Ming-Li Zhang

Plant phylogeography in arid Northwest China: Retrospectives and perspectives

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 regions flora.

Phylogeny of Caragana (Fabaceae) based on DNA sequence data from rbcL, trnS-trnG, and ITS

Phylogenetic relationships of 48 species of Caragana (Fabaceae: tribe Hedysareae) and one representative each of Astragalus, Calophaca, Halimodendron, and Hedysarum are estimated from DNA sequences of the rbcL gene, trnS-trnG intron and spacer, and ITS region. At least one representative of all five sections and 12 series within Caragana are included. Analyses yielded strongly supported clades corresponding to sections Caragana, Bracteolatae, and Frutescentes. The species of section Jubatae are distributed among three strongly supported clades, i.e., one with the species of section Bracteolatae, another with two species of section Spinosae, and a third as sister to section Frutescentes. All but the last of these six clades are corroborated by at least one unambiguously traced morphological character. The placement of the other four species of section Spinosae are not well supported and lack unambiguous morphological synapomorphies, and the samples of Calophaca and Halimodendron nest within Caragana with weak support.

Fruit and Seed Anatomy of Chenopodium and Related Genera (Chenopodioideae, Chenopodiaceae/Amaranthaceae): Implications for Evolution and Taxonomy

A comparative carpological study of 96 species of all clades formerly considered as the tribe Chenopodieae has been conducted for the first time. The results show important differences in the anatomical structure of the pericarp and seed coat between representatives of terminal clades including Chenopodium s.str.+Chenopodiastrum and the recently recognized genera Blitum, Oxybasis and Dysphania. Within Chenopodium the most significant changes in fruit and seed structure are found in members of C. sect. Skottsbergia. The genera Rhagodia and Einadia differ insignificantly from Chenopodium. The evolution of heterospermy in Chenopodium is discussed. Almost all representatives of the tribe Dysphanieae are clearly separated from other Chenopodioideae on the basis of a diverse set of characteristics, including the small dimensions of the fruits (especially in Australian taxa), their subglobose shape (excl. Teloxys and Suckleya), and peculiarities of the pericarp indumentum. The set of fruit and seed characters evolved within the subfamily Chenopodioideae is described. A recent phylogenetic hypothesis is employed to examine the evolution of three (out of a total of 21) characters, namely seed color, testa-cell protoplast characteristics and embryo orientation.

Diversification of plant species in arid Northwest China: species-level phylogeographical history of Lagochilus Bunge ex Bentham (Lamiaceae).

Lagochilus occurs in the arid zones across temperate steppe and desert regions of Northwest China. Cooling with strong dessication in the Pleistocene, along with rapid uplift of mountain ranges peripheral to the Qinghai-Tibet Plateau, appear to have had major impacts on the genetic structure of the flora. To understand the evolutionary history of Lagochilus and the divergence related to these past shifts of habitats among these regions, we sequenced the plastid intergenic spacers, psbA-trnH and trnS-trnG from populations throughout the known distributions of ten species of the genus. We investigated species-level phylogeographical patterns within Lagochilus. Phylogenetic trees were constructed using Neighbor-joining and Bayesian inference. The divergence times of major lineages were estimated with BEAST and IMa. Genetic structure and demographic history were inferred by AMOVA, neutrality tests, mismatch distribution, and Bayesian skyline plot analyses. The results showed that most chloroplast haplotypes were species-specific, and that the phylogeny of Lagochilus is geographically structured. The estimated Bayesian chronology and IMa suggested that the main divergence events for species between major eastern and western portions of the Chinese desert occurred at the Plio-/Pleistocene boundary (ca. 2.1-2.8 Ma ago), and likely coinciding with the formation of these deserts in Northwest China. The regional demographic expansions, in the western region at ca. 0.39 Ma, and in the eastern at ca. 0.06 Ma, or across all regions at ca. 0.26 Ma, showed the response to aridification accompanied by cooling of the Pleistocene sharply increased aridity in the Chinese deserts, which reflects a major influence of geologic and climatic events on the evolution of species of Lagochilus. We suggest that diversification is most likely the result of the past fragmentation due to aridification; the expansion of the range of species along with the deserts was an adaptation to dry and cold environments during the Quaternary.

Phylogeny of Salsoleae s.l. (Chenopodiaceae) based on DNA sequence data from ITS, psbB–psbH, and rbcL, with emphasis on taxa of northwestern China

To reconstruct phylogeny and verify the monophyly of major subgroups, a total of 52 species representing almost all species of Salsoleae s.l. in China were sampled, with analysis based on three molecular markers (nrDNA ITS, cpDNA psbB–psbH and rbcL), using maximum parsimony, maximum likelihood, and Bayesian inference methods. Our molecular evidence provides strong support for the following: (1) Camphorosmeae is nested within Salsoleae s.l. instead of the previously suggested sister relationship. (2) Tribe Salsoleae s.l. is monophyletic and is composed of three monophyletic subunits, Caroxyloneae, the Kali clade, and Salsoleae s.str. (3) Climacoptera is separated from Salsola s.l. It does not form a monophyletic group but is split into two monophyletic parts, Climacoptera I and Climacoptera II. (4) Halogeton is clearly polyphyletic, as are Anabasis and the genus Salsola s.l. (5) Caroxylon, Haloxylon, Kali, and Petrosimonia are well-supported monophyletic genera. Additional evidence is needed regarding the monophyly of Halimocnemis, which remains unclear.

Retreating or Standing: Responses of Forest Species and Steppe Species to Climate Change in Arid Eastern Central Asia

Background The temperature in arid Eastern Central Asia is projected to increase in the future, accompanied by increased variability of precipitation. To investigate the impacts of climate change on plant species in this area, we selected two widespread species as candidates, Clematis sibirica and C. songorica, from montane coniferous forest and arid steppe habitats respectively. Methodology/Principal Findings We employed a combined approach of molecular phylogeography and species distribution modelling (SDM) to predict the future responses of these two species to climate change, utilizing evidence of responses from the past. Genetic data for C. sibirica shows a significant phylogeographical signal (N ST > F ST, P<0.05) and demographic contraction during the glacial-interglacial cycles in the Pleistocene. This forest species would likely experience range reduction, though without genetic loss, in the face of future climate change. In contrast, SDMs predict that C. songorica, a steppe species, should maintain a consistently stable potential distribution under the Last Glacial Maximum (LGM) and the future climatic conditions referring to its existing potential distribution. Molecular results indicate that the presence of significant phylogeographical signal in this steppe species is rejected and this species contains a high level of genetic differentiation among populations in cpDNA, likely benefiting from stable habitats over a lengthy time period. Conclusions/Significance Evidence from the molecular phylogeography of these two species, the forest species is more sensitive to past climate changes than the steppe species. SDMs predict that the forest species will face the challenge of potential range contraction in the future more than the steppe species. This provides a perspective on ecological management in arid Eastern Central Asia, indicating that increased attention should be paid to montane forest species, due to their high sensitivity to disturbance.

Identifying a contact zone between two phylogeographic lineages of Clematis sibirica (Ranunculeae) in the Tianshan and Altai Mountains

Abstract  Clematis sibirica, a woody vine occurring primarily under conifer forests, is widespread in northern Eurasia. In this study, we intend to illustrate how the taxon has responded in the area of the Tianshan and Altai Mountains of Central Asia to the Pleistocene climatic fluctuations. The chloroplast intergenic spacer psbA‐trnH was sequenced for 125 individuals from 28 populations, and a total of eight chlorotypes were identified. The presence of definite phylogeographic structure was detected for the species (NST > GST, P < 0.001), and phylogenetic analysis indicated that the eight chlorotypes were clustered into two divergent lineages. They split at approximately 550–690 ka BP, according to coalescence analysis, coincident with the Pleistocene maximum glacial stage in these mountains, which suggests the restriction of these lineages to separate refugia at that time. Spatial analysis of molecular variance likewise divided the sampled populations into two associations, an Altai and eastern Tianshan group (populations 1–17), and a western Tianshan group (populations 18–28). Low levels of genetic diversity and unimodal mismatch distributions were obtained for both of these groups, suggesting postglacial range expansions. During the course of these expansions, mountain ranges surrounding the Dzungarian Basin probably served as migration corridors. In addition, a contact zone was identified in the central Tianshan and eastern Altai Mountains between the two phylogeographic lineages.

Phylogeography of the rare Gymnocarpos przewalskii (Caryophyllaceae): indications of multiple glacial refugia in north-western China

We investigated the phylogeography of Gymnocarpos przewalskii Maxim. (Caryophyllaceae), a rare relictual shrub restricted to north-western China, in the context of Quaternary climate oscillations. Three cpDNA regions (psbA–trnH, ycf6–psbM and rpl32–trnL (UAG)) were sequenced for 160 individuals from 16 populations. High genetic diversity (hT = 0.930, hS = 0.425) and a significant phylogeographic structure (NST > GST, P < 0.01) were identified; 31 different cpDNA haplotypes were detected. Phylogenetic analyses showed that the haplotypes were clustered into five clades, consistent with their distributions in the following four geographic regions: the Tarim Basin, Hami Basin, the western Yumen of Gansu Province and an easternmost region, consisting of populations in the Wulate Rear Banner region in Inner Mongolia, the Jinta and Jingyuan regions in Gansu Province and the Zhongwei region in Ningxia. The existence of regional divergence was supported by AMOVA, which revealed that ~63% of variation was due to differences among the four geographic regions. Four independent glacial refugia were inferred, in the western Tarim Basin, Hami Basin, the Liuyuan region in western Gansu and the easternmost region mentioned. Population bottlenecks and postglacial recolonisation were identified in the northern Tarim Basin, western Yumen and the Jinta region in Gansu Province.

Phylogenetic Origin of Phyllolobium with a Further Implication for Diversification of Astragalus in China

Astragalus is a species-rich genus occurring in the western arid habitats in China and its diversification and infrageneric relationships in this region remain unclear. In the present study, based on molecular data, we aim to (i) test whether Phyllolobium (previously treated as a subgenus Pogonophace in Astragalus) should be warranted; and (ii) date the origin of Phyllolobium and probable diversification of Astragalus sensu stricto (s.s.). We sequenced five species from Phyllolobium first and collected all related sequences from the genus, Astragalus s.s and their close relatives (Oxytropis and Caragana etc.). Our phylogenetic analyses suggested that all species of Phyllolobium comprise a monophyletic sister-group to genera of the subtribe Coluteinae. Molecular dating suggested that Phyllolobium and Astragalus s.s. originated around 8 and 10 million years ago. These two estimates are highly consistent with the intense uplifts of the Qinghai-Tibetan Plateau inferred from geological evidence. In addition, one section of Pogonophace (Sect. Robusti) was estimated to originate 2.5 million years ago and this section with a tendency for dry habitats seems to be evidence of Asian intensified aridity resulting from the intense uplift of the Qinghai-Tibetan Plateau.

Himalayan origin and evolution of Myricaria (Tamaricaeae) in the neogene.

Background Myricaria consists of about twelve-thirteen species and occurs in Eurasian North Temperate zone, most species in the Qinghai-Tibet Plateau (QTP) and adjacent areas. Methodology/Principal Findings Twelve species of Myricaria plus two other genera Tamarix and Reaumuria in Tamaricaceae, were sampled, and four markers, ITS, rps16, psbB-psbH, and trnL-trnF were sequenced. The relaxed Bayesian molecular clock BEAST method was used to perform phylogenetic analysis and molecular dating, and Diva, S-Diva, and maximum likelihood Lagrange were used to estimate the ancestral area. The results indicated that Myricaria could be divided into four phylogenetic clades, which correspond to four sections within the genus, of them two are newly described in this paper. The crown age of Myricaria was dated to early Miocene ca. 20 Ma, at the probable early uplifting time of the Himalayas. The Himalayas were also shown as the center of origin for Myricaria from the optimization of ancestral distribution. Migration and dispersal of Myricaria were indicated to have taken place along the Asian Mountains, including the Himalayas, Kunlun, Altun, Hendukosh, Tianshan, Altai, and Caucasus etc., westward to Europe, eastward to Central China, and northward to the Mongolian Plateau. Conclusions/Significance Myricaria spatiotemporal evolution presented here, especially the Himalayan origin at early Miocene ca. 20 Ma, and then migrated westward and eastward along the Asian mountains, offers a significant evolutionary case for QTP and Central Asian biogeography.