Sneaker males affect fighter male body size and sexual size dimorphism in salmon

Laura K. Weir, Holly K. Kindsvater, Kyle A. Young, John D. Reynolds

Research output: Contribution to journalComment/debatepeer-review

13 Scopus citations


Large male body size is typically favored by directional sexual selection through competition for mates. However, alternative male life-history phenotypes, such as “sneakers,” should decrease the strength of sexual selection acting on body size of large “fighter” males. We tested this prediction with salmon species; in southern populations, where sneakers are common, fighter males should be smaller than in northern populations, where sneakers are rare, leading to geographical clines in sexual size dimorphism (SSD). Consistent with our prediction, fighter male body size and SSD (fighter male∶female size) increase with latitude in species with sneaker males (Atlantic salmon Salmo salar and masu salmon Oncorhynchus masou) but not in species without sneakers (chum salmon Oncorhynchus keta and pink salmon Oncorhynchus gorbuscha). This is the first evidence that sneaker males affect SSD across populations and species, and it suggests that alternative male mating strategies may shape the evolution of body size.

Original languageEnglish (US)
Pages (from-to)264-271
Number of pages8
JournalAmerican Naturalist
Issue number2
StatePublished - Aug 2016

All Science Journal Classification (ASJC) codes

  • Ecology, Evolution, Behavior and Systematics


  • Alternative mating strategies
  • Competition
  • Latitudinal clines
  • Salmonids
  • Sexual selection


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