Gender specialization in <Emphasis Type="Italic">Palicourea demissa</Emphasis> (Rubiaceae), a distylous,hummingbird-pollinated treelet |
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Authors: | Hamleth Valois-Cuesta Pascual J Soriano Juan Francisco Ornelas |
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Institution: | 1.Programa de Biología con énfasis en Recursos Naturales, Facultad de Ciencias Básicas,Universidad Tecnológica del Chocó,Quibdó,Colombia;2.Postgrado en Ecología Tropical, Facultad de Ciencias, Instituto de Ciencias Ambientales y Ecológicas,Universidad de Los Andes,Mérida,Venezuela;3.Departamento de Biología Evolutiva,Instituto de Ecología A.C,Xalapa,Mexico |
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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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