Atributos florais em um sistema de polinização especializado: Calathea cylindrica (Roscoe) K. Schum. (Marantaceae) e abelhas Euglossini

Abstract

-(Floral traits in a specialized pollination system: Calathea cylindrica (Roscoe) K. Schum. (Marantaceae) and Euglossini bees). Pollination specialization is promoted by floral features that favor pollinator fidelity and hinder the access to resources by other visitors. We investigated the pollination mechanism of one understory herb in southeastern Brazil. Calathea cylindrica flowers year-round and its flowers are peculiar because of the fusion and modification of some elements, asymmetry, secondary pollen presentation, hidden nectar, and a long and narrow tube, which is closed before pollinator visit. Pollination occurs by means of an explosive mechanism, and once it is triggered, the floral parts do not return to their initial position. Thus, there is only a single possibility for pollen transference. Pollinators are female Euglossini bees and all flowers have already been visited by mid-morning. Specific movements with enough force are necessary for the visitors to access the nectar. Bagged flowers secreted around 13 µL of nectar with 32% of sugar concentration. Nectar secretion continues after removals, but in small volumes. Continual flowering, high production of nectar and secretion after pollination may promote pollinator fidelity. The complex floral structure, the secretion in which the flower base (nectar chamber) is dipped, and the narrow tube with inner hairs make the access to nectar difficult and may work as barriers for other visitors. Altogether, these factors seem to regulate the highly specialized pollination system of Calathea cylindrica.Key words -bee, Euglossini, floral specialization, nectar, pollination RESUMO -(Atributos florais em um sistema de polinização especializado: Calathea cylindrica (Roscoe) K. Schum. (Marantaceae) e abelhas Euglossini). Sistemas de polinização especializados estão ligados a características que incentivam as visitas por polinizadores e desestimulam visitas por outros animais. O mecanismo de polinização de uma espécie de Marantaceae foi estudado com ênfase nessa questão. Calathea cylindrica é uma erva com flores disponíveis o ano todo. As flores são peculiares pela fusão e modificação dos elementos, assimetria, apresentação secundária de pólen, néctar pouco acessível e tubo longo, estreito e fechado até a visita do polinizador. A polinização consiste em um mecanismo explosivo, sendo que uma vez disparado, as estruturas florais não retornam à posição inicial. Assim, há uma única possibilidade para transferência de pólen. Os polinizadores são fêmeas de abelhas Euglossini (Apidae) e no meio da manhã todas as flores já haviam sido visitadas. O acesso ao néctar em flores intactas requer a realização de movimentos específicos e com força apropriada, o que exclui outros insetos. A quantidade de néctar produzido em flores ensacadas foi em torno de 13 µL com 32% de concentração de açúcares. O néctar continua sendo secretado em quantidades pequenas depois do disparo do mecanismo. A floração contínua, a quantidade alta de néctar produzido e a continuidade de secreçã...

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