Abstract
Encompassing some of the major hotspots of biodiversity on Earth, large mountain systems have long held the attention of evolutionary biologists. The region of the Qinghai‐Tibet Plateau (QTP) is considered a biogeographic source for multiple colonization events into adjacent areas including the northern Palearctic. The faunal exchange between the QTP and adjacent regions could thus represent a one‐way street (“out of” the QTP). However, immigration into the QTP region has so far received only little attention, despite its potential to shape faunal and floral communities of the QTP. In this study, we investigated centers of origin and dispersal routes between the QTP, its forested margins and adjacent regions for five clades of alpine and montane birds of the passerine superfamily Passeroidea. We performed an ancestral area reconstruction using BioGeoBEARS and inferred a time‐calibrated backbone phylogeny for 279 taxa of Passeroidea. The oldest endemic species of the QTP was dated to the early Miocene (ca. 20 Ma). Several additional QTP endemics evolved in the mid to late Miocene (12–7 Ma). The inferred centers of origin and diversification for some of our target clades matched the “out of Tibet hypothesis’ or the “out of Himalayas hypothesis” for others they matched the “into Tibet hypothesis.” Three radiations included multiple independent Pleistocene colonization events to regions as distant as the Western Palearctic and the Nearctic. We conclude that faunal exchange between the QTP and adjacent regions was bidirectional through time, and the QTP region has thus harbored both centers of diversification and centers of immigration.
Highlights
Many of the World's biodiversity hotspots are located in large mountain systems, such as the Andes, the East African Arc or the Himalayas (Marchese, 2015) and the role of mountains in organismic evolutionary diversification is considered to be manifold (Fjeldså, Bowie, & Rahbeck, 2012; Hoorn, Perrigo, & Antonelli, 2018; Muellner-Riehl, 2019; Rahbek, Borregaard, Antonelli, et al, 2019; Rahbek, Borregaard, Colwell, et al, 2019)
Alpine avian communities on the Qinghai-Tibet Plateau (QTP) are generally less species rich than those of the Himalayan forest ecosystems (Fjeldså et al, 2012), they harbor a couple of wide-range and narrow-range endemics as well as widespread trans-Palearctic species (Figure 1)
Weigold's ideas fell into oblivion, until the out of Tibet hypothesis was reanimated in the discussion on the Tibetan origin of Palearctic cold-adapted mammals inferred from fossil evidence (Deng et al, 2011; Tseng, Li, & Wang, 2013; Tseng et al, 2014; Wang, Li, & Takeuchi, 2016; Wang, Tseng, Li, Takeuchi, & Xie, 2014)
Summary
Many of the World's biodiversity hotspots are located in large mountain systems, such as the Andes, the East African Arc or the Himalayas (Marchese, 2015) and the role of mountains in organismic evolutionary diversification is considered to be manifold (Fjeldså, Bowie, & Rahbeck, 2012; Hoorn, Perrigo, & Antonelli, 2018; Muellner-Riehl, 2019; Rahbek, Borregaard, Antonelli, et al, 2019; Rahbek, Borregaard, Colwell, et al, 2019). The “out of Tibet hypothesis” for the montane and alpine fauna and flora of Eurasia is not a new concept, dating back to the work of the German ornithologist Hugo Weigold in the early 20th century. He was the first to postulate a Tibetan center of diversification (“Entwicklungszentrum”) for Palearctic terrestrial vertebrates, and earliest emergences of Tibetan faunal elements already during the Early Tertiary (Weigold, 1935, 1949, 2005). Some of these studies suggested a “Himalayan origin” (Wang et al, 2014)
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