The promise and pitfalls of synteny in phylogenomics

Explosion of goby fish diversity at the Eocene-Oligocene transition

A rapid drop of sea level at the Eocene-Oligocene transition (EOT; 34-33 Ma) triggered a marine mass extinction event and the turnover of terrestrial fauna, but its influence on the diversification of nearshore marine fish communities is unclear. Goby fishes (Acanthomorpha: Percomorpha: Gobiiformes) provide an ideal system to investigate the hypothesis that ecological opportunity at the EOT triggered the proliferation of coastal marine fishes. However, despite more than 30 years of molecular evolutionary research, divergence time estimates for gobies are widely variable, incomplete with respect to sampling of taxonomic families and sub-familial lineages, and far older than evident by the modest fossil record. Here we use 1,314 ultraconserved element (UCE) sequences sampled from 121 species, including all gobiiform families and sub-familial goby lineages, to infer phylogeny and node ages under species tree and relaxed molecular clock models. Our time-calibrated phylogenomic hypothesis reconciles molecular clock- and fossil-based estimates for gobiiform diversification, dating the origin of Apogonidae and Gobioidei to the uppermost Late Cretaceous, with lower to middle Paleogene divergence of the gobioid backbone and an explosion of goby lineages at the EOT. Our results support a remarkably recent evolutionary origin of goby families and stimulate new questions on the seemingly exceptional diversity of the group.

Exploring genome architecture as a source of phylogenetic characters for resolving the apulmonate arachnid polytomy

Chromosome-level genome assemblies are powerful tools for identifying the presence of rare genomic changes that can overcome phylogenetically intractable problems. Chelicerata, the sister group to the remaining arthropods, harbors a soft polytomy at the base of an internal node named Euchelicerata, which is variably resolved across phylogenomic studies. As a result, seven orders, comprising horseshoe crabs and six apulmonate arachnid lineages, exhibit highly unstable placements from one study to the next, typically with maximal nodal support. Here, we analyzed recently released chromosome-level genomes of two of these orders, Opiliones (harvestmen) and Solifugae (camel spiders). We show that both Opiliones and Solifugae exhibit an unduplicated genome condition, as inferred from analysis of gene clusters, microRNAs, and macrosynteny. These results are congruent with phylogenomic studies that have refuted traditional morphological placements of Opiliones and Solifugae as close relatives of orders within Arachnopulmonata, a subset of six arachnid orders that are united by a shared whole genome duplication. Additionally, we examine irreversible chromosome fusion-with-mixing events as potential sources of phylogenetic data. We show that while fusion and mixing events are common in apulmonate arachnids, multiple mixing events support incompatible unrooted tree topologies. These results suggest that fusion and mixing events have evolved convergently in the chelicerate tree of life, particularly for extant lineages with a small number of chromosomes. Overall, our findings demonstrate that broader sampling of chelicerate genomes and establishment of genomic resources for key missing orders are essential to unlocking the potential of rare genomic changes as phylogenetic data sources.

Scaffolded and annotated nuclear and organelle genomes of the North American brown alga Saccharina latissima

Increasing the genomic resources of emerging aquaculture crop targets can expedite breeding processes as seen in molecular breeding advances in agriculture. High quality annotated reference genomes are essential to implement this relatively new molecular breeding scheme and benefit research areas such as population genetics, gene discovery, and gene mechanics by providing a tool for standard comparison. The brown macroalga Saccharina latissima (sugar kelp) is an ecologically and economically important kelp that is found in both the northern Pacific and Atlantic Oceans. Cultivation of Saccharina latissima for human consumption has increased significantly this century in both North America and Europe, and its single blade morphology allows for dense seeding practices used in the cultivation of its Asian sister species, Saccharina japonica. While Saccharina latissima has potential as a human food crop, insufficient information from genetic resources has limited molecular breeding in sugar kelp aquaculture. We present scaffolded and annotated Saccharina latissima nuclear and organelle genomes from a female gametophyte collected from Black Ledge, Groton, Connecticut. This Saccharina latissima genome compares well with other published kelp genomes and contains 218 scaffolds with a scaffold N50 of 1.35 Mb, a GC content of 49.84%, and 25,012 predicted genes. We also validated this genome by comparing the synteny and completeness of this Saccharina latissima genome to other kelp genomes. Our team has successfully performed initial genomic selection trials with sugar kelp using a draft version of this genome. This Saccharina latissima genome expands the genetic toolkit for the economically and ecologically important sugar kelp and will be a fundamental resource for future foundational science, breeding, and conservation efforts.

SOI: robust identification of orthologous synteny with the Orthology Index and broad applications in evolutionary genomics

With the explosive growth of whole-genome datasets, accurate detection of orthologous synteny has become crucial for reconstructing evolutionary history. However, current methods for identifying orthologous synteny face great limitations, particularly in scaling with varied polyploidy histories and accurately removing out-paralogous synteny. In this study, we developed a scalable and robust approach, based on the Orthology Index (OI), to effectively identify orthologous synteny. Our evaluation across a large-scale empirical dataset with diverse polyploidization events demonstrated the high reliability and robustness of the OI method. Simulation-based benchmarks further validated the accuracy of our method, showing its superior performance against existing methods across a wide range of scenarios. Additionally, we explored its broad applications in reconstructing the evolutionary histories of plant genomes, including the inference of polyploidy, identification of reticulation, and phylogenomics. In conclusion, OI offers a robust, interpretable, and scalable approach for identifying orthologous synteny, facilitating more accurate and efficient analyses in plant evolutionary genomics.

Unbiased anchors for reliable genome-wide synteny detection

Orthology inference lies at the foundation of comparative genomics research. The correct identification of loci which descended from a common ancestral sequence is not only complicated by sequence divergence but also duplication and other genome rearrangements. The conservation of gene order, i.e. synteny, is used in conjunction with sequence similarity as an additional factor for orthology determination. Current approaches, however, rely on genome annotations and are therefore limited. Here we present an annotation-free approach and compare it to synteny analysis with annotations. We find that our approach works better in closely related genomes whereas there is a better performance with annotations for more distantly related genomes. Overall, the presented algorithm offers a useful alternative to annotation-based methods and can outperform them in many cases.

Molluscan systematics: historical perspectives and the way ahead

Mollusca, the second-most diverse animal phylum, is estimated to have over 100,000 living species with great genetic and phenotypic diversity, a rich fossil record, and a considerable evolutionary significance. Early work on molluscan systematics was grounded in morphological and anatomical studies. With the transition from oligo gene Sanger sequencing to cutting-edge genomic sequencing technologies, molecular data has been increasingly utilised, providing abundant information for reconstructing the molluscan phylogenetic tree. However, relationships among and within most major lineages of Mollusca have long been contentious, often due to limited genetic markers, insufficient taxon sampling and phylogenetic conflict. Fortunately, remarkable progress in molluscan systematics has been made in recent years, which has shed light on how major molluscan groups have evolved. In this review of molluscan systematics, we first synthesise the current understanding of the molluscan Tree of Life at higher taxonomic levels. We then discuss how micromolluscs, which have adult individuals with a body size smaller than 5 mm, offer unique insights into Mollusca's vast diversity and deep phylogeny. Despite recent advancements, our knowledge of molluscan systematics and phylogeny still needs refinement. Further advancements in molluscan systematics will arise from integrating comprehensive data sets, including genome-scale data, exceptional fossils, and digital morphological data (including internal structures). Enhanced access to these data sets, combined with increased collaboration among morphologists, palaeontologists, evolutionary developmental biologists, and molecular phylogeneticists, will significantly advance this field.

Decontamination of DNA sequences from a Streptomyces genome for optimal genome mining

Despite meticulous precautions, contamination of genomic DNA samples is not uncommon, which can significantly compromise the analysis of microorganisms' whole-genome sequencing data, thus affecting all subsequent analyses. Thanks to advancements in software and bioinformatics techniques, it is now possible to address this issue and prevent the loss of the entire dataset obtained in a contaminated whole-genome sequencing, where the DNA of another bacterium is present. In this study, it was observed that the sequencing reads from Streptomyces sp. BRB040, generated using the HiSeq System platform (Illumina Inc., San Diego, USA), were contaminated with the DNA of Bacillus licheniformis. To eliminate the contamination in Streptomyces sp. BRB040, a combination of tools available on the Galaxy platform and other web-based resources were used (MeDuSa and Blast). The contaminated reads were treated as a metagenome to isolate the genome of the contaminating organism. They were assembled using the metaSPAdes, resulting in a large scaffold of 4.187 Mb, which was identified as Bacillus licheniformis. After the identification of the contaminating organism, its genome was used as a filter to remove sequencing reads that could align using then Bowtie 2 software for this step. Once the contaminated reads were removed a new assembly was performed using the Unicycler software, yielding 117 contigs with a total size of 7.9 Mb. The completeness of this genome was assessed through BUSCO, resulting in a completeness of 95.9%. We also used an alternative tool (BBduk) to eliminate contaminated reads and the resulting assembly by Unicycler generated 85 contigs with a total size of 8.3 Mb and completeness of 99.5%. These results were better than the assembly obtained via SPAdes, which generated less complete genomes (maximum of 97.8% completeness) compared to Unicycler and which was unable to perform an adequate assembly of the data obtained from decontamination by BBduk. When compared with the uncontaminated BRB040 genome, which has a total size of 8.2 Mb and completeness of 99.8%, this pipeline revealed that the assembly performed with the decontaminated reads via BBduk presented better results, with completeness 0.3% lower than the reference. The genome mining of both genomes using antiSMASH 7.0 revealed the number of 24 Biosynthetic Gene Clusters (BGCs) for BBduk data as well as in the control assembly of the BRB040. In silico decontamination process allows the genome mining of BGCs despite the loss of nucleotides. These findings show that contamination can be effectively removed from a genome using readily available online tools, while preserving a dataset suitable for extracting valuable insights into the secondary metabolism of the target organism. This approach is particularly beneficial in scenarios where resequencing samples is not immediately feasible.

Fusion, fission, and scrambling of the bilaterian genome in Bryozoa

Groups of orthologous genes are commonly found together on the same chromosome over vast evolutionary distances. This extensive physical gene linkage, known as macrosynteny, is seen between bilaterian phyla as divergent as Chordata, Echinodermata, Mollusca, and Nemertea. Here, we report a unique pattern of genome evolution in Bryozoa, an understudied phylum of colonial invertebrates. Using comparative genomics, we reconstruct the chromosomal evolutionary history of five bryozoans. Multiple ancient chromosome fusions followed by gene mixing led to the near-complete loss of bilaterian linkage groups in the ancestor of extant bryozoans. A second wave of rearrangements, including chromosome fission, then occurred independently in two bryozoan classes, further scrambling bryozoan genomes. We also discover at least five derived chromosomal fusion events shared between bryozoans and brachiopods, supporting the traditional but highly debated Lophophorata hypothesis and suggesting macrosynteny to be a potentially powerful source of phylogenetic information. Finally, we show that genome rearrangements led to the dispersion of genes from bryozoan Hox clusters onto multiple chromosomes. Our findings demonstrate that the canonical bilaterian genome structure has been lost across all studied representatives of an entire phylum, and reveal that linkage group fission can occur very frequently in specific lineages.

Comprehensive analysis of 111 Pleuronectiformes mitochondrial genomes: insights into structure, conservation, variation and evolution

BACKGROUND

Pleuronectiformes, also known as flatfish, are important model and economic animals. However, a comprehensive genome survey of their important organelles, mitochondria, has been limited. Therefore, we aim to analyze the genomic structure, codon preference, nucleotide diversity, selective pressure and repeat sequences, as well as reconstruct the phylogenetic relationship using the mitochondrial genomes of 111 flatfish species.

RESULTS

Our analysis revealed a conserved gene content of protein-coding genes and rRNA genes, but varying numbers of tRNA genes and control regions across species. Various gene rearrangements were found in flatfish species, especially for the rearrangement of nad5-nad6-cytb block in Samaridae family, the swapping rearrangement of nad6 and cytb gene in Bothidae family, as well as the control region translocation and tRNA-Gln gene inversion in the subfamily Cynoglossinae, suggesting their unique evolutionary history and/or functional benefit. Codon usage showed obvious biases, with adenine being the most frequent nucleotide at the third codon position. Nucleotide diversity and selective pressure analysis suggested that different protein-coding genes underwent varying degrees of evolutionary pressure, with cytb and cox genes being the most conserved ones. Phylogenetic analysis using both whole mitogenome information and concatenated independently aligned protein-coding genes largely mirrored the taxonomic classification of the species, but showed different phylogeny. The identification of simple sequence repeats and various long repetitive sequences provided additional complexity of genome organization and offered markers for evolutionary studies and breeding practices.

CONCLUSIONS

This study represents a significant step forward in our comprehension of the flatfish mitochondrial genomes, providing valuable insights into the structure, conservation and variation within flatfish mitogenomes, with implications for understanding their evolutionary history, functional genomics and fisheries management. Future research can delve deeper into conservation biology, evolutionary biology and functional usages of variations.

Unraveling the Mysteries of Sleep: Exploring Phylogenomic Sleep Signals in the Recently Characterized Archaeal Phylum Lokiarchaeota near Loki's Castle

Sleep is a universally conserved behavior whose origin and evolutionary purpose are uncertain. Using phylogenomics, this article investigates the evolutionary foundations of sleep from a never before used perspective. More specifically, it identifies orthologs of human sleep-related genes in the Lokiarchaeota of the Asgard superphylum and examines their functional role. Our findings indicate that a conserved suite of genes associated with energy metabolism and cellular repair is involved, thus suggesting that sleep plays a primordial role in cellular maintenance. The data cited lend credence to the idea that sleep improves organismal fitness across evolutionary time by acting as a restorative process. Notably, our approach demonstrates that phylogenomics is more useful than standard phylogenetics for clarifying common evolutionary traits. By offering insight into the evolutionary history of sleep and putting forth a novel model framework for sleep research across taxa, these findings contribute to our growing understanding of the molecular foundation of sleep. This study lays the groundwork for further investigations into the importance of sleep in various organisms. Such investigations could have consequences for improving human health and more generally could provide a deeper comprehension of the fundamental processes of life.

Reticulate evolution: Detection and utility in the phylogenomics era

Phylogenomics has enriched our understanding that the Tree of Life can have network-like or reticulate structures among some taxa and genes. Two non-vertical modes of evolution - hybridization/introgression and horizontal gene transfer - deviate from a strictly bifurcating tree model, causing non-treelike patterns. However, these reticulate processes can produce similar patterns to incomplete lineage sorting or recombination, potentially leading to ambiguity. Here, we present a brief overview of a phylogenomic workflow for inferring organismal histories and compare methods for distinguishing modes of reticulate evolution. We discuss how the timing of coalescent events can help disentangle introgression from incomplete lineage sorting and how horizontal gene transfer events can help determine the relative timing of speciation events. In doing so, we identify pitfalls of certain methods and discuss how to extend their utility across the Tree of Life. Workflows, methods, and future directions discussed herein underscore the need to embrace reticulate evolutionary patterns for understanding the timing and rates of evolutionary events, providing a clearer view of life's history.

Annelid Comparative Genomics and the Evolution of Massive Lineage-Specific Genome Rearrangement in Bilaterians

The organization of genomes into chromosomes is critical for processes such as genetic recombination, environmental adaptation, and speciation. All animals with bilateral symmetry inherited a genome structure from their last common ancestor that has been highly conserved in some taxa but seemingly unconstrained in others. However, the evolutionary forces driving these differences and the processes by which they emerge have remained largely uncharacterized. Here, we analyze genome organization across the phylum Annelida using 23 chromosome-level annelid genomes. We find that while many annelid lineages have maintained the conserved bilaterian genome structure, the Clitellata, a group containing leeches and earthworms, possesses completely scrambled genomes. We develop a rearrangement index to quantify the extent of genome structure evolution and show that, compared to the last common ancestor of bilaterians, leeches and earthworms have among the most highly rearranged genomes of any currently sampled species. We further show that bilaterian genomes can be classified into two distinct categories-high and low rearrangement-largely influenced by the presence or absence, respectively, of chromosome fission events. Our findings demonstrate that animal genome structure can be highly variable within a phylum and reveal that genome rearrangement can occur both in a gradual, stepwise fashion, or rapid, all-encompassing changes over short evolutionary timescales.

Trees as a metaphor to understand relationships in biology

The phylogenetic tree has been a core conceptual tool for evolutionary biology for nearly 200 years. This editorial explores the role of the tree as a metaphor, discussing two new PLOS Biology Essays that look to the future.