The interplay of morphology, habitat, resource use, and genetic relationships in young yellow perch.

Morphological divergence resulting from differences in resource and habitat use is common in many fishes inhabiting postglacial ecosystems. We tested whether young yellow perch Perca flavescens differ in morphology, genetic composition, or diet in the nearshore (deep open-water) versus wetland and littoral habitats (shallow zones) of Lake Michigan and Saginaw Bay, Lake Huron. Twenty-one morphological measurements and six meristic counts were compared for 132 age-1 yellow perch, and the genetic variation at 12 nuclear DNA microsatellite loci was assessed for a subset of age-1 individuals across habitats and adults from nearshore zones. The results showed morphological and genetic divergence in yellow perch between Lake Michigan and Lake Huron and among those in nearshore versus wetland habitats in Lake Michigan (but not Lake Huron). Lake Huron yellow perch had deeper, longer bodies and larger dorsal fins than those from Lake Michigan. Those in nearshore habitats from both lakes had deeper, longer bodies and larger dorsal fins than did those occupying wetlands, which may reflect an adaptive response to predators and open-water cruising. In Lake Michigan, these differences may have a genetic basis that is not apparent in Lake Huron, suggesting a role for phenotypic plasticity. Piscivorous and zooplanktivorous individuals had similar morphologies, with larger body depths than insectivores, which may be useful for fast-starts during prey capture and provide protection from predation in open water. Comparisons of morphology, population structure, and diet thus reveal that the morphological diversity of yellow perch between habitats and lake basins reflects an interplay between phenotypic plasticity and genetic divergence.