Abstract
Introductions of Coregonus artedi from Lake Superior into several inland lakes in Minnesota in the 1920s and 1930s constituted a natural experiment of how phenotypic plasticity and adaptation can shape cisco diversity. Genetic data were consistent with a Lake Superior origin for the introduced populations, which resembled contemporary Lake Superior cisco in possessing large, elongated bodies and short fins, and in maturing at older ages. Native inland cisco had smaller, deeper bodies, longer fins, and matured at younger ages. Introduced populations also retained the Lake Superior characteristic of inhabiting the upper portion of the water column and showed a high degree of planktivory. However, introduced cisco exhibited small but measurable shifts in body shape and fin lengths toward native inland forms. These morphological shifts were possibly associated with greater benthivory after translocation. Assuming that native inland populations were well adapted to inland lakes and that selective pressures on native and introduced populations were similar, these results indicated that substantial further phenotypic, behavioral, and life history change is required before the introduced populations become similarly adapted to their new environments. The findings suggest that anthropogenic environmental alterations such as climate change and eutrophication might occur at a faster pace than adaptive evolutionary responses. In addition, translocated Great Lakes coregonines could possibly maintain traits exhibited in their source lake, and may not fully restore ecological functions of extirpated populations.