Actuarial senescence progresses similarly across sites and species in four boreal orchids

Whole-plant senescence, defined as a decrease in individual fitness as an
organism grows older, has often been assumed to not occur in plants;
however, it has now been detected in a range of plant taxa. Still,
reported senescence patterns vary substantially, and it remains unknown
how consistent patterns are within phylogenetic groups and how they may be
affected by environmental factors. Plants show a high diversity in
life-history traits within phylogenetic groups and environments, but
shared traits amongst related species are also common, making both diverse
and similar patterns probable.  Here, we explore how mortality
changes with advancing age in four closely related species (Dactylorhiza
incarnata, D. lapponica, D. maculata, and Gymnadenia conopsea) across two
sites in Norway: the coastal Nordmarka and inland Sølendet. Using data
collected over 34 years, following more than 2500 individual plants, we
conduct Bayesian survival trajectory analysis to assess mortality
age-trajectories.  A simple Weibull model, illustrating
increasing mortality at a decelerating rate with age, was the best fit for
all species at both sites. From these models, we calculate rates of
senescence and compare them using Kullback-Leibler divergences, finding no
notable differences in rates between species or sites. Synthesis. Our
findings suggest that actuarial senescence, an increase in mortality with
advancing age, may be common in orchids and show that demographic ageing
can proceed similarly in closely related taxa across different
environments.

整株衰老（Whole-plant senescence）被定义为生物体随年龄增长而出现的个体适合度下降，长期以来被认为不会在植物中发生；然而如今已在多个植物类群中被检测到。不过，已报道的衰老模式差异显著，目前仍不清楚系统发育类群内的模式是否具有一致性，以及环境因素会如何对其产生影响。
植物在系统发育类群与环境背景下展现出极高的生活史特征（life-history traits）多样性，但近缘物种间的共有特征也较为常见，这使得多样化与相似的衰老模式均有可能存在。本研究针对挪威两处样地——沿海的诺德马尔卡（Nordmarka）与内陆的瑟伦德特（Sølendet），探究4个近缘兰科物种（Dactylorhiza incarnata、D. lapponica、D. maculata以及Gymnadenia conopsea）的死亡率随年龄增长的变化规律。
研究依托34余年的监测数据，对超过2500株个体进行长期跟踪，并通过贝叶斯生存轨迹分析（Bayesian survival trajectory analysis）评估死亡率的年龄轨迹。结果显示，能够体现死亡率随年龄增长以减速速率递增的简单威布尔模型（Weibull model），在两处样地的所有物种中均为最优拟合模型。基于上述模型，我们计算了各物种的衰老速率，并通过库尔贝克-莱布勒散度（Kullback-Leibler divergences）进行组间比较，发现不同物种或样地间的衰老速率并无显著差异。
综合分析结果表明：精算衰老（actuarial senescence，即死亡率随年龄增长而上升）在兰科植物中或较为普遍，且近缘类群的种群人口统计学衰老过程在不同环境下可呈现相似的模式。