Data from: Actuarial senescence in a long-lived orchid challenges our current understanding of ageing

The dominant evolutionary theory of actuarial senescence—an increase in death rate with advancing age—is based on the concept of a germ cell line that is separated from the somatic cells early in life. However, such a separation is not clear in all organisms. This has been suggested to explain the paucity of evidence for actuarial senescence in plants. We used a 32 year study of Dactylorhiza lapponica that replaces its organs each growing season, to test whether individuals of this tuberous orchid senesce. We performed a Bayesian survival trajectory analysis accounting for reproductive investment, for individuals under two types of land use, in two climatic regions. The mortality trajectory was best approximated by a Weibull model, showing clear actuarial senescence. Rates of senescence in this model declined with advancing age, but were slightly higher in mown plots and in the more benign climatic region. At older ages, senescence was evident only when accounting for a positive effect of reproductive investment on mortality. Our results demonstrate actuarial senescence as well as a survival–reproduction trade-off in plants, and indicate that environmental context may influence senescence rates. This knowledge is crucial for understanding the evolution of demographic senescence and for models of plant population dynamics.

主流的精算式衰老（actuarial senescence）演化理论——即死亡率随年龄增长而升高的现象——基于生命早期生殖细胞系与体细胞相分离的概念。然而，并非所有生物都存在这类分离现象。这一点被用以解释植物中精算式衰老相关证据匮乏的问题。我们依托一项针对拉普兰手参（Dactylorhiza lapponica）的32年定位研究——该物种在每个生长季都会更替自身器官——来检验这种块茎兰的个体是否会发生衰老。我们针对两种土地利用方式下、两个气候区域内的个体，开展了纳入繁殖投入因素的贝叶斯存活轨迹分析。死亡率轨迹最符合威布尔模型（Weibull model），显示出明确的精算式衰老特征。该模型中的衰老速率随年龄增长而降低，但在刈割样地与气候更温和的区域中，衰老速率略高。在高龄阶段，只有当纳入繁殖投入对死亡率的正向影响时，衰老现象才会显现。我们的研究结果证实了植物中存在精算式衰老以及存活-繁殖权衡，并表明环境背景可能会影响衰老速率。这一认知对于理解种群统计衰老的演化过程以及植物种群动态模型构建均具有关键意义。