Landscape genetics reveals that adaptive genetic divergence in Pinus bungeana (Pinaceae) is driven by environmental variables relating to ecological habitats

Rolling with the punches: Organism-environment interactions shape spatial pattern of adaptive differentiation in the widespread mantis shrimp Oratosquilla oratoria

Investigating spatial pattern of adaptive variation and its underlying processes can inform the adaptive potential distributed within species ranges, which is increasingly important in the context of a changing climate. A correct interpretation of adaptive variation pattern requires that population history and the ensuing population genetic structure are taken into account. Here we carried out such a study by integrating population genomic analyses, demographic model testing and species distribution modeling to investigate patterns and causes of adaptive differentiation in a widespread mantis shrimp, Oratosquilla oratoria, along a replicated, broad-scale temperature gradient in the northwestern Pacific (NWP). Our results supported a strong hierarchical ecogeographic structure dominated by habitat-linked divergence among O. oratoria populations accompanied with introgressive hybridization. A combined FST outlier and environmental correlation analyses revealed remarkable temperature-associated clines in allele frequency across paired North-South populations on Chinese and Japanese coasts, and identified a suite of loci associated with temperature adaptation. Further demographic model testing revealed the observed clinal variation derived partly from Pleistocene divergence followed by recent secondary contact. More importantly, the likelihood of hybridization is predicted to increase as climate change progresses, which would break barriers to gene flow and enable the spread of adaptive genetic variation. These results support that not only is temperature-driven adaptive differentiation occurs in O. oratoria but that such pattern is likely attributed to ancient adaptive variation, sustained by contemporary ocean conditions and a semi-permeable barrier to gene flow maintained by selection. They moreover provide genomic insights into the distribution of adaptive potential across O. oratoria' s species range. This work can serve as a case study to characterize adaptive diversity of marine species in the NWP by integrating environmental and genetic data at temporal and spatial scales in a population genomic framework, which would improve management and conservation actions under climate change.

Genomic Insights into High-Altitude Adaptation: A Comparative Analysis of Roscoea alpina and R. purpurea in the Himalayas

Environmental stress at high altitudes drives the development of distinct adaptive mechanisms in plants. However, studies exploring the genetic adaptive mechanisms of high-altitude plant species are scarce. In the present study, we explored the high-altitude adaptive mechanisms of plants in the Himalayas through whole-genome resequencing. We studied two widespread members of the Himalayan endemic alpine genus Roscoea (Zingiberaceae): R. alpina (a selfing species) and R. purpurea (an outcrossing species). These species are distributed widely in the Himalayas with distinct non-overlapping altitude distributions; R. alpina is distributed at higher elevations, and R. purpurea occurs at lower elevations. Compared to R. purpurea, R. alpina exhibited higher levels of linkage disequilibrium, Tajima's D, and inbreeding coefficient, as well as lower recombination rates and genetic diversity. Approximately 96.3% of the genes in the reference genome underwent significant genetic divergence (FST ≥ 0.25). We reported 58 completely divergent genes (FST = 1), of which only 17 genes were annotated with specific functions. The functions of these genes were primarily related to adapting to the specific characteristics of high-altitude environments. Our findings provide novel insights into how evolutionary innovations promote the adaptation of mountain alpine species to high altitudes and harsh habitats.

Putative Local Adaptive SNPs in the Genus Avicennia

The genus Avicennia with eight species grow in intertidal zones of tropical and temperate regions, ranging in distribution from West Asia, to Australia, and Latin America. These mangroves have several medicinal applications for mankind. Many genetic and phylogenetic studies have been carried out on mangroves, but none is concerned with geographical adaptation of SNPs. We therefore, used ITS sequences of about 120 Avicennia taxa growing in different parts of the world and undertook computational analyses to identify discriminating SNPs among these species and to study their association with geographical variables. A combination of multivariate and Bayesian approaches such as CCA, RDA, and LFMM were conducted to identify the SNPs with potential adaptation to geographical and ecological variables. Manhattan plot revealed that many of these SNPs are significantly associated with these variables. The genetic changes accompanied by local and geographical adaptation were illustrated by skyline plot. These genetic changes occurred not under a molecular clock model of evolution and probably under a positive selection pressure imposed in different geographical regions in which these plants grow.

Landscape genomics reveals adaptive genetic differentiation driven by multiple environmental variables in naked barley on the Qinghai-Tibetan Plateau

Understanding the local adaptation of crops has long been a concern of evolutionary biologists and molecular ecologists. Identifying the adaptive genetic variability in the genome is crucial not only to provide insights into the genetic mechanism of local adaptation but also to explore the adaptation potential of crops. This study aimed to identify the climatic drivers of naked barley landraces and putative adaptive loci driving local adaptation on the Qinghai-Tibetan Plateau (QTP). To this end, a total of 157 diverse naked barley accessions were genotyped using the genotyping-by-sequencing approach, which yielded 3123 high-quality SNPs for population structure analysis and partial redundancy analysis, and 37,636 SNPs for outlier analysis. The population structure analysis indicated that naked barley landraces could be divided into four groups. We found that the genomic diversity of naked barley landraces could be partly traced back to the geographical and environmental diversity of the landscape. In total, 136 signatures associated with temperature, precipitation, and ultraviolet radiation were identified, of which 13 had pleiotropic effects. We mapped 447 genes, including a known gene HvSs1. Some genes involved in cold stress and regulation of flowering time were detected near eight signatures. Taken together, these results highlight the existence of putative adaptive loci in naked barley on QTP and thus improve our current understanding of the genetic basis of local adaptation.

Studies on genetic diversity, gene flow and landscape genetic in Avicennia marina: Spatial PCA, Random Forest, and phylogeography approaches

Mangrove forests grow in coastal areas, lagoons, estuaries, and deltas and form the main vegetation in tidal and saline wetlands. Due to the mankind activities and also changes in climate, these forests face degradations and probably extinction in some areas. Avicennia marina is one of the most distributed mangrove species throughout the world. The populations of A. marina occur in a limited region in southern parts of Iran. Very few genetic and spatial analyses are available on these plants from our country. Therefore, the present study was planned to provide detailed information on Avicennia marina populations with regard to genetic diversity, gene flow versus genetic isolation, effects of spatial variables on connectivity and structuring the genetic content of trees populations and also identifying adaptive genetic regions in respond too spatial variables. We used SCoT molecular markers for genetic analyses and utilized different computational approaches for population genetics and landscapes analyses. The results of present study showed a low to moderate genetic diversity in the studied populations and presence of significant Fst values among them. Genetic fragmentation was also observed within each province studied. A limited gene flow was noticed among neighboring populations within a particular province. One population was almost completely isolated from the gene flow with other populations and had peculiar genetic content.Spatial PCA analysis revealed both significant global and local genetic structuring in the studied populations. Spatial variables like humidity, longitude and altitude were the most important spatial features affecting genetic structure in these populations.

Start codon targeted (SCoT) polymorphism marker in plant genome analysis: current status and prospects

The present review illustrates a comprehensive overview of the start codon targeted (SCoT) polymorphism marker and their utilization in various applications related to genetic and genomic studies. Start codon targeted (SCoT) polymorphism marker, a targeted fingerprinting marker technique, has gained considerable importance in plant genetics, genomics, and molecular breeding due to its many desirable features. SCoT marker targets the region flanking the start codon, a highly conserved region in plant genes. Therefore, it can distinguish genetic variations in a specific gene that link to a specific trait. It is a simple, novel, cost-effective, highly polymorphic, and reproducible molecular marker for which there is no need for prior sequence information. In the recent past, SCoT markers have been employed in many commercially important and underutilized plant species for a variety of applications, including genetic diversity analysis, interspecific/generic genetic relationships, cultivar/hybrid/species identification, sex determination, construction of linkage map, association mapping/analysis, differential gene expression, and genetic fidelity analysis of tissue culture-raised plants. The main aim of this review is to provide up-to-date information on SCoT markers and their application in many commercially important and underutilized plant species, mainly progress made in the last 8-10 years.

Assessing the current genetic structure of 21 remnant populations and predicting the impacts of climate change on the geographic distribution of Phoebe sheareri in southern China

Phoebe sheareri is a valuable tree species known as "Golden Nanmu" and is one of the most important protected tree species in China. However, natural populations are decreasing because of climate change and anthropogenic factors. To evaluate the genetic diversity and structure of remnant populations and the impacts of climate change on the distribution of potential suitable habitats, we conducted a field investigation and sampled 21 P. sheareri natural populations to evaluate their genetic diversity and structure using simple sequence repeat (SSR) molecular markers. Then, we predicted the distribution of suitable P. sheareri habitats across China under future scenarios (RCP 2.6 and RCP 8.5) and periods (2050 and 2070) using multivariate modeling methods-the MaxEnt model. The results showed a medium level of genetic diversity and low inbreeding in the 21 P. sheareri natural populations, and genetic differentiation among populations was significant, with 21.2 % genetic variation among populations. The remnant populations of P. sheareri were grouped into four genetic clusters based on genetic structure; five environmental variables involving four temperature variables and precipitation seasonality (Bio12) might determine the distribution of P. sheareri populations. In the future, the suitable habitats of P. sheareri are manifested as northward migration, and the highly suitable habitats are expected to increase. Our results highlight the importance of conservation units in situ, giving priority to populations with higher genetic diversity (e.g., TMS, FJS, and THY populations); sampling strategies for ex situ conservation, breeding and reforestation should consider climate change, especially Bio1 (annual mean temperature) and Bio12 (annual precipitation). Overall, this study may provide useful genetic information for strategies for the protection, management, and utilization of P. sheareri.

Revealing the Genetic Structure and Differentiation in Endangered Pinus bungeana by Genome-Wide SNP Markers

Understanding the genetic variation and differentiation of natural populations is essential for their protection, specifically if the species status is endangered as with Pinus bungeana. Here, we used 346,840 high density and strong specificity SNP loci to carry out genetic analyses (i.e., genetic diversity, genetic structure, phylogeny, and geographical differentiation) on 52 P. bungeana individuals from 5 populations (4 natural and one artificial) representing the main regions of the species distribution in China. Genetic diversity assessment indicated a trend of genetic diversity gradual decrease from west to east across the species distribution areas. Population genetic structure, PCA and phylogenetic analyses consistently indicated that populations in the central and eastern regions were clustered together, while those from the western regions were separated. Mantel test values indicated the presence of geographic isolation among populations, an important factor contributing to the observed genetic differentiation. The maximum likelihood tree and potential migration events inferred from TreeMix analysis indicated the presence of historical genetic exchanges between the west of Qinling Mountains and the Lvliang Mountains populations. Based on the generated genetic information, in situ and ex situ conservation strategies for P.bungeana germplasm resources are proposed, these strategies could be valuable for the conservation, protection and genetic improvement of this endangered species.

Population structure and adaptive variation of Helichrysum italicum (Roth) G. Don along eastern Adriatic temperature and precipitation gradient

Immortelle (Helichrysum italicum (Roth) G. Don; Asteraceae) is a perennial plant species native to the Mediterranean region, known for many properties with wide application mainly in perfume and cosmetic industry. A total of 18 wild H. italicum populations systematically sampled along the eastern Adriatic environmental gradient were studied using AFLP markers to determine genetic diversity and structure and to identify loci potentially responsible for adaptive divergence. Results showed higher levels of intrapopulation diversity than interpopulation diversity. Genetic differentiation among populations was significant but low, indicating extensive gene flow between populations. Bayesian analysis of population structure revealed the existence of two genetic clusters. Combining the results of F_ST - outlier analysis (Mcheza and BayeScan) and genome-environment association analysis (Samβada, LFMM) four AFLP loci strongly associated with the bioclimatic variables Bio03 Isothermality, Bio08 Mean temperature of the wettest quarter, Bio15 Precipitation seasonality, and Bio17 Precipitation of driest quarter were found to be the main variables driving potential adaptive genetic variation in H. italicum along the eastern Adriatic environmental gradient. Redundancy analysis revealed that the partitioning of genetic variation was mainly associated with the adaptation to temperature oscillations. The results of the research may contribute to a clearer understanding of the importance of local adaptations for the genetic differentiation of Mediterranean plants and allow the planning of appropriate conservation strategies. However, considering that the identified outlier loci may be linked to genes under selection rather than being the target of natural selection, future studies must aim at their additional analysis.

EST-SSR-based landscape genetics of Pseudotaxus chienii, a tertiary relict conifer endemic to China

Pseudotaxus chienii, belonging to the monotypic genus Pseudotaxus (Taxaceae), is a relict conifer endemic to China. Its populations are usually small and patchily distributed, having a low capacity of natural regeneration. To gain a clearer understanding of how landscape variables affect the local adaptation of P. chienii, we applied EST-SSR markers in conjunction with landscape genetics methods: (a) to examine the population genetic pattern and spatial genetic structure; (b) to perform genome scan and selection scan to identify outlier loci and the associated landscape variables; and (c) to model the ecological niche under climate change. As a result, P. chienii was found to have a moderate level of genetic variation and a high level of genetic differentiation. Its populations displayed a significant positive relationship between the genetic and geographical distance (i.e., "isolation by distance" pattern) and a strong fine-scale spatial genetic structure within 2 km. A putatively adaptive locus EMS6 (functionally annotated to cellulose synthase A catalytic subunit 7) was identified, which was found significantly associated with soil Cu, K, and Pb content and the combined effects of temperature and precipitation. Moreover, P. chienii was predicted to experience significant range contractions in future climate change scenarios. Our results highlight the potential of specific soil metal content and climate variables as the driving force of adaptive genetic differentiation in P. chienii. The data would also be useful to develop a conservation action plan for P. chienii.