Phylogenetic and ecological correlates of pollen morphological diversity in a Neotropical rainforest

Luke Mander,Surangi W Punyasena,Christopher W Dick,Caroline Parins‐Fukuchi,Carlos Jaramillo

doi:10.1111/btp.12847

Abstract

AbstractMorphology varies enormously across clades, and the morphology of a trait may reflect ecological function or the retention of ancestral features. We examine the tension between ecological and phylogenetic correlates of morphological diversity through a case study of pollen grains produced by angiosperms in Barro Colorado Island, Panama (BCI). Using a molecular phylogeny of 730 taxa, we demonstrate a statistically significant association between morphological and genetic distance for these plants. However, the relationship is non‐linear, and while close relatives share more morphological features than distant relatives, above a genetic distance of ~ 0.7 increasingly distant relatives are not more divergent in phenotype. The pollen grains of biotically pollinated and abiotically pollinated plants overlap in morphological space, but certain pollen morphotypes and individual morphological traits are unique to these pollination ecologies. Our data show that the pollen grains of biotically pollinated plants are significantly more morphologically diverse than those of abiotically pollinated plants.Abstract in Spanish is available with online material.

Highlights

Morphological diversity varies strikingly across clades and morphological differences between taxa are thought to evolve for a variety of reasons (Vidal-Garcia, Byrne, Roberts, & Keogh, 2014)
Pollen grains contribute to the overall phenotypic diversity that is presented by plants to pollinators, and this may represent a link between pollination ecology and pollen morphology on BCI
By analogy with the role of morphological diversity among flowers (e.g., Ghazoul, 2006), and rather than attributing a particular set of pollen morphotypes or individual morphological traits to a particular pollination ecology, it could be hypothesized that pollen grains may contribute to the overall phenotypic diversity that is presented by plants to pollinators

Summary

| INTRODUCTION

Morphological diversity varies strikingly across clades and morphological differences between taxa are thought to evolve for a variety of reasons (Vidal-Garcia, Byrne, Roberts, & Keogh, 2014). It has been noted that certain morphological features of pollen grains may have multiple functional roles; for example, apertures regulate water ingress and egress, and are sites where substances may be transported between pollen and stigma (Heslop-Harrison, 1976), but they may serve as sites of pollen tube exit during germination in some (but not all) taxa (Chaloner, 2013), and guide folding pathways during the desiccation phase of pollen dispersal (Katifori, Alben, Cerda, Nelson, & Dumais, 2010) Such a broad range of functions associated with the micro-morphological features of pollen grains have led some authors to conclude that pollen grains are "not 'optimally' designed for a specific function, but merely structures that work with varying efficiency in a specific ecological and evolutionary context" Our specific aims are to: (a) compare the morphological distance between pollen morphotypes with branch-length genetic distance among BCI angiosperms; (b) examine the relationship between morphological diversity and pollination strategy on BCI; and (c) to identify the morphological traits that are characteristic of different pollination strategies on BCI

| METHODS

| DISCUSSION

Findings

| CONCLUDING REMARKS