Geographic patterns of genetic variation in three genomes of North American diploid strawberries with special reference to Fragaria vesca subsp. bracteata

Geographic patterns of genetic variation in wild species reflect the interplay of ecological and evolutionary processes. We assessed genetic variation in three genomes across four North American diploid strawberry taxa, with special emphasis on the gynodioecious Fragaria vesca subsp. bracteata (A. Heller) Staudt. Specifically, we sequenced one chloroplast (rpoC2) and two mitochondrial (atp8 and atp8-orf225) genes along with several nuclear microsatellite markers. In addition, we assessed indicators of breeding system (pollen viability and female frequency) for all taxa. The geographic perspective on the distribution of cytoplasmic and nuclear variation revealed the genetic affiliation of the restricted taxa (Fragaria vesca subsp. californica (Cham. & Schltdl.) Staudt and Fragaria mexicana Schltdl.) with the widespread F. vesca subsp. bracteata and identified a hotspot of hybridization within gynodioecious F. vesca subsp. bracteata. Higher pollen viability of hermaphrodites was found in the three hermaphroditic taxa relative to the gynodioecious one. Although theoretically predicted to be associated, the proportion of females within F. vesca subsp. bracteata populations was not correlated with population-level genetic variation, suggesting that the history of hybridization or population size variation is more influential on the distribution of genetic variation than sex ratio in this gynodioecious species. The documented patterns of genetic variation in this complex serve as an important point of reference for future ecological and evolutionary research in diploid Fragaria.