So close, so far: spatial genetic structure and mating system in Petunia exserta, an endemic from a peculiar landscape in the Brazilian Pampa grasslands

Abstract Gene flow via seed or pollen dispersal is fundamental for establishing population diversity and structure of plants, especially in naturally fragmented environments. Petunia exserta (Solanaceae) is endemic to small shelters in rocky towers in the Brazilian Pampa grassland, an ancient and isolated region. The landscape is a long-term fragmented habitat, and ecological conditions inside the shelters constitute an inhospitable environment for other Petunia spp., which usually inhabit open and sunny grasslands. We aimed to evaluate the mating system and gene flow impact on genetic diversity and population structure in P. exserta throughout its geographical range. We used eight microsatellite markers to employ fine-scale genetic structure and paternity analyses in 15 populations, including 361 adults and 244 progeny. Our results showed that P. exserta has low genetic diversity and a homozygous excess compared with its congeners. We identified four genetic clusters that did not reflect the spatial population distribution and a strong genetic structure at the first spatial distance. Pollen and seed dispersal mainly occurred at short distances, and the species has a mixed mating system with high selfing levels. We did not observe recent population reduction, and most population clusters showed a small effective population size. The landscape micro-habitat features contribute to pollen flow that occurs mainly inside shelters through geitonogamy or biparental inbreeding. The self-compatible status of P. exserta and related lineages could be important in the colonization of a new environment for the genus.