Darwin’s inflorescence syndrome is indeed associated with bee pollination

STRELIN, M., N.; LEME DA CUNHA, N.; A. RUBINI-PISANO; J. FORNONI; M.A. AIZEN

Plant Reproduction

Springer Science and Business Media Deutschland GmbH

Año: 2023 vol. 37 p. 37 - 45

Plant reproduction is not only determined by flower traits but also by the arrangement of flowers within inflorescences.Based on his observations of the orchid Spiranthes autumnalis, Darwin proposed in 1877 that bee-pollinated plantspresenting protandrous flowers on vertical acropetal inflorescences, where proximal flowers open first, can exploit the stereotypicalforaging behavior of their pollinators (i.e., upward movement through the inflorescence) to promote pollen exportationand reduce self-pollination. In these inflorescences, male-phase flowers lie spatially above female-phase flowers. To examinethis untested hypothesis, we compiled literature information from 718 angiosperms species and evaluated the associationbetween vertical acropetal inflorescences with protandrous flowers and bee pollination within a phylogenetic comparativeframework. Results reveal that this type of inflorescence is indeed more common in species pollinated by bees. Moreover,this association does not seem to be weakened by the presence of alternative self-pollination avoidance mechanisms, likeself-incompatibility, suggesting that this inflorescence type benefits mainly male rather than female fitness. Other inflorescencetypes placing male-phase flowers above female-phase flowers, e.g., vertical basipetal inflorescences with protogynousflowers, do not provide strong evidence of a differential association with pollination by bees. Female-biased nectar productionin vertical acropetal inflorescences with protandrous flowers may reinforce the behavior of bees to fly upwards, renderingDarwin’s configuration more adaptive than other inflorescence configurations.