Population Genomic Analyses Research Articles

Leveraging genomic insights from the neglected malaria parasites P. malariae and P. ovale using selective whole genome amplification (SWGA) approach

BackgroundSystematic genomics-guided population-based studies on the neglected malaria parasites, P. malariae, P. ovale curtisi, and P. ovale wallikeri species remain challenging due to their low parasitemia, underestimation, and lack of comprehensive genetic analysis. Techniques that cost-effectively allow the enriching of the genome of interest from complex genome backgrounds for sequencing studies help immensely to perform genomic analyses. One such technique is selective whole-genome amplification (SWGA).ResultsWe applied SWGA using specifically designed primer sets targeting the pathogen genome to enrich parasite DNA from clinical samples. This enabled cost-effective and high-quality WGS for these neglected malaria species. WGS on SWGA-treated samples demonstrated improved genome coverage. Our method outperformed the published protocol for P.malariae with higher enrichment of the targeted genome. On average, P. malariae had 93% of the genome covered by ≥ 10 reads; parallel improvements in genome coverage were achieved for both P. ovale spp. with 81% on average of the genome covered by ≥ 10 reads. Consequently, the detection of thousands of additional SNPs not detectable in pre-SWGA samples was facilitated after SWGA, allowing more substantial downstream population genomics analysis, particularly for the polymorphic and antimalarial genes of great interest for all the species. Furthermore, leveraging the long DNA fragments generated by SWGA, we achieved high-quality genome assemblies for P. malariae and P. ovale using PacBio long reads sequencing technology.ConclusionsSWGA approach implemented here provides a powerful tool for enhancing genomic analysis of these neglected parasites, revealing population diversity, drug resistance markers, and hypervariable regions. This methodology constitutes a transformative tool to surmount the challenges of genomic analysis for neglected malaria parasites and can improve malaria research and control.

The haplotype-resolved and chromosome-level reference genome assembly of Diospyros deyangensis provides insights into the evolution and juvenile growth of persimmon

Abstract The Diospyros genus, which includes both wild and cultivated species such as Diospyros lotus and Diospyros kaki, represents a diverse genetic pool with significant agricultural value. In this study, we present a high-quality, haplotype-resolved, chromosome-level genome assembly for D. deyangensis (hereinafter referred to as “Deyangshi”), an autotetraploid wild species notable for its short juvenile phase, by integrating high-fidelity single-molecule, nanopore sequencing, and high-throughput chromosome conformation capture techniques. The assembled genome size is approximately 3.01 Gb, anchored onto 60 pseudo-chromosomes. Comparative genomic analysis revealed that the D. deyangensis genome underwent an additional whole-genome duplication event following the eudicots shared ancient hexaploidy event. Resequencing and clustering on 63 samples representing 11 geographically diverse Diospyros accessions revealed significant genetic differentiation between D. deyangensis and D. kaki, as well as between D. kaki and other Diospyros species using population genomic analyses, suggesting that D. kaki followed an independent evolutionary pathway. Additionally, we identified DdELF4 (EARLY FLOWERING 4) from the “Deyangshi” backcross population using bulked segregant RNA sequencing (BSR-seq) with 50 early flowering and 50 non-early flowering individuals. Overexpression of DdELF4 in Arabidopsis resulted in delayed flowering and down-regulation of FT gene expression, indicating its role as a flowering repressor. This high-quality genome assembly of “Deyangshi” provides an essential genomic resource for the Diospyros genus, particularly for breeding programs focused on developing early-flowering persimmon varieties.

Biology, genetics, and ecology of the cosmopolitan ectomycorrhizal ascomycete Cenococcum geophilum.

The ascomycete Cenococcum geophilum is a cosmopolitan and ecologically significant ectomycorrhizal (ECM) fungus that forms symbiotic associations with diverse host plants worldwide. As the only known ECM species within the large class Dothideomycetes, C. geophilum exhibits several characteristics that distinguish it from other ECM fungi. This fungus significantly contributes to ecosystem stability and development as an early colonizer of primary forest succession. The capacity of this symbiont to rapidly colonize disturbed or newly formed environments promotes the development of conditions that support the growth of other plant species, thus playing a crucial role in the ecological progression and restoration of ecosystems. Several C. geophilum isolates are known to enhance the drought resistance of host plants, a trait that is becoming increasingly important in the context of climate change and frequent drought events. In this review, we examined genetic studies that have assessed the phylogenetic structure of C. geophilum populations and identified the genes associated with adaptation to environmental stress and symbiosis. The high genetic diversity of C. geophilum is particularly noteworthy, considering its putative asexual reproductive mode. Population genomic analyses have suggested that C. geophilum is not a single species but rather a species complex comprising multiple cryptic lineages. This genetic variability may contribute to its adaptability and extensive distribution across habitats from circumpolar to tropical biomes. These lineages exhibit potential host preferences, suggesting a degree of specialization within the complex. The nuclear genome of C. geophilum has been sequenced, providing valuable insights into the symbiont genetic traits. Notably, this genome encodes a large set of repeated sequences and effector-like small secreted proteins. Transcriptomics has been used to identify candidate genes related to symbiosis and adaptation to environmental stress. Additionally, we briefly discuss how C. geophilum offers potential for sustainable forestry practices by improving resilience to stress.

Genome of root celery and population genomic analysis reveal the complex breeding history of celery.

Celery (Apium graveolens L.) is an important vegetable crop in the Apiaceae family. It comprises three botanical varieties: common celery with solid and succulent petioles, celeriac or root celery with enlarged and fleshy hypocotyls and smallage or leaf celery with slender, leafy and usually hollow petioles. Here we present a chromosome-level genome assembly of a celeriac cultivar and a comprehensive genome variation map constructed through resequencing of 177 representative celery accessions. Phylogenetic analysis revealed that smallage from the Mediterranean region represented the most ancient type of cultivated celery. Following initial domestication in this region, artificial selection has primarily aimed at enlarging the hypocotyl, resulting in celeriac, and at solidifying the petiole, leading to common celery. Selective sweep analysis and genome-wide association study identified several genes associated with hypocotyl expansion and revealed that the hollow/solid petiole trait directly correlated with the presence/absence of a NAC gene. Our study elucidates the complex breeding history of celery and provides valuable genomic resources and molecular insights for future celery improvement and conservation efforts.

Functional traits and adaptation of lake microbiomes on the Tibetan Plateau

BackgroundTibetan Plateau is credited as the “Third Pole” after the Arctic and the Antarctic, and lakes there represent a pristine habitat ideal for studying microbial processes under climate change.ResultsHere, we collected 169 samples from 54 lakes including those from the central Tibetan region that was underrepresented previously, grouped them to freshwater, brackish, and saline lakes, and generated a genome atlas of the Tibetan Plateau Lake Microbiome. This genomic atlas comprises 8271 metagenome-assembled genomes featured by having significant phylogenetic and functional novelty. The microbiomes of freshwater lakes are enriched with genes involved in recalcitrant carbon degradation, carbon fixation, and energy transformation, whereas those of saline lakes possess more genes that encode osmolyte transport and synthesis and enable anaerobic metabolism. These distinct metabolic features match well with the geochemical properties including dissolved organic carbon, dissolved oxygen, and salinity that distinguish between these lakes. Population genomic analysis suggests that microbial populations in saline lakes are under stronger functional constraints than those in freshwater lakes. Although microbiomes in the Tibet lakes, particularly the saline lakes, may be subject to changing selective regimes due to ongoing warming, they may also benefit from the drainage reorganization and metapopulation reconnection.ConclusionsAltogether, the Tibetan Plateau Lake Microbiome atlas serves as a valuable microbial genetic resource for biodiversity conservation and climate research.9n3SXpnTm6EbgSwcGAa_6cVideo

Near-complete telomere-to-telomere de novo genome assembly in Egyptian clover (Trifolium alexandrinum).

Egyptian clover (Trifolium alexandrinum L.), also known as berseem clover, is an important forage crop to Semi-arid conditions that was domesticated in ancient Egypt since 6,000 years BC and introduced and well adapted to numerous countries including India, Pakistan, Turkey, and Mediterranean region. Despite its agricultural importance, genomic research on Egyptian clover has been limited to developing efficient modern breeding programs. In the present study, we constructed near-complete telomere-to-telomere-level genome assemblies for two Egyptian clover cultivars, Helaly and Fahl. Initial assemblies were established by using highly-fidelity long-read technology. To extend sequence contiguity, we developed a gap-targeted sequencing (GAP-Seq) method, in which contig ends are targeted for sequencing to obtain long reads bridging two contigs. The total length of the resultant chromosome-level assemblies was 547.7Mb for Helaly and 536.3Mb for Fahl. These differences in sequence length can be attributed to the expansion of DNA transposons. Population genomic analysis using single-nucleotide polymorphisms revealed genomic regions highly differentiated between two cultivars and increased genetic uniformity within each cultivar. Gene ontologies associated with metabolic and biosynthetic processes and developmental processes were enriched in these genomic regions, indicating that these genes may determine the unique characteristics of each cultivar. Comprehensive genomic resources can provide valuable insights into genetic improvements in Egyptian clover and legume genomics.

Ocean-Wide Conservation Genomics of Blue Whales Suggest New Northern Hemisphere Subspecies.

The blue whale is an endangered and globally distributed species of baleen whale with multiple described subspecies, including the morphologically and genetically distinct pygmy blue whale. North Atlantic and North Pacific populations, however, are currently regarded as a single subspecies despite being separated by continental land masses and acoustic call differences. To determine the degree of isolation among the Northern Hemisphere populations, 14 North Pacific and 6 Western Australian blue whale nuclear and mitochondrial genomes were sequenced and analysed together with 11 publicly available North Atlantic blue whale genomes. Population genomic analyses revealed distinctly differentiated clusters and limited genetic exchange among all three populations, indicating a high degree of isolation between the Northern Hemisphere populations. Nevertheless, the genomic and mitogenomic distances between all blue whale populations, including the Western Australian pygmy blue whale, are low when compared to other inter-subspecies distances in cetaceans. Given that the Western Australian pygmy blue whale is an already recognised subspecies and further supported by previously reported acoustic differences, a proposal is made to treat the two Northern Hemisphere populations as separate subspecies, namely Balaenoptera musculus musculus (North Atlantic blue whale) and Balaenoptera musculus sulfureus (North Pacific blue whale). Furthermore, a first molecular viability assessment of all three populations not only found a generally high genomic diversity among blue whales but also a lack of alleles at low frequency, non-neutral evolution and increased effects of inbreeding. This suggests a substantial anthropogenic impact on the genotypes of blue whales and calls for careful monitoring in future conservation plans.

High-Resolution Genome Assembly and Population Genetic Study of the Endangered Maple Acer pentaphyllum (Sapindaceae): Implications for Conservation Strategies

Abstract Acer pentaphyllum Diels (Sapindaceae), a highly threatened maple endemic to the dry-hot valleys of the Yalong River in western Sichuan, China, represents a valuable resource for horticulture and conservation. This study presents the first chromosomal-scale genome assembly of A. pentaphyllum (~626 Mb, 2n = 26), constructed using PacBio HiFi and Hi-C sequencing technologies. Comparative genomic analyses revealed significant recent genomic changes through rapid amplification of transposable elements, particularly long terminal repeat retrotransposons, coinciding with the dramatic climate change during recent uplift of the Hengduan Mountains. Genes involved in photosynthesis, plant hormone signal transduction, and plant-pathogen interaction showed expansion and/or positive selection, potentially reflecting adaptation to the species’ unique dry-hot valley habitat. Population genomic analysis of 227 individuals from 28 populations revealed low genetic diversity (1.04 ± 0.97 × 10-3) compared to other woody species. Phylogeographic patterns suggest an unexpected upstream colonization along the Yalong River, while Quaternary climate fluctuations drove its continuous lineage diversification and population contraction. Assessment of genetic diversity, inbreeding, and genetic load across populations revealed concerning levels of inbreeding and accumulation of deleterious mutations in small, isolated populations, particularly those at range edges (TKX, CDG, TES). Based on these results, we propose conservation strategies, including the identification of management units and recommendations for genetic rescue. These findings not only facilitate the conservation of A. pentaphyllum but also serve as a valuable resource for future horticultural development and as a model for similar studies on other endangered plant species adapted to extreme environments.

Genomic population structure and diversity of the endangered Aphanius iberus: strategies for killifish conservation

AbstractThe evolutionary potential of a species directly impacts its ability to survive in fluctuating environments. A fundamental goal in wildlife conservation is enhancing this potential since anthropogenic pressures and rapid climate change are shifting environments at an alarming rate. One way to increase a species’ adaptive potential is through the delineation of management units based on population genomic analyses. Such units consist of evolutionarily significant gene pools requiring immediate conservation action. The delineation of priority units is fundamental for species on the brink of extinction, a predicament shared by numerous killifish species worldwide which face human-driven habitat transformations leading to the destruction of functioning ecosystems. The Mediterranean coast of the Iberian Peninsula has undergone one of the greatest human-driven habitat transformations in Europe since the turn of the 20th century as a result of agricultural exploitation and urbanization, imposing novel environmental pressures on various aquatic organisms including killifish species, such as the endangered and endemic Spanish toothcarp (Aphanius iberus Valenciennes, 1846). In the present study, we performed a SNP-based genetic analysis to delineate management units, or Operational Conservation Units (OCUs) for A. iberus, sampling a total of 176 individuals from 18 sample locations and analyzing their genetic structure, diversity, levels of gene flow, and degrees of genetic differentiation. Overall, the populations were highly structured with low genetic diversity values. Little to no gene flow was detected and FST values were high, indicating a large degree of genetic differentiation between populations, most likely attributable to habitat fragmentation. The results of our genetic analyses suggested the recommendation of nine OCUs for A. iberus, which should be implemented immediately into recovery programs to enhance the conservation management of this species. Using A. iberus as a study model, our research exemplifies how to delineate conservation priorities pertinent to killifish species with limited dispersal opportunity as a result of disruptions in population connectivity.

Integrating genetic and morphological data to assess species delimitation of two Japanese large abalones: Haliotis discus discus and H. madaka

Two large abalone species prevalent in the Japanese archipelago, Haliotis discus discus and H. madaka, are considered to have different morphological characteristics, and previous population genomics analyses have suggested that they have distinct genomic features. However, integrated analyses comparing the genetic and morphological data from these species are lacking; thus, it remains unclear whether these two species are distinct biological species. In this study, we performed integrated genetic and morphological analyses on individuals of the two species captured in Tokushima Prefecture, Japan. Genetic analysis based on 118 species-diagnostic single-nucleotide polymorphism (SNP) loci showed that H. discus discus and H. madaka were clearly assigned to distinct genetic clusters corresponding to the two species, with the exception of one H. madaka individual showing evidence of genomic introgression from H. discus discus. Multiple statistical analyses based on quantitative characteristics of shell shape and foot muscle color suggested that this H. madaka individual with genomic introgression from H. discus discus had H. discus discus-like quantitative characteristics consistently. In summary, this study suggests that H. discus discus and H. madaka are distinct biological species reproductively isolated in natural environments, but genomic introgression possibly blurs the species boundary between H. discus discus and H. madaka.

Habitat Association Predicts Population Connectivity and Persistence in Flightless Beetles: A Population Genomics Approach Within a Dynamic Archipelago.

Habitat association has been proposed to affect evolutionary dynamics through its control on dispersal propensity, which is considered a key trait for lineage survival in habitats of low durational stability. The Habitat Constraint hypothesis predicts different micro- and macroevolutionary patterns for stable versus dynamic habitat specialists, but the empirical evidence remains controversial and in insects mostly derives from winged lineages. We here use genome-wide SNP data to assess the effect of habitat association on the population dynamics of two closely related flightless lineages of the genus Eutagenia (Coleoptera: Tenebrionidae), which are co-distributed across the Cyclades islands in the Eastern Mediterranean but are associated with habitat types of different presumed stability: the psammophilous lineage is associated with dynamic sandy coastal habitats, while the geophilous lineage is associated with comparatively stable compact soil habitats. Our comparative population genomic and demographic analyses support higher inter-island gene flow in the psammophilous lineage, presumably due to the physical properties of dynamic sand-dune habitats that promote passive dispersal. We also find consistent bottlenecks in the psammophilous demes, suggesting that lineage evolution in the dynamic habitat is punctuated by local extinction and recolonisation events. The inferred demographic processes are surprisingly uniform among psammophilous demes, but vary considerably among geophilous demes depending on historical island connectivity, indicating more stringent constraints on the dynamic habitat lineage. This study extends the Habitat Constraint hypothesis by demonstrating that selection on dispersal traits is not the only mechanism that can drive consistent differences in evolutionary dynamics between stable versus dynamic habitat specialists.

Haplotype-resolved genome and population genomics of the threatened garden dormouse in Europe.

Genomic resources are important for evaluating genetic diversity and supporting conservation efforts. The garden dormouse (Eliomys quercinus) is a small rodent that has experienced one of the most severe modern population declines in Europe. We present a high-quality haplotype-resolved reference genome for the garden dormouse, and combine comprehensive short and long-read transcriptomics data sets with homology-based methods to generate a highly complete gene annotation. Demographic history analysis of the genome reveal a sharp population decline since the last interglacial, indicating an association between colder climates and population declines before anthropogenic influence. Using our genome and genetic data from 100 individuals, largely sampled in a citizen-science project across the contemporary range, we conduct the first population genomic analysis for this species. We find clear evidence for population structure across the species' core Central European range. Notably, our data show that the Alpine population, characterized by strong differentiation and reduced genetic diversity, is reproductively isolated from other regions and likely represents a differentiated evolutionary significant unit (ESU). The predominantly declining Eastern European populations also show signs of recent isolation, a pattern consistent with a range expansion from Western to Eastern Europe during the Holocene, leaving relict populations now facing local extinction. Overall, our findings suggest that garden dormouse conservation may be enhanced in Europe through the designation of ESUs.

A Next Generation of Hierarchical Bayesian Analyses of Hybrid Zones Enables Model-Based Quantification of Variation in Introgression in R.

Hybrid zones, where genetically distinct groups of organisms meet and interbreed, offer valuable insights into the nature of species and speciation. Here, we present a new R package, bgchm, for population genomic analyses of hybrid zones. This R package extends and updates the existing bgc software and combines Bayesian analyses of hierarchical genomic clines with Bayesian methods for estimating hybrid indexes, interpopulation ancestry proportions, and geographic clines. Compared to existing software, bgchm offers enhanced efficiency through Hamiltonian Monte Carlo sampling and the ability to work with genotype likelihoods combined with a hierarchical Bayesian approach, enabling inference for diverse types of genetic data sets. The package also facilitates the quantification of introgression patterns across genomes, which is crucial for understanding reproductive isolation and speciation genetics. We first describe the models underlying bgchm and then provide an overview of the R package and illustrate its use through the analysis of simulated and empirical data sets. We show that bgchm generates accurate estimates of model parameters under a variety of conditions, especially when the genetic loci analyzed are highly ancestry informative. This includes relatively robust estimates of genome-wide variability in clines, which has not been the focus of previous models and methods. We also illustrate how both selection and genetic drift contribute to variability in introgression among loci and how additional information can be used to help distinguish these contributions. We conclude by describing the promises and limitations of bgchm, comparing bgchm to other software for genomic cline analyses, and identifying areas for fruitful future development.

Comparative population genomics analysis for chicken body sizes using genome-wide SNPs.

This study aims to investigate the selection history, genome regions, and candidate genes associated with different chicken body sizes, thereby providing insights into the genetic basis of complex economic traits such as chicken body size and growth. In this study, a total of 217 individuals from eight breeds were selected. According to body size, they were divided into two groups: large chickens and bantam chickens, with four breeds in each group. Firstly, we investigate population structure by principal component analysis (PCA), phylogenetic tree, and ancestry component analysis. Next, we recognize runs of homozygosity (ROH) islands through calculating ROH. Finally, we carry out selection signatures analysis utilizing population differentiation index and nucleic acid diversity. The population structure analysis show that large and bantam chickens are clearly separated. Large chickens are clustered together, the bantam chickens are relatively dispersed. The results of ROH island analysis show that 48 and 56 ROH islands were identified in large and bantam chickens respectively. Among the interesting ROH islands, a total of eight candidate genes were identified. In selection signatures analysis, a total of 322 selected genes were annotated in large chickens, such as POU1F1, BMP10, enrichment in 16 GO terms. In bantam chickens, a total of 447 selected genes were annotated, such as IGF1, GRB10, enrichment in 20 GO terms and 2 KEGG pathways. The haplotype analysis results show that GRB10 has differences in chickens of different body sizes. By population structure, ROH islands, and selection signatures analysis, we have identified multiple genes associated with chicken body size, growth, and development (such as BMP10, IGF1, GRB10, etc). This provides a theoretical reference for the subsequent development of molecular markers for chicken body size and the analysis of the genetic mechanism of chicken body size.

Chinese Populations of Magnaporthe oryzae Serving as a Source of Human-Mediated Gene Flow to Asian Countries: A Population Genomic Analysis.

Magnaporthe oryzae, a filamentous heterothallic ascomycete fungus that serves as the causative agent of rice blast disease, is globally distributed in rice-growing regions. Populations shaped by environmental factors and human intervention play important roles in the formation of genetic structure. In this study, population structures and spatiotemporal dynamics were investigated based on large-scale whole genomic sequences of rice-infecting M. oryzae around the world. By analyzing these genetic structures, we identified divergent clades that crossed geographic boundaries. While we observed associations between the isolates and their geographic origins, we also found that there were frequent migration events occurring across Asia in main rice cultivation regions. Within Asia, China was the migration origin, facilitating gene flows to Japan and South Korea. Since the 1970s, the genetic diversity of M. oryzae populations in China has also shown a steadily increasing trend, continuing through to the 2020s. Additionally, our analysis of the evolutionary history of Asian M. oryzae populations provided insights into the population expansion that has taken place in recent decades. Overall, our findings indicate that human-mediated gene flows played a pivotal role in shaping the genetic structure of M. oryzae.

Admixture With Cultivated Sunflower Likely Facilitated Establishment and Spread of Wild Sunflower (Helianthus annuus) in Argentina.

A better understanding of the genetic and ecological factors underlying successful invasions is critical to mitigate the negative impacts of invasive species. Here, we study the invasion history of Helianthus annuus populations from Argentina, with particular emphasis on the role of post-introduction admixture with cultivated sunflower (also H. annuus) and climate adaptation driven by large haploblocks. We conducted genotyping-by-sequencing of samples of wild populations as well as Argentinian cultivars and compared them with wild (including related annual Helianthus species) and cultivated samples from the native range. We also characterised samples for 11 known haploblocks associated with environmental variation in native populations to test whether haploblocks contributed to invasion success. Population genomics analyses supported two independent geographic sources for Argentinian populations, the central United States and Texas, but no significant contribution of related annual Helianthus species. We found pervasive admixture with cultivated sunflower, likely as result of post-introduction hybridization. Genomic scans between invasive populations and their native sources identified multiple genomic regions of divergence, possibly indicative of selection, in the invaded range. These regions significantly overlapped between the two native-invasive comparisons and showed disproportionally high crop ancestry, suggesting that crop alleles contributed to invasion success. We did not find evidence of climate adaptation mediated by haploblocks, yet outliers of genome scans were enriched in haploblock regions and, for at least two haploblocks, the cultivar haplotype was favoured in Argentina. Our results show that admixture with cultivated sunflower played a major role in the establishment and spread of H. annuus populations in Argentina.

Resilience of genetic diversity in forest trees over the Quaternary

The effect of past environmental changes on the demography and genetic diversity of natural populations remains a contentious issue and has rarely been investigated across multiple, phylogenetically distant species. Here, we perform comparative population genomic analyses and demographic inferences for seven widely distributed and ecologically contrasting European forest tree species based on concerted sampling of 164 populations across their natural ranges. For all seven species, the effective population size, Ne, increased or remained stable over many glacial cycles and up to 15 million years in the most extreme cases. Surprisingly, the drastic environmental changes associated with the Pleistocene glacial cycles have had little impact on the level of genetic diversity of dominant forest tree species, despite major shifts in their geographic ranges. Based on their trajectories of Ne over time, the seven tree species can be divided into three major groups, highlighting the importance of life history and range size in determining synchronous variation in genetic diversity over time. Altogether, our results indicate that forest trees have been able to retain their evolutionary potential over very long periods of time despite strong environmental changes.

Population Genomics of Adaptive Radiations: Exceptionally High Levels of Genetic Diversity and Recombination in an Endemic Spider From the Canary Islands.

The spider genus Dysdera has undergone a remarkable diversification in the oceanic archipelago of the Canary Islands, with ~60 endemic species having originated during the 20 million years since the origin of the archipelago. This evolutionary radiation has been accompanied by substantial dietary shifts, often characterised by phenotypic modifications encompassing morphological, metabolic and behavioural changes. Hence, these endemic spiders represent an excellent model for understanding the evolutionary drivers and to pinpoint the genomic determinants underlying adaptive radiations. Recently, we achieved the first chromosome-level genome assembly of one of the endemic species, D. silvatica, providing a high-quality reference sequence for evolutionary genomics studies. Here, we conducted a low coverage-based resequencing study of a natural population of D. silvatica from La Gomera island. Taking advantage of the new high-quality genome, we characterised genome-wide levels of nucleotide polymorphism, divergence and linkage disequilibrium, and inferred the demographic history of this population. We also performed comprehensive genome-wide scans for recent positive selection. Our findings uncovered exceptionally high levels of nucleotide diversity and recombination in this geographically restricted endemic species, indicative of large historical effective population sizes. We also identified several candidate genomic regions that are potentially under positive selection, highlighting relevant biological processes, such as vision and nitrogen extraction as potential adaptation targets. These processes may ultimately drive species diversification in this genus. This pioneering study of spiders that are endemic to an oceanic archipelago lays the groundwork for broader population genomics analyses aimed at understanding the genetic mechanisms driving adaptive radiation in island ecosystems.

Haplotype-resolved genome assembly and resequencing provide insights into the origin and breeding of modern rose.

Modern rose (Rosa hybrida) is a recently formed interspecific hybrid and has become one of the most important and widely cultivated ornamentals. Here we report the haplotype-resolved chromosome-scale genome assembly of the tetraploid R. hybrida 'Samantha' ('JACmantha') and a genome variation map of 233 Rosa accessions involving various wild species, and old and modern cultivars. Homologous chromosomes of 'Samantha' exhibit frequent homoeologous exchanges. Population genomic and genomic composition analyses reveal the contributions of wild Rosa species to modern roses and highlight that R. odorata and its derived cultivars are important contributors to modern roses, much like R. chinensis 'Old Blush'. Furthermore, selective sweeps during modern rose breeding associated with major agronomic traits, including continuous and recurrent flowering, double flower, flower senescence and disease resistance, are identified. This study provides insights into the genetic basis of modern rose origin and breeding history, and offers unprecedented genomic resources for rose improvement.

Evolution of gene networks underlying adaptation to drought stress in the wild tomato Solanum chilense.

Drought stress is a key limitation for plant growth and colonization of arid habitats. We study the evolution of gene expression response to drought stress in a wild tomato, Solanum chilense, naturally occurring in dry habitats in South America. We conduct a transcriptome analysis under standard and drought experimental conditions to identify drought-responsive gene networks and estimate the age of the involved genes. We identify two main regulatory networks corresponding to two typical drought-responsive strategies: cell cycle and fundamental metabolic processes. The metabolic network exhibits a more recent evolutionary origin and a more variable transcriptome response than the cell cycle network (with ancestral origin and higher conservation of the transcriptional response). We also integrate population genomics analyses to reveal positive selection signals acting at the genes of both networks, revealing that genes exhibiting selective sweeps of older age also exhibit greater connectivity in the networks. These findings suggest that adaptive changes first occur at core genes of drought response networks, driving significant network re-wiring, which likely underpins species divergence and further spread into drier habitats. Combining transcriptomics and population genomics approaches, we decipher the timing of gene network evolution for drought stress response in arid habitats.