Relationship between genetic distances and postzygotic reproductive isolation in diploid Fragaria (Rosaceae)

Studies of reproductive isolation are important for understanding speciation and species delimitation. We studied seven components of reproductive isolation at different taxonomic and geographical levels and their relationship with genetic distance in diploid Fragaria. Isolation was only evident between different taxa at later stages (post F-1 survivorship), and not at the earlier ones of fruit and seed set, F-1 seed germination, and survivorship. Within Fragaria vesca, isolation at the later stages was positively correlated with genetic distance, although this was not found at interspecific levels. The lack of isolation between F. vesca and the other species at the early stages provide the chance for hybrid formation, although high levels of infertility expressed among the offspring can lead to potentially opposing evolutionary outcomes. Within F. vesca, there was evidence of unexpected isolation promoting evolutionary diversification and incipient speciation. Reproductive isolation values between sympatric and allopatric species pairs were similar and indicate a lack of reinforcement in Fragaria. This, combined with the lack of correlation between genetic distance and isolation at interspecific levels, shows that genetic distance is not always proportionally correlated with the degree of isolation in plants and suggests that evolutionary processes may be playing differently in plants compared to animals. (C) 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104, 510-526.