Interspecific Pollen Transfer And Asymmetry Of Reproductive Interference Between Sagittaria Trifolia L. And S. Pygmaea L. In Natural Habitats

Closely-related species at sympatry are often at risk of interspecific reproductive interference due to similar reproductive biological characteristics.Interspecific pollen transfer is ubiquitous in plant communities and has long been recognized in the pollination literature as a form of reproductive interference,which plays a central role in angiosperm evolution.For co-flowering species that share pollinators,competition through interspecific pollen transfer can profoundly impact floral evolution,decreasing female fitness via heterospecific pollen deposition on stigmas and male fitness via pollen misplacement during visits to heterospecific flowers.And studies have shown that heterospecific pollen deposition may be the main mechanism of plant reproductive interference,which can waste maternal reproductive investment by causing fertilization failure,developmental defects or production of unfit or sterile offspring,reducing the quantity and quality of progeny,especially for pollen grains of closely related species.It has been reported that the fruits can be formed in hand-pollination hybridization experiments of Sagittaria trifolia L.and S.pygmaea L,but the arrival of interspecific pollen tubes to the ovule is delayed due to different growth routes.Here,we investigated sympatrically growing Sagittaria trifolia L.and S.pygmaea L.populations in natural habitats with overlapping flowering periods and observed the interspecific movement patterns of shared pollinators,using pollen tracers to detect the existence and intensity of interspecific pollen transfer.The existence of reproductive interference and its effect on sexual reproductive fitness were measured by seed set in single/mixed populations of the two species.Results showed that:(1)The main shared pollinators visited flowers of both species,but the frequency of interspecific movements was significantly lower than that of intraspecific movements,and the pollinators showed a preference for male flowers of S.trifolia L..(2)Interspecific pollen transfer by shared pollinators was detected in pistils of both species under natural conditions,and the proportion of stigma with alien pollen grains was only about 1.4%.The pollen of S.trifolia L.was carried further and in greater quantity to the flowers of S.pygmaea L.,while the pollen of S.pygmaea L.was mainly transferred in short distances.(3)When the two species coexisted in natural habitat,the proportion of undeveloped seeds of S.pygmaea L.increased significantly,while the proportion of developed seeds of S.trifolia L.remained above 80%,indicating the asymmetry of interspecific reproductive interference.The study investigated the reproductive interference intensity and avoidance mechanism between the coexisting Sagittaria trifolia L.and S.pygmaea L.in natural habitats.The results demonstrate that plant-pollinator interaction plays an important role in reducing interspecific reproductive interference and contains universal ecological significance.The sexual reproduction success of S.pygmaea L.in natural habitats depends on a trade-off of multiple factors,with pollinator-mediated facilitation alleviating pollen limitation in sparsely flowering plants.The ecological and physiological mechanisms between Sagittaria trifolia L.and S.pygmaea L.above provide a new perspective for understanding the sympatric coexistence of related plant species at risk of reproductive interference in the wild.