Understory herbs are an essential part of tropical rain forests, but little is known about factors limiting their reproduction. Many of these herbs are clonal, patchily distributed, and produce large floral displays of nectar-rich 1-d flowers to attract hummingbird pollinators that may transport pollen over long distances. The aim of this study was to investigate the effects of clonality, cross-proximity, and patchy distribution on the reproduction of the hummingbird-pollinated Amazonian herb Heliconia metallica. We experimentally pollinated flowers within populations with self-pollen and with pollen of different diversity, crossed flowers between populations, and added supplemental pollen to ramets growing solitarily or in conspecific patches. Only flowers pollinated early in the morning produced seeds. Selfed flowers produced seeds, but seed number and mass were strongly reduced, suggesting partial sterility and inbreeding depression after selfing. Because of pollen competition, flowers produced more seeds after crosses with several than with single donor plants. Crosses between populations mostly resulted in lower seed production than those within populations, suggesting outbreeding depression. Ramets in patches produced fewer seeds than solitary ramets and were more pollen-limited, possibly due to geitonogamy and biparental inbreeding in patches. We conclude that high rates of geitonogamy due to clonality and pollen limitation due to the short receptivity of flowers and patchy distribution constrain the reproduction of this clonal herb. Even in unfragmented rain forests with highly mobile pollinators, outbreeding depression may be a widespread phenomenon in plant reproduction. Las plantas herbáceas del sotobosque son parte esencial de los bosques tropicales. Sin embargo, poco se conoce de los factores que limitan su reproducción. Muchas de estas herbáceas clonales se distribuyen irregularmente en parches y producen grandes inflorescencias cuyas flores con rico néctar atraen a los polinizadores que pueden transportar el polen a largas distancias. El objetivo del presente estudio fue investigar los efectos de la clonalidad, la proximidad de cruzamiento y de la distribución irregular en la reproducción de una hierba amazónica (Heliconia metallica). Nosotros polinizamos flores experimentalmente dentro de las poblaciones con su propio polen y con polen de diferente diversidad, cruzamos flores entre las poblaciones, y añadimos polen suplementario a los rametos que crecían aislados o en parches. Sólo las flores polinizadas por la madrugada produjeron semillas. Flores autofecundadas produjeron semillas, pero el número de semillas y el peso fueron drásticamente reducidos, lo que indica incompatibilidad parcial y depresión por endogamia después de la autofecundación. Debido a la competencia de polen, las flores produjeron más semillas cuando se polinizaron con varios donantes que con un solo. El cruzamiento entre poblaciones produjo, en la mayoría, menos semillas que el cruzamiento dentro de las poblaciones, lo que sugiere una depresión por exogamia. Los rametos en parches produjeron menos semillas que rametos solitarios y fueron más limitados de polen, posiblemente debido a la geitonogamia y la endogamia biparental en los parches. Concluimos que la frecuente geitonogamia debido a la clonalidad y la limitación del polen debido a la corta receptividad de las flores y la distribución en parches limita la reproducción de esta herbácea clonal. Incluso en los bosques tropicales no fragmentados con polinizadores de gran movilidad, la depresión por exogamia puede ser un fenómeno generalizado en la reproducción de las plantas. TABLE S1. The effects of pollination with self-pollen and cross-pollen of different diversity (one or six donor ramets) on fruit set, seed set, and seed mass of H. metallica. TABLE S2. The effects of crosses within and between populations on fruit set, seed set, and seed mass of ramets of H. metallica in a patch in the River population, and in two patches in the Floodplain population. TABLE S3. The effects of supplemental pollen from the home and from a distant population on fruit set, seed set, and seed mass of solitary and patch ramets of H. metallica. Please note: Wiley-Blackwell is not responsible for the content or functionality of any supporting materials supplied by the authors. Any queries (other than missing material) should be directed to the corresponding author for the article. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
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