Data from: GxG epistasis in growth and condition and the maintenance of genetic polymorphism in Gambusia holbrooki

Theory on indirect genetic effects (IGEs) indicates that variation in the genetic composition of social groups can generate GxG epistasis that may promote the evolution of stable polymorphisms. Using a livebearing fish with a genetic polymorphism in coloration and associated behavioral differences, we tested whether genotypes of social partners interacted with focal individual genotypes to influence growth and condition over 16 weeks of development. We found that IGEs had a significant influence on patterns of feeding, regardless of focal fish genotype. There was no influence of social environment on juvenile length, but there was significant GxG epistasis for body condition. Each focal juvenile was in better condition when its own genotype was not present in adult social partners. These data are consistent with negative frequency-dependent selection in which each morph performs better when it is rare. Neither variation in feeding nor activity-related behaviors explained variation in body condition, suggesting that GxG epistasis for condition was caused by physiological differences between the two genotypes. These findings indicate that GxG epistasis in a given polymorphism can generate selection that contributes to the maintenance of that polymorphism and to maintenance of genetic variation for additional fitness-related traits.

间接遗传效应（indirect genetic effects, IGEs）理论指出，社会群体遗传组成的变异可产生基因型×基因型上位性（GxG epistasis），进而可能促进稳定多态性的演化。本研究以一种兼具体色遗传多态性与相关行为差异的胎生鱼类为实验材料，探究社交伙伴的基因型与焦点个体（focal individual）基因型之间的互作，是否会在16周的发育周期内对焦点个体的生长与身体状况产生影响。研究发现，无论焦点个体自身的基因型如何，间接遗传效应均对摄食行为模式存在显著影响。社交环境对幼体长无显著影响，但对身体状况存在显著的GxG上位性效应。当成年社交伙伴体内不存在焦点幼体自身的基因型时，该幼体的身体状况更佳。该研究数据与负频率依赖选择假说相符，即每一种形态型在种群中处于稀有状态时，其适合度表现更优。无论是摄食行为还是活动相关行为的变异，均无法解释身体状况的差异，这表明躯体状况的GxG上位性效应源于两种基因型间的生理差异。上述研究结果表明，特定多态性下的GxG上位性可产生选择压力，进而有助于维持该多态性，同时也有助于维持其他与适合度相关性状的遗传变异。