Data from: Multiple aspects of plasticity in clutch size vary among populations of a globally distributed songbird

1. Plasticity in life-history characteristics can influence many ecological and evolutionary phenomena, including how invading organisms cope with novel conditions in new locations or how environmental change affects organisms in native locations. Variation in reaction norm attributes is a critical element to understanding plasticity in life history, yet we know relatively little about the ways in which reaction norms vary within and among populations. 2. We amassed data on clutch size from marked females in eight populations of house sparrows (Passer domesticus) from North America and Europe. We exploited repeated measures of clutch size to assess both the extent of within-individual phenotypic plasticity and among-individual variation and to test alternative hypotheses about the underlying causes of reaction norm shape, particularly the decline in clutch size with date. 3. Across all populations, females of this multibrooded species altered their clutch size with respect to date, attempt order, and the interaction of date and order, producing a reaction norm in multidimensional environmental space. The reaction norm fits that predicted by a model in which optimal clutch size is driven by a decline with date hatched in the ability of offspring to recruit. Our results do not fit those predicted for other proposed causes of a seasonal decline in clutch size. 4. We also found significant differences between populations in response to date and the date by attempt order interaction. We tested the prediction that the relationship with date should be increasingly negative as breeding season becomes shorter but found steeper declines in clutch size with date in populations with longer seasons, contrary to the prediction. Populations also differed in the level of among-individual variation in reaction norm intercept, but we found no evidence of among-individual variation in reaction norm slope. 5. We show that complex reaction norms in life-history characters exhibit within- and among-population variance. The nature of this variance is only partially consistent with current life-history theory and stimulates expansions of such theory to accommodate complexities in adaptive life history.

1. 生活史特征的可塑性可影响诸多生态与进化现象，包括入侵生物如何应对新栖息地的陌生环境，或是环境变化如何影响本土分布的生物。反应规范（reaction norm）属性的变异是理解生活史可塑性的关键要素，但目前我们对种群内部及种群间反应规范的变异方式仍知之甚少。
2. 我们收集了来自北美与欧洲8个家雀（Passer domesticus）种群的标记雌性个体窝卵数数据。我们利用窝卵数的重复测量值，同时评估了个体内表型可塑性的程度与个体间变异，并检验了关于反应规范形状潜在成因的多种备选假说，尤其是窝卵数随繁殖日期下降的成因。
3. 在所有种群中，这种多窝繁殖物种的雌性个体的窝卵数会随繁殖日期、繁殖尝试序次以及二者的交互作用发生改变，从而在多维环境空间中形成反应规范。该反应规范符合下述模型的预测：最优窝卵数由后代种群补充能力随孵化日期下降所驱动。我们的研究结果并不支持其他关于窝卵数季节性下降成因的假说。
4. 我们还发现不同种群在响应繁殖日期以及繁殖日期与尝试序次的交互作用上存在显著差异。我们曾预测，随着繁殖季长度缩短，窝卵数与繁殖日期的负相关关系会愈发强烈，但实际结果却与之相反：在繁殖季更长的种群中，窝卵数随日期下降的幅度更陡。此外，不同种群在反应规范截距的个体间变异水平上存在差异，但我们未发现反应规范斜率存在个体间变异的证据。
5. 我们的研究表明，生活史性状的复杂反应规范存在种群内与种群间的变异。这类变异的特性仅部分符合现有的生活史理论，同时也推动该理论进一步拓展，以适配适应性生活史中的复杂现象。