Asymmetry in pollen flow promotes gender specialization in morphs of the distylous neotropical herb <Emphasis Type="Italic">Arcytophyllum lavarum</Emphasis> (Rubiaceae) |
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Authors: | Carlos García-Robledo |
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Institution: | (1) Department of Biology, University of Miami, P.O. Box 249118, Coral Gables, FL 33124-0421, USA |
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Abstract: | Distyly is a floral polymorphism, characterized by a reciprocal positioning between stigmas and anthers in different flowers,
where two floral morphs, long-styled (pin) and short-styled (thrum) occur within the population. Distyly is suggested as one
of the routes leading to the evolution of separate sexes in plants. In this evolutionary pathway, pollinators may disrupt
the complementarity of pollen transfer between morphs. Consequently, the floral morphs gradually specialize as either male
or female. A key process required for gender specialization in distylous plants is a deviation of the realized functional
gender (i.e. the proportion of genes transmitted to the next generation via pollen donation and seed production) from the
potential functional gender (i.e. the expected contribution of male and female function to reproductive success from the number
of ovules or pollen grains produced by each morph). I selected the distylous herb Arcytophyllum lavarum (Rubiaceae) to determine if asymmetry in pollen flow promotes differences in seed production, pollen donation and a discrepancy
between the potential and the realized functional genders in pin and thrum floral morphs. Pollen flow in A. lavarum is asymmetric and the pin morph is more efficient at performing cross-pollination than the thrum morph. Conversely, the thrum
morph produced two times more seeds than the pin morph. Male and female contributions to the potential functional gender were
equivalent in both morphs. However, the pin morph transmitted more genes through pollen donation and the thrum morph more
through seed production than expected from their potential functional genders. These results support the hypothesis that if
pollinators consistently promote asymmetric pollen flow between morphs over generations, it is possible that gender specialization
may evolve to the extreme of dioecism from an original distylous condition. |
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Keywords: | Distyly Evolution of sex Gender specialization Páramo Pollen flow |
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