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

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.

定向性配偶竞争选择通常倾向于青睐体型更大的雄性个体。然而，诸如‘偷配者（sneakers）’这类替代性雄性生活史表型，会削弱针对体型更大的‘格斗型’雄性的性选择强度。我们以鲑科物种为研究对象验证了这一假说：在偷配者较为常见的南部种群中，格斗型雄性的体型应小于偷配者罕见的北部种群，由此引发性体型二态性（sexual size dimorphism, SSD）的地理梯度变化。与我们的预测一致，在存在偷配雄性的物种（大西洋鲑（Salmo salar）与马苏大麻哈鱼（Oncorhynchus masou））中，格斗型雄性体型与性体型二态性（格斗型雄性∶雌性体型）均随纬度升高而增加；而在无偷配雄性的物种（狗鲑（Oncorhynchus keta）与粉鲑（Oncorhynchus gorbuscha））中则未出现此规律。本研究首次证实偷配雄性会通过种群间差异影响性体型二态性，同时表明替代性雄性交配策略可能驱动体型的演化。