Genetic monitoring of Sherardia arvensis. Genetic monitoring of an endangered arable weed reveals local maintenance of genetic variation in times of land use and climate change

Genetic monitoring is a powerful tool to reveal human impact on genetic variation in times of land use and climate change. Unfortunately, it is rarely applied in nature con-servation at present. Consequently, we conducted a genetic monitoring study of the rare and endangered arable weed Sherardia arvensis, which continuously decreased in the recent decades due to environmental changes. We applied multiplexed ISSR genotyping by sequencing (MIG-seq) to compare genetic variation within and among populations of the species using samples collected at the same sites in 2007 and 2020. In contrast to our expectations, we observed nearly similar levels of genetic variation within and among populations in 2007 and 2020, although 25% of the investigated pop-ulations went extinct in the study period. The observed maintenance of genetic variation may most likely be explained by the lon-gevity of seeds in the soil, which is generally high in many arable weeds. In the case of S. arvensis seeds may persist in the soil for up to 10 years. This allows the regeneration of populations and contributes to the maintenance of genetic variation. A potential im-pact of population loss on genetic variation may therefore be delayed, comparable to the already described phenomenon of an extinction debt in other species. Our study clearly underlines, that long-term genetic monitoring over long time periods is needed to reveal potential changes of genetic variation in the Anthropocene.

遗传监测是揭示土地利用与气候变化时期人类活动对遗传变异影响的有力工具。遗憾的是，目前该方法在自然保护领域鲜有应用。为此，我们针对因环境变化近几十年来种群持续衰退的珍稀濒危农田杂草锡阿德草（Sherardia arvensis）开展了遗传监测研究。我们采用多重简单序列重复区间扩增多态性（Inter-Simple Sequence Repeat, ISSR）测序基因分型技术（Multiplexed ISSR Genotyping by Sequencing, MIG-seq），以2007年与2020年在同一采样点位采集的样本为材料，对比分析该物种种内及种群间的遗传变异水平。与我们的预期相悖的是，尽管研究期间有25%的被调查种群发生灭绝，但2007年与2020年的种群内及种群间遗传变异水平几乎无显著差异。本次观测到的遗传变异维持现象，大概率可通过多数农田杂草普遍具备的土壤种子持久存活能力得到解释。就锡阿德草而言，其种子可在土壤中存活长达10年之久。这使得种群得以自然更新，进而助力遗传变异的维持。因此，种群丧失对遗传变异的潜在影响可能存在滞后性，这与其他物种中已被报道的灭绝债务（extinction debt）现象类似。本研究明确表明，在人类世（Anthropocene）时期，为揭示遗传变异的潜在变化，亟需开展长期的遗传监测工作。