The evolutionary potential of invasive Carpobrotus (Aizoaceae) taxa: are pollen-mediated gene flow potential and hybrid vigor levels connected?

摘要

Few studies have addressed the importance of native pollinators in shaping the breeding systems and evolutionary potential of invasive plants. We examined the pollination and gamete production of Carpobrotus affine acinaciformis (L.) L. Bol. and C. edulis (L.) N. E. Br. invading the coasts of southeast France (Provence), and found preliminary evidence that the pollen-mediated gene flow potential (PMGFP) within the four studied populations is positively correlated with their Relative Performance in Hybridization indices (RP_H), suggesting a link between pollinator services, gene flow, and Carpobrotus hybridization. Flower density (FD) may be a driver behind pollinator abundance and visitation patterns since it shows a significant, positive relationship with relative pollinator abundance (FR) and a significant negative relationship with per flower visit frequencies (FR/F). In the populations with the highest RP_H indices, and therefore high hybrid vigor, both taxa produce similar quantities of ovules and pollen per flower, whose ratios further indicate (facultative) xenogamy. Pollen diameter distributions include ～25% micro-pollen, and overall viability is less than one half. Viable pollen profiles consist of 3.5% micro, 85.5% normal and 10.9% macro pollen (considered as diplogametes) on average per flower for C. affine acinaciformis, and 0.7% micro, 73.0% normal and 26.2% macro pollen for C. edulis. Given the co-occurrence of (1) (facultative) xenogamic breeding strategies, (2) a significant, positive relationship between RP_H and PMGFP, and (3) frequent pollen abnormalities, it is probable that hybrid dysgenesis mediated by the local pollinators occurs in these populations. Furthermore, the unusually high frequency of potentially viable, diploid macro-pollen underlines the evolutionary/polyploid potential of these invasive, introgressed populations. Native pollinator interactions may greatly affect the taxonomic status and evolutionary potential of invasive plant complexes.