ASTRAL: genome-scale coalescent-based species tree estimation

Phylogeny of Palicoureeae (Rubiaceae) based on 353 low-copy nuclear genes - with particular focus on Hymenocoleus Robbr

Members of the tribe Palicoureeae of the coffee family (Rubiaceae) have a complex taxonomic history and have been the focus of few modern systematic studies. The tribe comprises about 1,100 tropical species in ten genera. To investigate phylogeny, we used a target capture approach and the angiosperm-wide Angiosperms353 bait set to produce genomic data for a representative taxon sample of Palicoureeae, with particular focus on the African genus Hymenocoleus. Using coalescent-based inference methods, we find that Puffia gerrardii (recently separated from Geophila) is sister to Hymenocoleus. The deepest split in Hymenocoleus is highly affected by incomplete lineage sorting, possibly as a consequence of rapid speciation during the early evolution of the clade. Remaining interspecific relationships in Hymenocoleus could be confidently resolved and while Robbrecht's traditional infrageneric classification scheme based on floral features is not supported as reflecting evolution in the group, we find that several other features do, e.g. characters of pyrenes and involucral cups. Although not free of challenges, a strong advantage with our analytical approach is that gene tree heterogeneity can be taken into account. Including flanking regions yielded data sets that had the strongest power to reject polytomies and produced less gene tree error, resulting in species trees with higher normalised quartet scores and higher average support compared to trees inferred only from exon data. Presumably paralogous loci are often filtered out prior to species tree estimation but we find that they may contribute important phylogenetic information when using an inference method that actively accounts for them.

Genomes of critically endangered saola are shaped by population structure and purging

The saola is one of the most elusive large mammals, standing at the brink of extinction. We constructed a reference genome and resequenced 26 saola individuals, confirming the saola as a basal member of the Bovini. Despite its small geographic range, we found that the saola is partitioned into two populations with high genetic differentiation (FST = 0.49). We estimate that these populations diverged and started declining 5,000-20,000 years ago, possibly due to climate changes and exacerbated by increasing human activities. The saola has long tracts without genomic diversity; however, most of these tracts are not shared by the two populations. Saolas carry a high genetic load, yet their gradual decline resulted in the purging of the most deleterious genetic variation. Finally, we find that combining the two populations, e.g., in an eventual captive breeding program, would mitigate the genetic load and increase the odds of species survival.

Phylogeny, species delimitation, and biogeographical history of Bredia

Species delimitation in plants is sometimes challenging due to morphological convergence, interspecific gene flow, and historically limited sampling. Bredia Blume as currently defined comprises 27 species and has been resolved as monophyletic in previous phylogenomic studies. However, relationships among several major lineages in the genus remain elusive, and the species boundaries of some problematic taxa have not been tested. In this study, we employed comprehensive taxon sampling and reconstructed the phylogeny of Bredia using single-copy orthologs (SCOs), genomic single nucleotide polymorphisms (SNPs), and whole plastomes. The species tree derived from SCOs provided the highest resolution, strongly supporting all interspecific relationships. We identified instances of morphological convergence and potential hybridization/introgression within groups of interest and discussed species limits based on monophyly, genetic divergence, and morphological diagnosability. Using this robust phylogeny, we inferred divergence times and biogeographical history for Bredia. The genus originated in the Yunnan-Myanmar-Thailand Border region and the Beibu Gulf region during the middle Miocene, initially adapting to karst habitats. Over time, certain lineages shifted to non-karst environments. One such lineage migrated to the southeastern part of the Eastern Asiatic Kingdom in the late Miocene, where it rapidly diversified forming several major lineages. Subsequently, a mainland lineage reached Taiwan via a land bridge between the late Pliocene and the early Pleistocene and diversified in the region, eventually spreading to the Ryukyu Islands in the middle Pleistocene.

Phylogenomics of the tetraploid Hawaiian lobeliads: Implications for their origin, dispersal history, and adaptive radiation

Hawaiian lobeliads exhibit extensive adaptive radiations and are considered the largest plant clade (143 species) endemic to any oceanic archipelago. Rapid insular radiations are prone to reticulate evolution, yet detecting hybridization is often limited by inadequate sampling of taxa or independent loci. We analyzed 633 nuclear loci (including tetraploid duplications) and whole plastomes for 89% of extant species to derive phylogenies for the Hawaiian lobeliads. Nuclear data provide strong support for nine major clades in both likelihood and ASTRAL analyses. All genera/sections are monophyletic except Clermontia and Cyanea. Nuclear and plastome phylogenies conflict on short, deep branches; the nuclear tree resolves a fleshy-fruited clade of Hawaiian Clermontia/Cyanea-Brighamia/Delissea, sister to Polynesian Sclerotheca, with both sister to a capsular-fruited Hawaiian clade. Incomplete lineage sorting in a rapid radiation starting 8.5-11.3 Ma is sufficient to explain uncertainty and cytonuclear discordance along the backbone. Sequence data support reticulation within Clermontia and especially Cyanea. Nuclear data identify 42 interisland dispersal events: 89% accord with the strict progression rule, involving movement to the next younger island in the hotspot chain, consistent with theory. Plastid data overestimate such events by 17%. Cyanea and Clermontia have undergone parallel adaptive radiations in elevational distribution and flower length on all major islands, with multiple founders and some interisland differences. Hawaiian lobeliad diversification was driven by an early intergeneric divergence in habitat, followed by parallel adaptive radiation and ecological speciation within Clermontia/Cyanea, combined with widespread single-island endemism, frequent interisland dispersal, and occasional hybridization.

Disconnecting trapdoors: Phylogenomic analyses reveal evolutionary contrasts in trapdoor spiders with intercontinental distribution (Idiopidae, Idiopinae)

Among Mygalomorphae spiders, the family Idiopidae is the second most diverse, consisting exclusively of trapdoor spiders and is divided into three subfamilies: Arbanitinae, Genysinae, and Idiopinae. The subfamily Idiopinae, distinguished mainly by anterior lateral eyes that project forward, includes 153 species across seven genera, distributed throughout South America, Africa, and parts of Asia. Within this subfamily, the genus Idiops includes the greatest diversity and is the only genus recorded in both the New and Old Worlds. Utilizing a taxon set from the Neotropical and Afrotropical regions, with specimens collected from 1947 to 2021, our study provides the first phylogenomic analysis of the family based on Ultraconserved Elements (UCEs). To assess the monophyly of Idiopinae and Idiops, as well as the relationships among genera within the subfamily, we conducted phylogenetic analyses employing maximum likelihood, Bayesian inference, and coalescent-based methods. The phylogenetic trees reveal that Idiopinae forms a monophyletic lineage, split into two geographically distinct groups: one with African species and the other with Neotropical species. We did not recover monophyly of the genus Idiops; Neotropical Idiops form a monophyletic lineage, while African Idiops species group with Titanidiops, forming a sister lineage to the remaining African Idiopinae. The relationship between the phylogenetic results obtained and the main morphological differences observed among the genera is discussed. Finally, our study challenges the monophyly of Idiopidae by including Neocteniza, which is found to be an independent lineage sister to Ctenizidae and the rest of Idiopidae.

Genomic and Methylomic Signatures Associated With the Maintenance of Genome Stability and Adaptive Evolution in Two Closely Allied Wolf Spiders

Pardosa spiders, belonging to the wolf spider family Lycosidae, play a vital role in maintaining the health of forest and agricultural ecosystems due to their function in pest control. This study presents chromosome-level genome assemblies for two allied Pardosa species, P. laura and P. agraria. Both species' genomes show a notable expansion of helitron transposable elements, which contributes to their large genome sizes. Methylome analysis indicates that P. laura has higher overall DNA methylation levels compared to P. agraria. DNA methylation may not only aids in transposable element-driven genome expansion but also positively affects the three-dimensional organisation of P. laura after transposon amplification, thereby potentially enhancing genome stability. Genes associated with hyper-differentially methylated regions in P. laura (compared to P. agraria) are enriched in functions related to mRNA processing and energy production. Furthermore, combined transcriptome and methylome profiling has uncovered a complex regulatory interplay between DNA methylation and gene expression, emphasising the important role of gene body methylation in the regulation of gene expression. Comparative genomic analysis shows a significant expansion of cuticle protein and detoxification-related gene families in P. laura, which may improve its adaptability to various habitats. This study provides essential genomic and methylomic insights, offering a deeper understanding of the relationship between transposable elements and genome stability, and illuminating the adaptive evolution and species differentiation among allied spiders.

Nine high-quality Anas genomes provide insights into Anas evolution and domestication

Evolutionary studies of wild and domestic organisms have yielded fascinating discoveries, while the species diversity and the domestication of ducks remain unclear. Here, we assembled eight chromosome-level Anas genomes, combined with the Pekin duck genome, to investigate Anas evolution and domestication. We found that, compared to autosomes, the Z chromosome was less affected by introgression and exhibited relatively stable local phylogenies. From the Z chromosome perspective, we proposed that the speciation of Anas platyrhynchos and Anas zonorhyncha was accompanied by continuous female-biased gene flow and remodeled duck domestication history. Moreover, we constructed an Anas pan-genome and identified several differentiated structural variations (SVs) between domestic and wild ducks. These SVs likely regulate their neighboring genes (i.e., GHR and FER), which represented the promising "domestication genes." Furthermore, a long terminal repeat (LTR) retrotransposon burst was found to have accelerated duck domestication, specifically contributing to functional shifts of the notable MITF and IGF2BP1 genes. These findings presented a live example for understanding animal evolutionary processes.

Phylogenomics resolves key relationships in Rumex and uncovers a dynamic history of independently evolving sex chromosomes

Sex chromosomes have evolved independently many times across eukaryotes. Despite a considerable body of literature on sex chromosome evolution, the causes and consequences of variation in their formation, degeneration, and turnover remain poorly understood. Chromosomal rearrangements are thought to play an important role in these processes by promoting or extending the suppression of recombination on sex chromosomes. Sex chromosome variation may also contribute to barriers to gene flow, limiting introgression among species. Comparative approaches in groups with sexual system variation can be valuable for understanding these questions. Rumex is a diverse genus of flowering plants harboring significant sexual system and karyotypic variation, including hermaphroditic and dioecious clades with XY (and XYY) sex chromosomes. Previous disagreement in the phylogenetic relationships among key species has rendered the history of sex chromosome evolution uncertain. Resolving this history is important for investigating the interplay of chromosomal rearrangements, introgression, and sex chromosome evolution in the genus. Here, we use new transcriptome assemblies from 11 species representing major clades in the genus, along with a whole-genome assembly generated for a key hermaphroditic species. Using phylogenomic approaches, we find evidence for the independent evolution of sex chromosomes across two major clades, and introgression from unsampled lineages likely predating the formation of sex chromosomes in the genus. Comparative genomic approaches revealed high rates of chromosomal rearrangement, especially in dioecious species, with evidence for a complex origin of the sex chromosomes through multiple chromosomal fusions. However, we found no evidence of elevated rates of fusion on the sex chromosomes in comparison with autosomes, providing no support for an adaptive hypothesis of sex chromosome expansion due to sexually antagonistic selection. Overall, our results highlight a complex history of karyotypic evolution in Rumex, raising questions about the role that chromosomal rearrangements might play in the evolution of large heteromorphic sex chromosomes.

Phylogenomics, historical biogeography, and diversification of leaf traits in the Malagasy-endemic genus Uncarina (Pedaliaceae)

PREMISE

Uncarina contains 14 species of woody plants endemic to Madagascar. Its occurrence across dryland biomes on the island make it an interesting system to study the diversification of the flora.

METHODS

Using samples of all species and 512 nuclear loci, we reconstructed phylogenetic trees to examine species relationships and assess their monophyly. We also studied the historical biogeography of the genus and combined leaf trait data derived from SEM photography of trichomes and geometric morphometric analysis of leaf shape to better understand its diversification across dryland biomes.

RESULTS

Uncarina is monophyletic, and major clades showed a clear biogeographical signal. Leaf traits also corroborated relationships among major clades. Although most species are monophyletic, at least one cryptic species exists. Uncarina, like many arid-adapted plant lineages in Madagascar originated in the Miocene or Pleistocene. Geographic movement has been primarily along a south-north axis, with river basins apparently acting as barriers to gene flow. The evolution of leaf traits corroborated movement from the spiny thicket to the dry forest biome.

CONCLUSIONS

As with Malagasy lemurs and other animals, riverine barriers may have been involved in the diversification of Uncarina and may apply more broadly to epizoochorous angiosperms of Madagascar. Leaf traits suggest either a loss of adaptations to extremely arid, high irradiance environments or a release from herbivores. As is likely needed in other Malagasy lineages, more thorough population-level sampling and specimen collecting is needed to fully understand the taxonomic and morphological diversity in the genus.

Specimen Identification Through Multilocus Species Tree Constructed From Single-Copy Orthologs (SCOs): A Case Study in Cymbidium Subgenus Jensoa

Standard barcodes and ultra-barcode encounter significant challenges when delimiting and discriminating closely related species characterized by deep coalescence, hybrid speciation, gene flow, or low sequence variation. Single-copy orthologs (SCOs) have been widely recognized as standardized nuclear markers in metazoan DNA taxonomy, yet their application in plant taxonomy remains unexplored. This study evaluates the efficacy of SCOs for identifying recently diverged species within the Cymbidium subgenus Jensoa, where ultra-barcodes have previously shown limited resolution. Remarkably, over 90% of the 9094 targeted reference SCOs, inferred from three Cymbidium genomes, were successfully retrieved for all 11 representative species in subg. Jensoa using ALiBaSeq at a minimal 5× depth from whole genome shotgun sequences. The species tree, reconstructed from multiple refined SCO matrices under the coalescent model, effectively distinguished all species and identified mislabeled or misidentified specimens. The comprehensive and refined SCO matrices produced by our pipeline not only enhance phylogenetic analysis but also improve the precision of species diagnosis. Additionally, biparentally inherited SCOs, serving as multi-locus markers, not only augment the effectiveness of DNA barcoding but also support a transition to multi-locus, species-tree-based specimen assignment strategies.

wQFM-TREE: highly accurate and scalable quartet-based species tree inference from gene trees

Motivation

methods are becoming increasingly popular for species tree estimation from multi-locus data in the presence of gene tree discordance. Accurate Species TRee Algorithm (ASTRAL), a leading method in this class, solves the Maximum Quartet Support Species Tree problem within a constrained solution space, while heuristics like Weighted Quartet Fiduccia-Mattheyses (wQFM) and Weighted Quartet MaxCut (wQMC) use weighted quartets and a divide-and-conquer strategy. Recent studies showed wQFM to be more accurate than ASTRAL and wQMC, though its scalability is hindered by the computational demands of explicitly generating and weighting Θ ( n 4 ) quartets. Here, we introduce wQFM-TREE, a novel summary method that enhances wQFM by avoiding explicit quartet generation and weighting, enabling its application to large datasets.

Results

Extensive simulations under diverse and challenging model conditions, with hundreds or thousands of taxa and genes, consistently demonstrate that wQFM-TREE matches or improves upon the accuracy of ASTRAL. It outperformed ASTRAL in 25 of 27 model conditions (statistically significant in 20) involving 200-1000 taxa. Moreover, applying wQFM-TREE to re-analyze the green plant dataset from the One Thousand Plant Transcriptomes Initiative produced a tree highly congruent with established evolutionary relationships of plants. wQFM-TREE's remarkable accuracy and scalability make it a strong competitor to leading methods. Its algorithmic and combinatorial innovations also enhance quartet-based computations, advancing phylogenetic estimation.

Availability and implementation

wQFM-TREE is freely available in open source form at https://github.com/abdur-rafi/wQFM-TREE.

Misspecification Strikes: ASTRAL can Mislead in the Presence of Hybridization, even for Nonanomalous Scenarios

ASTRAL is a powerful and widely used tool for species tree inference, known for its computational speed and robustness under incomplete lineage sorting. The method has often been used as an initial step in species network inference to provide a backbone tree structure upon which hybridization events are later added to such a tree via other methods. However, we show empirically and theoretically, that this methodology can yield flawed results. Specifically, we demonstrate that under the network multispecies coalescent model-including nonanomalous scenarios-ASTRAL can produce a tree that does not correspond to any topology displayed by the true underlying network. This finding highlights the need for caution when using ASTRAL-based inferences in suspected hybridization cases.

Branch Length Transforms using Optimal Tree Metric Matching

The abundant discordance between evolutionary relationships across the genome has rekindled interest in methods for comparing and averaging trees on a shared leaf set. However, most attempts at comparing and matching trees have focused on tree topology. Comparing branch lengths has been more elusive due to several challenges. Species tree branch lengths can be measured in various units, often different from gene trees. Moreover, rates of evolution change across the genome, the species tree, and specific branches of gene trees. These factors compound the stochasticity of coalescence times and estimation noise, making branch lengths highly heterogeneous across the genome. For many downstream applications in phylogenomic analyses, branch lengths are as important as the topology, and yet, existing tools to compare and combine weighted trees are limited. In this paper, we address the question of matching one tree to another, accounting for their branch lengths. We define a series of computational problems called Topology-Constrained Metric Matching (TCMM) that seek to transform the branch lengths of a query tree based on a reference tree. We show that TCMM problems can be solved in quadratic time and memory using a linear algebraic formulation coupled with dynamic programming preprocessing. While many applications can be imagined for this framework, we explore two applications in this paper: embedding leaves of gene trees in Euclidean space to find outliers potentially indicative of errors and summarizing gene tree branch lengths onto the species tree. In these applications, our method, when paired with existing methods, increases their accuracy at limited computational expense.

Code and Data availability

The software is available at https://github.com/shayesteh99/TCMM.git . Data is available on Github https://github.com/shayesteh99/TCMM-Data.git .

Hordeum I genome unlocks adaptive evolution and genetic potential for crop improvement

Crop wild relatives (CWRs) are invaluable for crop improvement. Among these, Hordeum I-genome species exhibit exceptional tolerance to alkali and salt stresses. Here we present a chromosome-scale genome assembly of Hordeum brevisubulatum (II, 2n = 2x =14) and genome resequencing of 38 diploid germplasms spanning 7 I-genome species. We reveal that the adaptive evolution of the H. brevisubulatum genome is shaped by structural variations, some of which may contribute to its adaptation to high alkali and salt environments. Evolutionary duplication of the stress sensor-responder module CaBP-NRT2 and the horizontally transferred fungal gene Fhb7 were identified as novel alkaline-saline tolerance mechanisms. We also demonstrate the potential of the Hordeum I genome in crop breeding through the newly synthesized hexaploid Tritordeum (AABBII) with enhanced alkaline-saline tolerance. Our study fills critical gaps in Hordeum genomics and CWR research, advancing introgression of CWR resources into current crops for sustainable agriculture.

Ancient large-scale gene duplications and diversification in bryophytes illuminate the plant terrestrialization

Large-scale gene duplications (LSGDs) are crucial for evolutionary adaptation and recurrent in vascular plants. However, the role of ancient LSGDs in the terrestrialization and diversification of bryophytes, the second most species-rich group of land plants, remains largely elusive due to limited sampling in bryophytes. Employing the most extensive nuclear gene dataset in bryophytes to date, we reconstructed a time-calibrated phylogenetic tree from 209 species, covering virtually all key bryophyte lineages, for phylogenomic analyses of LSGDs and diversification. We newly identified two ancient LSGDs: one in the most recent common ancestor (MRCA) of extant bryophytes and another in the MRCA of the majority of Jungermanniales s. lato. Duplicated genes from these two LSGDs show significant enrichment in photosynthesis-related processes and structures. Rhizoid-responsive ROOTHAIR DEFECTIVE SIX-LIKE (RSL) genes from ancient LSGDs are present in rhizoidless bryophytes, challenging assumptions about rhizoid absence mechanisms. We highlighted four major diversification rate upshifts, two of which slightly postdated LSGDs, potentially linked to the flourishing of gymnosperms and angiosperms and explaining over 80% of bryophyte diversity. Our findings, supported by extensive bryophyte sampling, highlight the significance of LSGDs in the early terrestrialization and diversification of bryophytes, offering new insights into land plant evolution.

Integrative species delimitation methods infer species boundaries in the Lomatium foeniculaceum complex and indicate an evolutionary history from the Southwest towards the Northeast in western North America

Delimiting species boundaries is a perennial challenge in the field of systematics. Resolving whether morphological variation is the result of environmental parameters, incipient speciation, or complete speciation is especially challenging when the variation is subtle. Within the perennial endemic North American clade of Apiaceae (PENA) there are numerous examples in which widespread species have subtle geographically defined morphological variants that have typically been recognized at the subspecific rank. The Lomatium foeniculaceum (Nutt.) Coult & Rose species complex is a salient case that has long been treated as a single species with five infrataxa, spanning much of the western United States and western Canada in a morphological continuum: L. foeniculaceum var. foeniculaceum, L. foeniculaceum var. daucifolium (Torr. & A. Gray) Cronquist, L. foeniculaceum var. macdougalii (J.M. Coult. & Rose) Cronquist, L. foeniculaceum var. fimbriatum (W.L. Theob.) B. Boivin, and L. foeniculaceum var. inyoense (Mathias & Constance) B. Boivin. We utilized the Angiosperm353 baits kit to sample nuclear loci from these five taxa to determine if the subspecific taxa formed discrete genetic groups with the molecular data. Groups that were identified were then examined for a combination of morphological and ecological traits that corresponded to these groups and could be used to determine the most appropriate taxonomic ranks of recovered groups. Molecular data recovers six well-supported monophyletic clades and a seventh clade of a single individual. Samples initially identified as L. foeniculaceum var. macdougalii are in two clades with one sister to L. foeniculaceum var. foeniculaceum/L. foeniculaceum var. daucifolium the other sister to L. foeniculaceum var. fimbriatum. Most samples of L. foeniculaceum var. foeniculaceum are in the same clade; others are in the clade with L. foeniculaceum var. daucifolium depending on the analysis. Each clade can be defined with a distinct morphological diagnostic character state. We conclude that molecular data and morphology support the recognition of five distinct species within the complex: L. inyoense Mathias & Constance, L. macdougalii J. M. Coult. & Rose, L. fimbriatum (W.L. Theob.) Botello & J.F. Sm., L. semivaginatum Botello & J.F. Sm., and L. foeniculaceum with two varieties retained, L. foeniculaceum var. foeniculaceum and L. foeniculaceum var. daucifolium. The data suggest that the Continental Divide has been influential in the evolution of these species, acting as an effective barrier facilitating speciation.

A pangenome reveals LTR repeat dynamics as a major driver of genome evolution in Chenopodium

The genus Chenopodium L. is characterized by its wide geographic distribution and ecological adaptability. Species such as quinoa (Chenopodium quinoa Willd.) have served as domesticated staple crops for centuries. Wild Chenopodium species exhibit diverse niche adaptations and are important genetic reservoirs for beneficial agronomic traits, including disease resistance and climate hardiness. To harness the potential of the wild taxa for crop improvement, we developed a Chenopodium pangenome through the assembly and comparative analyses of 12 Chenopodium species that encompass the eight known genome types (A-H). Six of the species are new chromosome-scale assemblies, and many are polyploids; thus, a total of 20 genomes were included in the pangenome analyses. We show that the genomes vary dramatically in size with the D genome being the smallest (∼370 Mb) and the B genome being the largest (∼700 Mb) and that genome size was correlated with independent expansions of the Copia and Gypsy LTR retrotransposon families, suggesting that transposable elements have played a critical role in the evolution of the Chenopodium genomes. We annotated a total of 33,457 pan-Chenopodium gene families, of which ∼65% were classified as shell (2% private). Phylogenetic analysis clarified the evolutionary relationships among the genome lineages, notably resolving the taxonomic placement of the F genome while highlighting the uniqueness of the A genome in the Western Hemisphere. These genomic resources are particularly important for understanding the secondary and tertiary gene pools available for the improvement of the domesticated chenopods while furthering our understanding of the evolution and complexity within the genus.

CASTER: Direct species tree inference from whole-genome alignments

Genomes contain mosaics of discordant evolutionary histories, challenging the accurate inference of the tree of life. Although genome-wide data are routinely used for discordance-aware phylogenomic analyses, because of modeling and scalability limitations, the current practice leaves out large chunks of genomes. As more high-quality genomes become available, we urgently need discordance-aware methods to infer the tree directly from a multiple genome alignment. In this study, we introduce Coalescence-Aware Alignment-Based Species Tree Estimator (CASTER), a theoretically justified site-based method that eliminates the need to predefine recombination-free loci. CASTER is scalable to hundreds of mammalian whole genomes. We demonstrate the accuracy and scalability of CASTER in simulations that include recombination and apply CASTER to several biological datasets, showing that its per-site scores can reveal both biological and artifactual patterns of discordance across the genome.

Phylogeny and species delimitation of ciliates in the genus Spirostomum (class Heterotrichea) using single-cell transcriptomes

BACKGROUND

Ciliates are single-celled microbial eukaryotes that diverged from other eukaryotic lineages more than a billion years ago. The long evolutionary timespan of ciliates has led to enormous genetic and phenotypic changes, contributing significantly to their high level of diversity. Recent analyses based on molecular data have revealed numerous cases of cryptic species complexes in different ciliate lineages, demonstrating the need for a robust approach to delimit species boundaries and elucidate phylogenetic relationships. Species of the genus Spirostomum are difficult to identify due to the lack of distinctive morphological characters. Previous molecular studies have focused on only a few loci, namely the nuclear ribosomal RNA genes, alpha-tubulin, and mitochondrial CO1, suggesting the presence of several cryptic Spirostomum species. In this study, we increased taxon sampling and obtained single-cell transcriptomes of 25 Spirostomum specimens (representing six morphospecies) sampled from South Korea and the USA. We evaluated the utility of the transcriptomic data by constructing species trees using concatenation and coalescent-based methods. In addition, we used neighbor-net network analysis to visualize and quantify potential phylogenetic conflicts within the concatenated dataset. Furthermore, coalescent-based species delimitation was performed with transcriptomic data to define the species boundaries within the genus Spirostomum.

RESULTS

Phylogenomic analysis of 37 Spirostomum specimens (25 newly generated transcriptomes and 12 from GenBank) and 265 protein-coding genes provides robust insight into the evolutionary relationships among Spirostomum species. Our results confirm that species with moniliform and compact macronucleus each form a distinct monophyletic lineage, with the compact macronucleus likely representing the ancestral state, while the moniliform macronucleus being a derived trait. Furthermore, our analyses suggest that ancestral polymorphism and rapid radiation may have shaped the genetic diversity and evolutionary history of Spirostomum, and the S. minus-like appearance represents the ancestral state of the species with a moniliform macronucleus. Therefore, the S. minus-like species share ancestral morphological traits and cannot be morphologically delimited. The multispecies coalescent (MSC) model suggests that two cryptic species from each of S. minus, S. ambiguum, S. subtilis, S. teres, and S. aff. minus represent distinct lineages within the genus Spirostomum. We also provide a workflow for reconstructing nuclear ribosomal RNA gene sequences from transcriptome sequences using a read mapping approach, and compare different mapping methods to reconstruct reliable contigs.

CONCLUSION

Our sampling of closely related Spirostomum populations and comprehensive single-cell RNA sequencing (scRNA-seq) data allowed us to reveal the hidden crypticity of species within the genus Spirostomum and to resolve and provide much stronger support than hitherto to the phylogeny of this model ciliate genus.

Species tree branch length estimation despite incomplete lineage sorting, duplication, and loss

Phylogenetic branch lengths are essential for many analyses, such as estimating divergence times, analyzing rate changes, and studying adaptation. However, true gene tree heterogeneity due to incomplete lineage sorting (ILS), gene duplication and loss (GDL), and horizontal gene transfer (HGT) can complicate the estimation of species tree branch lengths. While several tools exist for estimating the topology of a species tree addressing various causes of gene tree discordance, much less attention has been paid to branch length estimation on multi-locus datasets. For single-copy gene trees, some methods are available that summarize gene tree branch lengths onto a species tree, including coalescent-based methods that account for heterogeneity due to ILS. However, no such branch length estimation method exists for multi-copy gene family trees that have evolved with gene duplication and loss. To address this gap, we introduce the CASTLES-Pro algorithm for estimating species tree branch lengths while accounting for both GDL and ILS. CASTLES-Pro improves on the existing coalescent-based branch length estimation method CASTLES by increasing its accuracy for single-copy gene trees and extends it to handle multi-copy ones. Our simulation studies show that CASTLES-Pro is generally more accurate than alternatives, eliminating the systematic bias toward overestimating terminal branch lengths often observed when using concatenation. Moreover, while not theoretically designed for HGT, we show that CASTLES-Pro maintains relatively high accuracy under high rates of random HGT.

Code availability

CASTLES-Pro is implemented inside the software package ASTER, available at https://github.com/chaoszhang/ASTER .

Data availability

The datasets and scripts used in this study are available at https://github.com/ytabatabaee/CASTLES-Pro-paper .

CamITree: a streamlined software for phylogenetic analysis of viral and mitochondrial genomes

BACKGROUND

Over the past decade, the continuous and rapid advances in bioinformatics have led to an increasingly common use of molecular sequence comparison for phylogenetic analysis. However, the use of multi-software and cross-platform strategies has increased the complexity of phylogenetic tree estimation. Therefore, the development and application of streamlined phylogenetic analysis tools are growing in significance in the field of biology. Particularly for genomes with relatively short sequences, there is a lack of simple and integrative tools for phylogenetic analysis.

RESULTS

In this study, we present CamlTree (Concatenated alignments maximum-likelihood tree), a user-friendly desktop software designed to simplify phylogenetic analysis for viral and mitochondrial genomes, ultimately facilitating related research. CamlTree provides a workflow including gene concatenation (or coalescence), sequence alignment, alignment optimization, and the estimation of phylogenetic trees using both maximum-likelihood (ML) and Bayesian inference (BI) methods. CamlTree was written in TypeScript and developed using the Electron framework. It offers a primarily user-friendly interface based on the React framework.

CONCLUSIONS

CamlTree software has been released for the Windows OS. It integrates several popular analysis tools to optimize and simplify the process of estimating polygenic phylogenetic trees. The establishment of software can assist researchers in reducing their workload and enhancing data processing efficiency, enabling them to expedite their research progress. The software, along with a detailed user manual, is available at https://github.com/BioCrossCoder/camltree .

Phylotranscriptomic Analyses Resolve Evolutionary History of Eremopyrum (Triticeae; Poaceae)

Disentangling the phylogenetic relationship of polyploid species is essential for understanding how such polyploid species evolved following their origin. To investigate the speciation and evolutionary history of Eremopyrum, we analyzed 36 transcriptomes from 9 polyploid accessions of Eremopyrum and 27 diploid taxa representing 12 basic genomes in Triticeae. Phylogenetic reconstruction, divergence time, and introgression event demonstrated that (1) Eremopyrum and Agropyron shared a common ancestor; (2) Eremopyrum has undergone ongoing evolutionary diversification since its origin in Late Miocene; (3) the diploid E. triticeum and E. distans were the genome donors of the tetraploid species of Eremopyrum; (4) both Eremopyrum and Agropyron contribute to the nonmonophyletic origin of tetraploid E. orientale via introgression events. Our results shed new light on our understanding of the diversity and ecological adaptation of the species in Eremopyrum.

Bat genomes illuminate adaptations to viral tolerance and disease resistance

Zoonoses are infectious diseases transmitted from animals to humans. Bats have been suggested to harbour more zoonotic viruses than any other mammalian order1. Infections in bats are largely asymptomatic2,3, indicating limited tissue-damaging inflammation and immunopathology. To investigate the genomic basis of disease resistance, the Bat1K project generated reference-quality genomes of ten bat species, including potential viral reservoirs. Here we describe a systematic analysis covering 115 mammalian genomes that revealed that signatures of selection in immune genes are more prevalent in bats than in other mammalian orders. We found an excess of immune gene adaptations in the ancestral chiropteran branch and in many descending bat lineages, highlighting viral entry and detection factors, and regulators of antiviral and inflammatory responses. ISG15, which is an antiviral gene contributing to hyperinflammation during COVID-19 (refs. 4,5), exhibits key residue changes in rhinolophid and hipposiderid bats. Cellular infection experiments show species-specific antiviral differences and an essential role of protein conjugation in antiviral function of bat ISG15, separate from its role in secretion and inflammation in humans. Furthermore, in contrast to humans, ISG15 in most rhinolophid and hipposiderid bats has strong anti-SARS-CoV-2 activity. Our work reveals molecular mechanisms that contribute to viral tolerance and disease resistance in bats.

Functional evolution and diversification of CYP82D subfamily members have shaped flavonoid diversification in the genus Scutellaria

Flavonoids, the largest class of polyphenols, exhibit substantial structural and functional diversity, yet their evolutionary diversification and specialized functions remain largely unexplored. The genus Scutellaria is notable for its rich flavonoid diversity, particularly of 6/8-hydroxylated variants biosynthesized by the cytochrome P450 subfamily CYP82D. Our study analyzes metabolic differences between Scutellaria baicalensis and Scutellaria barbata, and the results suggest that CYP82Ds have acquired a broad range of catalytic functions over their evolution. By integrating analyses of metabolic networks and gene evolution across 22 Scutellaria species, we rapidly identified 261 flavonoids and delineated five clades of CYP82Ds associated with various catalytic functions. This approach revealed a unique catalytic mode for 6/8-hydroxylation of flavanone substrates and the first instance of 7-O-demethylation of flavonoid substrates catalyzed by a cytochrome P450. Ancestral sequence reconstruction and functional validation demonstrated that gradual neofunctionalization of CYP82Ds has driven the chemical diversity of flavonoids in the genus Scutellaria throughout its evolutionary history. These findings enhance our understanding of flavonoid diversity, reveal the intricate roles of CYP82Ds in Scutellaria species, and highlight the extensive catalytic versatility of cytochrome P450 members within plant taxa.

Double trouble: two retrotransposons triggered a cascade of invasions in Drosophila species within the last 50 years

Horizontal transfer of genetic material in eukaryotes has rarely been documented over short evolutionary timescales. Here, we show that two retrotransposons, Shellder and Spoink, invaded the genomes of multiple species of the melanogaster subgroup within the last 50 years. Through horizontal transfer, Spoink spread in D. melanogaster during the 1980s, while both Shellder and Spoink invaded D. simulans in the 1990s. Possibly following hybridization, D. simulans infected the island endemic species D. mauritiana (Mauritius) and D. sechellia (Seychelles) with both TEs after 1995. In the same approximate time-frame, Shellder also invaded D. teissieri, a species confined to sub-Saharan Africa. We find that the donors of Shellder and Spoink are likely American Drosophila species from the willistoni, cardini, and repleta groups. Thus, the described cascade of TE invasions could only become feasible after D. melanogaster and D. simulans extended their distributions into the Americas 200 years ago, likely aided by human activity. Our work reveals that cascades of TE invasions, likely initiated by human-mediated range expansions, could have an impact on the genomic and phenotypic evolution of geographically dispersed species. Within a few decades, TEs could invade many species, including island endemics, with distributions very distant from the donor of the TE.

Telomere-to-telomere genome assembly of Electrophorus electricus provides insights into the evolution of electric eels

BACKGROUND

Electric eels evolved remarkable electric organs that enable them to instantaneously discharge hundreds of volts for predation, defense, and communication. However, the absence of a high-quality reference genome has extremely constrained the studies of electric eels in various aspects.

RESULTS

Using high-depth, multiplatform sequencing data, we successfully assembled the first telomere-to-telomere high-quality reference genome of Electrophorus electricus, which has a genome size of 833.43 Mb and comprises 26 chromosomes. Multiple evaluations, including N50 statistics (30.38 Mb), BUSCO scores (97.30%), and mapping ratio of short-insert sequencing data (99.91%), demonstrate the high contiguity and completeness of the electric eel genome assembly we obtained. Genome annotation predicted 396.63 Mb repetitive sequences and 20,992 protein-coding genes. Furthermore, evolutionary analyses indicate that Gymnotiformes, which the electric eel belongs to, has a closer relationship with Characiformes than Siluriformes and diverged from Characiformes 95.00 million years ago. Pairwise sequentially Markovian coalescent analysis found a sharply decreased trend of the population size of E. electricus over the past few hundred thousand years. Furthermore, many regulatory factors related to neurotransmitters and classical signaling pathways during embryonic development were significantly expanded, potentially contributing to the generation of high-voltage electricity.

CONCLUSIONS

This study not only provided the first high-quality telomere-to-telomere reference genome of E. electricus but also greatly enhanced our understanding of electric eels.

Whole genome data confirm pervasive gene discordance in the evolutionary history of Coenonympha (Nymphalidae) butterflies

Phylogenetic inference is challenged by genealogical heterogeneity amongst molecular markers. Such discordance is driven predominantly by incomplete lineage sorting (ILS) and interspecific gene flow, and bears attendant consequences for the accurate resolution of species relationships. Understanding the distribution of gene conflict in organismal genomes is, therefore, a key aspect of phylogenetic analysis. In this study, three large phylogenomic datasets (i.e., whole mitogenomes, conserved nuclear protein-coding loci, and genomic windows) are used to probe the extent to which discordance pervades the unresolved phylogeny of Coenonympha (Nymphalidae) butterflies. Gene tree discordance is found to be elevated at multiple historically recalcitrant phylogenetic positions. In particular, species relationships near the crown of Coenonympha and within a rapidly diversifying subclade (the hero group) remain difficult to resolve, suggesting that ILS and gene flow have obscured the evolution of this genus. These findings have implications for the taxonomy of this butterfly group and the study of its diversification history. In addition, this work lends support to a growing body of evidence that gene conflict driven by biological processes stands to confound phylogeny, even when extensive data are used.

"Isolation by Gentes with Asymmetric Migration" shapes the genetic structure of the common cuckoo in China

Amid coevolutionary arms races between brood parasitic birds and their diverse host species, the formation of host-specific races, or gentes, has drawn significant research focus. Nevertheless, numerous questions about gentes evolutionary patterns persist. Here, we investigated the potential for gentes evolution across multiple common cuckoo (Cuculus canorus) populations parasitizing diverse host species in China. Using maternal (mitochondrial and W-linked DNA) and biparental (autosomal and Z-linked DNA) markers, we found consistent clustering of cuckoo gentes (rather than geographical populations) into distinct clades in matrilineal gene trees, indicating robust differentiation. In contrast, biparental markers indicated intermixing of all gentes, suggesting asymmetric gene flow regardless of geography. Unlike the mitonuclear discordance commonly resulting from incomplete lineage sorting, adaptive introgression, or demographic disparities, the observed pattern in brood parasitic cuckoos might reflect biased host preferences between sexes. We hereby present the "Isolation by Gentes with Asymmetric Migration" model. According to this model, the maternal line differentiation of the common cuckoo in China is potentially driven by host preferences in females, whereas males maintained the integrity of the cuckoo species through random mating. To achieve this, cuckoo males could perform flexible migration among gentes or engage in early copulation with females before reaching the breeding sites, allowing female cuckoos to store sperm from various gentes. Future studies collecting additional samples from diverse cuckoo gentes with overlapping distribution and investigating the migratory and copulation patterns of each sex would enhance our understanding of sex-biased differentiation among cuckoo populations in China.

A comprehensive molecular phylogeny of the genus Sylvirana (Anura: Ranidae) highlights unrecognized diversity, revised classification and historical biogeography

The genus Sylvirana includes 12 species widely distributed in South China and Southeast Asia. The phylogenetic relationships and species diversity for Sylvirana and allied genera remain unresolved and controversial due to insufficient data and incomplete taxon sampling. Using a combined dataset of mitochondrial genes (16S and COI) and 101 nuclear genes obtained through the amplicon sequence capture approach, we generated the most comprehensive phylogenetic analysis for the genus Sylvirana to date, inferring diversity, phylogenetic relationships, and historical biogeography with unprecedented levels of taxon and geographic sampling. Our results conservatively reveal six undescribed species, mostly distributed in peninsular Indochina. Phylogenetic analyses strongly support the non-monophyly of Sylvirana with respect to Pterorana. Additionally, phylogenetic results place Sylvirana guentheri and Pelophylax lateralis into genus Humerana, supporting the inclusion of Hylarana latouchii, Papurana milleti, and Hylarana attigua within Pterorana + Sylvirana. The long-disputed species of Hylarana bannanica (previously Sylvirana) cluster with genus Papurana. Because the results of multiple non-monophyletic genera create taxonomic confusion, we suggest relegating all genera to subgenus rank of Hylarana. Sylvirana is a junior synonym of the Pterorana. Biogeographically, we trace the origin of Pterorana to Southeast Asia during the early Miocene, with subsequent dispersal thereafter. Our study shows that climatic changes may have profoundly influenced the diversification of Pterorana during the Miocene.

Phylogenomic analyses shed new light on the spatiotemporal evolution of global larches: Implications for the dynamics of boreal forests

As the Earth warms, understanding the long-term dynamics of forest ecosystems is essential for guiding forest management and biodiversity conservation. Insights from past dynamics may provide valuable lessons for managing today's forests. Here, we investigated the spatiotemporal evolution of global larches to gain further insights into how boreal forests change over time. We first reconstructed a highly resolved and robust phylogeny of Larix covering all widely recognized species, using both transcriptome-based 1,301 orthologous genes (OGs) and plastid genomes. In sharp contrast to previous studies, an unexpected deep split between the circumboreal and Qinghai-Tibetan Plateau (QTP) larches was revealed in our study. Within each lineage, two geographically distinct clades were further resolved. Biogeographical analyses suggest that Larix might have an origin of Eocene in high-latitude uplands, and during the Miocene, all extant species have appeared. Cenozoic climate- and orogeny-triggered vicariance likely played a major role in the divergence of global larches. Our results also demonstrate that the proto-boreal forest biome may have a relatively old origin back to the early Miocene, and significant winnowing and species alteration would have occurred as the climate shifted to much colder and drier conditions during the Neogene. Ecological niche analyses show various responses of the circumboreal and QTP larches under different climate scenarios, but both lineages are negatively impacted by warming climates. These findings have important conservation implications given the sensitivity of boreal forests in the face of global warming. Our work further emphasizes the importance of a solid phylogenetic framework for evolutionary and biogeographical inferences.

Phylogenomics reveal species limits and inter-relationships in the narrow-range endemic lycian salamanders

Salamanders of the genus Lyciasalamandra are represented by as many as 20 narrow-range endemic taxa inhabiting the Mediterranean coast of Turkey and a handful of Aegean Islands. Despite recent molecular phylogenetic studies, the genus is rife with uncertainty about the number of contained species and their phylogenetic relationships, both of which can interfere with needed conservation actions. To test species limits and infer interrelationships we generated as many as 113,176 RAD loci containing 229,427 single nucleotide polymorphisms (SNPs), for 110 specimens of Lyciasalamandra representing 19 of the 20 described taxa. Through a conservative species delimitation approach, we found support for eight species in the genus which broadly agree with currently described species-level diversity. We then use multiple coalescent-based species tree methods to resolve relationships in this relatively old, synchronous species radiation. We recommend synonymization of the largely over-split subspecific taxa, and the elevation of L. luschani finikensis to full species status as L. finikensis. Our hope is that this revised taxonomic framework provides a stable foundation for conservation management in these fragile, microendemic taxa.

The planktonic freshwater ciliate Balanion planctonicum (Ciliophora, Prostomatea): A cryptic species complex or a "complex species"?

The globally distributed ciliate Balanion planctonicum is a primary consumer of phytoplankton spring blooms. Due to its small size (~20 μm), identification and quantification by molecular tools is preferable as an alternative to the laborious counting of specimen in quantitative protargol stains. However, previous sequencing of the 18S rDNA V9 region of B. planctonicum from Lake Zurich (Switzerland) and subsequent quantification by fluorescence in situ hybridization yielded significantly lower cell numbers than using morphotype counting. This raised the question of whether B. planctonicum shows a cryptic diversity or whether it is just a 'complex species' with intra-clonal polymorphisms. Over three years, we established numerous monoclonal cultures, and long-read sequencing of rDNA operons revealed four distinct dominant haplotypes (BpHs 1-4). The gene sequences of BpHs 1 and 3 differed by 6% and did not share intra-clonal polymorphisms, providing evidence for two distinct clades. Furthermore, phylogenetic analyses corroborate the sister relationship between Balanion and Askenasia (plus Hexasterias and Radiosperma). Morphologically, the two Balanion clades are nearly indistinguishable with small differences in macronucleus size and in the cell length to width ratio. CARD-FISH analyses indicated that the diversity of B. planctonicum is even more extensive with still unidentified clades.

Leaf transcriptomes from C3, C3-C4 intermediate, and C4Neurachne species give insights into C4 photosynthesis evolution

The C4 photosynthetic pathway is hypothesized to have evolved from the ancestral C3 pathway through progressive changes in leaf anatomy and biochemistry with extant C3-C4 photosynthetic intermediate species representing phenotypes between species demonstrating full C3 and full C4 states. The Australian endemic genus Neurachne is the only known grass group that contains distinct, closely related species that carry out C3, C3-C4 intermediate, or C4 photosynthesis. To explore and understand the molecular mechanisms underlying C4 photosynthesis evolution in this genus, leaf transcriptomes were generated from two C3, three photosynthetic intermediate (proto-Kranz, C2-like, and C2), and two C4Neurachne species. The data were used to reconstruct phylogenetic relationships in Neurachne, which confirmed two independent C4 origins in the genus. Relative transcript abundances substantiated the photosynthetic phenotypes of individual species and highlighted transcriptional investment differences between species, including between the two C4 species. The data also revealed proteins potentially involved in C4 cycle intermediate transport and identified molecular mechanisms responsible for the evolution of C4-associated proteins in the genus.

Ancient Hybridisation Fuelled Diversification in Acropora Corals

Introgression is the infiltration or flow of genes from one species to another through hybridisation followed by backcrossing. This may lead to incorrect phylogenetic reconstruction or divergence-time estimation. Acropora is a dominant genus of reef-building corals; however, whether this group has an introgression history before their diversification remains unclear, and previous divergence-time estimates of Acropora have not considered the impact of introgression. In this study, we broke through the limitation of a few genes and a few species and proved the existence of ancient introgression in the evolution of Acropora from whole-genome protein-coding sequences. We inferred 21.9% of all triplet loci (homologous loci from three different species) with a history of introgression and a series of introgression events with a genetic material contribution of up to 30.9% before diversification. Furthermore, 7756 nuclear loci were clustered into three groups using a multidimensional scaling algorithm, the heterogeneity of which resulted in different phylogenetic relationships. The diversification time of Acropora was estimated to be middle to late Miocene when we retained only the gene group with the lowest degree of introgression. The collision of Australia with the Pacific arcs and the Southeast Asian margin in the early Miocene, and a series of cooling events in the middle to late Miocene, may provide geographical and climatic conditions for the diversification of Acropora, respectively. Therefore, our results indicate that at the genome-wide level, ancient introgressive hybridisation may have promoted the radiation evolution of Acropora. Based on our results, the influence of introgression should be taken into account when reconstructing phylogenetic relationships and evaluating divergence time.

A multiomics investigation into the evolution and specialized metabolisms of three Toxicodendron cultivars

Toxicodendron species are economically and medicinally important trees because of their rich sources of natural products. We present three chromosome-level genome assemblies of Toxicodendron vernicifluum 'Dali', Toxicodendron succedaneum 'Vietnam', and T. succedaneum 'Japan', which display diverse production capacities of specialized metabolites. Genome synteny and structural variation analyses revealed large genomic differences between the two species (T. vernicifluum and T. succedaneum) but fewer differences between the two cultivars within the species. Despite no occurrence of recent whole-genome duplications, Toxicodendron showed evidence of local duplications. The genomic modules with high expression of genes encoding metabolic flux regulators and chalcone synthase-like enzymes were identified via multiomics analyses, which may be responsible for the greater urushiol accumulation in T. vernicifluum 'Dali' than in other Toxicodendron species. In addition, our analyses revealed the regulatory patterns of lipid metabolism in T. succedaneum 'Japan', which differ from those of other Toxicodendron species and may contribute to its high lipid accumulation. Furthermore, we identified the key regulatory elements of lipid metabolism at each developmental stage, which could aid in molecular breeding to improve the production of urushiol and lipids in Toxicodendron species. In summary, this study provides new insights into the genomic underpinnings of the evolution and diversity of specialized metabolic pathways in three Toxicodendron cultivars through multiomics studies.

Repeated shifts out of tropical climates preceded by whole genome duplication

While flowering plants have diversified in virtually every terrestrial clime, climate constrains the distribution of individual lineages. Overcoming climatic constraints may be associated with diverse evolutionary phenomena including whole genome duplication (WGD), gene-tree conflict, and life-history changes. Climatic shifts may also have facilitated increases in flowering plant diversification rates. We investigate climatic shifts in the flowering plant order Ericales, which consists of c. 14 000 species with diverse climatic tolerances. We estimate phylogenetic trees from transcriptomic data, 64 chloroplast loci, and Angiosperms353 nuclear loci that, respectively, incorporate 147, 4508, and 2870 Ericales species. We use these phylogenetic trees to analyse how climatic shifts are associated with WGD, gene-tree conflict, life-history, and diversification rates. Early branches in the phylogenetic trees are extremely short, and have high levels of gene-tree conflict and at least one WGD. On lineages descended from these early branches, there is a significant association between climatic shifts (primarily out of tropical climates), further WGDs, and life-history. Extremely short early branches, and their associated gene-tree conflict and WGDs, appear to underpin the explosive origin of numerous species rich Ericales clades. The evolution of diverse climatic tolerances in these species rich clades is tightly associated with WGD and life-history.

wQFM-DISCO: DISCO-enabled wQFM improves phylogenomic analyses despite the presence of paralogs

Motivation

Gene trees often differ from the species trees that contain them due to various factors, including incomplete lineage sorting (ILS) and gene duplication and loss (GDL). Several highly accurate species tree estimation methods have been introduced to explicitly address ILS, including ASTRAL, a widely used statistically consistent method, and wQFM, a quartet amalgamation approach experimentally shown to be more accurate than ASTRAL. Two recent advancements, ASTRAL-Pro and DISCO, have emerged in phylogenomics to consider GDL. ASTRAL-Pro introduces a refined quartet similarity measure, accounting for orthology and paralogy. On the other hand, DISCO offers a general strategy to decompose multi-copy gene trees into a collection of single-copy trees, allowing the utilization of methods previously designed for species tree inference in the context of single-copy gene trees.

Results

In this study, we first introduce some variants of DISCO to examine its underlying hypotheses and present analytical results on the statistical guarantees of DISCO. In particular, we introduce DISCO-R, a variant of DISCO with a refined and improved pruning strategy that provides more accurate and robust results. We then demonstrate with extensive evaluation studies on a collection of simulated and real data sets that wQFM paired with DISCO variants consistently matches or outperforms ASTRAL-Pro and other competing methods.

Availability and implementation

DISCO-R and other variants are freely available at https://github.com/skhakim/DISCO-variants.

Terraces in species tree inference from gene trees

A terrace in a phylogenetic tree space is a region where all trees contain the same set of subtrees, due to certain patterns of missing data among the taxa sampled, resulting in an identical optimality score for a given data set. This was first investigated in the context of phylogenetic tree estimation from sequence alignments using maximum likelihood (ML) and maximum parsimony (MP). It was later extended to the species tree inference problem from a collection of gene trees, where a set of equally optimal species trees was referred to as a "pseudo" species tree terrace which does not consider the topological proximity of the trees in terms of the induced subtrees resulting from certain patterns of missing data. In this study, we mathematically characterize species tree terraces and investigate the mathematical properties and conditions that lead multiple species trees to induce/display an identical set of locus-specific subtrees owing to missing data. We report that species tree terraces are agnostic to gene tree heterogeneity. Therefore, we introduce and characterize a special type of gene tree topology-aware terrace which we call "peak terrace". Moreover, we empirically investigated various challenges and opportunities related to species tree terraces through extensive empirical studies using simulated and real biological data. We demonstrate the prevalence of species tree terraces and the resulting ambiguity created for tree search algorithms. Remarkably, our findings indicate that the identification of terraces could potentially lead to advances that enhance the accuracy of summary methods and provide reasonably accurate branch support.

Phylogenomics, reticulation, and biogeographical history of Elaeagnaceae

The angiosperm family Elaeagnaceae comprises three genera and ca. 100 species distributed mainly in Eurasia and North America. Little family-wide phylogenetic and biogeographic research on Elaeagnaceae has been conducted, limiting the application and preservation of natural genetic resources. Here, we reconstructed a strongly supported phylogenetic framework of Elaeagnaceae to better understand inter- and intrageneric relationships, as well as the origin and biogeographical history of the family. For this purpose, we used both nuclear and plastid sequences from Hyb-Seq and genome skimming approaches to reconstruct a well-supported phylogeny and, along with current distributional data, infer historical biogeographical processes. Our phylogenetic analyses of both nuclear and plastid data strongly support the monophyly of Elaeagnaceae and each of the three genera. Elaeagnus was resolved as sister to the well-supported clade of Hippophae and Shepherdia. The intrageneric relationships of Elaeagnus and Hippophae were also well resolved. High levels of nuclear gene tree conflict and cytonuclear discordance were detected within Elaeagnus, and our analyses suggest putative ancient and recent hybridization. We inferred that Elaeagnaceae originated at ca. 90.48 Ma (95% CI = 89.91-91.05 Ma), and long-distance dispersal likely played a major role in shaping its intercontinentally disjunct distribution. This work presents the most comprehensive phylogenetic framework for Elaeagnaceae to date, offers new insights into previously unresolved relationships in Elaeagnus, and provides a foundation for further studies on classification, evolution, biogeography, and conservation of Elaeagnaceae.

The Meaning and Measure of Concordance Factors in Phylogenomics

As phylogenomic datasets have grown in size, researchers have developed new ways to measure biological variation and to assess statistical support for specific branches. Larger datasets have more sites and loci and therefore less sampling variance. While we can more accurately measure the mean signal in these datasets, lower sampling variance is often reflected in uniformly high measures of branch support-such as the bootstrap and posterior probability-limiting their utility. Larger datasets have also revealed substantial biological variation in the topologies found across individual loci, such that the single species tree inferred by most phylogenetic methods represents a limited summary of the data for many purposes. In contrast to measures of statistical support, the degree of underlying topological variation among loci should be approximately constant regardless of the size of the dataset. "Concordance factors" (CFs) and similar statistics have therefore become increasingly important tools in phylogenetics. In this review, we explain why CFs should be thought of as descriptors of topological variation rather than as measures of statistical support, and argue that they provide important information about the predictive power of the species tree not contained in measures of support. We review a growing suite of statistics for measuring concordance, compare them in a common framework that reveals their interrelationships, and demonstrate how to calculate them using an example from birds. We also discuss how measures of topological variation might change in the future as we move beyond estimating a single "tree of life" toward estimating the myriad evolutionary histories underlying genomic variation.

Gentrius: Generating Trees Compatible With a Set of Unrooted Subtrees and its Application to Phylogenetic Terraces

For a set of binary unrooted subtrees generating all binary unrooted trees compatible with them, i.e. generating their stand, is one of the classical problems in phylogenetics. Here, we introduce Gentrius-an efficient algorithm to tackle this task. The algorithm has a direct application in practice. Namely, Gentrius generates phylogenetic terraces-topologically distinct, equally scoring trees due to missing data. Despite stand generation being computationally intractable, we showed on simulated and biological datasets that Gentrius generates stands with millions of trees in feasible time. We exemplify that depending on the distribution of missing data across species and loci and the inferred phylogeny, the number of equally optimal terrace trees varies tremendously. The strict consensus tree computed from them displays all the branches unaffected by the pattern of missing data. Thus, by solving the problem of stand generation, in practice Gentrius provides an important systematic assessment of phylogenetic trees inferred from incomplete data. Furthermore, Gentrius can aid theoretical research by fostering understanding of tree space structure imposed by missing data.

Data-driven guidelines for phylogenomic analyses using SNP data

Premise

There is a general lack of consensus on the best practices for filtering of single-nucleotide polymorphisms (SNPs) and whether it is better to use SNPs or include flanking regions (full "locus") in phylogenomic analyses and subsequent comparative methods.

Methods

Using genotyping-by-sequencing data from 22 Glycine species, we assessed the effects of SNP vs. locus usage and SNP retention stringency. We compared branch length, node support, and divergence time estimation across 16 datasets with varying amounts of missing data and total size.

Results

Our results revealed five aspects of phylogenomic data usage that may be generally applicable: (1) tree topology is largely congruent across analyses; (2) filtering strictly for SNP retention (e.g., 90-100%) reduces support and can alter some inferred relationships; (3) absolute branch lengths vary by two orders of magnitude between SNP and locus datasets; (4) data type and branch length variation have little effect on divergence time estimation; and (5) phylograms alter the estimation of ancestral states and rates of morphological evolution.

Discussion

Using SNP or locus datasets does not alter phylogenetic inference significantly, unless researchers want or need to use absolute branch lengths. We recommend against using excessive filtering thresholds for SNP retention to reduce the risk of producing inconsistent topologies and generating low support.

The Influence of the Number of Tree Searches on Maximum Likelihood Inference in Phylogenomics

Maximum likelihood (ML) phylogenetic inference is widely used in phylogenomics. As heuristic searches most likely find suboptimal trees, it is recommended to conduct multiple (e.g., 10) tree searches in phylogenetic analyses. However, beyond its positive role, how and to what extent multiple tree searches aid ML phylogenetic inference remains poorly explored. Here, we found that a random starting tree was not as effective as the BioNJ and parsimony starting trees in inferring the ML gene tree and that RAxML-NG and PhyML were less sensitive to different starting trees than IQ-TREE. We then examined the effect of the number of tree searches on ML tree inference with IQ-TREE and RAxML-NG, by running 100 tree searches on 19,414 gene alignments from 15 animal, plant, and fungal phylogenomic datasets. We found that the number of tree searches substantially impacted the recovery of the best-of-100 ML gene tree topology among 100 searches for a given ML program. In addition, all of the concatenation-based trees were topologically identical if the number of tree searches was ≥10. Quartet-based ASTRAL trees inferred from 1 to 80 tree searches differed topologically from those inferred from 100 tree searches for 6/15 phylogenomic datasets. Finally, our simulations showed that gene alignments with lower difficulty scores had a higher chance of finding the best-of-100 gene tree topology and were more likely to yield the correct trees.

OHDLF: A Method for Selecting Orthologous Genes for Phylogenetic Construction and Its Application in the Genus Camellia

Accurate phylogenetic tree construction for species without reference genomes often relies on de novo transcriptome assembly to identify single-copy orthologous genes. However, challenges such as whole-genome duplication (WGD), heterozygosity, gene duplication, and loss can hinder the selection of these genes, leading to limited data for constructing reliable species trees. To address these issues, we developed a new analytical pipeline, OHDLF (Orthologous Haploid Duplication and Loss Filter), which filters orthologous genes from transcript data and adapts parameter settings based on genomic characteristics for further phylogenetic tree construction. In this study, we applied OHDLF to the genus Camellia and evaluated its effectiveness in constructing phylogenetic trees. The results highlighted the pipeline's ability to handle challenges like high heterozygosity and recent gene duplications by selectively retaining genes with a missing rate and merging duplicates with high similarity. This approach ensured the preservation of informative sites and produced a highly supported consensus tree for Camellia. Additionally, we evaluate the accuracy of the OHDLF phylogenetic trees for different species, demonstrating that the OHDLF pipeline provides a flexible and effective method for selecting orthologous genes and constructing accurate phylogenetic trees, adapting to the genomic characteristics of various plant groups.

Phylogenomics, Lineage Diversification Rates, and the Evolution of Diadromy in Clupeiformes (Anchovies, Herrings, Sardines, and Relatives)

Migration independently evolved numerous times in animals, with a myriad of ecological and evolutionary implications. In fishes, perhaps the most extreme form of migration is diadromy, the migration between marine and freshwater environments. Key and long-standing questions are: how many times has diadromy evolved in fishes, how frequently do diadromous clades give rise to non-diadromous species, and does diadromy influence lineage diversification rates? Many diadromous fishes have large geographic ranges with constituent populations that use isolated freshwater habitats. This may limit gene flow between some populations, increasing the likelihood of speciation in diadromous lineages relative to nondiadromous lineages. Alternatively, diadromy may reduce lineage diversification rates if migration is associated with enhanced dispersal capacity that facilitates gene flow within and between populations. Clupeiformes (herrings, sardines, shads, and anchovies) is a model clade for testing hypotheses about the evolution of diadromy because it includes an exceptionally high proportion of diadromous species and several independent evolutionary origins of diadromy. However, relationships among major clupeiform lineages remain unresolved, and existing phylogenies sparsely sampled diadromous species, limiting the resolution of phylogenetically informed statistical analyses. We assembled a phylogenomic dataset and used multi-species coalescent and concatenation-based approaches to generate the most comprehensive, highly resolved clupeiform phylogeny to date, clarifying associations among several major clades and identifying recalcitrant relationships needing further examination. We determined that variation in rates of sequence evolution (heterotachy) and base-composition (nonstationarity) had little impact on our results. Using this phylogeny, we characterized evolutionary patterns of diadromy and tested for differences in lineage diversification rates between diadromous, marine, and freshwater lineages. We identified 13 transitions to diadromy, all during the Cenozoic Era (10 origins of anadromy, 2 origins of catadromy, and 1 origin of amphidromy), and 7 losses of diadromy. Two diadromous lineages rapidly generated nondiadromous species, demonstrating that diadromy is not an evolutionary dead end. We discovered considerably faster transition rates out of diadromy than to diadromy. The largest lineage diversification rate increase in Clupeiformes was associated with a transition to diadromy, but we uncovered little statistical support for categorically faster lineage diversification rates in diadromous versus nondiadromous fishes. We propose that diadromy may increase the potential for accelerated lineage diversification, particularly in species that migrate long distances. However, this potential may only be realized in certain biogeographic contexts, such as when diadromy allows access to ecosystems in which there is limited competition from incumbent species.

Chromosome-level genome of diamondback terrapin provides insight into the genetic basis of salinity adaptation

Diamondback terrapins (Malaclemys terrapin centrata) exhibit strong environmental adaptability and live in both freshwater and saltwater. However, the genetic basis of this adaptability has not been the focus of research. In this study, we successfully constructed a ∼2.21-Gb chromosome-level genome assembly for M. t. centrata using high-coverage and high-depth genomic sequencing data generated on multiple platforms. The M. t. centrata genome contains 25 chromosomes and the scaffold N50 of ∼143.75 Mb, demonstrating high continuity and accuracy. In total, 53.82% of the genome assembly was composed of repetitive sequences, and 22 435 protein-coding genes were predicted. Our phylogenetic analysis indicated that M. t. centrata was closely related to the red-eared slider turtle (Trachemys scripta elegans), with divergence approximately ∼23.6 million years ago (Mya) during the early Neogene period of the Cenozoic era. The population size of M. t. centrata decreased significantly over the past ∼14 Mya during the Cenozoic era. Comparative genomic analysis indicated that 36 gene families related to ion transport were expanded and several genes (AQP3, solute carrier subfamily, and potassium channel genes) underwent specific amino acid site mutations in the M. t. centrata genome. Changes to these ion transport-related genes may have contributed to the remarkable salinity adaptability of diamondback terrapin. The results of this study not only provide a high-quality reference genome for M. t. centrata but also elucidate the possible genetic basis for salinity adaptation in this species.

Challenges in Assembling the Dated Tree of Life

The assembly of a comprehensive and dated Tree of Life (ToL) remains one of the most formidable challenges in evolutionary biology. The complexity of life's history, involving both vertical and horizontal transmission of genetic information, defies its representation by a simple bifurcating phylogeny. With the advent of genome and metagenome sequencing, vast amounts of data have become available. However, employing this information for phylogeny and divergence time inference has introduced significant theoretical and computational hurdles. This perspective addresses some key methodological challenges in assembling the dated ToL, namely, the identification and classification of homologous genes, accounting for gene tree-species tree mismatch due to population-level processes along with duplication, loss, and horizontal gene transfer, and the accurate dating of evolutionary events. Ultimately, the success of this endeavor requires new approaches that integrate knowledge databases with optimized phylogenetic algorithms capable of managing complex evolutionary models.

Chromosome-level genome provides insights into evolution and diving adaptability in the vulnerable common pochard (Aythya ferina)

The common pochard (Aythya ferina) is a freshwater diving duck found in the Palearctic region that has been classified as vulnerable by the IUCN due to continuous and rapid population declines across their distribution. To gain a better understanding of its genetic mechanism of adaptive evolution, we successfully sequenced and assembled the first high-quality chromosome-level genome of A. ferina using Illumina, Nanopore and Hi-C sequencing technologies. A total assembly length of 1,130.78 Mbp was obtained, with over 98.81% (1,117.37Mbp) of sequence anchored to 35 pseudo-chromosomes. We predicted 17,232 protein-coding genes, 95.9% of which were functionally annotated. We identified 339 expanded and 937 contracted gene families in the genome of A. ferina, and detected 95 genes that have been positively selected. The significantly enriched Gene Ontology and enriched pathways were related to energy metabolism, immune, nervous, and sensory systems, suggests that these factors likely played an important role in its evolution. Importantly, we recovered signatures of positive selection on genes related to vasoconstriction that may be associated with thermoregulatory adaptations of A. ferina for underwater diving. Overall, the high-quality genome assembly and annotation in this study provides valuable genomic resources for ecological and evolutionary studies, as well as toward the conservation of A. ferina.

Phylogenetic insights into the Salicaceae: The evolution of willows and beyond

The Salicaceae includes approximately 54 genera and over 1,400 species with a cosmopolitan distribution. Members of the family are well-known for their diverse secondary plant metabolites, and they play crucial roles in tropical and temperate forest ecosystems. Phylogenetic reconstruction of the Salicaceae has been historically challenging due to the limitations of molecular markers and the extensive history of hybridization and polyploidy within the family. Our study employs whole-genome sequencing of 74 species to generate an extensive phylogeny of the Salicaceae. We generated two RAD-Seq enriched whole-genome sequence datasets and extracted two additional gene sets corresponding to the universal Angiosperms353 and Salicaceae-specific targeted-capture arrays. We reconstructed maximum likelihood-based molecular phylogenies using supermatrix and coalescent-based supertree approaches. Our fossil-calibrated phylogeny estimates that the Salicaceae originated around 128 million years ago and unravels the complex taxonomic relationships within the family. Our findings confirm the non-monophyly of the subgenus Salix s.l. and further support the merging of subgenera Chamaetia and Vetrix, both of which exhibit intricate patterns within and among different sections. Overall, our study not only enhances our understanding of the evolution of the Salicaceae, but also provides valuable insights into the complex relationships within the family.

Phylogenomics supports a single origin of terrestriality in isopods

Terrestriality, the adaptation to life on land, is one of the key evolutionary transitions, occurring numerous times across the tree of life. Within Arthropoda, there have been several independent transitions: in hexapods, myriapods, arachnids and isopods. Isopoda is a morphologically diverse order within Crustacea, with species adapted to almost every environment on Earth. The order is divided into 11 suborders with the most speciose, Oniscidea, including terrestrial isopods such as woodlice and sea-slaters. Recent molecular phylogenetic studies have challenged traditional isopod morphological taxonomy, suggesting that several well-accepted suborders, including Oniscidea, may be non-monophyletic. This implies that terrestriality may have evolved multiple times. Current molecular hypotheses, however, are based on limited sequence data. Here, I collate available genome and transcriptome datasets for 36 isopods and four peracarid crustaceans from public sources, generate assemblies and use 970 single-copy orthologues to estimate isopod relationships and divergence times with molecular dating. The resulting phylogenetic analyses support monophyly of terrestrial isopods and suggest conflicting relationships based on nuclear ribosomal RNA sequences may be caused by long-branch attraction. Dating analyses suggest a Permo-Carboniferous origin of isopod terrestriality, much more recently than other terrestrial arthropods.