Abstract
Animal-pollinated plants show a broad variation in floral morphology traits and gametophyte production within populations. Thus, floral traits related to plant reproduction and sexuality are usually exposed to pollinator-mediated selection. Such selective pressures may be even stronger in heterantherous and pollen flowers, in which pollen contributes to both bee feeding and pollination, overcoming the “pollen dilemma” or the inability to perform both functions simultaneously. We describe the phenotypic gender and sexual organ morphology of flowers in two populations of Macairea radula (Melastomataceae), a heterantherous and buzz-pollinated species with pollen flowers. We estimated selection gradients on these traits through female and male fitness components. Both populations showed sizeable phenotypic gender variation, from strict hermaphrodites to increased femaleness or maleness. We found a continuous variation in style and stamen size, and this variation was correlated with corresponding shape values of both sexual organs. We detected bee-mediated selection towards short and long styles through seed number and towards intermediate degrees of heteranthery through pollen removal in one population, and selection towards increased maleness through pollen dispersal in both populations. Our results suggest that bee-mediated selection favors floral sex specialization and stylar dimorphism in M. radula, optimizing reproductive success and solving the pollen dilemma.
Highlights
Animal-pollinated hermaphroditic plants commonly show morphological variation in floral sex organs
If the plant gametophytes are taken as discrete units during the estimation of plant sexuality, hermaphroditic plants would depart from strict equisexuality [6,7], and the phenotypic gender of a plant may naturally differ from its morphological sexual expression [4,5]
Considering that floral traits of most animal-pollinated plants are under partial selection exerted by pollinators [12,13,14], it is important to take into account their impact in plant phenotypic gender selection
Summary
Animal-pollinated hermaphroditic plants commonly show morphological variation in floral sex organs. Such morphological variations are interpreted as adaptations to avoid or, at least, optimize sexual conflicts within and between male and female functions (e.g., gamete wastage, sexual interference, self-pollination [1,2]). The sexuality of animal-pollinated plants is often described by the occurrence and position of floral sex organs (stamens and carpels) in time and space, pollen and ovule production contribute to sexual expression [4,5]. Despite the fact that phenotypic gender expression is not a novel topic in the literature, this trait has rarely been considered in studies of pollinator-mediated selection in natural populations [7,9,10,11]. Considering that floral traits of most animal-pollinated plants are under partial selection exerted by pollinators [12,13,14], it is important to take into account their impact in plant phenotypic gender selection
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
