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.

定向性选择（通过配偶竞争）通常会青睐体型更大的雄性个体。然而，诸如“偷配者”（sneakers）这类雄性生活史替代表型，会削弱针对大型“格斗雄性”体型的性选择强度。我们以鲑科鱼类为类群验证了这一预测：在偷配者较为常见的南部种群中，格斗雄性的体型应小于偷配者罕见的北部种群，由此形成性别大小二态性（sexual size dimorphism, SSD）的地理梯度分布。与预测结果一致，存在偷配雄性的鲑鱼物种（大西洋鲑*Salmo salar*与樱鳟*Oncorhynchus masou*）中，格斗雄性体型与性别大小二态性（格斗雄性体型/雌性体型）随纬度升高而增大；而无偷配者的物种（大麻哈鱼*O. keta*与粉鲑*O. gorbuscha*）则未呈现该规律。本研究首次证实偷配雄性可在种群与物种层面影响性别大小二态性，同时表明雄性替代交配策略可能推动体型的演化进程。