1 © 2020 The Linnean Society of London, Biological Journal of the Linnean Society, 2020, 131, 1–11 Biological Journal of the Linnean Society, 2020, 131, 1–11. With 4 figures. Towards a new understanding of the division of labour in heterantherous flowers: the case of Pterolepis glomerata (Melastomataceae) FRANCISMEIRE JANE TELLES 1,2, * , , CRISTIAN LUAN KLUNK 2 , FABIANO RODRIGO DA MAIA 3 , VINÍCIUS LOURENÇO GARCIA DE BRITO 4 , and ISABELA GALARDA VARASSIN 5 1 Programa de Pós-Graduação em Ecologia e Conservação de Recursos Naturais, Universidade Federal de Uberlândia, Campus Umuarama, Bloco 2D, Sala 26, Uberlândia, MG, Brazil 2 Programa de Pós-Graduação em Ecologia e Conservação, Centro Politécnico, Universidade Federal do Paraná, Curitiba, 81531-990 Paraná, Brazil 3 Programa de Pós-Graduação em Botânica, Centro Politécnico, Universidade Federal do Paraná, Curitiba, 81531-980 Paraná, Brazil 4 Instituto de Biologia, Universidade Federal de Uberlândia, Campus Umuarama, Uberlândia, MG, Brazil 5 Departamento de Botânica, Centro Politécnico, Universidade Federal do Paraná, Curitiba, PR 81531–980, Brazil Received 5 April 2020; revised 9 June 2020; accepted for publication 12 June 2020 Pollen-flowers with heteromorphic stamens have been shown to promote an intrafloral division of labour as a solution to fitness costs arising from pollen consumption by bees, known as the pollen dilemma. Usually, the division is based on morphological differences in anther and pollen traits that correlate with stamen function: pollinating anthers are larger and contain more and higher-quality pollen grains than feeding anthers. Here, we present a new strategy based on a high investment in reward production and thus attraction, in the heterantherous Pterolepis glomerata, to overcome short flower longevity and maintain reproductive success. In P. glomerata small feeding anthers not only produced more pollen grains and more grains with cytoplasmic content, but also released more pollen than pollinating anthers after a single visit. This pattern was consistent until the end of floral anthesis, showing the existence of pollen-dosing mechanisms. Bees equally visited flowers with yellow feeding anthers and pollinating anthers with yellow connective appendages, indicating a visual similarity, as predicted by bee vision modelling. Our results demonstrate that the division of labour might have different outcomes. Instead of the classical expectation of more investment in reproductive pollen in pollinating stamens, P. glomerata invested more in attraction and reward in feeding stamens. ADDITIONAL KEYWORDS: buzz-pollination – floral traits – pollen dilemma – pollen removal – stamen dimorphism. INTRODUCTION Pollen-flowers (sensu Vogel, 1978) usually have only pollen as a resource for their pollinators, which are often bees. In these flowers, pollen plays a dual role as both male gametophytes and as nutritional resource for bee larvae, resulting in a conflict between plant reproduction and pollinator attraction, known as the pollen dilemma (Buchmann & Buchmann, 1981; Westerkamp, 1996, 1997). The selective pressure imposed by this conflict has led many plants to develop different mechanisms to reduce excessive pollen loss (Buchmann & Cane, 1989; Harder & Thomson, 1989; King & Buchmann, 1996; Amorim et al., 2017), among which are poricidal anthers and heteranthery (Vogel, 1978; Buchmann, 1983). Heteranthery, the occurrence of two or more types of stamens within the same flower, is often present in *Corresponding author. E-mail: meirecuesta@gmail.com Downloaded from https://academic.oup.com/biolinnean/article/131/1/1/5881237 by guest on 05 July 2022