LongTermPre-treatment.R 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中发挥关键作用，但有关适应性跨代可塑性（adaptive transgenerational plasticity）的证据仍较为匮乏。本研究以浮萍物种多根紫萍（Spirodela polyrhiza）为实验材料，探究了铜过量胁迫在多代无性繁殖过程中对子代防御能力与适合度（fitness）的影响。我们在铜过量胁迫环境下培养个体数逾10000的大型单克隆种群（monoclonal populations）达30代，结果显示：短期胁迫后该种群出现适合度负面效应，而经长期周期性胁迫培养后则未出现适合度变化。这种随时间变化的生长特征，大概率受到环境诱导的跨代响应（transgenerational responses）的调控：若将植株以单株后代的形式在铜过量胁迫环境中繁殖2至10代，则子代适合度会呈现正向、负向或中性效应，具体效应取决于初始胁迫与周期性胁迫之间的间隔时长（5至15代）。周期性胁迫下的适合度获益与黄酮类（flavonoid）物质积累无关，但黄酮类积累与植株体内铜浓度的变化存在关联。铜过量胁迫会以基因型特异性的方式，改变周期性胁迫下的子代适合度；且增大初始胁迫与周期性胁迫的间隔时长，会逆转这类基因型特异性的适合度效应。综上，本研究数据证实了周期性胁迫下存在时间与基因型依赖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无性植物谱系（clonal plant lineages）的进化轨迹。