Incongruences between nuclear and plastid phylogenies challenge the identification of correlates of diversification in Gentiana in the European Alpine System

Adrien Favre,Juraj Paule,Jana Ebersbach

doi:10.1007/s00035-021-00267-6

Abstract

Mountains are reservoirs for a tremendous biodiversity which was fostered by a suite of factors acting in concert throughout evolutionary times. These factors can be climatic, geological, or biotic, but the way they combine through time to generate diversity remains unknown. Here, we investigate these factors as correlates of diversification of three closely related sections of Gentiana in the European Alpine System. Based upon phylogenetic approaches coupled with divergence dating and ancestral state reconstructions, we attempted to identify the role of bedrock preferences, chromosome numbers coupled with relative genome sizes estimates, as well as morphological features through time. We also investigated extant climatic preferences using a heavily curated set of occurrence records individually selected for superior precision, and quantified rates of climatic niche evolution in each section. We found that a number of phylogenetic incongruences derail the identification of correlates of diversification, yet a number of patterns persist regardless of the topology considered. All the studied correlates are likely to have contributed to the diversification of Gentiana in Europe, however, their respective importance varied through time and across clades. Chromosomal variation and divergence of climatic preferences appear to correlate with diversification throughout the evolution of European Gentiana (Oligocene to present), whereas shifts in bedrock preferences appear to have been more defining during recent diversification (Pliocene). Overall, a complex interaction among climatic, geological and biotic attributes appear to have supported the diversification of Gentiana across the mountains of Europe, which based upon phylogenetic as well as other evidence, was probably also bolstered by hybridization.

Highlights

Mountain systems around the world are more species-rich than their adjacent lowlands, as evident from the global distribution of species richness in plant (e.g., Kier et al 2005)
Phylogenetic relationships among sections, and the relative position of G. terglouensis and G. froelichii to their congeners differed between the trees
The first one included G. nivalis L., G. pumila Jacq. and G. utriculosa L., whereas the second clade included the remaining species (e.g., G. verna), of which phylogenetic relationships were well supported in the plastid tree, and less so in the rDNA tree

Summary

Introduction

Mountain systems around the world are more species-rich than their adjacent lowlands, as evident from the global distribution of species richness in plant (e.g., Kier et al 2005). The survival of most of the European alpine flora during the LGM occurred ex-situ at the periphery of the Alps and beyond (e.g., Schönswetter et al 2002; Kropf et al 2003; Windmaißer et al 2016) except for a few nunatak refugia (Schönswetter et al 2005; Kosiński et al 2019; Schönswetter and Schneeweiss 2019; Pan et al 2020) These drastic displacements of distribution ranges have certainly contributed to prolonged isolation of lineages in geographically distant glacial refugia, contributing to a considerable degree to divergence and possibly diversification (Kadereit et al 2004; Nieto Feliner 2011; Paule et al 2018), this might not constitute a species-pump effect per se

Methods

Results

Discussion

Conclusion