Origin and diversification of Indian Ceropegieae(Apocynaceae)and its possible relation to the Indian monsoon

摘要

The Indian subcontinent has experienced a major shift in climatic regime from a wet tropical regime to increased seasonal rainfall,since the late Miocene.This shift has been attributed to the intensification of monsoons,which led to opening up of dry habitats in humid forests and formation of deciduous forests.We explored the role of this climatic shift in the origin and diversification of dry-adapted plant genera Ceropegia and Brachystelma(Ceropegiae,Asclepiadoideae,Apocynaceae).We sampled Ceropegia and Brachystelma from across India and used five markers(two nuclear and three plastid regions)to reconstruct a global phylogeny of this group.Indian members of the tribe Ceropegiae were derived from Africa through at least four independent dispersal events.All dispersal events occurred in late Miocene after establishment of a monsoon climate.One of these early dispersing lineages underwent rapid radiation in peninsular India,giving rise to around 50 species.Thus,both dispersal and diversification events coincided with the intensification of monsoons and concomitant aridification.The role of environment in the evolution of floral characteristics and root type in the Indian radiation is also discussed.This is one of the first reports on a dry-adapted endemic radiation of plants in India.