Island geography drives evolution of rattan palms in tropical Asian rainforests.

Distributed across two continents and thousands of islands, the Asian tropics are among the most species-rich areas on Earth. The origins of this diversity, however, remain poorly understood. Here, we reveal and classify contributions of individual tropical Asian regions to their overall diversity by leveraging species-level phylogenomic data and new fossils from the most species-rich Asian palm lineage, the rattans and relatives (Arecaceae, Calamoideae). Radiators (Borneo) generate and distribute diversity, incubators (Indochina, New Guinea, and Sulawesi) produce diversity in isolation, corridors (Java, Maluku, Sumatra, and the Thai-Malay Peninsula) connect neighboring regions, and accumulators (Australia, India, Palawan, and the Philippines) acquire diversity generated elsewhere. These contrasting contributions can be explained by differences in region size and isolation, elucidating how the unique island-dominated geography of the Asian tropics drives their outstanding biodiversity. Tropical Asia is a hotspot of biodiversity, with approximately 50,000 species of plants alone. However, the role of dispersal versus speciation in producing this diversity is not well understood. Kuhnhäuser . investigated the biogeographic history of tropical Asia using a species-rich taxonomic group, the rattan palms and relatives, Arecaceae and Calamoideae (see the Perspective by Holmquist and Gillespie). The authors analyzed a time-calibrated phylogenetic tree created using data from natural history collections and the fossil record, including two newly described fossils. The authors found that most rattan diversity in the Asian tropics originated from speciation within regions. The size and isolation of different regions helps to explain how geography contributes to the origin and spread of biodiversity. —Bianca Lopez