Data from: Among-strain consistency in the pace and shape of senescence in duckweed

1.Comparative studies have demonstrated extensive variation in age-trajectories of mortality and fecundity, both within and among species, with many taxa exhibiting a general pattern of age-related demographic decline referred to as senescence. Whereas a considerable body of theory is devoted to explaining the origin and persistence of senescence, the evolutionary forces underlying variation in demographic trajectories more generally remain poorly understood.

2.Studying variation in demographic trajectories is complicated by the fact that different species (or even different populations of a given species) may live and reproduce on different time scales, which, for comparative purposes, can make it challenging to disentangle patterns of age-related demographic change (the shape of demographic age trajectories) from the time scale on which those changes happen (the pace of demographic age trajectories).

3.Here we examine variation in the pace and shape of demographic trajectories among strains of the aquatic plant Lemna turionifera Landolt from 24 sites across Alberta, Canada. Our main objectives were to describe the shape of demographic trajectories in L. turionifera, and test for among-strain variation in pace and shape. We also tested whether potential variation in pace and shape is (i) constrained by tradeoffs with other life history traits, and (ii) consistent with local adaptation to environmental characteristics at the sites of strain origin.

4.The strains we examined were overwhelmingly subject to age-related increases in mortality and declines in fecundity, with increases in mortality tending to decelerate and plateau at advanced ages. Despite substantial among-strain variation in cumulative fecundity and plant size, measures of pace and shape did not in themselves vary significantly among strains. Both within and among strains, we observed a negative relationship between plant size and the shape of fecundity trajectories, but we found no other evidence for life history tradeoffs involving pace or shape, nor for local adaptation.

5.Synthesis. Angiosperms display remarkable demographic variation. Our results suggest that the pace and shape of demographic trajectories are highly conserved within one particular angiosperm species (L. turionifera), despite substantial among-strain variation in other life history traits.

1. 比较研究已证实，物种内部及跨物种的死亡率与繁殖力的年龄轨迹存在广泛变异，诸多类群呈现出与年龄相关的种群统计学衰退的通用模式，即衰老（senescence）。尽管已有大量理论致力于解释衰老的起源与维持机制，但总体而言，驱动种群统计学轨迹变异的进化力量仍远未得到充分阐明。
2. 研究种群统计学轨迹的变异面临一项核心挑战：不同物种（乃至同一物种的不同种群）的生存与繁殖时间尺度存在差异，这使得比较研究中难以将与年龄相关的种群统计学变化模式（即种群年龄轨迹的形状）与这些变化发生的时间尺度（即种群年龄轨迹的速率）区分开来。
3. 本研究针对加拿大阿尔伯塔省24个采样点的块根浮萍（Lemna turionifera Landolt）品系，分析其种群统计学轨迹的速率与形状变异。本研究的主要目标为：描述L. turionifera的种群统计学轨迹形状，并检验不同品系间的速率与形状是否存在变异。此外，我们还验证了两点假设：一是速率与形状的潜在变异是否受到与其他生活史性状权衡的约束，二是该变异是否与品系来源地的环境特征的本地适应相一致。
4. 本研究所涉及的品系几乎均呈现出与年龄相关的死亡率上升与繁殖力下降的模式，且死亡率的增长会随年龄增加逐渐放缓并趋于平稳。尽管不同品系的累积繁殖力与植株大小存在显著变异，但种群统计学轨迹的速率与形状指标本身在品系间并无显著差异。无论是在品系内部还是品系之间，我们均观测到植株大小与繁殖力轨迹的形状呈负相关关系，但未发现其他涉及速率或形状的生活史性状权衡的证据，也未找到本地适应的相关支撑。
5. 总结。被子植物展现出显著的种群统计学变异。本研究结果表明，尽管某一特定被子植物物种（L. turionifera）的其他生活史性状存在显著的品系间变异，但其种群统计学轨迹的速率与形状具有高度保守性。