Pollination of Pagamea duckei Standl. (Rubiaceae): a functionally dioecious species

Abstract

The floral biology, pollination and breeding system of Pagamea duckei Standl. (Rubiaceae) were studied at the Reserva Biológica da Campina, Manaus, Amazonas, Brazil. Floral morphology suggested that P. duckei is a distylous species. However, crossing experiments revealed that it is functionally dioecious. The flowers are actinomorphic, yellowish, produce nectar and a sweet odor, which is more intense in the morning. Anthesis started in the morning between 5.00 and 6.00 AM and extended until dusk, when the corolla tube abscissed. The flowers were visited mostly by bees of the genus Melipona. Pagamea duckei is not agamospermic and thus needs pollen vectors for effective pollination. The results of this study strengthen the idea that, in Pagamea, species with distylous flower morphology are actually functionally dioecious. A morfologia floral sugere que P. duckei é uma espécie distílica. Entretanto, cruzamentos experimentais revelaram que essa espécie é funcionalmente dióica. As flores são actinomorfas, amareladas, produzem néctar e um aroma adocicado que é mais intenso no período da manhã. A antese das flores iniciou de manhã, entre 05h00 e 06h00 e se estendeu até o anoitecer, quando o tubo da corola sofria abscisão. As flores foram visitadas principalmente por abelhas do gênero Melipona. Pagamea duckei não é agamospérmica e logo necessita de vetores de pólen para que haja polinização efetiva. Os resultados desse estudo fortalecem a hipótese de que muitas espécies de Pagamea com flores heterostílicas são na verdade funcionalmente dióicas. Palavras-chave: biologia floral, heterostilia, florestas de campinarana, Amazônia Central. Neotrop., vol. 12, no. 4 grade of homostylous species (Vicentini 2007). A few exceptions are found in three widespread species of Pagamea that present intraspecific variation in breeding system, sometimes at the population level (Vicentini 2007), which are still poorly characterized. These patterns of breeding system variation in Pagamea make this clade particularly interesting for studying the evolution of breeding systems. However, it is also clear that flower morphology should be used with caution when characterizing breeding systems (Barrett & Richards 1990, Owens et al. 1993) and, as consequence, additional studies are needed, particularly experimental studies on pollination and a better sampling of population-level intra-specific variation. Pagamea duckei Standl. is a small tree or shrub found in whitesand Campinarana forest and is only known from two disjunct areas: one near Manaus and another close to Benjamin Constant, at the border between Brazil and Colombia (Vicentini 2007). This species is common in open Campinarana forests north of Manaus and has been described as characteristic of these forests (Anderson 1981). The floral morphology of P. duckei suggests dioecy (flowers with either vestigial stamens or pistils) and this species is sister to the other dioecious species of Pagamea (Vicentini 2007). This study aimed to characterize the morphology and floral biology...