Two-Way but Asymmetrical Reproductive Interference between an Invasive <i>Veronica</i> Species and a Native Congener

Abstract

Recent studies have suggested that reproductive interference, a deleterious interspecific interaction in the mating process, plays an important role in biological invasions. In the system of plant species, however, the border with the pollen limitation has often been vague in past studies. This study, using field and laboratory experiments and field observations, examined the reproductive success of an endangered native herbaceous plant, Veronica polita lilacina, in the context of the reproductive interference by the alien congener, V. persica. The auto-pollination experiment confirmed that both species can usually produce seeds even without external conspecific pollens. Results of the artificial pollination experiment demonstrated that pollination with the heterospecific pollens significantly decreases the number of seeds in the native species, but not in the alien species. A transplant experiment revealed that the coexistence with the alien species reduced the fruiting success of the native species. Field observations have shown the interaction between two species in the native patch with only one intruding alien species. They demonstrated that native individuals placed closer to the alien individual suffered a greater decrease in fruiting success and the seed production and that the alien intruder produced no seed. These results demonstrate that species that could reproduce via the auto-pollination suffered the reproductive interference and that the native species also exert the resistive reproductive interference slightly. These interactions can explain the displacement pattern of the native species by the alien congener in Japan.

Island biogeography as a test of reproductive interference

“…In the present study, islands were treated as experimental replicates in which invasions of alien species occurred repeatedly. Results of field surveys of such islands reinforced our hypothesis that the alien V. persica excluded the native congener, V. p. lilacina, although the hypothesis has been suggested strongly by the test of the reproductive interference at the mechanistic level (Takakura 2013).…”

“…They rapidly expanded their ranges (Makino 1907(Makino , 1919. During that range expansion, V. persica probably excluded the native species, V. p. lilacina, from its expanding range via nearly one-sided reproductive interference (Takakura 2013). On the other hand, for other alien species, V. arvensis and V. hederifolia, the exclusive pattern to the native species was not observed in this study.…”

“…Our ISSR-PCR analysis did not support the alternative hypothesis that these ecological differences of V. p. lilacina between the mainland and islands should be ascribed to the phylogenetic differentiation before the alien species invasion: it is more possible that its increasing rarity, altering habitat use, and changing fruit morphology have been triggered by the V. persica invasion. Results of this study and a previous report (Takakura 2013) present the history of the interspecific interaction among Veronica species in Japan during the last century and a half. Two alien species, V. persica and V. arvensis, were introduced to the Japanese mainland in the midnineteenth century.…”

“…In the present day, V. persica is apparent all around Japan (Yamazaki 1981). No direct adverse effect of V. persica on V. p. lilacina had been reported before our previous study (Takakura 2013). Differently from V. p. lilacina, V. persica has not been known as a chasmophyte.…”

“…lilacina (Yamazaki) and an alien species, V. persica Poiret (Takakura 2013). That report explained that the native species suffered the loss of the seed production with the additional deposition of pollens of the alien species, but the alien species suffered little from the native species.…”