A alternância de vetores de polinização direcionou a evolução do grão de pólen em Costaceae (Zingiberales)

Abstract

The relationship between the evolution of floral morphology and its pollinators allowed the establishment of the paradigm that floral phenotypes reflect the type of pollinator. The Costaceae family is an excellent study model since the evolutionary association between floral morphology and pollination vectors is widely established. Thus, the study of the relationship between architecture and pattern of ornamentation of pollen grains in Costaceae can provide subsidies to the understanding of diversification in the Neotropics. In this study, we address the following questions: 1. Are there morphological differences in the pollen architecture of Costaceae species associated with the pollination vector? 2. Which pollen morphological attributes are convergent? The pollen of fourteen neotropical species of Costaceae was studied. Samples were previously obtained from flower buds of living specimens and were prepared with acetolysis and mounted on slides for Light Microscopy and prepared for Scanning Electron Microscopy. Principal Component Analysis (PCA) and Principal Coordinate Analysis (PCoA) were used to analyze the variation in quantitative morphological attributes of pollens. To test the phylogenetic signal of five quantitative functional traits of the pollen grain, Blomberg's K test and Pagel's lambda (λ) test were performed. The inference of character evolutionary rates was analyzed using functions from the phytools, geiger, and ape packages in R language, assessing previously published phylogenetic relationships in Costaceae. We found that species of Costaceae pollinated by bees have larger pore diameter and exine thickness compared to those pollinated by hummingbirds. We did not find significant differences between the number of pores in pollen grains of species pollinated by bees and species pollinated by hummingbirds. The morphology of the Zingiberales pollen grain is treated in the literature as of little relevance, due to the absence of exine in most members of the group. However, in Costaceae, the morphological variation presented here reflects the role of alternation between pollination vectors in the morphological diversification of the pollen grain and furthermore indicates potential for identification of taxonomic groups.