Phylogenetic comparative methods improve the selection of characters for generic delimitations in a hyperdiverse Neotropical orchid clade

Diego Bogarín,Barbara Gravendeel,Franco Pupulin,Melania Fernández,Jaco Kruizinga,Oscar A Pérez-Escobar,Adam P Karremans,Erik Smets

doi:10.1038/s41598-019-51360-0

Abstract

Taxonomic delimitations are challenging because of the convergent and variable nature of phenotypic traits. This is evident in species-rich lineages, where the ancestral and derived states and their gains and losses are difficult to assess. Phylogenetic comparative methods help to evaluate the convergent evolution of a given morphological character, thus enabling the discovery of traits useful for classifications. In this study, we investigate the evolution of selected traits to test for their suitability for generic delimitations in the clade Lepanthes, one of the Neotropical species-richest groups. We evaluated every generic name proposed in the Lepanthes clade producing densely sampled phylogenies with Maximum Parsimony, Maximum Likelihood, and Bayesian approaches. Using Ancestral State Reconstructions, we then assessed 18 phenotypic characters that have been traditionally employed to diagnose genera. We propose the recognition of 14 genera based on solid morphological delimitations. Among the characters assessed, we identified 16 plesiomorphies, 12 homoplastic characters, and seven synapomorphies, the latter of which are reproductive features mostly related to the pollination by pseudocopulation and possibly correlated with rapid diversifications in Lepanthes. Furthermore, the ancestral states of some reproductive characters suggest that these traits are associated with pollination mechanisms alike promoting homoplasy. Our methodological approach enables the discovery of useful traits for generic delimitations in the Lepanthes clade and offers various other testable hypotheses on trait evolution for future research on Pleurothallidinae orchids because the phenotypic variation of some characters evaluated here also occurs in other diverse genera.

Highlights

Taxonomic delimitations are challenging because of the convergent and variable nature of phenotypic traits
We want to answer the following questions: (1) which monophyletic genera can be recognized based on a phylogenetic framework? (2) what are the phylogenetically informative characters of each clade based on ancestral state reconstructions (ASR)? (3) how did such diagnostic morphological characters evolve in the clade? We provide a detailed generic circumscription of Lepanthes
The inferences of the Bayesian inference (BI), maximum likelihood (ML) and maximum parsimony (MP) from the nrITS dataset yielded similar topologies and high support for the 14 genera recognized as members of the Lepanthes clade but with some differences in the topology among the relationships of those clades (Appendices S3, S4)

Summary

Introduction

Taxonomic delimitations are challenging because of the convergent and variable nature of phenotypic traits. In the past 10 years, several phylogenetic studies aimed to increase taxon sampling or add more markers to the previous phylogenetic reconstructions, supported or redefined most of the taxonomic and generic concepts proposed by Pridgeon[9] and Luer[16] These phylogenetic re-evaluations covered almost all clades in the subtribe[17,18,19,20,21]. Earlier phylogenetic studies in the Pleurothallidinae did not investigate morphological evolutionary patterns, homoplasy and contrasting differences in reproductive traits by combining ancestral state reconstructions (ASR) and a solid phylogenetic framework[9,11] This is essential to test hypotheses of morphological evolution and to disentangle recalcitrant generic delimitations due to phenotypic similarities. The role of pollinator interactions in the evolution of the Lepanthes clade is currently unknown because only two pollination systems have been reported so far for Lepanthes and Trichosalpinx[25,26]

Methods

Results

Discussion

Conclusion