Abstract
The genetic architecture within a species in the Himalaya-Hengduan Mountains (HHM) region was considered as the consolidated consequence of historical orogenesis and climatic oscillations. The visualization of dispersal corridors as the function of population genetic connectivity became crucial to elucidate the spatiotemporal dynamics of organisms. However, geodiversity and physical barriers created by paleo geo-climatic events acted vigorously to impact notable alterations in the phylogeographic pattern and dispersal corridors. Therefore, to achieve detailed phylogeography, locate dispersal corridors and estimate genetic connectivity, we integrated phylogeography with species distribution modelling and least cost path of Mirabilis himalaica (Edgew.) Heimerl in the HHM. We amplified four cpDNA regions (petL-psbE, rps16-trnK, rps16 intron, trnS-trnG), and a low copy nuclear gene (G3pdh) from 241 individuals of 29 populations. SAMOVA, genealogical relationships, and phylogenetic analysis revealed four spatially structured phylogroups for M. himalaica with the onset of diversification in late Pliocene (c. 3.64 Ma). No recent demographic growth was supported by results of neutrality tests, mismatch distribution analysis and Bayesian skyline plot. Paleo-distribution modelling revealed the range dynamics of M. himalaica to be highly sensitive to geo-climatic change with limited long-distance dispersal ability and potential evolutionary adaptation. Furthermore, river drainage systems, valleys and mountain gorges were identified as the corridors for population genetic connectivity among the populations. It is concluded that recent intense mountain uplift and subsequent climatic alterations including monsoonal changes since Pliocene or early Pleistocene formulated fragmented habitats and diverse ecology that governed the habitat connectivity, evolutionary and demographic history of M. himalaica. The integrative genetic and geospatial method would bring new implications for the evolutionary process and conservation priority of HHM endemic species.
Highlights
The Himalaya and the Hengduan Mountains (HHM) are one of the main biodiversity hotspots of the Northern Hemisphere formed as a result of the collision between the Indian and Eurasian plate, started c. 55–50 million years ago (Ma) (Yin and Harrison, 2000; Dupont-Nivet et al, 2010). Mulch and Chamberlain (2006) suggests that the orogeny of the Hengduan Mountains occurred as a final propagation of the uplift after late Miocene (c. 10 Ma)
The present study focuses on the HHM endemic Mirabilis himalaica (Nyctaginaceae) that distributes from the Western Himalaya to the Hengduan Mountains that stretch from N India, WC Nepal, Bhutan, and S Xizang, SW Gansu, N Sichuan, NW Yunnan in the HHM region (Lu et al, 2003; Wang et al, 2019)
It was speculated that the ancestor of Mirabilis himalaica might have migrated from North America to the Himalayas either by Beringia or through long-distance dispersal, evolving allopatrically into the extant species (Wang et al, 2019)
Summary
The Himalaya and the Hengduan Mountains (HHM) are one of the main biodiversity hotspots of the Northern Hemisphere formed as a result of the collision between the Indian and Eurasian plate, started c. 55–50 million years ago (Ma) (Yin and Harrison, 2000; Dupont-Nivet et al, 2010). Mulch and Chamberlain (2006) suggests that the orogeny of the Hengduan Mountains occurred as a final propagation of the uplift after late Miocene (c. 10 Ma). The geological and climatic factors enormously influence the spatiotemporal pattern of temperate plant species, including historical dispersal and gene flow among the populations (Yu et al, 2015). Such orogenic uplift of mountains results in the formation of the geographical barriers, leading to fragmented habitat, loss of dispersal corridors, and restricted gene flow among populations; such factors furnish circumstances for divergence owing to genetic drift and natural selection (Liu et al, 2006; Meng et al, 2017). Historical dispersal process is likely to be a key factor to determine the current spatial population structure of species affected by the geological and climatic alterations (Hewitt, 2000). It is crucial to locate historical dispersal for a better understanding of the demographic and evolutionary history of species, as an outcome of paleo geo-climatic events (Brown and Yoder, 2015)
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