Genetic monitoring of Sherardia arvensis

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.