Spatiotemporal Evolution of the Global Species Diversity of Rhododendron

Abstract

Evolutionary radiation is a widely recognized mode of species diversification, but its underlying mechanisms have not been unambiguously resolved for species-rich cosmopolitan plant genera. In particular, it remains largely unknown how biological and environmental factors have jointly driven its occurrence in specific regions. Here, we use Rhododendron, the largest genus of woody plants in the Northern Hemisphere, to investigate how geographic and climatic factors, as well as functional traits, worked together to trigger plant evolutionary radiations and shape the global patterns of species richness based on a solid species phylogeny. Using 3,437 orthologous nuclear genes, we reconstructed the first highly supported and dated backbone phylogeny of Rhododendron comprising 200 species that represent all subgenera, sections, and nearly all multispecies subsections, and found that most extant species originated by evolutionary radiations when the genus migrated southward from circumboreal areas to tropical/subtropical mountains, showing rapid increases of both net diversification rate and evolutionary rate of environmental factors in the Miocene. We also found that the geographically uneven diversification of Rhododendron led to a much higher diversity in Asia than in other continents, which was mainly driven by two environmental variables, that is, elevation range and annual precipitation, and were further strengthened by the adaptation of leaf functional traits. Our study provides a good example of integrating phylogenomic and ecological analyses in deciphering the mechanisms of plant evolutionary radiations, and sheds new light on how the intensification of the Asian monsoon has driven evolutionary radiations in large plant genera of the Himalaya-Hengduan Mountains.

Plastome sequences fail to resolve shallow level relationships within the rapidly radiated genus Isodon (Lamiaceae)

“…Moreover, our results demonstrate that plastome data does not accurately reflect species relationships and is insufficient to resolve shallow level relationships within a rapidly radiated genus like Isodon . To achieve for a better resolved phylogeny of the genus, significant larger data sets derived from nuclear genome with next-generation sequencing technology might be helpful, such as targeted enrichment ( Gardner et al, 2020 ; Reichelt et al, 2021 ; Giaretta et al, 2022 ), deep genome skimming ( Liu et al, 2021 ), and RNA-seq ( Nevado et al, 2016 ; Jin et al, 2021 ; Kong et al, 2022 ; Xia et al, 2022 ), which are compatible with more comprehensive tools for disambiguating genetic lineages and causes of gene tree conflicts.…”

Evolutionary history of two evergreen Rhododendron species as revealed by chromosome-level genome assembly

“…Although the Rhododendron genus contains the most diverse species of woody plants, there was no evidence for the occurrence of a recent WGD in the common ancestor of Rhododendron (Ericaceae). A study based on phylogenomic and ecological analyses shed light on the evolutionary radiations and species diversity of Rhododendron are driven by geographic, climatic factors and functional traits of leaves ( Xia et al., 2022 ).…”

Evidence for divergence in phenology over morphology in response to limiting similarity in montane communities of Rhododendron

“…The ability of Rhododendron species to produce fertile hybrids, long exploited in horticulture, has been documented in field studies of hybrid zones and introgression in natural populations across the world (Kron et al, 1993; Marczewski et al, 2015; Milne et al, 2003; Tagane et al, 2008; Yan et al, 2017). More recently, genomic evidence has mounted that reticulation, including hybrid speciation, has been pervasive throughout the phylogenetic history of Rhododendron , mostly within subgenera (Milne et al, 2010; Xia et al, 2022). Our own phylogenomic investigations of the species sampled from Mt.…”