Biologia floral de Mabea uleana Pax & K. Hoffm. (Euphorbiaceae): diversidade de visitantes florais em uma área de campinarana na Amazônia Central

Abstract

Mabea Aubl. (Euphorbiaceae) is a Neotropical genus with approximately 50 species, with the greatest diversity in the Amazon. Pollination has been investigated in only two species of the genus, M. fistulifera in the state of Minas Gerais, Brazil, and M. occidentalis in Panama. Potential pollinators of these species include insects, birds, cebid monkeys, phyllostomid bats, and marsupials. Here, we studied the floral biology of Mabea uleana, the foraging behavior of floral visitors, and the potential of visitors as pollinators. Data were obtained through direct field observation and collection of inflorescences to infer pollen viability, stigma receptivity, nectar volume, and sugar concentration. Cross-pollination, natural pollination, and self-pollination experiments were performed to investigate the mechanisms of the plant's reproductive system. Floral visitors were observed on three inflorescences of six individuals (N = 18). Each focal inflorescence was monitored for 14 days between 7 am and 6 pm (daytime) and 7 pm and 6 am (nighttime) at 30-minute intervals with one-hour breaks, totaling 252 hours, divided into daytime (126 hours) and nighttime (126 hours). Nectar begins to be secreted during the final opening phase, from 6:00 pm onwards, with an average volume of up to 70 μl per inflorescence. The average sugar concentration in the nectar varied between 4% and 6%. Pollen viability ranged from 85% to 98%, and the stigma was receptive throughout the anthesis period. Floral visitors from the orders Hymenoptera (141 events), Diptera (30), Blattaria (18), Lepidoptera (12), and Orthoptera (3) were observed. The reproductive system is functionally self-incompatible. The frequency and foraging behavior indicate that cockroaches, Diptera, moths, and bees may be important pollinators of Mabea uleana. The cockroaches, both adults and nymphs, had the most contact with the plant's reproductive organs, acting as the main nocturnal pollinators. In addition, diurnal bees were also observed contributing to this process. Moths, dipterans, and occasionally ants contributed complementarily to pollen deposition in the pollination process. M. uleana has an entomophilous pollination syndrome and differs from previously studied species. The study contributed to the knowledge of the floral and reproductive biology of the species, in addition to the diversity of pollinators in the genus.