Mechanisms promoting outcrossing in plants include self-incompatibility, unisexuality (dioecy), dichogamy (temporal separation of sexual expression) and herkogamy (spatial separation of sexual expression); however, these mechanisms differ in effectiveness. The most successful forms for outcrossing are self-incompatibility and dioecy. Self-incompatibility is considered the most common reproductive form in neotropical plant communitiesand it is frequently associated with perennial or arborescent life forms. On the contrary, self-compatible species are herbaceous species frequently associated with early successional ecosystems or disturbed areas where pollinator fauna is scarce and/or inefficient. Dichogamy and herkogamy are widespread in outcrossing angiosperms and play a vital role in the successful functioning of blossom. Through these mechanisms, pollen–stigma interference is avoided, self-fertilization is reduced, and cross-pollination is promoted due to the non-simultaneous presentation of pollen and stigma. Studies addressing breeding systems, sexual systems, dichogamy and herkogamy in heterogeneous vegetation, including disturbance, situated in the same geographic areas allow fair comparisons between plant communities.
In a study recently published in AoBP, Ramírez & Hokche evaluated breeding system, sexual system, dichogamy and herkogamy of seven herbaceous-shrubby communities from the Gran Sabana Plateau, Venezuela. The analysis was conducted considering the life form, substrate type, succulence, carbon metabolism, nutritional relation, successional stage, pollination system specificity and endemism of plant species. Of the 348 plant species studied, 73.8 % were hermaphrodite, 16.9 % were monoecious and 9.2 % were dioecious. The communities studied displayed diverse mating strategies associated to life forms, pollination system specificity, successional stage, endemism, vegetation structure and community isolation. High levels of outbreeding strategies (dioecy, monoecy, non-agamospermy, non-spontaneous self-pollination, xenogamy, and partial self-incompatibility) occurred mainly in woody species from shrublands and secondary bushland. Inbreeding strategies (non-herkogamy, spontaneous self-pollination and partial cross-incompatibility) were primarily associated to herbaceous life forms from disturbed communities. The authors discuss these results in detail in the context of evolutionary and ecological trends.
Ramírez, N., & Hokche, O. (2019). Outbreeding and inbreeding strategies in herbaceous-shrubby communities in the Venezuelan Gran Sabana Plateau. AoB PLANTS, 11(4). https://doi.org/10.1093/aobpla/plz032