Data from: Offspring fitness and the optimal propagule size in a fluctuating environment

Propagule size is an important maternal effect on offspring fitness and phenotype in birds and other oviparous animals. The performance of propagules often increases with size, but a fluctuating environment may introduce temporal variation in the optimal phenotype. Understanding these mechanisms will provide novel insights into the eco-evolutionary dynamics of life history strategies in parental reproductive investment. We investigated the interaction between propagule size (measured as egg volume) and environmental conditions on offspring mortality and phenotype in a Norwegian house sparrow population. Increased propagule size reduced offspring mortality in early life, with more pronounced effects under heavy precipitation. However, the optimal propagule size for low offspring mortality until recruitment shifted from large to small as temperature increased. Propagule size had no significant effect on fledgling body mass and tarsus length. These results reveal a potential for eco-evolutionary dynamics in propagule size, as populations adapt to fluctuating environmental conditions. The ultimate outcome of this dynamic process will also depend on variation in parental fitness and trade-offs with other life-history traits, particularly clutch size.

繁殖体大小（propagule size）是鸟类及其他卵生动物中影响子代适合度（offspring fitness）与表型的重要母体效应（maternal effect）。繁殖体的性能通常随其体积增大而提升，但波动的环境可能会使最优表型出现时间上的变异。明晰这类机制，将为亲本繁殖投入相关生活史策略（life history strategies）的生态-进化动态（eco-evolutionary dynamics）提供全新的研究视角。本研究针对挪威家麻雀种群，探究了以卵体积（egg volume）为衡量指标的繁殖体大小与环境条件对子代死亡率（offspring mortality）及表型的交互作用。更大的繁殖体大小可降低子代早期死亡率，且在强降水环境下的效应更为显著。然而，随着气温升高，直至幼鸟完成种群补充（recruitment）前，维持低子代死亡率的最优繁殖体大小会从较大值逐渐转为较小值。繁殖体大小对出飞雏鸟（fledgling）的体重及跗跖长度（tarsus length）无显著影响。上述结果表明，当种群适应波动的环境条件时，繁殖体大小存在产生生态-进化动态的潜在可能。这一动态过程的最终结局，还将取决于亲本适合度（parental fitness）的变异，以及与其他生活史特征（life-history traits）之间的权衡关系（trade-offs），尤其是窝卵数（clutch size）。