Department of Biology, University of Southern Denmark, Campusvej 55, 5230, Odense M, Denmark.
Interdisciplinary Centre on Population Dynamics, University of Southern Denmark, Odense, Denmark.
Oecologia. 2019 Oct;191(2):369-375. doi: 10.1007/s00442-019-04491-0. Epub 2019 Aug 19.
Despite being central concepts for life history theory, little is known about how reproductive effort and costs vary with individual age once plants have started to reproduce. We conducted a 5-year field study and estimated age-dependent reproductive effort for both sexes in the extraordinarily long-lived dioecious plant Borderea pyrenaica. We also evaluated costs of reproduction on vital rates for male and female plants, both by examining effects of differences in individual reproductive effort under natural conditions, and by conducting a flower removal experiment, aimed at decreasing reproductive effort. Reproductive effort was fairly constant and independent of age for males, which may reflect a strategy of adjusting overall reproductive output by spreading reproduction over the life course. Females had a higher total effort, which first increased and then decreased with age. The latter may be a response to an increasing reproductive value-an inverse of a terminal investment-or a sign of reproductive senescence due to an age-related physiological decline. Seed production was lower in plants with higher previous reproductive effort and this effect increased with age. We found no evidence for costs of reproduction on other vital rates for either sex. Experimental flower removal only resulted in progressively more negative effects on flower production in older male plants, whereas female vital rates were unaffected. Overall, this study demonstrates that not only sex, but also age influences resource allocation trade-offs and, thus, plant life history evolution.
尽管繁殖努力和成本随个体年龄变化是生活史理论的核心概念，但对于已经开始繁殖的植物，其繁殖努力和成本如何随个体年龄变化却知之甚少。我们进行了一项为期 5 年的野外研究，估计了雌雄异株的超长寿命植物 Borderea pyrenaica 的性别相关的年龄依赖性繁殖努力。我们还通过研究自然条件下个体繁殖努力的差异对雄性和雌性植物生命率的影响，以及通过进行旨在降低繁殖努力的花朵去除实验，评估了繁殖的成本。雄性的繁殖努力相当稳定且与年龄无关，这可能反映了一种通过在生命过程中分散繁殖来调整整体繁殖输出的策略。雌性的总繁殖努力更高，随着年龄的增长先增加后减少。后者可能是生殖价值增加的反应——生殖投入的倒数——或者是由于与年龄相关的生理衰退导致生殖衰老的迹象。具有较高先前繁殖努力的植物的种子产量较低，这种影响随年龄的增长而增加。我们没有发现繁殖对任何生命率的性别都有成本的证据。实验性的花朵去除仅导致老年雄性植物的花朵产生越来越多的负面影响，而雌性植物的生命率不受影响。总的来说，这项研究表明，不仅性别，而且年龄会影响资源分配的权衡，从而影响植物的生活史进化。
