Ecomorphological variation of pumpkinseed sunfish ( Lepomis gibbosus ) in exposed littoral shoreline habitat of a postglacial lake

The spatial distribution of phenotypes across the environment has important consequences for population biology, community ecology, and evolution. Populations of pumpkinseed sunfish (Centrarchidae: Lepomis gibbosus ) have repeatedly diversified between the littoral and pelagic habitats of postglacial lakes, but we know little about the natural history of pumpkinseed in exposed rocky littoral shorelines relative to those in sheltered littoral bays. We addressed three general questions with respect to the pumpkinseed found in exposed littoral shoreline relative to conspecifics from sheltered littoral and pelagic habitats: (1) What phenotype is associated with the exposed littoral shoreline? (2) What is their summer diet? (3) What is the condition of pumpkinseed from exposed littoral shorelines? Reference sheltered littoral and pelagic pumpkinseed were phenotypically and ecologically differentiated in a pattern consistent with several previous studies; pelagic pumpkinseed had deeper bodies, smaller jaws (narrower oral jaw width and shorter premaxilla), and a more terminal mouth, as well as having more zooplankton and less insects in their diet. Pumpkinseed from exposed shoreline habitat had jaw and body shape phenotypes, as well as diets, that were similar to sheltered littoral reference pumpkinseed in some traits while others were more intermediate. We found no evidence that differences between habitats in phenotype or diet translated into differences in body condition at the end of the summer growing season, suggesting that exposed littoral shorelines are unlikely to be an ecological ‘sink’ habitat. This study expands our understanding of the spatial distributions of polyphenic pumpkinseed, and their habitat use in postglacial lakes.