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

Theoretical links between fluctuating asymmetry (FA) and fitness have led many to use FA as a proxy for average fitness. However, studies examining whether asymmetry 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 asymmetry 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 asymmetry. 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 asymmetry 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（fitness）之间的理论关联，促使众多研究者将FA作为平均适合度的替代指标。然而，针对野生种群中不对称性是否确实与个体适合度相关的研究相对较少，且这类研究往往仅采用简单的关联分析方法（如相关系数），因此野外环境中针对不对称性的选择模式往往尚不明确。本研究针对一种海水鱼类——海带鲈（Brachyistius frenatus）的两个野生种群，分析了其胸鳍形态的波动不对称性所受的选择压力。正如预期，初始样本中带符号波动不对称性的方差显著高于存活种群，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，表型最适值为完全对称，并表明存在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差异，然而初始样本中的FA水平存在种群间差异，进而导致选择死亡率的整体水平存在显著不同。本研究结果提示，野生种群中针对不对称性的选择可能具有强烈的非线性特征，同时表明不对称性带来的种群人口统计学成本可能对种群动态发挥重要作用。