Genome Biology and Evolution最新文献

Comparative genomic analyses among closely related species provide an opportunity to assess their evolutionary history. The relatedness between species can depend on a variety of factors, including reproductive isolation, introgression, and incomplete lineage sorting, and this can impact divergence across the genome. Here, we use a combination of long- and short-read sequencing and HI-C scaffolding to assemble genomes for each of the four species in the testacea species group of Drosophila, including D. testacea, D. orientacea, D. neotestacea, and D. putrida, and its outgroup, D. bizonata. First, among species, we find many structural rearrangements across the genome as well as a large size difference in the dot chromosome that we infer is due to the expansion of repetitive elements. Second, we assess phylogenetic discordance and uncover a difference in the phylogeny inferred from genes on Muller E and the mitogenome relative to the rest of the genome, which may be due to recent hybridization. Lastly, we assess the rate of molecular evolution of genes shared across all species and identify genes evolving at different rates across the phylogeny. Our results present genomic resources for this species group and begin to probe into some of the evolutionary characteristics that contribute to variation in genome structure, while highlighting the need for high-quality genome resources to fully capture and understand the evolutionary history among closely related species.

The transition from small genetic to genome-scale datasets for studying biodiversity has revealed that genetic exchange through introgressive hybridization is a widespread phenomenon in nature. Despite this, a lack of high-quality reference genomes for most non-model species limits our understanding of the impact of this process for many taxonomic groups. This restricts the range of insights that genomic tools can provide for conservation biologists, who often hope to employ genomic datasets to accurately identify historically isolated lineages to protect and to predict their evolutionary fate in the face of environmental change. Tiger whiptail lizards (Aspidoscelis tigris complex) are an abundant and important ecological component of ecosystems across the southwestern United States. In this study, we assembled and annotated a chromosome-level reference genome for A. t. stejnegeri from coastal California. We then used this reference genome to reconstruct patterns of speciation and admixture within the larger species complex, finding evidence that gene flow is widespread both geographically and across the genome.

Clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (Cas) systems of bacteria and archaea provide immunities against mobile genetic elements, like viruses. In addition, protospacer analyses revealed a very specific acquisition of CRISPR spacers derived from genomes of related species or from closely interacting episymbiont genomes as recently shown for subsurface archaea. However, the origin of most of the spacers that can be found in CRISPR-Cas systems from natural environments has not been deciphered. Here, by analyzing CRISPR-Cas systems of metagenome-assembled genomes (MAGs) from two subsurface environments spanning more than 1 Tb of sequencing data, we show that a substantial proportion of CRISPR spacers are acquired from DNA of other prokaryotes inhabiting the same environment. As such, we found that the number of respective spacers can be up to three times higher than the number of self-targeting spacers. Statistical analyses demonstrated that the acquisition of CRISPR spacers from other prokaryotic genomes is partly explained by the relative abundance of the MAG containing the protospacer, as well as by other factors, such as the total number of CRISPR arrays present in a MAG with the respective spacers. Further, we found that spacer acquisition from foreign prokaryotic DNA occurs in almost all types of CRISPR-Cas systems, but shows preferences for subtypes of CRISPR-Cas systems that differ across the investigated ecosystems. Taken together, our results shed new light on the diversity of CRISPR spacers in natural microbial communities and provide an explanation for some of the many unmatched spacers in public databases.

Genomic diversity within species encompasses a range of sequence-related, structural, and regulatory features. To illustrate their complexity, we invoke the analogy of a kaleidoscope: while the DNA sequence represents its core, the genome has a dynamic, multidimensional configuration shaped by interactions across these features, generating an array of dimensions of genomic variation. In this perspective, we highlight underexplored dimensions of genomic variation that contribute to phenotypic diversity. We begin by revisiting the existence of noncanonical chromosomes and by emphasizing the role of large-scale structural changes and the 3D genome architecture in modulating genomic function. We then examine the regulatory mechanisms shaping transcriptional activity and genetic variation that, instead of regulating mean trait values, defines the degree of trait variability. Finally, we discuss the influence of sequence composition on its mutational potential. These dimensions, though rooted in sequence, are context dependent, interconnected, and often difficult to disentangle, reflecting a level of structural and regulatory complexity that challenges traditional genotype-phenotype models. By synthesizing recent findings across these dimensions, we argue for a broader framework for studying within-species genomic diversity: one that accounts for the diverse molecular architectures underlying phenotypic output. This expanded view not only deepens our knowledge of the genome itself but also contributes to our understanding of genome evolution and within-species phenotypic variation.

The prevalence and evolutionary importance of inversion polymorphisms in natural populations is poorly known because of limited genome-wide sequence data availability for most species. Inversion studies in wild populations usually target rare cases of major trait polymorphisms or local adaptation whose genetic basis involves inversions, creating a strong impression that inversions in nature are generally maintained by natural selection through links to ecologically relevant phenotypes. By contrast, genome-wide studies in humans and model organisms suggest that inversion polymorphisms are common, subject to highly complex evolutionary processes, and generally difficult to link with clearly observable cases of phenotypic variation. Using a large comparative population genomic dataset generated from 35 codistributed species of birds, we tested the hypothesis that inversions are common even within populations that lack known phenotypic polymorphisms. We leveraged analytical methods suitable for low-coverage whole genome sequencing to reveal evidence for over 170 putative inversion polymorphisms within 28 species. We find that many polymorphisms are large and present at balanced frequencies, and some are shared across species boundaries. Yet, most polymorphisms do not deviate significantly from Hardy-Weinberg Equilibrium, raising the possibility that many of these massive haploblocks could be segregating neutrally. Our results thereby reveal evidence that inversions show a variety of complex yet largely hidden patterns in natural populations, beyond cases where they contribute to known variation in ecologically relevant traits.

NUPTs are DNA sequences of plastid origin that are present in plant nuclear genomes in varying, though typically low, amounts. It is assumed that they are continuously formed and, due to their potentially mutagenic effect, they are removed at a constant turnover rate, which should result in an exponential decay of their age distributions and a negative correlation between age and size. However, these assumptions are based on analyses from a limited number of species and have never been explicitly tested. To gain insight into the mechanisms driving the origin and evolution of NUPTs, here we surveyed the plastid and nuclear genomes of 30 species representing the main angiosperm (flowering plants) lineages. By modeling the distribution of ages and sizes, examining their linear arrangement across the plastid genome, and statistically assessing spatial biases with respect to other genomic features, we showed that NUPTs are: (i) formed by both continuous and episodic mechanisms; (ii) unevenly represented across the plastid genome; (iii) consistently associated with certain classes of RNA genes, in particular rRNA, tRNA, and regulatory RNA genes; (iv) differentially contributing to structural genes; and (v) closer than expected to different superfamilies of transposons in a species-specific manner. Our results reveal the unexpected complexity in the mechanisms driving the origin of NUPTs, which not only involve their continuous formation but also episodic events, highlight their role as a major source of noncoding RNA genes and other genomic features, and provide a more complete picture of the different drivers of evolutionary change at the genome level.

Key unanswered questions in biology center on the causes, consequences, and maintenance of sexual reproduction ("sex"). Genome-driven processes are central to the evolutionary and genetic mechanisms inherent to sex, making genomic resources a fundamental part of answering these questions. We present the first genome assembly for a species that is uniquely well-suited for the study of (a)sex in nature, Potamopyrgus antipodarum. This New Zealand snail is unusual in featuring multiple separate transitions from obligately sexual to obligately asexual reproduction, leading to the coexistence of phenotypically similar sexual and asexual forms, a feature that is required to directly study the maintenance of sex. These separately derived asexual lineages constitute separate evolutionary experiments, providing a powerful means of characterizing how the absence of sex affects genome evolution. Our genome assembly provides critical steps toward understanding the causes and consequences of sex in this system and important resources for the rapidly growing P. antipodarum and molluscan genomics research community. In characterizing this genome, we uncovered unexpected evidence for a recent whole-genome duplication (WGD) in P. antipodarum. This discovery sets the stage for using P. antipodarum to evaluate processes of rediploidization following WGD and to assess whether WGD might drive transitions to asexuality.

Biology is in a genomics era, but many researchers may still be alienated from these techniques as a lack of genomic resources remains for many animal groups, necessitating further democratization. Hybrid capture is a popular phylogenomic approach in molecular systematics, with ultraconserved elements being the most popular. However, access to ultraconserved element data is more expensive per sample relative to other commonly used genetic/genomic approaches. Using published genomes, we developed a metazoan ultraconserved element probe set, the universality of which allows multiple research groups working on vastly different animal lineages to share costs and resources across labs. We demonstrated the utility of this probe set both in silico against 58 published metazoan genomes and in vitro with 130 samples representing 33 metazoan phyla, showing that these probes target loci useful for both deep and shallow level relationships. The proportion of target ultraconserved elements sequenced by the Metazoa probe is equivalent to that of taxon-specific probe sets, but from across all animal phyla. We explored general patterns of ultraconserved element recovery across Metazoa using published genomes and the majority of publicly available ultraconserved element probe sets. The Metazoa probe set is available in three forms: the full set, containing 19,986 probes targeting 2,146 loci, a set containing 10,749 probes targeting 1,022 loci, and the reduced cost set, containing 5,098 probes targeting 466 loci. The development of a universal ultraconserved element probe set should expand the use of genomic data to a much larger segment of the zoological community, with strong potential for broad applications in phylogenomics across all animal phyla.

The staphylococcal cassette chromosome mec (SCCmec) is a mobile genetic element that carries the mecA gene conferring resistance to beta-lactam antibiotics. While SCCmec is widely disseminated in Staphylococcus aureus, its diversity and evolutionary history across different taxonomic scales have not been investigated in detail. To elucidate the mechanisms governing the diversification of SCCmec, we carried out the largest systematic analysis of SCCmec to date. We focused on the Staphylococcaceae family, which is the primary cellular host of SCCmec. We scanned 2,556 complete genomes, representing 75 species and 8 genera within Staphylococcaceae. For this, we developed SCCeeker, a tailored pipeline to detect SCCmec across a large-scale genomic dataset. We uncovered 1,419 candidate SCCmec regions in 3 of 5 Mammaliicoccus species and 32 of 54 Staphylococcus species. SCCmec-carrying species are not more cladistically related than those without the SCCmec. The present study reveals that the evolution of SCCmec locus is driven by multiple mechanisms of horizontal transfer: transposition of insertion sequences IS1272 and IS6/IS431, transfer of entire cassette or fragments of it, cassettes carried by putative plasmids, formation of chimeric cassettes, and recombination of homologous sequences. The multimodal shuffling of SCCmec elements creates a genetically diverse cassette pool and sheds light on the independent evolution of mobile elements and the origins of SCCmec.

Indrella ampulla is a polymorphic, brightly colored, forest-dwelling land snail endemic to the Western Ghats of India. Studying and understanding evolutionary processes occurring within this species has remained a challenge largely due to a paucity of genomic resources. We present high-quality annotated nuclear and mitochondrial genome assemblies of I. ampulla. The nuclear genome is assembled through a hybrid approach using Illumina short reads and Oxford Nanopore long reads, with an N50 value of 632 kb and 93.5% BUSCO genome completeness. The mitogenome is 13,887 bp long. The demographic history reconstruction based on the genomic data exhibits signatures of population decline during the last 100,000 years. This genome will aid in deciphering the color polymorphism in I. ampulla and augmenting the general understanding of the evolution of gastropods.