Large-scale phylogenetic analyses reveal fagalean diversification promoted by the interplay of diaspores and environments in the Paleogene

Abstract

The order Fagales (ca. 1325 species, 32 genera) is one of the most important orders of woody angiosperms in both tropical and temperate forests. Fagalean plants have diverse diaspores and dispersal modes, and have abundant macrofossil records. Here, we present, to our knowledge, the most comprehensive phylogenetic analysis of Fagales to date based on five plastid loci. We reconstructed the phylogenetic relationships within Fagales using parsimony, likelihood and Bayesian approaches. We inferred the evolutionary shifts of diaspore types, dispersal modes, habitats, and pollination syndromes, and estimated divergence times and rates of diversification. Fossil fruit records of Fagales were also reviewed. Our results suggest that fagalean families are all monophyletic and 29 of the 32 genera are monophyletic. The majority of inter-familial and inter-generic relationships were well resolved. Our evolutionary reconstructions indicate that winged diaspore is synapomorphic, and animal dispersal system is symplesiomorphic in Fagales. Within the order, the families diverged in the mid-Cretaceous but mainly diversified after the Cretaceous-Paleogene (K-Pg) boundary. The overwhelming majority of winged and wingless fruited genera diverged or diversified during the Paleogene, reflecting adaptation to wind and animal dispersals, respectively. Correlated evolution analyses strongly supported the correlated transitions between dispersal mode and habitat. The winged fruited groups often inhabit open habitats and are commonly dispersed abiotically, whereas the wingless fruits usually inhabit closed habitats and have a vertebrate-dispersal mode. Environmental changes triggered increased diversification of Fagales in the Paleogene together with evolution of diaspores and dispersal modes. Additionally, our paleobotanically calibrated time-scale for Fagales may be useful for ecological and physiological studies. (C) 2014 Geobotanisches Institut ETH, Stiftung Ruebel. Published by Elsevier GmbH. All rights reserved.