Biologia da polinização e reprodução de especies de Melastomataceae do Parque Nacional da Serra da Canastra (MG) / Pollination and reproductive biology of Melastomataceae from Serra da Canastra National Park (MG, Brazil)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

This study examines the reproductive phenology, pollination ecology, and mating systems of 10 species of Melastomataceae that occur in the Serra da Canastra National Park, Minas Gerais. Seasonality exposes plants to periodic changes in quality and abundance of resources. Flowers of many species can be found throughout the year, but there are well-defined peaks of abundance. There are species with extensive flowering periods throughout the year, but the peaks are short. There are no significant correlations between climatic factors and phenology, which suggests that flowering, may be constrained by phylogeny. Stamens in the two whorls lack a functional distinction, and their arrangement confers radial or zygomorphic symmetry to the flowers. Generally, pollinators are large enough to grasp the stamens and stigma simultaneously before vibrating to collect pollen. Anther dehiscence and stigma receptivity are synchronous, but pollen is released gradually and stigmas remain receptive for an extended period, thereby increasing pollination and fruit-set. Flower color changes with age (senescence) and is not hastened by pollination. There was no production of fruit either by self-pollination or agamospermy. Except for Microlicia viminalis (for which data are insufficient to determine its mating system), all species are self-compatible. High values of viable seeds were obtained from both hand-pollinated flowers and those pollinated under natural conditions. The visiting bees showed morphological and behavioral adaptations to pollinate the flowers of Melastomataceae, except Trigona sp., which did not vibrate, but rather pierced anthers to steal pollen. In general, larger bees are pollinators of large and small flowers, whereas smaller bees pollinate small flowers but rob large flowers of pollen. For all bee species, second visits to the same flower increased fruit-set and seed number. To determine the actual effectiveness of each visitor, it is necessary to measure its efficiency and frequency, as well as its behavior as a pollinator or pollen robber. Three flower morphs occur in Macairea radula, two of which show reciprocal heights of one of the stamen whorls and style. The third morph displays intermediate characteristics. This is the first report of floral heteromorphism in Melastomataceae. The morphs occur in similar frequencies and bees visit them at similar rates. Differential pollen deposition on the bodies of pollinators promotes pollen transfer between morphs, resulting in cross-pollination.

ASSUNTO(S)

pollination heteromorphism buzz pollination reprodução polinização vibratil polinização melastomataceae heteromorfismo

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