Spatio-temporal evolution of Allium L. in the Qinghai–Tibet-Plateau region: Immigration and in situ radiation

Abstract

A plethora of studies investigating the origin and evolution of diverse mountain taxa has assumed a causal link between geological processes (orogenesis) and a biological response (diversification). Yet, a substantial delay (up to 30 Myr) between the start of orogenesis and diversification is often observed. Evolutionary biologists should therefore identify alternative drivers of diversification and maintenance of biodiversity in mountain systems. Using phylogenetic, biogeographic, and diversification rate analyses, we could identify two independent processes that most likely explain the diversity of the widespread genus Allium in the Qinghai–Tibet Plateau (QTP) region: (1) While the QTP-related taxa of the subgenus Melanocrommyum diversified in situ, (2) QTP-related taxa of other subgenera migrated into the QTP from multiple source areas. Furthermore, shifts in diversification rates within Allium could not be attributed spatially and temporally to the uplift history of the QTP region. Instead, global cooling and climate oscillations in the Quaternary were major contributors to increased speciation rates in three clades of Allium. Our study therefore adds to the growing evidence supporting the “mountain-geo-biodiversity hypothesis”, which highlights the role of climate oscillations for the diversification of mountain organisms.

Polyploidy promotes species diversification of Allium through ecological shifts

“…The inferred phylogenetic tree of Allium based on the concatenated dataset was well resolved (Figs a, S1a). The phylogeny was congruent with previous studies, hypothesising that there are three main evolutionary lines (ELs) in Allium (Friesen et al ., ; Hauenschild et al ., ), with EL1 dominated by species from North America (NAM, 58% of EL1 species) and EUR (Europe, 14%), EL2 mainly including species from central and western Asia (CWA, 71% of EL2 species), and EL3 from a combination of CWA (35% of EL3), EA (temperate and boreal East Asia, 27%), and EUR (18%) (Fig. S1b).…”

“…Li et al ., ; Zhang et al ., ; Xie et al ., ). However, few studies have ever quantified these processes to identify the underlying mechanisms (Hauenschild et al ., ).…”

Increasing phylogenetic support for explosively radiating taxa: The promise of high‐throughput sequencing for Oxytropis (Fabaceae)

“…Admittedly, a prerequisite for the above analyses is the availability of a robust phylogeny, which could present some challenges for fast evolving taxa. For the mountains of Asia, only a few studies fulfill the above mentioned requirements (Milne et al, 2010;Eaton et al, 2012;Zhang et al, 2014;Favre et al, 2016;Ebersbach et al, 2017;Hauenschild et al, 2017;Xing & Ree, 2017). Yet, most of these studies have concentrated on taxa particularly diverse in Asian mountains benefitting from generous rainfall of the monsoon systems (Himalaya, Hengduan Mountains; reviewed in Wen et al, 2014).…”

Phylogeography of two closely related species of Allium endemic to East Asia: Population evolution in response to climate oscillations

“…The study of Hauenschild et al. () about the widespread genus Allium also supported this hypothesis.…”

“…In this period, Taihang Mountains nearly formed a S-N-striking uplifted mountain range within the central North China block. However, the divergence time is different from that in Hauenschild et al (2017), which may result from the different analysis methods. Our analyses is as solid as theirs, and that even if our results would be slightly older, our interpretation remains similar and plausible.…”