Evidence for asymmetrical hybridization despite pre- and post-pollination reproductive barriers between two Silene species

Co-flowering species may undergo interspecific hybridization if they are closely related and share pollinators. However, a series of reproductive barriers between species can prevent interspecific gene flow, making natural hybridization a transient, rare event. In a recent study published in AoB PLANTS, Zhang et al. evaluated interspecific hybridization and potential isolating barriers between co-flowering Silene asclepiadea and S. yunnanensis in an alpine community in southwest China. Both morphological and molecular data indicated putative natural hybrids between these species, with pollen from S. yunnanensis fertilizing ovules of S. asclepiadae. The authors also found that pollen production and viability were significantly lower in putative hybrids than the parental species. The low fecundity of the hybrids and other reproductive barriers between the two species could contribute to species fidelity.