Abstract

MORALES GUZMAN, Israel; LARA, Carlos  and  CASTILLO-GUEVARA, Citlalli. Differential transport of pollen by hummingbirds in a distylous plant: is not the same short than long bills. Huitzil [online]. 2012, vol.13, n.1, pp.74-86. ISSN 1870-7459.

Distylous populations usually have individuals that produce either flowers with long styles and short stamens (short-styled, Pin) or individuals with short styles and long stamens (short-styled, Thrum). These characteristics promote disassortative pollination assuming reciprocal herkogamy. Nevertheless, it has been suggested that when the visits of pollinators are selective towards some morph, the flow of pollen may be highly asymmetric. Also, the correspondence between stamens and styles of both morphs may not be perfectly reciprocical, and promote a differential reproductive success between morphs, and consequently can lead the species to evolve other reproductive systems such as dioecy. These characteristics make dystylous plants an interesting model to study processes related to the specialization of the sexual functions and to evaluate the role of pollinators in promoting it. Bouvardia ternifolia is a dystylous plant growing in the Malinche, Tlaxcala. Its main visitors are five hummingbird species. In the present study, we evaluated the level of reciprocity of the sexual organs (anthers and styles) of the floral morphs of this plant, and we did qualitative and quantitative tests on the sites of pollen deposition on their hummingbird visitors. We also carried out tests of pollination in both morphs with these hummingbird species, and the production of seeds was quantified. The results showed that the flowers of B. ternifolia are not completely reciprocal in their sexual structures, which can affect the form in which the pollen of both morphs is deposited on the hummingbird visitors. Moreover, we showed that the differential deposition of pollen could be the product of a lack of total reciprocity and of differences in hummingbirds’ bill length. Likewise, the differential transference of pollen seems to have consequences on the reproductive success of the visited morphs.

Keywords : distyly; heterostyly; pollination; reciprocity.

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