Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 1047
Title: Mating success of alternative male phenotypes and evidence for frequency-dependent selection in Chinook salmon, Oncorhynchus tshawytscha
Author: B. A. Berejikian, Donald M. Van Doornik, R. Endicott, Timothy L. Hoffnagle, E. P. Tezak, M. E. Moore, J. Atkins
Publication Year: 2010
Journal: Canadian Journal of Fisheries and Aquatic Sciences
Volume: 67
Issue: 12
Pages: 1933-1941
Keywords: frequency -dependent selection, reproduction, chinook salmon, jack male, sexual selection

As with other species, frequency-dependent selection during reproduction has long been proposed as an important mechanism in maintaining alternative male reproductive phenotypes in Pacific salmon (Oncorhynchus spp.). Jack salmon mature one year earlier than the youngest females in a population and are much smaller than older adult males. We tested the hypothesis that mating success of both phenotypes is consistent with the frequency-dependent selection model. By holding male density constant and varying the frequency of adults and jacks in eight separate breeding groups, we found that adult male access to females, participation in spawning events, and adult-to-fry reproductive success increased with their decreasing frequency in a breeding group. Jacks exhibited the same pattern (increasing success with decreasing frequency), although the relationships were not as strong as for adults. Overall, jack and adult males mated with a similar number of females, but jacks sired only 20% of all offspring. Observational data suggested that adult males benefited from sperm precedence associated with their ability to court females and enter the nest first at the time of spawning. Our work provides the first experimental evidence of frequency-dependent selection during mating in the family Salmonidae.

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