LongTermPretreat_broad.csv from Transgenerational non-genetic inheritance has fitness costs and benefits under recurring stress in the clonal duckweed <i>Spirodela polyrhiza</i>

Although non-genetic inheritance is thought to play an important role in plant ecology and evolution, evidence for adaptive transgenerational plasticity is scarce. Here, we investigated the consequences of copper excess on offspring defences and fitness under recurring stress in the duckweed Spirodela polyrhiza across multiple asexual generations. Growing large monoclonal populations (greater than 10 000 individuals) for 30 generations under copper excess had negative fitness effects after short and no fitness effect after prolonged growth under recurring stress. These time-dependent growth rates were likely influenced by environment-induced transgenerational responses, as propagating plants as single descendants for 2 to 10 generations under copper excess had positive, negative or neutral effects on offspring fitness depending on the interval between initial and recurring stress (5 to 15 generations). Fitness benefits under recurring stress were independent of flavonoid accumulations, which in turn were associated with altered plant copper concentrations. Copper excess modified offspring fitness under recurring stress in a genotype-specific manner, and increasing the interval between initial and recurring stress reversed these genotype-specific fitness effects. Taken together, these data demonstrate time- and genotype-dependent adaptive and non-adaptive transgenerational responses under recurring stress, which suggests that non-genetic inheritance alters the evolutionary trajectory of clonal plant lineages in fluctuating environments.尽管非基因遗传（non-genetic inheritance）被认为在植物生态学与进化领域扮演关键角色，但有关适应性跨代可塑性（adaptive transgenerational plasticity）的实证证据仍较为稀缺。本研究以多根紫背浮萍（Spirodela polyrhiza）为实验材料，探究了胁迫反复出现的场景下，铜过量暴露对其后代防御能力与进化适合度的影响，实验覆盖多个无性世代。在铜过量胁迫环境中培养个体数逾10000的大型单克隆种群长达30个世代后，短期胁迫会对种群适合度产生负面效应，而长期持续的反复胁迫则未对适合度造成显著影响。这类随时间变化的生长速率特征，大概率受环境诱导的跨代响应调控：当在铜过量环境下以单株后代为繁殖单元传代2至10个世代时，后代适合度会呈现正向、负向或中性的变化趋势，具体取决于初始胁迫与后续反复胁迫之间的间隔时长（5至15个世代）。反复胁迫下的适合度获益与黄酮类（flavonoid）物质的积累并无关联，但黄酮类积累水平与植物体内铜浓度的改变存在显著关联。铜过量胁迫会以基因型特异性的方式，改变反复胁迫环境下的后代适合度；且增大初始胁迫与反复胁迫的间隔时长，会逆转这类基因型特异性的适合度效应。综合以上结果，本研究数据证实了反复胁迫环境下存在时间与基因型依赖性的适应性与非适应性跨代响应，这表明非基因遗传会改变波动环境中克隆植物谱系的进化轨迹。