Co-Existence of Lake Trout Morphs in a Small Post-Glacial Lake Challenges the Prevailing Model of Lake Trout Diversification

Geologically-young post-glacial lakes tend to contain relatively few species, often associated with reduced interspecific competition that can promote intraspecific diversity. However, diversification within Lake Trout Salvelinus namaycush has been documented in a relatively small number of North American lakes, despite its geographical distribution that includes thousands of such young, depauperate lakes. Although Lake Trout diversity is generally thought to be associated with different depth-related habitats, likely a result of specialized foraging, and restricted to large, deep, “great” lakes, recent studies have shown this model to be incomplete. Among recent challenges to the prevailing ideas of Lake Trout diversity is Rush Lake (MI, USA), a small post-glacial lake (1.3km²), with co-existing shallow- and deep-water morphs. These morphs also show differences in morphology, habitat use, diet, and life-history, evoking strong resemblances to lean- and humper-like forms. Little differentiation based on neutral genetic markers has been found, however, implying incomplete reproductive isolation between morphs. The Rush Lake example suggests that the prevailing model of the origin and/or maintenance of Lake Trout diversity is incomplete, indicating that we still have much to learn about variability in Lake Trout.