Genome Biology and Evolution

The haplochromine cichlid fishes of Lake Malawi form one of the most dramatic examples of recent rapid radiation in vertebrates. Here we describe nine new diploid telomere-to-telomere (T2T) genome sequences generated using ultra-long ONT reads, which include 78 ungapped chromosomes. We provide accurate annotations of transposable elements and tandem repeats, identify rDNA cluster regions and putative centromeres, and confirm previously reported large chromosomal inversions. The putative centromeres are primarily composed of satellite tandem arrays of previously reported 237 bp repeats, but notably on most chromosomes these are organised in a novel structure in which four blocks of satellites in alternating orientation are separated by an inverted pair of ~15 kb sequences we term 'centroids', which have similarity to a non-autonomous DNA transposable element and containing potential CENP-B binding boxes. The methylation dip region indicating the likely active centromere always lies between the centroids, whose separation is almost always around 200 kb (interquartile range 151-221kb). A structurally equivalent but non-homologous organisation is seen in the distantly related Etroplus cichlid genera from South Asia. By comparing these structures across chromosomes and species, we suggest how they may have evolved, and potentially how they could contribute to the rampant sympatric speciation seen in these species, based on meiotic drive and chromosome missegregation.

BackgroundThe black soldier fly (Hermetia illucens) is an emerging model for bioconversion and industrial rearing. Its genome is highly repetitive, yet the contribution of transposable elements (TEs) to population divergence and demographic processes. The sampled populations represent a gradient of demographic histories, including wild and near-wild North American populations, and domesticated European strains with shared industrial origins. Difference in TE composition may influence genome structure, regulatory variation, and evolutionary responses to captive environments. ResultsA comparative analysis of the repetitive landscape was done for four H. illucens genomes, one of which is a wild-caught specimen. Total repeat content was high across all assemblies (67.6% to 70.8%) and dominated by LINE elements. Class-level TE diversity was nearly identical among genomes, but multiple DNA transposon families showed distinct lineage-specific differences. Large families including Maverick and Academ were generally depleted relative to the wild sample. Divergence profiles revealed patterns consistent with recent turnover in several families. Family level turnover, rather than class level change, accounted for the most difference among the genomes. TE-associated structural variants (TESVs) were also not uniformly distributed. Most chromosomes showed mid-chromosome enrichment, and a pronounced TESV peak on chromosome 5 overlapped a histone rich region containing many unclassified repeats. Use of a repeat library derived from multiple genomes increased the number of detected TESVs and improved classification within complex regions, demonstrating that multi-genome libraries enhance annotation accuracy compared to single reference-based models. ConclusionsMultiple DNA transposon families show evidence of recent or lineage-specific amplification in H. illucens, suggesting that TE amplification contributes to genome variation during demography-associated TE turnover. The multi-genome-based library improved TE detection and classification, providing a proof of concept that even a small lineage-inclusive repeat library enhances annotation accuracy and capture TE diversity missed by single-reference approaches. Together, these findings demonstrate that TE family turnover plays a significant role in shaping genome architecture and adaptation in this species.

Transposable elements (TE) jump from one genomic locus to another. Since increase in their copy number is a metabolic burden for the host, TE are considered as genomic parasites. Although host-TE co-existence is regarded as an evolutionary arms race, the hypothesis is not extensively tested especially using evolutionary genomics. We provide a hypothesis testing framework to understand the distribution of TE in genic regions of the host genome, variation in the regulation of TE by host, and effect of these two factors on host-TE co-evolutionary dynamics. We test our hypothesis by understanding the distributions of potentially active TEs in the genome of 78 teleost fishes, representing major families and orders within the clade. Our analysis reveals coevolutionary arms race predicted by the Red Queen dynamics.

Most cyanobacterial genomes are rich in the GCGATCGC octamer, also known as Highly Iterated Palindrome 1 (HIP1). Despite its description over three decades ago, the biological function of this highly abundant sequence is only beginning to be elucidated. HIP1 is recognized by two DNA methylases, DmtA and DmtC, and is characterized by its evolutionary conservation and a quasi-periodic distribution within genomes. However, whether the phylogenetic distribution of HIP1 correlates with the presence of functional categories of protein families remains unknown. Here we investigated whether certain protein families share a phylogenetic distribution with this abundant palindromic sequence across cyanobacterial genomes. Our analysis revealed a strong phylogenetic correlation between several proteins of the Type IV secretion system (T4SS) and the abundance of HIP1. This finding aligns with recent discoveries demonstrating that HIP1 enhances DNA transformation in a methylation-dependent manner in two distinct cyanobacterial species. Consequently, we hypothesize that HIP1 function as a conserved adaptation for horizontal gene transfer (HGT) at the phylum level, potentially by serving as a DNA-uptake recognition sequence in cyanobacteria. Significance statementScientists have long been baffled by the HIP1 sequence, a short, highly common, repetitive DNA pattern found across almost all cyanobacterial genomes. Our study used a whole-genome evolutionary approach and found that the presence of this repetitive pattern is tightly linked to the presence of a cells external DNA uptake system. This tight co-evolutionary relationship suggests that HIP1 isnt just random genomic feature, but a conserved evolutionary adaptation used by the entire cyanobacterial phylum to specifically enhance their ability to acquire new genes from one another.

Population genetic theory predicts that a species demographic history shapes patterns of genome-wide variation. However, conservation genomic studies have disproportionately focused on small or declining species, where low genetic diversity and inbreeding are major concerns, while highly abundant species have attracted comparatively less attention. Here, we investigate the crabeater seal (Lobodon carcinophaga) which, despite being one of the most numerous large mammals on Earth, remains largely uncharacterised in terms of its genomic diversity and demographic history. We assembled a high-quality crabeater seal reference genome from a combination of Illumina and PacBio HiFi reads, generating a 2.44 Gb assembly spanning 138 scaffolds with high completeness. To evaluate genomic diversity in a comparative context, we whole-genome resequenced 20 crabeater seals alongside 20 individuals each of three Antarctic phocids spanning a population size gradient: the Weddell seal (Leptopnychotes weddellii), leopard seal (Hydrurga leptonyx) and southern elephant seal (Mirounga leonina). Crabeater seals carried 61.5 million SNPs compared to 1216 million in the other species and exhibited markedly higher nucleotide diversity and negligible genomic inbreeding. We observed an excess of rare alleles, with nearly half of all variants segregating at frequencies below 5%. Demographic reconstruction revealed persistently large effective population sizes over the past million years and sustained population expansion, paralleling inferred increases in Antarctic krill associated with sea-ice expansion during the late Pleistocene. This study provides a new genomic resource and sheds new light on the evolutionary dynamics of the worlds most abundant pinniped.

Recent studies have characterised the mutational profile across multiple mammalian species, highlighting substantial differences across lineages. However, none of these studies investigated whether mutation profiles and geography are significantly correlated. In this study, we present a multi-genome alignment spanning several Capra taxa, reconstruct the ancestral genome of Capra hircus and use it to characterize the mutational profiles across multiple Capra species by using the 1000 genomes VarGoats dataset. Results confirmed that the scale of differences among Capra species largely reflects their phylogenetic relationships, in particular with the Bezoar being genetically closer to domestic goats than to other wild species. Subsequently, we correlated the mutational profile and the geographical origin of the different individuals. In particular, ACG>ATG changes have the strongest correlation with longitude (r = -0.79, P-value = 3.02*10-204), while TCA>TGA are strongly correlated with latitude (r = -0.51, P-value = 4.30*10-63). We highlight how sequential dinucleotide mutations (SDMs) place cosmopolitan breeds closer to the sampling location, rather than the country of origin, showing how the recent relocation of cosmopolitan breeds to new continents is reshaping the genome of these animals. Finally, we used the mutational profile to predict the coordinate of origin of each animal in the dataset. In conclusion, we show the important role that geography had in shaping the genomes of domestic goats.

Whole-genome duplication (WGD) is hypothesized to spur evolutionary diversification by producing genome-wide duplicate gene sets (Ohnologs) that are initially functionally redundant but can diverge markedly as the effects of relaxed selection accumulate over time. However, the underlying mechanisms remain unclear, in part because genomic studies often reconstruct Ohnolog evolution over millions of years, during which subsequent mutations can obscure deep-time signals. Investigating the relationship between Ohnolog evolution and diversification on a contemporary timescale offers clearer insights. We explore this relationship in Lake Charr (Salvelinus namaycush), where ~10% of genes are retained highly conserved polyploid duplicates following the Salmonid-Specific Fourth Round WGD. Using 31 chromosome-level assemblies of Lake Charr from morphologically and ecologically diverse populations, joined into a pangenome graph, we characterized 189,555 structural variants (SVs) that were significantly less likely to affect genes retained as sequence-conserved Ohnolog pairs, nuancing the hypothesis that gene redundancy, relaxed selection, and functional diversification are intertwined. However, we found that SVs affecting such conserved Ohnologs may be potent drivers of adaptive evolution. Notably, we identified a putative 938-Kb interchromosomal translocation containing 25 genes with highly conserved Ohnologs in a paralogous (but untranslocated) genomic block. This putative translocation appears to have facilitated Ohnolog divergence in ankrd11 and hp, genes putatively linked to craniofacial and lipid metabolic diversity in sympatric Lake Superior morphs. This research reveals that conserved Ohnologs previously presumed to be redundant remain a reservoir for adaptive change.

Long-term studies of isolated animal populations have greatly improved the understanding of various evolutionary processes. However, potentially elevated inbreeding in those compared to wild populations is a common concern. Conventionally, inbreeding has been investigated using reconstructed pedigrees, but nowadays it can be done directly at the genomic level. Here, we utilize genomic data from an intensively studied isolated rhesus macaque (Macaca mulatta) population on the small island Cayo Santiago (Puerto Rico), which was founded in 1938 with wild animals from India. We quantified inbreeding levels by inferring runs of homozygosity (ROH), i.e., long identical haplotypes inherited from both parents. We identified ROH in 97 ~5x-coverage genomes from Cayo Santiago and, for comparison, in 79 rhesus macaque genomes from five wild populations from China. Notably, this conventionally considered low-coverage data proved sufficient to infer ROHs >4 centimorgans long after imputing the genomes using a reference panel. Our results revealed that the ROH-derived effective population size on Cayo Santiago, 420 individuals, falls within the ranges we inferred in wild populations. Moreover, a general scarcity of individuals with long ROH in both the Cayo and wild populations indicates very few cases of close-kin breeding, suggesting that mechanisms to avoid close-kin breeding operate in rhesus macaques, both in wild and isolated populations. Taken together, our results suggest that Cayo Santiago remains a representative study population.

Multicellularity has evolved multiple times across the eukaryotic tree of life, including among protist lineages. Because transposable elements (TEs) strongly influence genome architecture and gene regulation, understanding their potential impact on genome structure and their relationship with gene expression may provide insight into the evolution of multicellularity. Here, we generated a new genome assembly for the facultatively multicellular amoeba Acrasis kona and performed comparative analyses of TE composition, TE diversity, and TE-density organization across diverse protist lineages. Comparative analyses included unicellular and multicellular representatives from across the tree of eukaryotes, (Heterolobosea, Filasterea, Cristidiscoidea, and Chlorophyceae), including Naegleria spp., Tetramitus jugosus, Capsaspora owczarzaki, Pigoraptor spp., Fonticula alba, Parvularia atlantis, Volvox carteri, and Chlamydomonas reinhardtii. To examine relationships between TEs and gene regulation, we integrated transcriptomic datasets from A. kona, Capsaspora owczarzaki, and Volvox carteri with genome-wide TE-density analyses of differentially expressed genes. TE abundance and composition varied substantially among lineages, with species that exhibit more complex developmental or cellular organization generally containing higher TE proportions than closely related unicellular taxa. Patterns of TE-density organization near up-regulated, down-regulated, and non-differentially expressed genes also differed among systems, ranging from strong TE depletion in A. kona to weaker or cell-type-specific patterns in Capsaspora and Volvox. Together, these findings suggest that transposable elements are associated with multicellularity across diverse protist lineages, although the specific roles they play appear to be complex, lineage-specific, and not yet fully understood.

The rat tapeworm, Hymenolepis diminuta, is an important laboratory model for uncovering molecular processes that underly the success of tapeworms as parasites. Despite its importance, a high-quality reference genome for this species is lacking. Here we present a highly contiguous and effectively complete genome of H. diminuta assembled from PacBio HiFi long-read sequencing data. Our primary assembly consists of 7 scaffolds (N50=29.25 Mb) with total length of 186.53 Mb, has only 7 gaps, and contains 95.7% complete Lophotrochozoan BUSCOs. Our assembly allows us to confirm aspects of Hymenolepis genome organization, such as high repeat content and unusual chromosomal ends, and to show that Hymenolepis genomes encode [~]10,000 genes. Together with annotations of nuclear tRNAs, mtDNA protein coding genes, and mtDNA tRNAs, our assembly currently provides one of the most complete genome resources for a tapeworm species and will enable research on parasitism, animal regeneration, development, and evolution.

The Wangs garden lizard, Calotes wangi, is a widely distributed agamid species in Southern China and Northern Vietnam and exhibits pronounced colour variation and rapid body colour change. Despite increasing interest in the genomic basis of colour variation, chromosome-level genomic resources remain limited in agamid lizards. Here, we generated a chromosome-level reference genome of C. wangi using PacBio HiFi sequencing and Hi-C scaffolding. The final genome assembly was approximately 1.66 Gb in size and comprised 6 macrochromosomes and 11 microchromosomes, with a contig N50 of 110.09 Mb and 98.9% complete BUSCO genes. A total of 20,442 protein-coding genes were annotated. Comparative genomic analyses identified 297 significantly expanded gene families, with enriched functions associated with steroid metabolism, chromatin regulation, and epigenetic processes. This high-quality genome assembly provides an important genomic resource for future studies of colour variation, phenotypic plasticity, and evolutionary diversification in agamid lizards.

The evolutionary transition to terrestrial life required overcoming several physiological hurdles; however, such challenges were amplified in desert environments. While several xeric-adapted arachnids utilize permanent burrows or "sit-and-wait" foraging strategies as possible energy conservation adaptations in harsh habitats, camel spiders exhibit a counterintuitive, high-energy lifestyle. To investigate the molecular underpinnings distinguishing Solifugae within Chelicerata, we utilized a comparative genomics framework that incorporates a newly sequenced, previously unpublished solifuge genome. We identified lineage-specific expanded orthogroups and evaluated selective pressures acting upon paralogous sequences within our ingroup solifuge species. Additionally, we also focused on fatty acid-associated proteins and heat shock proteins to elucidate how Solifugae may have evolved such anomalous behaviors compared to their arachnid relatives. Our analyses revealed significant signatures of positive selection within key gene families across the solifuge lineage. Notably, paralogs within the cytochrome P450 and biotinidase families showed consistent evidence of selection across all three taxa, suggesting specialized metabolic or detoxification requirements. Furthermore, we identified candidate loci implicated in axonal guidance and lipid metabolism, and a specialized fatty acid enzyme repertoire. While subsequent research is required to determine whether some of the genomic signatures unveiled here are shared across a broader phylogenetic distribution within Solifugae, we establish a critical baseline for future functional validation.

A fundamental unresolved question in molecular evolution is how novel genes arise from noncoding DNA and become fixed within stable gene repertoires. Here, we performed comparative genomic analyses across evolutionary timescales in insects using chromosome-scale genome assemblies of two cricket species, Teleogryllus occipitalis and Tarbinskiellus portentosus. Using conservative criteria, we identified 41 de novo gene candidates derived from intergenic regions in the Te. occipitalis lineage. These genes are simple and compact, exhibit hallmarks of evolutionarily young genes, and frequently contain fragments of transposable elements and simple sequence repeats. Across insects, such repetitive sequence fragments show positional homology but lack sequence conservation in older genes, suggesting that they serve as sequence material for gene emergence during early stages of gene evolution. In contrast, insertions after gene establishment are strongly constrained. We propose a model in which stages of gene evolution are characterized by shifts in selective pressure on the incorporation of sequence material.

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 W and Z 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 collapsed, and resolves 82 chromosomes total. While larger chromosomes show broadly conserved synteny across owl assemblies, the recovery of additional conserved microchromosome-associated genes suggests that ONT reads improved resolution of the smallest chromosomes relative to HiFi-based assemblies.

Compared with bacterial and archaeal extremophiles, single-celled eukaryotes living in extreme habitats are understudied and underrepresented in genomic databases. An exception is the obligately halophilic stramenopile Halocafeteria seosinensis strain EHF34. A transcriptome-focused analysis of this extremophilic protists revealed the importance of organic osmolyte regulation and transport in its adaptation to hypersaline environments. However, genomic resources for H. seosinensis are currently limited to a highly fragmented assembly generated by short-read sequencing, which has hindered further investigation of the genome biology and evolution of this fascinating organism. Here, we used long-read Oxford Nanopore sequencing to generate a highly contiguous, chromosome-scale genome assembly for H. seosinensis. The assembly is 38.8 megabase pairs (Mbp) in size and contains 60 nuclear contigs, making it the most contiguous genome for a member of the order Bicosoecida. Approximately 19% of the genome is comprised of transposable elements. Of the 11,684 predicted protein-coding genes, many appear to be associated with DNA mobility-related functions, and several may be linked to adaptation to a hypersaline environment. Analysis of the H. seosinensis long-read genome assembly presented herein will facilitate our understanding of the ways in which protists have adapted to extreme environments. SignificanceHalocafeteria seosinensis is an extremophilic protist adapted to hypersaline environments. Previous analyses of a transcriptome and short-read draft genome assembly for this organism provided insights into the molecular mechanisms underlying osmotic regulation, which facilitate its adaptation to high-salt conditions. However, the lack of contiguity and quality of the draft assembly prevented the characterization of complex genomic regions, including transposable elements and viral insertions, as well as genomic comparisons with related species. Here we present a highly contiguous, chromosome-scale genome assembly for H. seosinensis that enables accurate gene prediction, detailed analysis of repeat content, and comparative genomic analysis. This long-read genome assembly will serve as a valuable resource for studying one of the few tractable halophilic protists sequenced to date.

Allele frequency (AF) timeseries allow us to directly observe the dynamics of evolution at a genetic level. However, extracting useful inferences from AF timeseries has proved difficult due to the model uncertainties and noisiness inherent in AF change at fine temporal scales. Here we present three new permutation tests --- which do not assume a model of evolutionary change or a parametric statistical model --- to detect AF timeseries features of evolutionary interest. The features identified by these approaches are: 1) any evolutionary change (as opposed to apparent change due to measurement error); 2) directional selection; 3) fluctuating selection with a propensity to change sign (negative autocorrelation). We are not aware of existing tests for features 1 and 3. Feature 2 is commonly tested using standard evolutionary models such as the Wright-Fisher; we show that the permutation approach has comparable statistical power. We apply our new approaches to AF timeseries data from D. melanogaster and D. pulex.

Background: The gut environment is hostile to life, yet the human virome, dominated by bacteriophages, persists. Adaptations to the major capsid protein (MCP) may explain this. Phage MCPs conserve the HK97 fold, ideal for detecting convergent features across phage populations. Prior capsid stability research focused on individual phages, limiting broader pattern identification. Methods: MCPs from the Gut Phage Database (GPD) (n=8,478) and INPHARED (n=4,905) were predicted using ProtPhage + Phold and clustered using MMseqs2 (GPD=902 vs INPHARED=606). Structural predictions, conservation analysis, and capsomere modeling were used to characterize cysteine environments. Results: Biochemical analysis identified cysteine enrichment in GPD MCPs. Phylogenetic mapping was consistent with convergent evolution of high-cysteine MCPs. Over 50% of cysteines were [&ge;]90% conserved within and between clusters. Simulated capsomeres showed 83% of cysteines are buried (RSA <10%). Conclusions: These findings suggest gut phages may have convergently evolved cysteine-based capsid stabilization, with implications for engineering therapeutic phages.

Hearing in Lepidoptera mediates a range of ecologically important behaviours, including mate communication, predator avoidance, and acoustic signalling. In moths, the evolution of predator-prey interactions with bats has further shaped hearing through a sensory arms race, with repeated co-option of auditory organs to detect and evade echolocating predators. Despite significant prior characterization of the neurophysiology and behaviour of hearing in moths, the genetic basis of hearing is poorly understood in most insects. In this study, we identify a core set of putative auditory genes in Lepidoptera using a combination of homology-based searches from Drosophila and evolutionary rate analyses. We find 56 genes present across all species and investigate whether gene copy number varies among non-hearing and hearing lineages and among 3 different ear types. We discovered seven genes associated with ear type and one with ear presence, but did not find significant losses in gene copy number in non-hearing species. We identified three genes (btv, Dnai2, and nompB) with strong evidence of selection in hearing clades and five genes with weaker evidence of selection. We discuss the potential roles of btv, nompB, and Dnai2 in ciliary transport and the aging of hair cells, as well as the possibility of actively amplified hearing. Our study serves as a primer and resource for further gene mining and functional testing of auditory genes in moths and other insects.

Mesodinium rubrum, a marine microbial eukaryote associated with some of the largest red tides on Earth, has the remarkable ability to commandeer the plastids, mitochondria and nuclei from the alga Teleaulax amphioxeia for photosynthesis. Here we report analyses of assemblies of M. rubrums two nuclear genomes. Unexpectedly, M. rubrum appears to have completely lost its spliceosomal introns, most spliceosomal molecules, and the key genes for an intron splicing-associated process, Nonsense-mediated mRNA Decay (NMD). In contrast, non-spliceosomal tRNA introns have been retained, as have thousands of intron analogs spliced out of DNA during ciliate somatic genome development (internal eliminated sequences - IESs). Intron-containing genes, especially from intron-rich species like T. amphioxeia, would likely be defunct if horizontally transferred to a host without a spliceosome like M. rubrum, and thus we propose that introns can be a roadblock to progressive endosymbiotic genomic integration.

Horizontal gene transfer mediated by mobile genetic elements (MGEs) is a major driver of bacterial evolution and ecological adaptation. In the plant-associated genus Xanthomonas, multiple MGEs have been implicated in virulence, host specialisation, and environmental persistence, yet MGE diversity and evolutionary dynamics across the genus remain poorly understood. Here, we performed a comparative analysis of conjugative and mobilisable plasmids, integrative and conjugative elements (ICEs), integrative and mobilisable elements (IMEs), and their cargo genes across 516 complete genomes of three major Xanthomonas species: X. campestris, X. cissicola, and X. oryzae. We identified pronounced interspecific differences, with X. cissicola and X. campestris harbouring large and diverse MGE repertoires, comprising 28.3% and 26.7% of their respective pangenomes, whereas X. oryzae contained far fewer MGEs, making up only 3.6% of the identified pangenome. These differences were associated with host defence systems, including CRISPR-Cas and restriction-modification systems, and with variation in CRISPR spacer diversity. IMEs were the most abundant MGEs across all species, encoding diverse defence systems and accessory genes. ICEs exhibited signatures of horizontal transfer within and between species, and across genera. Notably, nearly identical ICEs carrying heavy-metal resistance genes were identified in Xanthomonas and Pseudomonas aeruginosa, indicating recent transfer between genera. MGEs collectively carried genes involved in virulence, interbacterial interactions, defence against phages, and plant cell wall degradation, with several elements associated with specific pathovars. Together, our findings establish MGEs as key drivers of genome plasticity and adaptive evolution in Xanthomonas, shaped by a dynamic interplay with host defence systems.