Data for "Repeatability of an extended phenotype: potential causes and consequences of nest variation in Northern House Wrens (Troglodytes aedon)"

Construction behavior is an aspect of the extended phenotype that allows organisms to build structures that alter their environments in potentially beneficial ways. Although individuals vary in the expression of this extended phenotype (e.g., structure morphology), the repeatability of construction behaviors remains understudied, especially among free-living populations. Many oviparous taxa construct nests, making them of particular interest because variation in nest architecture may directly affect fitness. Using a free-living, cavity-nesting songbird, the Northern House Wren (Troglodytes aedon), as our model, we estimated the contribution of the primary builder (the female) to nest variability by measuring the repeatability of nest morphology between successive clutches. We further examined whether nest morphology was related to the dimensions of the nesting cavity, breeding date, or nest success. We found the composition of the cup lining to be a highly repeatable feature of the nesting female’s nest, although the size and composition of the structural platform appeared more related to the dimensions of the cavity. Nest morphology remained variable throughout the breeding season, showing no significant correlations with breeding date, and it was unrelated to clutch size or offspring survival. Our study suggests that variation in construction behavior is likely the product of multiple factors including the preferences of the builder and physical constraints. The absence of any clear links between construction behavior and fitness indicates that nest morphology is not under strong selection. As a result, diverse female building preferences may explain the extreme among-individual variation in nest structure in this species.

筑巢行为属于扩展表型（extended phenotype）的范畴，该表型可使生物构筑能够潜在改善自身生存环境的结构。尽管不同个体在该扩展表型的表达（如结构形态）上存在差异，但筑巢行为的重复性仍未得到充分研究，在自由生活的种群中更是如此。产卵类群（oviparous taxa）中有诸多类群会构筑巢穴，因此该类群备受关注——因为巢结构的差异可能直接影响个体的适合度（fitness）。我们以自由生活的洞栖鸣禽家鹪鹩（Troglodytes aedon）为研究模型，通过测量其连续繁殖窝次间的巢形态重复性，评估了主要筑巢者（雌性）对巢窝变异的贡献。我们进一步探究了巢形态是否与筑巢洞穴的尺寸、繁殖日期或繁殖成功率相关。研究发现，巢杯内衬的组成是雌性筑巢者巢窝形态的高重复性特征，而结构平台的尺寸与组成则更多与洞穴尺寸相关。整个繁殖季中，巢形态始终存在变异，且与繁殖日期无显著相关性，同时也与窝卵数或后代存活率无关。本研究表明，筑巢行为的变异可能由多种因素共同导致，包括筑巢者的偏好以及物理约束条件。筑巢行为与适合度之间未发现明确关联，这说明巢形态并未受到强烈的选择压力。因此，雌性个体多样化的筑巢偏好或许可以解释该物种巢结构在个体间存在的极端变异现象。