The dramatic transition to parthenogenetic reproduction is often accompanied by similarly dramatic changes in genome organisation. Genomic changes may precede or succeed the onset of parthenogenesis and may directly or indirectly contribute to the success of this reproductive transition and fitness of parthenogenetic animals. To gain greater understanding of these changes, we combined cytogenetic and comparative analyses to document variation in heterochromatin and large-scale rearrangements among 18 strains of Drosophila mercatorum capable of varying degrees of parthenogenetic reproduction. This revealed that element F is 4.4-fold larger (95% confidence interval 4.0-4.8) in strains capable of parthenogenesis but that multiple large chromosomal inversions (2.8-9 megabases) on element B likely arose earlier. We combined phylogenetic analysis with comparisons of these genomic changes and parthenogenetic ability in D. mercatorum strains collected in South America, North America, Hawaii, and Africa. This indicated that the heterochromatin expansion has arisen once and appears to gradually increase with the rate of parthenogenetic ability. However, since this increase was also present in obligate sexually reproducing strains, heterochromatin expansion was not a consequence of parthenogenesis. It is therefore possible that heterochromatin expansion and parthenogenetic ability are unrelated but are carried together; that a shared underlying mechanism promotes both; or that heterochromatin expansion itself drives the capacity for parthenogenetic reproduction.

Evaluation of genome size has been extensively used in different fields. In many studies, it has been employed to test correlation with other parameters such as metabolic rates, longevity and ecological/geographical distribution. Moreover, genome size assessed with cytometrical methods can be useful to evaluate the completeness of genome assemblies. In this latter case, knowledge of the accuracy of cytometry-based genome size measurement is fundamental, and a pivotal factor is the internal standard used during measurement. In the present article, I tested the correlation between cytometry-measured genome sizes and assembly sizes, finding a probable systemic error. Indeed, the two most widely used internal standard, i.e., human and chicken, are traditionally set equal to 3.5 and 1.25 pg, respectively. With the advent of telomere-to-telomere genome assembly, we can now know the real genome size for several species, being actually 3.19 pg for human and 1.12 pg for chicken. Recalculating the genome size for 912 vertebrate species, I assessed the level of genome assembly completeness, explored the influence of factors such as sequencing platform and gave some suggestions for future studies.

Genomic tools are increasingly important for conservation and wildlife health surveillance, yet their use is often constrained by limited resources, sample quality, and the need for minimally invasive approaches. Here we show that untargeted low-coverage sequencing applied to scale-clip DNA can jointly address population structure, genotype-phenotype associations, and pathogen surveillance in timber rattlesnakes (Crotalus horridus), a species threatened by habitat fragmentation, human encroachment, and the emerging fungal pathogen Ophidiomyces ophidiicola. We sequenced 107 snakes sampled from eight populations in the Appalachian Mountains of the northeastern United States to a mean depth of 0.94x per individual. Population differentiation is pronounced and only weakly correlated with geographic distance, and inbreeding coefficients in some populations are high enough to suggest fitness consequences. Genome-wide association analysis identifies a locus for black-to-yellow color morph containing ALDH4A1, a member of a gene family implicated in vertebrate pigmentation but distinct from melanin pathway pigmentation genes. Our untargeted sequencing method also captures host-associated microbes: O. ophidiicola loads are higher in snakes with clinical signs of snake fungal disease, though some asymptomatic individuals carry substantial loads, and skin-associated microbial communities are disrupted in snakes with higher fungal burdens. That all of these inferences derive from the same minimally invasive sampling and sequencing workflow highlights the scalability of this approach for biodiversity conservation.

We present a chromosome-level genome assembly of a female great grey owl (Strix nebulosa lapponica). The assembly comprises two pseudo-haplotypes of 1554 Mb and 1242 Mb, with 83.2% and 91.4% scaffolded into 40 autosomal chromosomes, in addition to the Z and W sex chromosomes both placed in hap1. Assembly completeness is high (BUSCO 99.2% and 94.8%), with 18,493 and 17,279 annotated protein-coding genes for hap1 and hap2, respectively. This genome establishes a reference for investigating genetic variation and chromosome evolution in great grey owls. Compared with the previous S. nebulosa assembly, this assembly includes both sex chromosomes, separates regions that were previously misassembled, and supports a diploid chromosome number of 2n = 82. While larger chromosomes show broadly conserved synteny across owl assemblies, the recovery of additional conserved dot microchromosome-associated marker proteins suggests that ONT reads improved resolution of the smallest chromosomes relative to HiFi-based assemblies.

Local adaptation at fine spatial scales depends on whether selection can maintain trait divergence despite ongoing gene flow, yet the spatial scale at which this occurs remains poorly resolved in natural populations. Heterogeneous landscapes containing geographically proximate populations provide natural experiments to test how gene flow and selection jointly shape adaptive divergence. We studied 12 annual populations of Mimulus guttatus distributed across two nearby ridges in the Cascade Mountains of Oregon, USA, and combined field fitness estimates, common garden phenotyping, and genome-wide SNP data to assess genetic variation, quantify phenotypic divergence, and test whether contemporary selection explains observed population differences. Populations had high levels of genetic diversity yet exhibited clear population structure between mountain ridges. Phenotypic divergence among populations exceeded expectations from genetic structure for several traits including flowering time, stem height, and trichome number. Earlier flowering time and larger flower sizes were associated with hotter and drier populations, matching patterns of temporally-fluctuating selection in a nearby population. Phenotypic selection analyses indicated that contemporary selection gradients were generally weak or non-significant, indicating that past selection likely produced variation between populations. Together, our results demonstrate that strong phenotypic differentiation can arise at microgeographic scales despite substantial gene flow and temporal heterogeneity in environments.

Hybridization between domestic and wild species is an increasing conservation concern, as continued introgression could lead to genomic extinction. The Endangered Ethiopian wolf (Canis simensis) is thought to be threatened by hybridization with free-roaming domestic dogs (C. familiaris) and African golden wolves (C. lupaster), particularly in human-dominated landscapes. Phenotype-based assessments during two field seasons in 1989 and 1991 have suggested that 8-17% of individuals in the Bale Mountains show signs of admixture, but the extent and timing of gene flow remain unresolved. This study analyzed 27 whole genomes, including nine Ethiopian wolves that showed no obvious signs of admixture, collected in 2003, to quantify patterns of introgression among African canids. Population structure analyses identified limited signals of hybridization, with most Ethiopian wolves forming a distinct genetic cluster. Although two related Ethiopian wolves exhibited subtle but significant excess allele sharing with African golden wolves, the overall genomic data provide little support for strong recent or directional introgression. Linkage disequilibrium decay analyses suggest an admixture event occurring approximately 800 generations ago; however, estimates of timing and admixture proportion were not robust, indicating substantial uncertainty in the precise parameters. Forward-in-time simulations indicate that, despite currently limited introgression, continued small population sizes could facilitate gradual genomic replacement over evolutionary timescales. Therefore, hybridization may become increasingly important under sustained demographic decline.

Reindeer and caribou (Rangifer tarandus) play key ecological, cultural, and economical roles across Arctic and Subarctic regions. However, genome-wide patterns of genetic diversity and population structure in semi-domesticated reindeer from Norway remain insufficiently characterized. Here we generated a high-quality chromosome-level genome assembly (GCA_965153185.1) for Norwegian semi-domesticated Eurasian tundra reindeer (Rangifer tarandus tarandus). The genome spans 2.54 Gb, with a scaffold N50 of 75.6 Mb, 96.1% complete BUSCOs, and 39,855 predicted protein-coding genes. Using this reference, we performed whole-genome resequencing of 175 individuals from five reindeer populations from Norway and 28 individuals from Iceland, identifying ~19.9 million genetic variants. Genetic differentiation was low among Norwegian populations (FST = 0.005-0.011), but substantially higher between Norway and Iceland (FST = 0.140-0.161). Populations from Norway exhibited similar levels of nucleotide diversity (π = 1.39-1.62 × 10-3), whereas the Icelandic population showed reduced diversity (π = 0.99 × 10-3) and approximately half as many segregating variants. Analyses of runs of homozygosity (ROH) and genome-wide heterozygosity indicated low levels of recent inbreeding across all populations, with long ROHs (>8 Mb) being rare. Despite reduced genetic diversity, the Icelandic population showed limited evidence of recent inbreeding. These patterns are consistent with contrasting demographic histories, with gene flow maintaining diversity among populations from Norway, while founder effects combined with long-term isolation have shaped the Icelandic population.

High-quality genome assemblies are essential for robust research across biological and medical fields. Assembly errors can have far-reaching consequences for downstream analyses, including gene annotation and the inference of synteny. In contrast to the rapid growth of genomic data volume, there is a notable lag in the integration of chromosome-level assemblies with cytogenetic data. We conducted the first direct genome-to-genome comparison, integrating comparative chromosome painting, the alignment of chromosome-specific probes to available genome assemblies, and synteny-based comparison of independent chromosome-level assemblies of the loggerhead sea turtle (Caretta caretta, 2n = 56) and the red-eared slider (Trachemys scripta elegans, 2n = 50). Using two independent sets of flow-sorted chromosome-specific probes in cross-species hybridizations, together with the sequencing and mapping of chromosome-derived DNA libraries, we assigned assembled scaffolds to all physical chromosomes of both species. In C. caretta, chromosomal assignments and genome-wide synteny were fully consistent with the published assembly, except for the reduced sizes of two microchromosome scaffolds, which we attribute to under-representation of repetitive DNA. In contrast, in T. s. elegans, cytogenetic validation of the assemblies revealed a false rearrangement compared to a missed one. Our results show that even highly contiguous vertebrate genome assemblies can misrepresent chromosome structure. When cytogenetic analyses reveal such inaccuracies, updated reference genomes should be generated for widely studied species to enable accurate inference of karyotype evolution and downstream comparative genomic analyses.

Most vertebrate species reproduce sexually. The whiptail lizards (Aspidoscelis) are a notable exception; at least 11 of the 45 recognized species are parthenogenetic. Here, we focus on one such species (Aspidoscelis tesselatus) as a case study to understand how parthenogenetic species originate and evolve. Using genome-wide sequence data and ecological niche modelling, we find that A. tesselatus likely arose from a single hybrid speciation event between A. scalaris and A. marmoratus less than 500,000 years ago. The geographic ranges of A. tesselatus and its parental species overlap currently, and niche modelling shows this zone of sympatry was even broader during the period when A. tesselatus likely formed. We additionally show evidence that A. tesselatus has a dynamic genome post-formation, with de novo mutations, introgression, and double-strand break associated events all contributing to variation within the species. These results show that asexual lineages can continue to be shaped by ongoing genomic and ecological dynamics, illuminating the processes that influence transitions in reproductive mode.

We established primary fibroblast cultures from a Japanese raccoon dog (Nyctereutes viverrinus) and a Japanese red fox (Vulpes vulpes japonica) and generated highly contiguous reference genome assemblies using Oxford Nanopore Technologies PromethION long-read sequencing. The Japanese raccoon dog assembly spanned 2.69 Gb in 813 scaffolds, with a scaffold N50 of 52 Mb and a Benchmarking Universal Single-Copy Orthologs (BUSCO) completeness score of 98.2%. The Japanese red fox assembly spanned 2.47 Gb in 903 scaffolds, with a scaffold N50 of 139 Mb and a BUSCO completeness score of 97.5%. Phylogenomic analysis placed the Japanese raccoon dog in a lineage distinct from the continental raccoon dog, supporting its evolutionary differentiation within Nyctereutes. The Japanese red fox formed a distinct lineage within the red fox clade, consistent with its recognized regional differentiation. These genome assemblies and associated fibroblast cultures provide resources for studies of canid systematics, population history, local adaptation, comparative genome evolution, and conservation genetics.

We present a reference genome assembly for the trapdoor spider Aptostichus stephencolberti. This species, described in 2008, is endemic to the highly fragmented coastal dune habitats of Northern California from Monterey to the San Francisco Bay Area. Trapdoor spiders are ideal taxa for landscape scale genomic studies owing to their extreme site fidelity and limited dispersal capabilities; these same characteristics make them prone to extinction. Genomic studies of species like A. stephencolberti can reveal novel areas of endemism and high conservation value that may not be evident in species with wider ranges and greater dispersal capabilities. As part of the California Conservation Genomics Project, we constructed the A. stephencolberti reference genome from high quality long-read sequences, scaffolded with proximity ligation Omni-C data. The primary assembly comprises 551 scaffolds spanning 3.63 Gbp, a scaffold N50 of 62.2 Mbp and BUSCO completeness of 95.6%. We estimate 52 chromosomes yet find no (TTAGG)n telomer repeats. Expanding the telomeric repeat search finds an ancestral loss of the repeat from all spiders. Automated annotation using the NCBI refseq pipeline and RNAseq data from whole adults finds 14,067 genes with a BUSCO annotation completeness of 95.56%. Repeat annotation identified 77% of the genome to be interspersed repeats. This resource, the first for family Euctenizidae will facilitate future study and resulting conservation actions of A. stephencolberti and other Aptostichus sp. populations associated with the rapidly changing California coastal dune ecosystem.

Advances in genetic tools such as next and third generation sequencing, paired with a focus on representative clades, provide insight into how processes including adaptation, admixture, and genome structure shape the evolution and maintenance of species. However, our understanding of the genomics of speciation is dominated by systems where ecological adaptations are thought to cause initial barriers to gene exchange. In contrast to other model systems, the 38 species of the genus Laupala constitute a very rapid radiation, where evolution of reproductive barriers and speciation is thought to be driven by sexual selection. Here, with novel PacBio HiFi reads and RNA- and Iso-Seq data, we provide a highly contiguous, chromosome-level genome and markedly improved annotation of the endemic Hawaiian cricket, Laupala kohalensis Otte, 1994. Our new resources advance previous efforts, placing 99% of 47 scaffolds on 7 autosomes and 1 sex chromosome in the 1.67 Gb assembly, with a 98.8% BUSCO score (insecta_db10), N50 of ~268 Mb, and L50 of 3. Using a custom repeat library, we estimate the genome to have 46.09% repeat content, and the new annotation includes an increased estimate of 17,670 genes, which coincides with that known from other Orthopterans. Notably, we find a large nuclear DNA segment of mitochondrial origin on chromosome 7. This new resource provides a powerful tool to identify and compare genomic causes of phenotypic diversification in a system characterized by strong signatures of sexual differentiation, representing an underappreciated but potentially widespread cause of speciation.

The olfactory receptor (OR) gene represent a significant multigene family in vertebrates, forming the core molecular basis of olfactory perception and playing a crucial role in the environmental adaptation of species. High-altitude ecosystems represent extreme habitats characterized by specific abiotic stresses, including low oxygen levels, low temperatures, and intense ultraviolet radiation. These environments also exhibit low aquatic biodiversity and a limited variety of odor molecules, factors that have influenced the adaptive evolution of the sensory systems in endemic species. However, the genetic mechanisms underlying olfactory adaptation in high-altitude freshwater fish remained inadequately understood. In this study, we performed comparative genomics analyses to reveal the evolutionary processes underlying the adaptive and functional evolution of OR genes in S. younghusbandi, a cyprinid fish endemic to the Qinghai-Xizang Plateau. The results indicated that, compared to their low-altitude relatives, S. younghusbandi possessed a significantly smaller number of OR genes, with only 98 genes, which revealed the contraction of the gene family. Phylogenetic analysis revealed that the OR genes of cyprinid fish could be categorized into two major lineages: type I and type II. The η and δ families, which perceive water-soluble odors, in S. younghusbandi underwent significant and specific expansion, while the ε family was completely absent. This pattern reflected adaptive changes in olfactory recognition to accommodate the simplified odor spectrum of high-altitude water bodies. Chromosomal localization analysis demonstrated that OR genes were clustered, and collinearity analysis confirmed the presence of conserved genomic fragments among species. Selection pressure analysis revealed that the Ka/Ks values of all homologous gene pairs were less than 1, indicating that the OR genes of S. younghusbandi underwent strong purifying selection as a group to preserve core olfactory function. A few genes exhibited relaxed selection characteristics, which may have facilitated the fine-tuning of adaptability to high-altitude environments. In conclusion, this study elucidated the evolutionary dynamics and adaptive characteristics of the OR gene in S. younghusbandi, offering a new perspective on the molecular mechanisms underlying olfactory adaptation at high altitudes and enriching the research on sensory evolution in vertebrates.

We present a reference-quality genome assembly for the desert night lizard (Xantusia vigilis). The night lizards (Xantusiidae) are a family of small-bodied lizards found in North America (Xantusia), Central America (Lepidophyma), and Cuba (Cricosaura). The night lizard family has an independent evolutionary history of at least 80 million years from its sister taxa within Scincoidea. The Xantusiids have several unique ecological, behavioral and evolutionary characteristics. For instance, the family contains the only squamate species that form diploid, unisexual, parthenogenic lineages. In addition, most night lizards are viviparous and form stable kin groups that are maintained over multiple years, an unusual life history strategy among lizards. Combining PacBio long-read sequencing, Hi-C, and RNAseq data we developed a reference-quality genome for the desert night lizard, X. vigilis. We assembled a complete mitochondrion and ~ 2.2 Gb nuclear genome, with 20 scaffolds that correlate in size to the X. vigilis karyotype. In addition, we found that X. vigilis chromosome 1 aligns with gene content of both of macrochromosome 1 and microchromosome 9 from a genome assembly of a species in the sister family Cordylidae (Hemicordylus capensis).