Water Transparency Drives Intra-Population Divergence in Eurasian Perch (Perca fluviatilis)

Trait combinations that lead to a higher efficiency in resource utilization are important drivers of divergent natural selectionand adaptive radiation. However, variation in environmental features might constrain foraging in complex ways andtherefore impede the exploitation of critical resources. We tested the effect of water transparency on intra-populationdivergence in morphology of Eurasian perch (Perca fluviatilis) across seven lakes in central Sweden. Morphologicaldivergence between near-shore littoral and open-water pelagic perch substantially increased with increasing watertransparency. Reliance on littoral resources increased strongly with increasing water transparency in littoral populations,whereas littoral reliance was not affected by water transparency in pelagic populations. Despite the similar reliance onpelagic resources in pelagic populations along the water transparency gradient, the utilization of particular pelagic preyitems differed with variation in water transparency in pelagic populations. Pelagic perch utilized cladocerans in lakes withhigh water transparency and copepods in lakes with low water transparency. We suggest that under impaired visualconditions low utilization of littoral resources by littoral perch and utilization of evasive copepods by pelagic perch may leadto changes in morphology. Our findings indicate that visual conditions can affect population divergence in predatorpopulations through their effects on resource utilization.