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

Abstract1.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.
Usage notesRaw data and codeZip archive containing the raw data, R script, and associated materials required to reproduce our analyses.pace-shape-duckeed.zip

摘要
1. 比较研究已证实，不同物种乃至同一物种内部，死亡率与繁殖力的年龄轨迹存在广泛变异，许多类群呈现出与年龄相关的种群统计衰退的普遍模式，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，但更广泛存在的种群动态轨迹变异背后的进化力量，目前仍知之甚少。
2. 研究种群动态轨迹的变异颇具挑战性：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各不相同，若开展比较研究，便难以将与年龄相关的种群统计变化模式（即种群动态轨迹的形态）与其发生变化的时间尺度（即种群动态轨迹的速率）区分开来。
3. 本研究针对来自加拿大阿尔伯塔省24个采样点的水生植物紫背浮萍（Lemna turionifera Landolt）的不同株系，考察了其种群动态轨迹的速率与形态变异。本研究的核心目标为：描述紫背浮萍的种群动态轨迹形态，并检验不同株系间的速率与形态变异。此外，我们还检验了两个潜在假设：（i）速率与形态的潜在变异是否受与其他生活史性状间的权衡约束，（ii）该变异是否与株系来源地的环境特征所驱动的本地适应相一致。
4. 本研究所考察的株系普遍呈现出死亡率随年龄升高、繁殖力随年龄降低的模式，且死亡率的上升趋势在高龄阶段趋于减缓并趋于平稳。尽管不同株系的累积繁殖力与植株大小存在显著变异，但种群动态轨迹的速率与形态指标本身并未在株系间呈现显著差异。在株系内部及株系之间，我们均观测到植株大小与繁殖力轨迹形态之间存在负相关关系，但未发现其他涉及速率或形态的生活史权衡证据，也未发现本地适应的相关证据。
5. 总结。被子植物（Angiosperms）展现出显著的种群统计变异。本研究结果表明，尽管紫背浮萍的其他生活史性状存在显著的株系间变异，但其种群动态轨迹的速率与形态在该物种内部高度保守。

使用说明
原始数据与代码
包含可复现本研究分析所需的原始数据、R脚本及相关材料的压缩归档文件：pace-shape-duckeed.zip