Evol Ecol Res 16: 569-580 (2014)     Full PDF if your library subscribes.

Cannibalistic growth polyphenism in Atlantic cod

David C. Hardie¹ and Jeffrey A. Hutchings^2,3,4

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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