Abstract
Exploring the effects of orographic events and climatic shifts on the geographic distribution of organisms in the Himalayas-Hengduan Mountains (HHM) region and Qinghai-Tibetan Plateau (QTP) is crucial to understand the impact of environmental changes on organism evolution. To gain further insight into these processes, we reconstructed the evolutionary history of nine Chamaesium species distributed across the HHM and QTP regions. In total, 525 individuals from 56 populations of the nine species were analyzed based on three maternally inherited chloroplast fragments (rpl16, trnT-trnL, and trnQ-rps16) and one nuclear DNA region (internal transcribed spacer, ITS). Fifty-two chloroplast DNA (cpDNA) and 47 ITS haplotypes were identified in nine species. All of the cpDNA and ITS haplotypes were species-specific. Phylogenetic analysis suggested that all nine species form a monophyletic clade with high support. Dating analysis and ancestral area reconstruction revealed that the ancestral group of Chamaesium originated in the southern Himalayan region at the beginning of the Paleogene (60.85 Ma). The nine species of Chamaesium then separated well during the last 25 million years started in Miocene. Our maxent modeling indicated the broad-scale distributions of all nine species remained fairly stable from LIG to the present and predicted that it will remain stable into the future. The initial split of Chamaesium was triggered by climate changes following the collision of the Indian plate with the Eurasia plate during the Eocene. Subsequently, divergences within Chamaesium may have been induced by the intense uplift of the QTP, the onset of the monsoon system, and Central Asian aridification. Long evolutionary history, sexual reproduction, and habitat fragmentation could contribute to the high level of genetic diversity of Chamaesium. The higher genetic differentiation among Chamaesium populations may be related to the drastic changes of the external environment in this region and limited seed/pollen dispersal capacity.
Highlights
The Himalayan-Hengduan Mountains (HHM) are key features of the biodiversity hotspots of South and East Asia (Myers et al, 2000; Zhang et al, 2002; Marchese, 2015), with alpine plant diversity being a significant contributor to the hotspot (Wu et al, 2011)
Like chloroplast DNA (cpDNA) haplotypes, all ITS haplotypes were species-specific in Chamaesium (Figure 4B), and more than 53.57% of the populations from each studied species were fixed for a single haplotype and 26.78% of the populations had two haplotypes
Genetic diversity is the product of the long-term evolution of species, which is caused by many factors and is one of the prerequisites for survival, adaptation and evolution of species (Soltis and Soltis, 1991)
Summary
The Himalayan-Hengduan Mountains (HHM) are key features of the biodiversity hotspots of South and East Asia (Myers et al, 2000; Zhang et al, 2002; Marchese, 2015), with alpine plant diversity being a significant contributor to the hotspot (Wu et al, 2011). Previous studies have suggested that the HHM region was formed by the collision of the Indian plate with Eurasia and the consequent rise of the Himalayas and QTP (DupontNivet et al, 2010; Zhang et al, 2012; Chatterjee et al, 2013). During the uplift in the Miocene, the Himalayan basins Thakkhola, Gyirong, and Zhada reached a mean elevation of 4,000 or 6,000 m (Garzione et al, 2001; Rowley et al, 2001; Saylor et al, 2009). The paleobotanical and paleoclimatic data suggests that Hengduan Mts. reached peak elevation shortly before the Late Pliocene, and the orogeny of Hengduan Mts. occurred as a final propagation of the uplift after 10 Ma (Sun et al, 2011)
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