Data from: Operational sex ratio but not density affects sexual selection in a fish

The operational sex ratio (OSR) and density are considered important factors affecting the strength of sexual selection. While there is increasing evidence that OSR and density affect the potential for sexual selection, few studies have addressed whether this is realized in phenotypic selection and how the two factors interact. We manipulated OSR (three levels) and male density (two levels) in 36 experimental breeding populations of Gobiusculus flavescens – a fish with paternal care. We measured mating competition behavior, the opportunity for selection (I), and selection on four morphological traits in males. We found sexual selection on two male traits, with the strongest selection being 20% of I. As predicted from OSR theory, increasing female scarcity caused males to become more competitive, concomitant with an increase in I and selection on morphological traits. Model simulations of I based on random mating (Imin) and maximum mate monopolization (Imax) demonstrated that the potential for sexual selection was close to its theoretical maximum across the range of OSRs. However, male density and its interaction with the OSR did not affect sexual selection. We argue that a multifaceted approach, combining mating behavior and selection analyses, can help us to understand how ecological factors affect sexual selection.

操作性别比（operational sex ratio, OSR）与种群密度，被视为影响性选择强度的关键驱动因素。尽管已有越来越多的研究证实OSR与种群密度会影响性选择的潜在可能性，但鲜有研究探讨这一效应是否能在表型性选择中得以体现，以及二者的交互作用模式。我们在36个具父本抚育（paternal care）行为的双斑栉眼虾虎（Gobiusculus flavescens）实验繁殖种群中，操控了OSR（设置3个梯度水平）与雄性密度（设置2个梯度水平）。我们测定了雄性个体的交配竞争行为、选择机会（opportunity for selection, I），以及4项形态性状所受的选择压力。研究结果显示，雄性的2项形态性状受到性选择，其中最强的选择强度可达选择机会（I）的20%。正如OSR理论的预测，雌性稀缺程度的提升会加剧雄性的竞争烈度，同时伴随选择机会（I）与雄性形态性状所受选择压力的升高。基于随机交配（I_min）与最大配偶垄断（I_max）的选择机会模型模拟结果显示，在所有OSR梯度范围内，性选择的潜在可能性均接近理论最大值。然而，雄性密度及其与OSR的交互作用，并未对性选择产生显著影响。我们认为，结合交配行为观测与选择分析的多维度研究框架，有助于我们厘清生态因子如何调控性选择的作用过程。