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, O. keta, and pink salmon, O. gorbuscha). This is the first evidence that sneaker males affect SSD across populations and species, and suggests that alternative male mating strategies may shape the evolution of body size.

通过配偶竞争实现的定向性选择通常倾向于青睐体型更大的雄性个体。然而，诸如‘偷袭型雄性（sneakers）’这类雄性替代生活史表型，会削弱作用于大型‘格斗型雄性’体型的性选择强度。我们以鲑科物种为研究对象验证了这一预测：在偷袭型雄性较为常见的南部种群中，格斗型雄性的体型应小于偷袭型雄性稀少的北部种群，进而导致体型性二态性（sexual size dimorphism, SSD）呈现地理梯度分布。与我们的预测一致，在存在偷袭型雄性的物种（大西洋鲑Salmo salar、樱鳟Oncorhynchus masou）中，格斗型雄性体型与体型性二态性（格斗型雄性:雌性体型比值）随纬度升高而增大；而在无偷袭型雄性的物种（大麻哈鱼O. keta、粉鲑O. gorbuscha）中则未观察到此规律。本研究首次证实偷袭型雄性可在种群与物种层面影响体型性二态性，同时表明雄性替代交配策略可能参与塑造体型的演化进程。