ESMfiles_rev.xlsx from Transgenerational non-genetic inheritance has fitness costs and benefits under recurring stress in the clonal duckweed Spirodela polyrhiza

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）被认为在植物生态与进化过程中发挥重要作用，但有关适应性跨代表型可塑性（adaptive transgenerational plasticity）的相关证据仍较为匮乏。本研究以紫背浮萍（Spirodela polyrhiza）为实验材料，探究了重复胁迫条件下过量铜暴露对子代防御能力与适合度（fitness）的影响，实验覆盖多代无性繁殖周期。在过量铜胁迫环境下培养种群规模超过10000个个体的大型单克隆种群（monoclonal populations）至第30代时，短期胁迫会对种群适合度产生负面影响，而长期持续的重复胁迫则未对适合度造成显著影响。这种随时间动态变化的生长速率或受环境诱导的跨代响应调控：当将植株以单株后代的形式在过量铜环境中传代2至10代后，子代适合度会呈现正向、负向或中性的变化趋势，具体变化取决于初始胁迫与后续重复胁迫之间的间隔时长（5至15代）。重复胁迫下的适合度优势与类黄酮积累（flavonoid accumulations）无关，而类黄酮积累则与植株体内铜浓度的改变存在显著关联。过量铜暴露会以基因型特异性（genotype-specific）的方式改变重复胁迫条件下的子代适合度，且增大初始胁迫与后续重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。综上，本研究数据证实了重复胁迫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（clonal plant lineages）的进化轨迹。