenotypic and genotypic shifts with a causative agent. In order to explore the role of predation in the divergence of lateral plates of the threespine stickleback, I used data generated from a manipulative experiment where a toothed and gape limited predator was manipulated. I sought to estimate natural selection on lateral plate number and area, to see if there was evidence of an effect of predation. I also used existing genomic data and quantitative trait mapping data to determine if there was a genetic basis for the two plate phenotypes. Tracking shifts in plate phenotypes over one generation of selection revealed evidence that lateral plate number was generally selected against, yet greater plate area was favored in the presence of predators. This indicates that the plate area is potentially a key trait that can aid in the protection of stickleback and is under selection by toothed predators. Several genetic regions on chromosomes 7, 11, 20, and 21 were identified that explained variance in the two lateral plate traits.