Search

To explore the influence of vicariance on differentiation patterns of taxa in arid regions, we systematically assessed the genetic diversity and variability of Capparis spinosa , a typical xerophyte that is widely distributed in the Tianshan Mountains and adjacent areas. In total, 300 individuals from 25 populations were sampled, and 14 haplotypes were identified using two cpDNA sequences ( rpS 12- rpL 20 and ndh F). A high level of total genetic diversity ( H T = 0.859) was detected, and this was attributed to the extensive distribution range, which included numerous large populations. The SAMOVA results suggested that the 25 populations were clustered into 4 major geographical groups; a similar divergence trend was found by constructing a BEAST phylogenetic tree and a network diagram. The AMOVA results revealed that significant genetic differentiation occurred among groups. Our results indicated a considerable correlation between genetic divergence and geographical distribution. Isolation due to complex mountain and desert geography might limit gene exchange between disjunct populations, resulting in high differentiation between geographical groups. [ABSTRACT FROM AUTHOR]

Zygophyllum xanthoxylon, a desert species, displaying a broad east-west continuous distribution pattern in arid Northwestern China, can be considered as a model species to investigate the biogeographical history of this region. We sequenced two chloroplast DNA spacers ( psbK- psbI and rpl32- trnL) in 226 individuals from 31 populations to explore the phylogeographical structure. Median-joining network was constructed and analysis of AMOVA, SMOVA, neutrality tests and distribution analysis were used to examine genetic structure and potential range expansion. Using species distribution modeling, the geographical distribution of Z. xanthoxylon was modeled during the present and at the Last Glacial Maximum (LGM). Among 26 haplotypes, one was widely distributed, but most was restricted to either the eastern or western region. The populations with the highest levels of haplotype diversity were found in the Tianshan Mountains and its surroundings in the west, and the Helan Mountains and Alxa Plateau in the east. AMOVA and SAMOVA showed that over all populations, the species lacks phylogeographical structure, which is speculated to be the result of its specific biology. Neutrality tests and mismatch distribution analysis support past range expansions of the species. Comparing the current distribution to those cold and dry conditions in LGM, Z. xanthoxylon had a shrunken and more fragmented range during LGM. Based on the evidences from phylogeographical patterns, distribution of genetic variability, and paleodistribution modeling, Z. xanthoxylon is speculated most likely to have originated from the east and migrated westward via the Hexi Corridor. [ABSTRACT FROM AUTHOR]

Despite the absence of major Quaternary glaciations in arid Northwest China, significant climatic oscillations definitely impacted the evolution of the biota in situ. Phylogeography has grown as a discipline because it has provided explicit tools for the study of geographical subdivision among populations. But phylogeographical application for arid Northwest China has begun to blossom, which has provided evidence that aridification played a significant role in the increase of genetic diversity and species diversification. The time frame corresponds with Pleistocene climatic oscillations, which caused extreme aridity and the expansion of sandy deserts. In the Asian desert flora subkingdom and Eurasian forest subkingdom of Northwest China, the recurrent phylogeographical scenarios, identified by different case studies, broadly agree with longstanding biogeographic, floristic, and topographic concepts: (i) aridification promoted diversification and speciation of desert plants; (ii) desert expansion caused habitat fragmentation; (iii) the Altay-Tianshan Mountains included glacial refugia for plants; (iv) population expansion and recolonization from glacial refugia occurred during the postglacial period; and (v) desert plants persistence and alpine plants retreat during climate oscillations. We discuss the main phylogeographical findings in light of molecular and paleo-environmental evidence, emphasizing notable gaps in our knowledge and outlining future research perspectives for disentangling the evolutionary history of this arid region's flora. [ABSTRACT FROM AUTHOR]

Abstract: To investigate the phylogeographic structure of Ribes meyeri (Saxifragaceae) in northwestern China, we sequenced two cpDNA intergenic spacers (psbA-trnH, psbK-psbI) in 237 individuals from 30 natural populations across the species range. A total of 20 haplotypes were identified. High levels of haplotype diversity (h = 0.8377) and total genetic diversity (H T = 0.857) were detected at the species level, whereas low levels of diversity (Hs = 0.332) in intra-population, high levels of genetic divergence (Gst = 0.613, Nst = 0.855, Fst = 0.796), and significant phylogeographic structure (Nst > Gst, P < 0.001). The dominant haplotypes, located at internal nodes and derived from an extinct ancestral haplotype in the network, were found to be distinct between western and eastern population groups of the species. According to our IMa result, the split of these groups occurred at approximately 495 ka BP, this coincidents with the Pleistocene maximum glacial stage in this area. While the unimodal mismatch distributions suggested the postglacial range expansions. The refugia among populations of the western and eastern groups were inferred. [Copyright &y& Elsevier]