Evol Ecol Res 9: 1005-1021 (2007)     Full PDF if your library subscribes.

Contrasting niche-based variation in trophic morphology within Arctic charr populations

Rune Knudsen,* Per-Arne Amundsen, Raul Primicerio, Anders Klemetsen and Pål Sørensen

Department of Aquatic BioSciences, Norwegian College of Fishery Science, University of Tromsø, Breivika, NO-9037 Tromsø, Norway

Author to whom all correspondence should be addressed.
e-mail: runek@nfh.uit.no


Hypothesis: The opportunity for inter-individual niche differences in contrasting resource environments can induce divergent natural selection in trophic morphology within single gene pools.

Organisms: Arctic charr (Salvelinus alpinus) caught in the littoral and pelagic habitats of two neighbouring sub-arctic lakes.

Field sites: Two post-glacial lakes (Fjellfrøsvatn and Lille Rostavatn, North Norway) of similar size and physical structures, but with different fish diversities (two and six species, respectively).

Methods: Analysis and comparison of trophic niche (habitat and diet usage) and trophic morphology (body form and head structure) data from individual fish. Only immature charr 19–25 cm long were used to reduce the effects of allometric growth and secondary sex traits.

Conclusions: The utilization of multiple resource types has facilitated incipient steps towards the evolution of polymorphism in one lake, but not in the other. In Fjellfrøsvatn, individual specializations in benthivore and planktivore diet niches are correlated with inter-individual morphological differentiation. In contrast, the Arctic charr in Lille Rostavatn were restricted to zooplanktivory, and distinct morphological diversification was absent. We conclude that the two lakes have dissimilar opportunities for individual niche specialization and evolution of polymorphism.

Keywords: adaptive trophic morphology, feeding, incipient speciation, polymorphism, post-glacial fish, Salvelinus alpinus.

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