Dipterocarps used India as a raft from Gondwana to Eurasia

It has been hypothesized that most Asian tropical lineages have originated in Gondwana with the Indian subcontinent playing a crucial role in the dispersal of ancestral Gondwanan taxa. The disjunct distribution of dipterocarps and the fossil record in India support the Gondwana hypothesis. This is the first comprehensive study addressing the evolutionary and biogeographic relationships of dipterocarps in the Indian subcontinent to test the Gondwana hypothesis. A Bayesian phylogenetic tree of the Dipterocarpaceae family including the Indian counterparts corroborates the monophyly of subfamilies/tribes and shows new biogeographic affinities. Molecular dating reveals the Cretaceous origin of Dipterocarpaceae. Diversification of major lineages occurred during the Pliocene-Miocene epochs. The DEC analysis ascertains the Gondwanan origin and dispersal route from the Madagascar (Africa)-India-Sri Lanka-Seychelles block to Eurasia. The biogeographic analysis suggests early vicariance followed by an out-of-India dispersal of Dipterocarpaceae. Three dispersal events from India to the remainder of Asia at 47.6 Ma, 42.53 Ma and 37.6 Ma are identified. There probably was a biotic interchange between India and mainland Asia via Sumatra following the collision of the Indian plate with Eurasia. Molecular dating and dispersal events coincide with the geological events. During the Miocene, uplift of the Himalayan-Tibetian plateau induced climatic variation, which seems to have resulted in the extinction of major Indian dipterocarp lineages and reverse dispersal into India. Hopea-Shorea, one of the earliest diverged lineages, originated in Southeast Asia. The establishment of Southeast Asian monsoon climate may have favoured allopatric speciation and diversification of Southeast Asian lineages also resulting in further dispersal into India.

Automated summary

This is the first comprehensive study on the evolution and biogeographic relationships of dipterocarps in the Indian subcontinent. The results support the Gondwana hypothesis, suggesting that most Asian tropical lineages originated in Gondwana with India playing a crucial role in their dispersal. Molecular dating shows that dipterocarps originated in the Cretaceous and diversified during the Pliocene-Miocene epochs. Biogeographic analysis suggests a dispersal route from Gondwana to Eurasia through Madagascar-India-Sri Lanka-Seychelles, with three dispersal events from India to other parts of Asia.