Reproductive interference between alien species in Veronica

Abstract Reproductive interference can lead to the exclusive distribution of species. Although interference from alien to native species has been reported, reports on reproductive interference between alien species are scarce. However, because alien species are becoming more abundant, evaluations of reproductive interference between aliens and its influence on community structure are essential. We therefore investigated the presence of interference in two alien species of Veronica, V. cymbalaria and V. persica. Hand-pollination experiments revealed that heterospecific pollen adversely affected both species, but asymmetrically: in V. cymbalaria, it reduced the number of seeds both before and after conspecific pollination, but in V. persica it reduced the number of seeds only when it occurred before conspecific pollination. Field observation showed that the number of seeds produced by V. cymbalaria decreased when the frequency of surrounding V. persica flowers increased. However, this association could be due to the positive effect on seed set of conspecific flowers. Pot experiments showed that the presence of heterospecific individuals did not lead to reductions in the number of seeds in either species. Observations of visiting pollinators revealed no pollinator preference between the plant species. Although we demonstrated asymmetrical reproductive interference between V. cymbalaria and V. persica, its effect in the field seemed limited. An essential factor mitigating the adverse effect of reproductive interference might be a shortage of pollinators that might facilitate interspecific pollination. This issue needs to be further investigated in the future.