Study system and sampling
Our study focused on viruses infecting natural populations ofPlantago lanceolata in the Ă…land Island, SW of Finland. These
populations have been monitored since 1993, and they form a highly
fragmented network of ~4000 populations (Ojanen et
al. 2013). We used a stratification process to select 20 focal
populations that were sampled in early June 2017 for their virus
communities. We collected leaf samples from 20 randomly selected plants
in each population, resulting in altogether 400 samples for small RNA
sequencing. For more details on the study system and sampling, see
Supplementary Material and Methods.