Data from: Lifespan and reproductive cost explain interspecific variation in the optimal onset of reproduction

Fitness can be profoundly influenced by the age at first reproduction (AFR), but to date the AFR-fitness relationship only has been investigated intraspecifically. Here we investigated the relationship between AFR and average lifetime reproductive success (LRS) across 34 bird species. We assessed differences in the deviation of the Optimal AFR (i.e., the species-specific AFR associated with the highest LRS) from the age at sexual maturity, considering potential effects of life-history as well as social and ecological factors. Most individuals adopted the species-specific Optimal AFR and both the mean and Optimal AFR of species correlated positively with lifespan. Interspecific deviations of the Optimal AFR were associated with indices reflecting a change in LRS or survival as a function of AFR: a delayed AFR was beneficial in species where early AFR was associated with a decrease in subsequent survival or reproductive output. Overall, our results suggest that a delayed onset of reproduction beyond maturity is an optimal strategy explained by a long lifespan and costs of early reproduction. By providing the first empirical confirmations of key predictions of life-history theory across species, this study contributes to a better understanding of life-history evolution.适合度（fitness）会受到首次繁殖年龄（Age at First Reproduction, AFR）的深刻影响，但截至目前，仅在种内层面开展了首次繁殖年龄与适合度之间的关系研究。本研究针对34种鸟类，探究了首次繁殖年龄与终身平均繁殖成功率（Lifetime Reproductive Success, LRS）之间的关联。本研究评估了最优首次繁殖年龄（即与最高终身平均繁殖成功率对应的物种特异性首次繁殖年龄）与性成熟年龄之间的偏差差异，并考量了生活史、社会及生态因素的潜在效应。多数个体采用了该物种的最优首次繁殖年龄，且物种的平均首次繁殖年龄与最优首次繁殖年龄均与寿命呈正相关。最优首次繁殖年龄的种间偏差，与反映终身平均繁殖成功率或存活率随首次繁殖年龄变化的指标相关：在早期首次繁殖年龄与后续生存或繁殖产出下降相关的物种中，推迟首次繁殖年龄是有利的。总体而言，本研究结果表明，突破性成熟阶段推迟繁殖，是由长寿命与早期繁殖成本所支撑的最优策略。本研究首次在跨物种层面验证了生活史理论的核心预测，为深化对生活史演化的理解提供了实证支撑。