Data from: Patterns of age-related change in reproductive effort differ in the pre-natal and post-natal periods in a long-lived mammal

Age-related changes in maternal reproductive allocation for long-lived species are a key prediction from life-history theory. Theoretical and empirical work suggests that allocation may increase with age due to constraint (increases with experience) or restraint (increases with age in the face of declining residual reproductive value), and may decrease among the oldest aged animals due to senescence in reproductive function. Here, we use a hierarchical modelling approach to investigate the age-related patterns of change in maternal reproductive effort in the Weddell seal, a long-lived marine mammal with a protracted period of maternal care during which mothers allocate a large proportion of body mass while feeding little. We find that maternal allocation increases with age for young mothers during both the pre-natal and post-natal periods. In contrast, older mothers demonstrate a senescent decline in pre-natal allocation but allocate more of their declining resources to their offspring during the post-natal period. We also find strong evidence for the importance of individual effects in reproductive allocation among mothers: some mothers consistently produce heavier (or lighter) pups than expected. Our results indicate that maternal allocation changes over a mother's reproductive life span and that age-specific differences differ in notable ways in pre-natal and post-natal periods.长寿物种种群的母体繁殖分配随年龄变化的规律，是生活史理论（life-history theory）的关键预测之一。 理论与实证研究表明，繁殖分配可能因两种机制随年龄增长而提升：一是经验约束效应，即随着个体经验积累而提升；二是繁殖限制效应，即当剩余繁殖价值（residual reproductive value）随年龄下降时，繁殖分配随年龄提升；而在最年长的个体中，由于生殖功能衰老（senescence），繁殖分配则可能出现下降。 本研究采用分层建模（hierarchical modelling）方法，以威德尔海豹（Weddell seal）为研究对象，探究其母体繁殖投入随年龄变化的年龄模式。该物种为长寿海洋哺乳动物，育幼周期漫长，母体在育幼期间几乎不进食，却会将大量体质量分配给后代。 研究结果显示，在产前与产后阶段，年轻母体的繁殖分配均随年龄增长而提升。与之相反，年长母体的产前繁殖分配会因生殖衰老出现下降，但在产后阶段却会将自身不断减少的资源更多地分配给后代。此外，本研究还发现母体间存在显著的个体效应：部分母体产下的幼崽体重始终高于（或低于）预期值。 本研究结果表明，母体繁殖分配会在其整个繁殖生涯中发生动态变化，且产前与产后阶段的年龄特异性繁殖分配模式存在显著差异。