Abstract
To assess the role of the Qinghai-Tibetan Plateau uplift in shaping the intercontinental disjunction in Northern Hemisphere, we analyzed the origin and diversification within a geological timeframe for two relict herbaceous genera, Theligonum and Kelloggia (Rubiaceae). Phylogenetic relationships within and between Theligonum and Kelloggia as well as their relatives were inferred using five chloroplast markers with parsimony, Bayesian and maximum-likelihood approaches. Migration routes and evolution of these taxa were reconstructed using Bayesian relaxed molecular clock and ancestral area reconstruction. Our results suggest the monophyly of each Theligonum and Kelloggia. Eastern Asian and North American species of Kelloggia diverged at ca.18.52 Mya and the Mediterranean species of Theligonum diverged from eastern Asian taxa at ca.13.73 Mya. Both Kelloggia and Theligonum are Tethyan flora relicts, and their ancestors might have been occurred in warm tropical to subtropical environments along the Tethys coast. The Qinghai-Tibetan Plateau separated the eastern and western Tethyan area may contribute significantly to the disjunct distributions of Theligonum, and the North Atlantic migration appears to be the most likely pathway of expansion of Kelloggia to North America. Our results highlight the importance role of the QTP uplift together with corresponding geological and climatic events in shaping biodiversity and biogeographic distribution in the Northern Hemisphere.
Highlights
Clarifying the major factors underlying intercontinental disjunct distributions in the Northern Hemisphere has long been regarded as one of the central problems of plant biogeography[1]
Since the Cretaceous, one of the most remarkable geological changes in Eurasia is the uplift of the Qinghai-Tibetan Plateau (QTP) that resulted from the collision of the Indian Plate with Eurasian Plate in early Cenozoic[5,6,7]
It is generally accepted that the QTP uplifted multiple times at different scales and the Himalayas reached their current elevation in the middle-late Miocene, but the uplift histories of the different terranes that comprise this plateau currently remain unclear[9,10]
Summary
Clarifying the major factors underlying intercontinental disjunct distributions in the Northern Hemisphere has long been regarded as one of the central problems of plant biogeography[1]. Since the Cretaceous, one of the most remarkable geological changes in Eurasia is the uplift of the QTP that resulted from the collision of the Indian Plate with Eurasian Plate in early Cenozoic[5,6,7] These collision and uplift closed the Tethys Sea followed with the permanent closure of the Turgai Seaway and contributed significantly to continentalization in Europe in the middle to late Cenozoic[8]. All these events opened up new corridors for biotic exchange and created various types of new habitats, which produced great effects on climate and biodiversity in the Northern Hemisphere[9,10]. The effects of QTP uplift, continentalization in Europe and aridification in Central Asia in Cenozoic in producing many biogeographic disjunctions are well recognized[19,22,33,34,35,36], very few plant taxa has been evolved to elaborate the detailed date and process of biotic evolution during or after this uplift
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