Sympatric Divergence in Whitefish Dwarfs : An investigation of phenotype-environment correlations in whitefish dwarfs

Sammanfattning: Recent studies have found populations of European Whitefish (Coregonus lavaretus) to be under the process of divergence induced by a predator (pike, Esox lucius). This has caused whitefish to diverge into similar ecotypes but in separate lakes. Even though there are established ecotypes, these do display a high degree of variation, especially among whitefish dwarfs. The underlying mechanisms has not been fully understood and other determining ecological factors than predation are yet to be explored. In this study, I examine whether there are phenotype-environment correlation between whitefish dwarfs that could help identifying the selection pressures shaping this variation between whitefish dwarfs in different lakes. The morphological features of interest were body size and number of gill rakers since these are determining features of divergence. The environmental variables of interest were features of the lake in questions and its surrounding area. No significant correlations were found between the environmental variables and the body size of whitefish dwarfs. I was however through this study able to conclude significant results regarding phenotype-environment correlations between the number of gill rakers in whitefish dwarfs and the combined effects of lake percentage, lake area, temperature and number of (other fish) species in the lake from which they were sampled. It is probable that this is due to these variables affecting the niche space in which the whitefish dwarfs can diverge. Lakes with more potential refuges from pike will result in more divergence in whitefish dwarfs and vice versa. I can hereby propose a model containing these four environmental variables for how they affect the number of gill rakers in whitefish dwarfs.