Biogeography and Diversification of the Tropical and Subtropical Asian Genus Gastrochilus (Orchidaceae, Aeridinae)

Tropical and subtropical Asia are major orchid diversity and endemism centers. However, the evolutionary dynamics of orchids in these areas remain poorly studied. Gastrochilus D. Don, a species-rich orchid genus from tropical and subtropical Asian forests, was employed to investigate the issue. We firstly used eight DNA regions to reconstruct the phylogeny and estimate the divergence times within Gastrochilus. We inferred the ancestral ranges and conducted a diversification analysis based on empirical and simulated data. Subsequently, we assessed the ancestral niche state and tested for phylogenetic signals in the evolution of niche conditions. Our results suggested that the most recent common ancestor of Gastrochilus occurred in the subtropical area of the East Asiatic region in the late Miocene (8.13 Ma). At least eight dispersal events and four vicariant events were inferred to explain the current distribution of Gastrochilus, associated with the global cooling from the Plio-Pleistocene. The genus experienced a slowly decreasing diversification rate since its origin, and no significant correlation between current niches and phylogenetic relatedness was observed. The diversification of Gastrochilus was attributed to accumulation through time, integrated with the intensification of the Asian Monsoon system during the Plio-Pleistocene, pollination, and epiphytism.