Evol Ecol Res 10: 1051-1066 (2008)     Full PDF if your library subscribes.

Trophically mediated divergence of Arctic charr (Salvelinus alpinus L.) populations in contemporary time

Wendy K. Michaud1, Michael Power2 and Michael T. Kinnison1

1Department of Biological Sciences, University of Maine, Orono, Maine, USA and 2Department of Biology, University of Waterloo, Waterloo, Ontario, Canada

Correspondence: W.K. Michaud, Department of Biology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
e-mail: wmichaud@sciborg.uwaterloo.ca


Hypothesis: Trophic specializations can evolve in contemporary time in response to changes in trophic opportunities afforded by different ecosystems.

Organism: Lacustrine populations of Arctic charr (Salvelinus alpinus L.), a model species in studies of trophic specialization and divergence.

Time and location: A natural experiment in divergence began when piscivorous Arctic charr were translocated from Floods Pond to Long Pond, Maine (USA) in the late 1970s.

Analytical methods: Stomach contents, carbon and nitrogen stable isotope ratios, head and body shape, gill raker morphology, and size-at-age were compared between the translocated and indigenous populations after approximately six generations (25 years) of divergence. The relative rate at which divergence arose in growth and morphological traits was estimated using haldanes.

Results: Despite the fact that ancestrally preferred prey items (fish) were available in both lakes, the translocated population of Arctic charr exhibited a clear shift in both diet and phenotype relative to its source. Differences in diet were primarily attributed to changes in the timing of an ontogenic shift, with Arctic charr from the translocated population becoming piscivorous at a later age. Divergence was also detected in several phenotypic characteristics, including body depth, fin lengths, eye width, maxilla length, gill raker design, and size-at-age.

Conclusions: Significant phenotypic differences between a translocated population of Arctic charr and its ancestral source suggest trophic specializations can diverge in contemporary time. The phenotypic differences noted in this case appear broadly consistent with long-term patterns of trophic specialization, and arose at a relatively rapid rate, even for a contemporary time scale. This suggests that the rudiments of post-glacial diversification, or perhaps even speciation, may arise in response to ecological opportunities very early in the divergence process.

Keywords: contemporary rapid evolution, geometric morphometrics, ontogenic shift, rate of divergence, resource polymorphism, trophic specialization, stable isotopes.

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