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The European green toad (Bufotes viridis) is geographically widely distributed. While the species global conservation status is labeled as of least concern by the IUCN, it is declining in many parts of its range where populations are fragmented and isolated. A high-quality reference genome is an important resource for conservation genomic researchers who are trying to understand and interpret the genomic signals of population decline, inbreeding, and the accumulation of deleterious mutations. Here, we assembled and annotated a chromosome-level reference genome for B. viridis as part of the European Reference Genome Atlas pilot project. The genome assembly, with a size of similar to 3.89 Gb consists of 11 chromosomes and an additional 2,096 unplaced scaffolds. The final assembly had a scaffold N50 value of 478.39 Mb and covered 90.4% single copy tetrapod orthologs, and 46.7% repetitive elements. Finally, a total of 23,830 protein-coding genes matching a known gene, together with 56,974 mRNAs were predicted. This high-quality reference genome will benefit amphibian evolutionary genomics research and enable conservation genetic studies to inform practical conservation work on this species.

How species adapt to diverse environmental conditions is essential for understanding evolution and the maintenance of biodiversity. The European cisco (Coregonus albula) is a salmonid that occurs in both fresh and brackish water, and this together with the presence of sympatric spring- and autumn-spawning lacustrine populations provides an opportunity for studying the genetics of adaptation in relation to salinity and timing of reproduction. Here, we present a high-quality reference genome of the European cisco based on PacBio HiFi long read sequencing and HiC-directed scaffolding. We generated low-coverage whole-genome sequencing data from 336 individuals across 12 population samples to explore population structure and genetics of ecological adaptation. We found a major subdivision between two groups of populations most likely reflecting colonisation from different glacial refugia. Within the two major groups, we detected further genetic differentiation between spring- and autumn-spawning populations and between populations from freshwater lakes, rivers and brackish water (Bothnian Bay). A genome-wide screen for genetic differentiation among populations identified a set of outlier SNPs strongly correlated with spawning timing and salinity. Several of the genes associated with spawning time, including BHLHE40, TIMELESS and CPT1A, have previously been shown to have a role in circadian rhythm biology. As many as 17 loci were associated with genetic differentiation between populations reproducing in fresh and brackish water. This study provides insights into the genomic basis of ecological adaptation in European cisco with implications for sustainable fishery management.

Population genomics can reveal trends and drivers of biodiversity loss, but it is still unclear how best to use measures of genome variation to understand population vulnerability in insects. Here we study genome variation in three species of Anthophora bees that show contrasting population trends in northern Europe. Two species, Anthophora plagiata and Anthophora retusa , have experienced declines and recoveries of different magnitudes in the last 50 years, whereas a third species, Anthophora quadrimaculata , has relative population stability. We generate highly contiguous genome assemblies and use them to study genome variation in 136 samples of these species collected throughout Sweden. We find exceedingly low genetic variation in A. plagiata , which has experienced a severe recent bottleneck, but high genetic variation in A. retusa , despite a similar recent population trajectory. Fragmented populations of the threatened species A. plagiata appear isolated from each other, but in A. retusa, there is a lack of deep population structure among geographically separated subpopulations. We infer population size in the distant past using MSMC2 and recent past using GONE. These methods are remarkably concordant and indicate ancient fluctuations in population size dating back to the Pleistocene, with moderate expansions in the past century in all three species. These results are comparable to some other studies of endangered insects, which have experienced population declines that predate the modern era. We detect long blocks of identity-by-state in A. plagiata , indicative of severe recent inbreeding. Translocations between isolated populations of this species could have a positive effect on their resilience.

Distyly, an example of convergent evolution, is governed by a supergene, the S-locus, in several species. Recent studies highlight similar genomic architectures of independently evolved S-loci, but its mode of origin and whether similar regulatory pathways underlie the convergent evolution of distyly remains unclear. We examined the evolution of supergenes and mechanisms underlying distyly in Linum species that diverged c. 33 million years ago (Ma). Using haplotype-resolved genomes and population genomics, we identified and characterized the S-loci of Linum perenne (distylous) and Linum grandiflorum (style length dimorphic), and compared them to that of Linum tenue (distylous). We then tested for a conserved hormonal mechanism regulating style length polymorphism in Linum. The S-locus supergene was consistently hemizygous in short-styled individuals across all three species, although it showed variation in size, gene content, repeat elements and extent of recombination suppression. Two S-linked candidate genes, TSS1 (style length) and WDR-44 (anther height/pollen self-incompatibility), were conserved. Consistent with a brassinosteroid-dependent role of TSS1, epibrassinolide treatment revealed a conserved, morph-specific effect on style length. S-locus structural polymorphism, candidate distyly genes and mechanisms regulating style length remain conserved > 30 Ma in Linum. In combination with findings from other systems, our results suggest that the brassinosteroid pathway frequently contributes to style length polymorphism.

Chromosomal inversions, by suppressing recombination, can profoundly shape genome evolution and drive adaptation. In the common quail (Coturnix coturnix), a highly mobile bird with a vast Palearctic breeding range, we previously identified a massive inversion on chromosome 1 associated with distinct phenotypes and restricted geographic distribution. Here, using a new de novo genome assembly, we characterise this inversion and uncover additional, ancient structural variation on chromosome 2 that segregates across the species' range: either two putatively linked inversions or a single, large inversion that appears as two due to scaffolding limitations. Together, the inversions encompass a remarkable 15.6% of the quail genome (153.6 Mbp), creating highly divergent haplotypes that diverged over a million years ago. While the chromosome 1 inversion is linked to phenotypic differences, including morphology and migratory behaviour, the chromosome 2 inversion(s) show no such association. Notably, all inversion regions exhibit reduced effective population size and a relaxation of purifying selection, evidenced by elevated nonsynonymous-to-synonymous substitution ratios (N/S). This suggests that inversions, particularly the geographically restricted one on chromosome 1, may act as engines of diversification, accelerating the accumulation of functional variation and potentially contributing to local adaptation, especially within isolated island populations. Our findings demonstrate how large-scale chromosomal rearrangements can compartmentalise a genome, fostering distinct evolutionary trajectories within a single, highly mobile species.

Humans have relied on animal fur for centuries, yet fur farming only began recently during the mid-19th Century. Little is known about this incipient domestication or the genomic processes involved. Domestication may involve founder effects, population bottlenecks and low population size, which, when combined with intense artificial selection, lead to inbreeding, a limited gene pool and reduced fitness. The arctic fox (Vulpes lagopus) has been farmed intensively since the early 1900s and has been artificially selected for economic phenotypes. We investigated the origin of these lineages and the genomic consequences of intensive farming by comparing the genomes of farmed and wild arctic foxes from across their range. Our research indicates recent inbreeding through long Runs of Homozygosity and reduced genomic variation in farmed foxes relative to their respective wild populations. We identified a coastal ecotype origin for all Fennoscandian farmed arctic foxes, aligning them phylogenetically with the wild Icelandic population, a geographically isolated and phenotypically distinct coastal lineage. The depleted genome-wide heterozygosity and increased recent inbreeding in farmed fox lineages is consistent with a heavy consequence of domestication, shedding light on the demographic history and genomic consequences of human manipulation. We highlight the need for increased genomic investigations into fur farm populations to understand the incipient domestication process and uncover the cost of intense farming. The genomic consequences of domestication must be considered in the management of fur farms, with actionable steps needed to prevent descendants of escaped farmed foxes from polluting the gene pool in the wild through introgression.

The clouded apollo (Parnassius mnemosyne) is a palearctic butterfly distributed over a large part of western Eurasia, but population declines and fragmentation have been observed in many parts of the range. The development of genomic tools can help to shed light on the genetic consequences of the decline and to make informed decisions about direct conservation actions. Here, we present a high-contiguity, chromosome-level genome assembly of a female clouded apollo butterfly and provide detailed annotations of genes and transposable elements. We find that the large genome (1.5 Gb) of the clouded apollo is extraordinarily repeat rich (73%). Despite that, the combination of sequencing techniques allowed us to assemble all chromosomes (n_c = 29) to a high degree of completeness. The annotation resulted in a relatively high number of protein-coding genes (22,854) compared with other Lepidoptera, of which a large proportion (21,635) could be assigned functions based on homology with other species. A comparative analysis indicates that overall genome structure has been largely conserved, both within the genus and compared with the ancestral lepidopteran karyotype. The high-quality genome assembly and detailed annotation presented here will constitute an important tool for forthcoming efforts aimed at understanding the genetic consequences of fragmentation and decline, as well as for assessments of genetic diversity, population structure, inbreeding, and genetic load in the clouded apollo butterfly.

The B-cell acute lymphoblastic leukemia (ALL) cell line REH, with the t(12;21) ETV6::RUNX1 translocation, is known to have a complex karyotype defined by a series of large-scale chromosomal rearrangements. Taken from a 15-yr-old at relapse, the cell line offers a practical model for the study of pediatric B-ALL. In recent years, short- and long-read DNA and RNA sequencing have emerged as a complement to karyotyping techniques in the resolution of structural variants in an oncological context. Here, we explore the integration of long-read PacBio and Oxford Nanopore whole-genome sequencing, IsoSeq RNA sequencing, and short-read Illumina sequencing to create a detailed genomic and transcriptomic characterization of the REH cell line. Whole-genome sequencing clarified the molecular traits of disrupted ALL-associated genes including CDKN2A, PAX5, BTG1, VPREB1, and TBL1XR1, as well as the glucocorticoid receptor NR3C1. Meanwhile, transcriptome sequencing identified seven fusion genes within the genomic breakpoints. Together, our extensive whole-genome investigation makes high-quality open-source data available to the leukemia genomics community.

The joint expression of particular colors, morphologies, and behaviors is a common feature of adaptation, but the genetic basis for such "phenotypic syndromes" remains poorly understood. Here, we identified a complex genetic architecture associated with a sexually selected syndrome in common wall lizards, by capitalizing on the adaptive introgression of coloration and morphology into a distantly related lineage. Consistent with the hypothesis that the evolution of phenotypic syndromes in vertebrates is facilitated by developmental linkage through neural crest cells, most of the genes associated with the syndrome are involved in neural crest cell regulation. A major locus was a similar to 400-kb region, characterized by standing structural genetic variation and previously implied in the evolutionary innovation of coloration and beak size in birds. We conclude that features of the developmental and genetic architecture contribute to maintaining trait integration, facilitating the extensive and rapid introgressive spread of suites of sexually selected characters.

Krill are vital as food for many marine animals but also impacted by global warming. To learn how they and other zooplankton may adapt to a warmer world we studied local adaptation in the widespread Northern krill (Meganyctiphanes norvegica). We assemble and characterize its large genome and compare genome-scale variation among 74 specimens from the colder Atlantic Ocean and warmer Mediterranean Sea. The 19 Gb genome likely evolved through proliferation of retrotransposons, now targeted for inactivation by extensive DNA methylation, and contains many duplicated genes associated with molting and vision. Analysis of 760 million SNPs indicates extensive homogenizing gene-flow among populations. Nevertheless, we detect signatures of adaptive divergence across hundreds of genes, implicated in photoreception, circadian regulation, reproduction and thermal tolerance, indicating polygenic adaptation to light and temperature. The top gene candidate for ecological adaptation was nrf-6, a lipid transporter with a Mediterranean variant that may contribute to early spring reproduction. Such variation could become increasingly important for fitness in Atlantic stocks. Our study underscores the widespread but uneven distribution of adaptive variation, necessitating characterization of genetic variation among natural zooplankton populations to understand their adaptive potential, predict risks and support ocean conservation in the face of climate change.