Data from: Parental behavior exhibits among-individual variance, plasticity and heterogeneous residual variance

Phenotypic variance should have a hierarchical structure because differences arise between species, between individuals within species, and, for labile phenotypes, also within individuals across circumstances. Within-individual variance could exist because of responses to variable environments (plasticity) or because exhibiting variance per se has fitness consequences. To evolve, the latter requires between-individual variance in within-individual variance. Here, we investigate the parental behavior of female red-winged blackbirds (Agelaius phoeniceus) and assess if the distribution of within-individual variance also differs between individuals or changes with respect to environmental conditions. We used a statistical approach that models both the mean and variance iteratively. We found that the amount of food delivered per second on each visit was influenced by female identity, nestling age, and the location (on vs. off territory) where the female foraged. Moreover, we also found that unexplained within-individual variance (residual variance), after controlling for mean effects, independently declined with nestling age and was smaller when females foraged off their mate’s territory. In addition, females differed in residual variance more than expected by chance. These results confirm that phenotypic variance has a hierarchical structure and they support preconditions for the evolution of mean phenotypic values as well as the variance in phenotype. In the case of provisioning as a form of parental care, our data suggest that female red-winged blackbirds could be managing stochastic variance either directly through choice of foraging location or indirectly in how they budget their time, and we discuss these patterns in relation to adaptive variance sensitivity.

表型方差（phenotypic variance）理应具备层级结构，因为差异既存在于物种之间，也存在于同一物种内的不同个体之间；对于易变表型（labile phenotypes）而言，个体内部在不同环境下也会产生差异。个体内方差（within-individual variance）的产生可能源于对可变环境的响应（即表型可塑性，plasticity），或是方差本身便会带来适合度后果（fitness consequences）。若要令“方差本身具备适合度效应”这一性状发生演化，则需要个体内方差在个体间存在差异。本研究针对雌性红翅黑鹂（Agelaius phoeniceus）的亲代行为（parental behavior）展开调查，旨在探究个体内方差的分布是否会因个体而异，或是随环境条件发生变化。我们采用了一种可迭代建模均值与方差的统计方法（statistical approach）。研究结果显示，雌性每次造访时每秒递送的食物量，受到雌性个体身份、雏鸟日龄以及雌性觅食地点（领地内与领地外）的影响。此外，在控制均值效应后，未被解释的个体内残差方差（residual variance）会随雏鸟日龄的增加而独立下降，且当雌性在其配偶的领地之外觅食时，该残差方差更小。同时，雌性个体间的残差方差差异也显著高于随机预期水平。这些结果证实了表型方差具备层级结构，同时为表型均值以及表型方差的演化提供了前提条件。就育雏投喂（provisioning）这一亲代抚育形式而言，我们的数据表明，雌性红翅黑鹂或可通过选择觅食地点直接调控随机方差，或是通过调整时间分配间接实现该调控；最后我们将结合适应性方差敏感性（adaptive variance sensitivity）对这些模式展开讨论。