The importance of the uplift of the Qinghai-Tibetan Plateau for the subtribe Gentianinae (Gentianaceae): the relative contribution of in situ speciation versus colonisation

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This project is designed to study evolutionary processes that lead to the establishment high levels of biodiversity in the mountainous region of the Qinghai-Tibetan Plateau (QTP). It is often assumed that the uplift of the QTP triggered adaptive radiations in many plant lineages. Yet, there is a remarkable delay between uplift and biological response (diversification), indicating that geological processes alone cannot explain the observed accumulation of biodiversity in this region. Among others, the species pump effect driven by climate oscillation, and variations of ploidy levels might both have fostered diversification.Climatic niche and ploidy evolution will be investigated in the light of phylogenies derived from High-Throughput sequence data. The study of climatic niche evolution will provide indications whether shifts in climatic niche preferences promoted the diversification of a species-rich genus, Gentiana (Gentianaceae), which has been shown to originate in the region of the QTP. Furthermore, species distribution modelling (based upon occurrence and Worldclim data) will be performed for glacials and interglacials in order to evaluate the extent of range expansion/contraction, and the species pump effect during climate oscillations in the QTP region. Similar analyses will be performed for a clade of the Rocky Mountains, allowing to compare between these mountain systems. Species distribution modelling for glacials and interglacials, performed with the support of climate modellers (umbrella project proposal A), will be further completed by refined biogeographical analyses in order to identify major dispersal routes out of Tibet. Because these routes might vary according to the ecology of a taxon, three subclades with contrasting ecology (representing two to three thermal belts) within Gentiana will be compared. In the course of this study, I want to answer the following questions: (1) Is the shift in diversification rates in the lineage Gentiana sect. Cruciata/G. sect. Pneumonanthe associated with a shift in climatic niche requirements, and does this shift in climatic niche requirements correspond to variation of biome distribution through time? (2) Did lineages with contrasting ecology (G. sections Cruciata and Pneumonanthe, Frigida, Monopodiae) disperse out of the QTP under different climatic conditions and by different dispersal routes? (3) Did the mountainous regions of the QTP and North America act as species pumps in the sister sections Cruciata (mainly QTP), and Pneumonanthe (mainly North America), respectively? (4) Do polyploids have a broader climatic niche than diploids?