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）理应具有层级结构，因为差异产生于物种间、种内个体之间，而对于易变表型（labile phenotypes）而言，个体内部在不同情境下同样会存在差异。个体内部方差的成因可分为两类：一是对可变环境的响应（即表型可塑性），二是方差本身会对适合度产生影响。若要使后者（即方差本身具备适合度后果的情况）发生演化，则要求个体内部方差在个体间存在差异。
本研究针对雌性红翅黑鹂（Agelaius phoeniceus）的育幼行为展开调查，旨在评估个体内部方差的分布是否存在个体间差异，抑或随环境条件发生变化。我们采用了一种可同时对均值与方差进行迭代建模的统计分析方法。
结果表明，每次喂食探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 vs 领地外）的显著影响。此外，在控制均值效应后，个体内部不可解释方差（残差方差，residual variance）会随雏鸟日龄独立降低，且当雌性于其配偶领地外觅食时，该残差方差水平更低。进一步研究发现，雌性个体间的残差方差差异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先决条件。就育雏这一育幼行为形式而言，本研究数据表明，雌性红翅黑鹂既可以通过选择觅食位置直接调控随机方差，也可以通过合理分配时间间接实现该调控目标。最后，我们结合适应性方差敏感性（adaptive variance sensitivity）对上述模式展开了讨论。