Data from: Strong, nonlinear selection against fluctuating asymmetry in wild populations of a marine fish

Theoretical links between fluctuating asymmetry (FA) and fitness are so compelling that FA is often used as a proxy for fitness. However, studies examining whether FA actually correlates with individual fitness in wild populations are relatively rare and often use simple measures of association (e.g., correlation coefficients). Consequently, the pattern of selection on FA in the wild is seldom clear. We examined selection on FA of pectoral fin morphology in two wild populations of a marine fish (the kelp perch; Brachyistius frenatus). As expected, variance in signed FA in each initial sample was significantly greater than that found in the surviving population, indicating selection against FA. Our estimate of the fitness surface confirmed perfect symmetry as the phenotypic optimum and indicated strong, nonlinear selection against FA. No difference in the form of selection was detected between populations. However, the level of FA in the initial samples varied among populations, leading to an overall difference in the level of selective mortality. Our results suggest that selection on FA in wild populations may be strongly nonlinear, and indicate that the demographic costs of asymmetry may play a substantial role in the dynamics of populations.

波动不对称性（fluctuating asymmetry, FA）与适合度之间的理论关联极具说服力，因此FA常被用作适合度的替代指标。然而，检验FA在野生种群中是否真正与个体适合度相关的研究相对稀少，且此类研究多采用简单的关联分析方法（如相关系数）。正因如此，野生种群中针对FA的选择模式往往难以明晰。本研究针对两个野生海洋鱼类种群——海带鲈（学名：Brachyistius frenatus）的胸鳍形态波动不对称性开展了选择压力分析。正如预期，初始样本中带符号的FA方差显著高于存活种群的方差，表明存在针对FA的选择淘汰。我们对适合度曲面的估算证实，完全对称为表型最优值，并揭示出强烈的非线性选择以淘汰不对称个体。两个种群间的选择模式未检测到显著差异。不过，初始样本中的FA水平存在种群间差异，进而导致选择性死亡率的整体差异。本研究结果提示，野生种群中针对FA的选择可能具有强烈的非线性特征，同时表明不对称性的种群统计成本可能对种群动态发挥重要作用。