Genetic admixture and lineage separation in a southern Andean plant

An Evolutionary Study of Carex Subg. Psyllophorae (Cyperaceae) Sheds Light on a Strikingly Disjunct Distribution in the Southern Hemisphere, With Emphasis on Its Patagonian Diversification

Carex subgenus Psyllophorae is an engaging study group due to its early diversification compared to most Carex lineages, and its remarkable disjunct distribution in four continents corresponding to three independent sections: sect. Psyllophorae in Western Palearctic, sect. Schoenoxiphium in Afrotropical region, and sect. Junciformes in South America (SA) and SW Pacific. The latter section is mainly distributed in Patagonia and the Andes, where it is one of the few Carex groups with a significant in situ diversification. We assess the role of historical geo-climatic events in the evolutionary history of the group, particularly intercontinental colonization events and diversification processes, with an emphasis on SA. We performed an integrative study using phylogenetic (four DNA regions), divergence times, diversification rates, biogeographic reconstruction, and bioclimatic niche evolution analyses. The crown age of subg. Psyllophorae (early Miocene) supports this lineage as one of the oldest within Carex. The diversification rate probably decreased over time in the whole subgenus. Geography seems to have played a primary role in the diversification of subg. Psyllophorae. Inferred divergence times imply a diversification scenario away from primary Gondwanan vicariance hypotheses and suggest long-distance dispersal-mediated allopatric diversification. Section Junciformes remained in Northern Patagonia since its divergence until Plio-Pleistocene glaciations. Andean orogeny appears to have acted as a northward corridor, which contrasts with the general pattern of North-to-South migration for temperate-adapted organisms. A striking niche conservatism characterizes the evolution of this section. Colonization of the SW Pacific took place on a single long-distance dispersal event from SA. The little ecological changes involved in the trans-Pacific disjunction imply the preadaptation of the group prior to the colonization of the SW Pacific. The high species number of the section results from simple accumulation of morphological changes (disparification), rather than shifts in ecological niche related to increased diversification rates (radiation).

Connection, isolation and reconnection: Quaternary climatic oscillations and the Andes shaped the phylogeographical patterns of the Patagonian bee Centris cineraria (Apidae)

The joint effect of the Andes as a geographical barrier and the Quaternary glaciations as promoters of genetic divergence remains virtually unexplored in southern South America. To help fill this knowledge gap, in this study we investigated the demographic history of Centris cineraria, a solitary bee mainly distributed in Patagonia. We used mitochondrial and nuclear markers and performed phylogeographical and dating analyses, adjusted spatio-temporal diffusion and species distribution models, and used Approximate Bayesian Computation to identify likely historical demographic scenarios. Our results revealed that during glacial periods the Andes represented a barrier due to the extent of the ice-sheets and the occurrence of unsuitable habitats, while interglacials allowed for gene flow across the Andes. Secondary contact between previously isolated lineages was evident across at least two low-altitude Andean areas, the northern one being a putative glacial refugium. Our findings also suggest that C. cineraria has persisted in situ in four periglacial refugia located along a north–south transect, congruent with the maximum extent of the ice sheet during the Greatest Patagonian Glaciation. As the first phylogeographical study of Patagonian insects, our work reveals that the interaction between Quaternary climatic oscillations and the Andes as a barrier was the main driver of the spatial and demographic history of C. cineraria.

AFLP-based genetic diversity of wild orchardgrass germplasm collections from Central Asia and Western China, and the relation to environmental factors

Dactylis glomerata L. (orchardgrass) is an important perennial forage species in temperate areas of the world. It is usually used for silage, grazing and hay because of its high nutritional value and reproducibility. Central Asia, Xinjiang and Tibetan Plateau in China possess various special micro-environments that harbor many valuable resources, while different degrees of degradation of the grassland ecosystem occurred due to climatic changing and human activities. Investigating the genetic diversity of wild D. glomerat could provide basis for collection, protection, and utilization of some excellent germplasm resources. Totally 210 individuals from 14 populations—five from Xinjiang, two from Kangding (Tibetan Plateau), and seven from Central Asia were identified using AFLP technology. The average values of Nei’s genetic diversity (H_j) and Shannon information index (H_o) were 0.383 and 0.394 respectively. UPGMA tree, STRUCTURE analysis and principal coordinate analysis (PCoA) showed populations from same region clustered together. AMOVA revealed 35.10% of the genetic differentiation (F_st) occurred among populations. Gene flow (N_m) was limited among all populations. Genetic diversity of D. glomerata was high but limited under isolation-by-distance pattern, resulting in high genetic differentiation and low gene flow among populations. Adjacent regions also exhibited similar results because of the barriers of high mountains. The environmental factors, such as precipitation, elevation, latitude and longitude also had some impacts on genetic diversity and structure pattern of populations.

Genetic Structure and Eco-Geographical Differentiation of Wild Sheep Fescue (Festuca ovina L.) in Xinjiang, Northwest China

Glaciation and mountain orogeny have generated new ecologic opportunities for plants, favoring an increase in the speciation rate. Moreover, they also act as corridors or barriers for plant lineages and populations. High genetic diversity ensures that species are able to survive and adapt. Gene flow is one of the most important determinants of the genetic diversity and structure of out-crossed species, and it is easily affected by biotic and abiotic factors. The aim of this study was to characterize the genetic diversity and structure of an alpine species, Festuca ovina L., in Xinjiang, China. A total of 100 individuals from 10 populations were analyzed using six amplified fragment length polymorphism (AFLP) primer pairs. A total of 583 clear bands were generated, of which 392 were polymorphic; thus, the percentage of polymorphic bands (PPB) was 67.24%. The total and average genetic diversities were 0.2722 and 0.2006 (0.1686-0.2225), respectively. The unweighted group method with arithmetic mean (UPGMA) tree, principal coordinates analysis (PCoA) and Structure analyses revealed that these populations or individuals could be clustered into two groups. The analysis of molecular variance analysis (AMOVA) suggested that most of the genetic variance existed within a population, and the genetic differentiation (Fst) among populations was 20.71%. The Shannon differentiation coefficient (G'st) among populations was 0.2350. Limited gene flow (Nm = 0.9571) was detected across all sampling sites. The Fst and Nm presented at different levels under the genetic barriers due to fragmentation. The population genetic diversity was significant relative to environmental factors such as temperature, altitude and precipitation.

Phylogeography, genetic diversity and population structure in a Patagonian endemic plant

Phylogeographical patterns provide valuable insight into the historical processes underlying diversification, and may provide a better understanding of biodiversity, dispersal modes, diversification times, extinctions, refuge areas and other species-/population-level processes. Here, we examine the genetic structure of Oxalis laciniata, a representative of Oxalis, which is an important emerging model in evolutionary biology and phylogenetic studies. We analyse genetic correlation, haplotype diversity and genetic structure. In this study, cpDNA reveals the presence of 16 haplotypes, connected in tree networks. Genetic diversity is high and polymorphism is low among populations based on ISSR markers. Both clustering and analysis of the structure of the population indicate two different groups. Distribution modelling predicts two potential distribution areas. Our main conclusions are: (i) The phylogeographical pattern demonstrates non-random organization of genetic variability since two distinct groups can be distinguished; (ii) two refugia are proposed: one is situated in the SE, holding the most ancestral haplotypes; and the second one is situated in the SW; (iii) we propose an in situ diversification hypothesis for the populations located in the steppe; (iv) the centre of diversification coincides with the centre of the distribution; (v) distribution modelling shows a strong correspondence with the distribution of the species but it also suggests the possibility of occurrence in the Central Andes.