Evidence for multiple origins and sympatric divergence of trophic ecotypes of smelt (Osmerus) in northeastern North America

Rainbow smelt Osmerus mordax exhibits extensive life-history diversity throughout watersheds of NE North America. There are both sea-run (anadromous) and lake-resident (lacustrine) populations and the latter have diversified further into "dwarf-' and "normal-sized' life-history types. Anadromous and lacustrine smelt may inhabit the same watershed and there are several instances where dwarf and normal populations reside within the same lake. The authors assayed variation among smelt for morphological traits linked to feeding performance in fishes to see if trophic ecology might promote life-history diversity. They also examined mitochondrial DNA (mtDNA) restriction site variation among forms to assess their evolutionary interrelationships. Conclusions are 1) that trophic ecology is an important factor promoting differentiation in smelt life histories; 2) that smelt ecotypes are polyphyletic and there have been multiple, independent divergences of Osmerus life-history types throughout NE North America; and 3) that the biological mtDNA differences between coexisting dwarf and normal lake smelt argue strongly that their genetic isolation may have developed sympatrically. -from Authors