Data from: Fitness consequences of artificial selection on relative male genital size

Male genitalia often show remarkable differences among related species in size, shape and complexity. Across poeciliid fishes, the elongated fin (gonopodium) that males use to inseminate females ranges from 18 to 53% of body length. Relative genital size therefore varies greatly among species. In contrast, there is often tight within-species allometric scaling, which suggests strong selection against genital–body size combinations that deviate from a species’ natural line of allometry. We tested this constraint by artificially selecting on the allometric intercept, creating lines of males with relatively longer or shorter gonopodia than occur naturally for a given body size in mosquitofish, Gambusia holbrooki. We show that relative genital length is heritable and diverged 7.6–8.9% between our up-selected and down-selected lines, with correlated changes in body shape. However, deviation from the natural line of allometry does not affect male success in assays of attractiveness, swimming performance and, crucially, reproductive success (paternity).雄性外生殖器在近缘物种间往往在尺寸、形态与复杂程度上表现出显著差异。就花鳉科鱼类而言，雄性用于向雌性授精的伸长型鳍肢——生殖足（gonopodium），其长度占体长的比例介于18%至53%之间。因此，不同物种的相对生殖器尺寸差异悬殊。与之相对，同一物种内部通常存在严格的异速生长缩放（allometric scaling）规律，这意味着存在强烈的选择压力，以筛选掉偏离该物种自然异速生长线的生殖器与体型的组合模式。我们通过对异速生长截距实施人工选择，在霍氏食蚊鱼（Gambusia holbrooki）中培育出了相对于给定体型而言，生殖足长度分别长于或短于自然种群的雄性品系，以此检验这一约束效应。研究表明，相对生殖器长度具备可遗传性，正向选择与负向选择品系间的相对生殖足长度分化幅度达7.6%至8.9%，同时伴随体型形状的相关性变化。然而，偏离自然异速生长线并未对雄性的吸引力、游泳表现，以及至关重要的繁殖成功率（父权）产生影响。