Sneaker Males Affect Fighter Male Body Size and Sexual Size Dimorphism in Salmon

• Main Authors: Weir, Laura K, Kindsvater, Holly K, Young, Kyle A, Reynolds, John D
• Format: Article in Journal/Newspaper
• Language: English
• Published: University of Chicago Press 2016
• Subjects: Institute of Evolutionary Biology and Environmental Studies; 570 Life sciences; biology; 590 Animals (Zoology); alternative mating strategies; competition; latitudinal clines; salmonids; sexual selection; Atlantic salmon; Oncorhynchus gorbuscha; Pink salmon; Salmo salar
• Online Access: https://www.zora.uzh.ch/id/eprint/157734/; https://www.zora.uzh.ch/id/eprint/157734/1/687253.pdf; https://doi.org/10.5167/uzh-157734; https://doi.org/10.1086/687253

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.