Data from: Phenotypic integration in an extended phenotype: among‐individual variation in nest‐building traits of the alfalfa leafcutting bee (Megachile rotundata)

Structures such as nests and burrows are an essential component of many organisms’ life-cycle and requires a complex sequence of behaviors. Because behaviors can vary consistently among individuals and be correlated with one another, we hypothesized that these structures would 1) show evidence of among-individual variation, 2) be organized into distinct functional modules, and 3) show evidence of trade-offs among functional modules due to limits on energy budgets. We tested these hypotheses using the alfalfa leafcutting bee, Megachile rotundata, a solitary bee and important crop pollinator. M. rotundata constructs complex nests by gathering leaf materials to form a linear series of cells in pre-existing cavities. In this study, we examined variation in the following nest construction traits: reproduction (number of cells per nest and nest length), nest protection (cap length and number of leaves per cap), cell construction (cell size and number of leaves per cell), and cell provisioning (cell mass) from 60 nests. We found a general decline in investment in cell construction and provisioning with each new cell built. In addition, we found evidence for both repeatability and plasticity in cell provisioning with little evidence for trade-offs among traits. Instead, most traits were positively, albeit weakly, correlated (r ~ 0.15), and traits were loosely organized into covarying modules. Our results show that individual differences in nest construction are detectable at a level similar to that of other behavioral traits and that these traits are only weakly integrated. This suggests that nest components are capable of independent evolutionary trajectories.诸如巢穴与洞穴这类生物构筑结构，是诸多生物体生命周期中不可或缺的组成部分，且需要一系列复杂的行为序列方可完成构筑。由于行为在个体间存在稳定的差异且彼此相互关联，我们据此提出三项假设：其一，这类结构会展现出个体间变异的特征；其二，可被组织为不同的功能模块（functional modules）；其三，受限于能量预算，功能模块间会呈现出权衡（trade-offs）关系。我们以苜蓿切叶蜂（Megachile rotundata）——一种独居蜂与重要的作物传粉昆虫——为研究对象，对上述假设进行了验证。该蜂会通过采集叶片材料，在预先存在的空腔中构筑出一系列线性排列的蜂房，以此构建复杂的巢穴。本研究共分析了60个巢穴的筑巢性状变异，涵盖四类性状：繁殖相关性状（每巢蜂房数量与巢长）、巢穴防护性状（蜂房盖长度与每盖所用叶片数）、蜂房构建性状（蜂房尺寸与每蜂房所用叶片数）以及蜂房饲喂性状（蜂房质量）。我们发现，随着每一个新蜂房的构筑，个体在蜂房构建与饲喂上的投入整体呈下降趋势。此外，我们在蜂房饲喂性状中发现了可重复性与可塑性的相关证据，但几乎未发现性状间存在权衡关系的佐证。与之相反，绝大多数性状间呈微弱的正相关（相关系数r ≈ 0.15），且性状松散地整合为共变模块。我们的研究结果表明，筑巢行为的个体差异可被有效检测，其检测水平与其他行为性状相当，且这些性状仅存在微弱的整合性。这意味着巢穴的不同组成部分具备独立的演化路径。