Evol Ecol Res 16: 569-580 (2015)     Full PDF if your library subscribes.

Cannibalistic growth polyphenism in Atlantic cod

David C. Hardie1 and Jeffrey A. Hutchings2,3,4

1Fisheries and Oceans Canada, Dartmouth, Nova Scotia, Canada,  2Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada,  3Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, Oslo, Norway and  4Department of Natural Sciences, University of Agder, Kristiansand, Norway

Correspondence: D.C. Hardie, Fisheries and Oceans Canada, 1 Challenger Drive, Dartmouth, Nova Scotia B2Y 4A2, Canada.
e-mail: david.hardie@dfo-mpo.gc.ca

ABSTRACT

Background: Phenotypic variability in Atlantic cod in the Canadian Arctic is characterized by a distinctive resource polymorphism manifest by the co-existence of cannibalistic and non-cannibalistic individuals in the same populations.

Questions: What are the fitness consequences of this variation in foraging tactic? What maintains the two phenotypes?

Method: Measure and compare condition and growth trajectories between the two morphs from three meromictic lakes on Baffin Island, Canada. Use life-history invariants to estimate natural mortality and other components of fitness.

Results: Compared with non-cannibals, cannibals are predicted to achieve greater maximum size, experience higher mortality in early life, and mature at a larger size, albeit at the same age. Growth trajectories of cannibals and non-cannibals diverge as early as one year of age. Condition indices do not differ between forage morphs. The evidence does not support a genetic difference between cannibals and non-cannibals.

Conclusion: The co-existence of alternative foraging tactics by cod within Arctic lake populations can be explained as phenotypic variability maintained by environments that pose similar fitness consequences to cannibalistic and non-cannibalistic individuals.

Keywords: alternative foraging tactics, Arctic Canada, Gadus morhua L., life history, natural mortality.

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