Aim

The Qinghai–Tibet Plateau (QTP) harbours high levels of species diversity and endemism, and multiple out-of-QTP dispersal routes have been put forward. However, whether different dispersal directions out of the QTP resulted in contrasting evolutionary trajectories remains unknown. Here, we use the sister genera Calathodes and Trollius (Ranunculaceae) as an ideal model to investigate the out-of-QTP diversification patterns.

Location

The Northern Hemisphere.

Taxon

Calathodes and Trollius (Ranunculaceae).

Methods

We sampled all four species of Calathodes and 38 species of Trollius to reconstruct a near-complete species-level phylogeny based on 12 molecular loci from the nuclear and plastid genomes. Within the phylogenetic framework, divergence times, ancestral ranges and diversification rates were estimated, and ancestral habitat, elevation and climate niche were inferred.

Results

The most recent common ancestor of Calathodes and Trollius occupied the QTP at ~8 Ma. Calathodes migrated eastward from the QTP to subtropical mainland China at ~4 Ma and then further to Taiwan at ~0.5 Ma. Trollius dispersed into North Asia at ~6 Ma and further reached Northeast Asia, Japan, Taiwan, Europe and North America. Net diversification rates of subtropical Calathodes and North Asian Trollius clades were 0.28 and 0.54 My⁻¹, respectively. Calathodes and its subtropical clade both prefer the middle-elevation closed, warm, and humid habitats, while Trollius and its North Asian clade inhabit open, cold, and dry areas.

Main Conclusions

Calathodes and Trollius both originated in the QTP in the late Miocene and exhibited long-term habitat and climatic niche conservatism. The distinct out-of-QTP dispersal directions in the two genera probably resulted in their subsequent different diversification patterns, associated with the conservatism in habitat- and climate-related niches. Our study suggests the QTP serves as an important source of Northern Hemisphere biodiversity and advances the knowledge of how distinct dispersal directions out of the QTP resulted in contrasting evolutionary trajectories