Abstract
Distyly has been interpreted as a mechanism that promotes cross-pollination among conspecific plants and as one of the routes leading to the evolution of dioecy. In one of the possible evolutionary pathways, pollinators may disrupt intermorph pollen flow, and, as a consequence, floral morphs may gradually specialize as either male or female (functional dioecy). Natural patterns of pollen deposition and fruit and seed production were estimated in Palicourea demissa (Rubiaceae) and used as parameters to assess functional gender differences between floral morphs. Pollen flow was asymmetrical in P. demissa. Long-styled flowers were more effective than short-styled flowers in pollen deposition towards compatible stigmas, whereas short-styled flowers were more effective in legitimate pollen receipt. Accordingly, short-styled plants produced more fruits and viable seeds than long-styled plants. The contributions of male and female function to the potential functional gender were equivalent in both morphs. However, the realized functional gender deviated significantly from the potential functional gender in both morphs, in which short-styled plants were more successful through their female function, but long-styled plants through their male function. If pollinators disrupt the complementarities of pollen transfer between the two morphs (asymmetric pollen flow), the expression of a more profitable gender is expected in each morph. Thus, our results support the hypothesis that dioecy may evolve in distylous populations through the gradual specialization of each morph as either male or female.
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Acknowledgments
We are grateful to S. Ecce-Homo, Z. Betancourt, C. Rengifo, R. Pacheco, J.H. Castaño, and J. Murillo for assistance during fieldwork. We thank M.E. Naranjo, J. Estrada, C. García, A. Jaramillo, N. Ramírez, Marlies Sazima and two anonymous reviewers for their constructive comments on an earlier draft of the manuscript. This work was funded by the Red Latinoamericana de Botánica (code: RLB06-M03 and RLB08-SP-1 to H.V-C.) and the Consejo de Desarrollo Científico, Humanístico y Tecnológico of the Universidad de Los Andes, Mérida-Venezuela (code: C-1557-08-01EM to H.V-C. and P.S.). Staff from La Mucuy Bird’s Observatory, Sierra Nevada National Park and the Laboratorio de Ecología Animal “A” of the Universidad de Los Andes, Mérida, Venezuela provided logistical support.
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Valois-Cuesta, H., Soriano, P.J. & Ornelas, J.F. Gender specialization in Palicourea demissa (Rubiaceae), a distylous, hummingbird-pollinated treelet. Plant Syst Evol 298, 975–984 (2012). https://doi.org/10.1007/s00606-012-0607-7
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DOI: https://doi.org/10.1007/s00606-012-0607-7