The adaptiveness of distyly has been typically investigated in terms of its female function, specifically pollen receipt. However, pollen loads on stigmas can only provide moderate support for Darwin's hypothesis of the promotion of legitimate crosses. To determine the effectiveness of hummingbirds as pollen vectors between floral morphs and the consequences in terms of male (pollen transfer) and female function (pollen receipt) in Palicourea padifolia (Rubiaceae), floral visitors, their foraging modes, and temporal patterns of floral visitation were observed and documented. Differences in pollen and stigma morphology, pollen flow, rates of pollen deposition, and/or stigmatic pollen loads were then evaluated for their contribution toward differences in reproductive output between floral morphs. A pollination experiment with stuffed hummingbirds that varied in bill size was done to evaluate the contribution of bill variation toward differences between floral morphs in pollen receipt and pollen transfer and female reproductive output. Anthers of long-styled flowers contained significantly more and smaller pollen grains than those of short-styled flowers, independently of corolla and anther lengths. The shape and orientation of the stigma lobes differed between morphs and were significantly longer among short-styled flowers. Hummingbird visitation rates did not differ significantly between floral morphs, and foraging movements from focal plants towards neighboring plants were independent of floral morph. Stigmatic pollen loads under field conditions and those after controlled hummingbird visitation, along with rates of pollen accumulation through the day indicated that stigmas of short-styled flowers receive proportionately more legitimate (intermorph) pollen grains than did those of long-styled flowers. However, the species of hummingbird was marginally significant in explaining variation in pollen deposition on stigmas. Lastly, intermorph pollinations of P. padifolia resulted in significant differences in fruit production between floral morphs, independent of pollination treatment and pollinator species; short-styled flowers proportionately developed almost twice the number of fruits developed by long-styled flowers.

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Knowledge of developmental pathways for achieving differences in style and anther heights, in concert with those of ancillary features accompanied with data in regard to biomass investment to male and female function, provide an excellent opportunity for examining the developmental correlations between primary and ancillary floral traits so as to understand the evolution of heterostyly. The ontogenetic relationships between bud length and anther height and between bud length and style height, and between bud length versus bud width, anther length, and number of pollen grains per anther for long-styled (LS) and short-styled (SS) morphs of P. PADIFOLIA are described. We also described the ontogenetic biomass allocation to male and female function and to corolla with elongation of buds harvested at regular intervals. We observed an early termination of stylar growth in SS buds, whereas LS styles steadily increased in size. Morph differences for relative growth rates were significant for anther height, anther length, and pollen number but not for bud width. Bud width and anther length had a negative allometric relationship with bud elongation. The relationship between bud length and number of pollen grains per anther was positive and morph differences in pollen number were detected at later stages of development. An increase in corolla mass involved a disproportionate allocation to the female function in SS flowers and male allocation was similar for the two morphs over the course of development. Our results are consistent with theoretical and empirical data for distylous species with an approach herkogamous ancestor, and with the more general hypothesis of ontogenetic lability of heterostyly, in which morph differences in style and anther heights are achieved in various ways. Variations observed in sexual investment between floral morphs suggest differences in sex expression during flower development.

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L a extraordinaria diversidad de flores de las angiospermas es el producto del cambio evolutivo a partir de una base reducida de diseños florales de donde se han originado cambios morfológicos repetidos. La forma, el tamaño y el número de flores son aspectos importantes de diversificación morfológica entre las plantas con flores (Worley y Barrett, 2000;Galen y Cuba, 2001). A lo largo de la evolución de las angiospermas, es posible que las estructuras florales que originalmente aparecieron para una función determinada hayan cambiado completamente su función original, lo que dificulta la identificación de factores que moldearon su evolución (Walker-Larsen y Harder, 2000). Por ello, es importante explorar los factores que puedan explicar la variación en la morfología floral de muchas especies de angiospermas para lograr un entendimiento integral de la evolución floral. La mayoría de los estudios se han enfocado CORRELACIÓN MORFO-ESPECÍFICA EN FLORES DEResumen: La distilia es un polimorfismo floral en donde aproximadamente la mitad de las plantas en una población tienen los estilos largos y los estambres cortos (Pin) y la otra mitad estilos cortos y estambres largos (Thrum). Se ha sugerido que la posición relativa de anteras y estigmas en las flores distílicas promueve el flujo de polen entre flores de morfos opuestos (polinización legítima), en comparación con el flujo de polen entre flores del mismo morfo (polinización ilegítima). Estudiamos la morfología floral de ambos morfos (seis variables) en Palicourea padifolia (Rubiaceae) y encontramos diferencias significativas entre morfos florales en los rasgos que definen al polimorfismo floral. Sin embargo, las relaciones entre los rasgos morfológicos de las flores difieren entre morfos florales (morfo-específico) y las relaciones significativas fueron más fuertes en el morfo con los estilos cortos. Los patrones de correlación entre algunos de los rasgos florales sugieren presiones de selección diferencial entre morfos florales, independientemente del tamaño de la corola. Palabras clave: colibríes, distilia, Palicourea, polimorfismo floral.Abstract: Distyly is a floral polymorphism in which about half of the plants in a population have long styles and short stamens (Pin), whereas the remainder possess short styles and long stamens (Thrum). It has been suggested that the relative position of anthers and stigmas in distylous flowers enhances pollen flow between flowers of opposite morphs (legitimate pollination), in comparison to pollen flow between flowers of the same morph (illegitimate pollination). We studied the floral morphology of both floral morphs (six variables) in Palicourea padifolia (Rubiaceae) and found significant differences between floral morphs in floral traits that define the floral polymorphism. However, the correlations between morphological traits of flowers differed between floral morphs (morph-specific), and the significant correlations were stronger in the shortstyled morph. The morph-specific correlation patterns among some of the floral traits ...