Data from: Genetic variation in variability: phenotypic variability of fledging weight and its evolution in a songbird population

Variation in traits is essential for natural selection to operate and genetic and environmental effects can contribute to this phenotypic variation. From domesticated populations, we know that families can differ in their level of within-family variance, which leads to the intriguing situation that within-family variance can be heritable. For offspring traits, such as birth weight, this implies that within-family variance in traits can vary among families and can thus be shaped by natural selection. Empirical evidence for this in wild populations is however lacking. We investigated whether within-family variance in fledging weight is heritable in a wild great tit (Parus major) population and whether these differences are associated with fitness. We found significant evidence for genetic variance in within-family variance. The genetic coefficient of variation (GCV) was 0.18 and 0.25, when considering fledging weight a parental or offspring trait, respectively. We found a significant quadratic relationship between within-family variance and fitness: families with low or high within-family variance had lower fitness than families with intermediate within-family variance. Our results show that within-family variance can respond to selection and provides evidence for stabilizing selection on within-family variance.

性状变异是自然选择发挥作用的必要前提，遗传与环境效应均可促成此类表型变异。现有针对驯化种群的研究表明，不同家系的家系内方差（within-family variance）水平存在差异，这催生了一个引人关注的现象：家系内方差本身可遗传。以出生体重等子代性状为例，这意味着不同家系的性状家系内方差存在差异，因此这类方差可受自然选择塑造。然而，野生种群中该现象的实证证据仍较为匮乏。我们以野生大山雀（Parus major）种群为研究对象，探究了其出飞体重的家系内方差是否可遗传，以及这类方差差异是否与适合度相关。研究发现，家系内方差存在显著的遗传变异：若将出飞体重视作亲本性状或子代性状，遗传变异系数（GCV）分别为0.18与0.25。此外，我们还发现家系内方差与适合度之间存在显著的二次关联：家系内方差处于极低或极高水平的家族，其适合度均低于方差处于中等水平的家族。本研究结果证实，家系内方差可对选择作出响应，同时为家系内方差所受的稳定选择提供了实证依据。