Correlations between early- and late-life performance are a major prediction of life-history theory. Negative early-late correlations can emerge because biological processes are optimized for early but not late life (e.g., rapid development may accelerate the onset of senescence; "developmental theory of ageing") or because allocation to early life performance comes at a cost in terms of late-life performance (as in the disposable soma theory). But, variation in genetic and environmental challenges that each individual has to cope with during early life may also lead to positive early-late life-history trait correlations (the "fixed heterogeneity" or "individual quality" hypothesis). We analyzed individual life-history trajectories of 7,420 known-age female southern elephant seals (Mirounga leonina) monitored over 36 years to determine how actuarial senescence (a proxy for late-life performance) correlate with age at first reproduction (a proxy for early-life performance). As some breeding events may not be detected in this field study, we used a custom "multievent" hierarchical model to estimate the age at first reproduction and correlate it to other life-history traits. The probability of first reproduction was 0.34 at age 3, with most females breeding for the first time at age 4, and comparatively few at older ages. Females with an early age of first reproduction outperformed delayed breeders in all aspects we considered (survival, rate of senescence, net reproductive output) but one: early breeders appeared to have an onset of actuarial senescence one year earlier compared to late breeders. Genetics and environmental conditions during early-life likely explain the positive correlation between early- and late-life performance. Our results provide the first evidence of actuarial senescence in female southern elephant seals.

中文翻译：

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象海豹早晚生活史特征的正相关性

早年和晚年表现之间的相关性是生活史理论的主要预测。可能会出现负早晚相关性，因为生物过程针对早期而非晚期进行了优化（例如，快速发育可能会加速衰老的开始；“衰老的发展理论”），或者因为分配给早期的生活表现是有代价的晚年表现（如在一次性躯体理论中）。但是，每个人在生命早期必须应对的遗传和环境挑战的变化也可能导致生命早期-晚期生命史特征的正相关（“固定异质性”或“个体质量”假设）。我们分析了 7 个人的生活史轨迹，对 420 只已知年龄的雌性南象海豹 (Mirounga leonina) 进行了 36 年的监测，以确定精算衰老（晚年表现的代表）与首次繁殖年龄（早年表现的代表）之间的相关性。由于在本实地研究中可能无法检测到某些繁殖事件，我们使用自定义的“多事件”层次模型来估计首次繁殖的年龄并将其与其他生活史特征相关联。第一次繁殖的概率在 3 岁时为 0.34，大多数女性在 4 岁时第一次繁殖，而在较大年龄时则相对较少。在我们考虑的所有方面（存活率、衰老率、净繁殖产量），第一次繁殖较早的雌性都优于延迟繁殖者，但有一个：与晚期育种者相比，早期育种者似乎提前一年开始精算衰老。早年的遗传和环境条件可能解释了早年和晚年表现之间的正相关关系。我们的结果提供了雌性南象海豹精算衰老的第一个证据。