Data from: The effect of trait type and strength of selection on heritability and evolvability in an island bird population

The heritability (h2) of fitness traits is often low. Although this has been attributed to directional selection having eroded genetic variation in direct proportion to the strength of selection, heritability does not necessarily reflect a trait's additive genetic variance and evolutionary potential (“evolvability”). Recent studies suggest that the low h2 of fitness traits in wild populations is caused not by a paucity of additive genetic variance (VA) but by greater environmental or nonadditive genetic variance (VR). We examined the relationship between h2 and variance-standardized selection intensities (i or βσ), and between evolvability (IA:VA divided by squared phenotypic trait mean) and mean-standardized selection gradients (βμ). Using 24 years of data from an island population of Savannah sparrows, we show that, across diverse traits, h2 declines with the strength of selection, whereas IA and IR (VR divided by squared trait mean) are independent of the strength of selection. Within trait types (morphological, reproductive, life-history), h2, IA, and IR are all independent of the strength of selection. This indicates that certain traits have low heritability because of increased residual variance due to the age at which they are expressed or the multiple factors influencing their expression, rather than their association with fitness.

适合度性状的遗传力（heritability, h²）通常较低。尽管此前将这一现象归因于定向选择会按照选择强度的比例侵蚀遗传变异，但遗传力并不一定能反映某一性状的加性遗传方差与进化潜力，即可进化性（evolvability）。近期研究表明，野生种群中适合度性状的低h²并非源于加性遗传方差（additive genetic variance, VA）的匮乏，而是源自更大的环境或非加性遗传方差（environmental or nonadditive genetic variance, VR）。我们依托某海岛上草原麻雀（Savannah sparrow）种群长达24年的监测数据，探究了h²与方差标准化选择强度（i或β_σ）之间的关联，以及可进化性（I_A：VA除以表型性状均值的平方）与均值标准化选择梯度（β_μ）之间的关联。结果显示，在多种性状中，h²随选择强度的增强而降低，而I_A与I_R（VR除以性状均值的平方）则与选择强度无关。在同一性状类别，即形态性状、繁殖性状、生活史性状内，h²、I_A以及I_R均与选择强度无显著关联。这表明，部分性状之所以遗传力较低，并非因其与适合度相关，而是由于其表达时的年龄或影响其表达的多重因素所导致的剩余方差升高。