Modeling Substitution Rate Evolution across Lineages and Relaxing the Molecular Clock

Relaxing the molecular clock using models of how substitution rates change across lineages has become essential for addressing evolutionary problems. The diversity of rate evolution models and their implementations are substantial, and studies have demonstrated their impact on divergence time estimates can be as significant as that of calibration information. In this review, we trace the development of rate evolution models from the proposal of the molecular clock concept to the development of sophisticated Bayesian and non-Bayesian methods that handle rate variation in phylogenies. We discuss the various approaches to modeling rate evolution, provide a comprehensive list of available software, and examine the challenges and advancements of the prevalent Bayesian framework, contrasting them to faster non-Bayesian methods. Lastly, we offer insights into potential advancements in the field in the era of big data.

A Guide to Phylogenomic Inference

Phylogenomics aims at reconstructing the evolutionary histories of organisms taking into account whole genomes or large fractions of genomes. Phylogenomics has significant applications in fields such as evolutionary biology, systematics, comparative genomics, and conservation genetics, providing valuable insights into the origins and relationships of species and contributing to our understanding of biological diversity and evolution. This chapter surveys phylogenetic concepts and methods aimed at both gene tree and species tree reconstruction while also addressing common pitfalls, providing references to relevant computer programs. A practical phylogenomic analysis example including bacterial genomes is presented at the end of the chapter.

Summary Tests of Introgression Are Highly Sensitive to Rate Variation Across Lineages

The evolutionary implications and frequency of hybridization and introgression are increasingly being recognized across the tree of life. To detect hybridization from multi-locus and genome-wide sequence data, a popular class of methods are based on summary statistics from subsets of 3 or 4 taxa. However, these methods often carry the assumption of a constant substitution rate across lineages and genes, which is commonly violated in many groups. In this work, we quantify the effects of rate variation on the D test (also known as ABBA-BABA test), the D3 test, and HyDe. All 3 tests are used widely across a range of taxonomic groups, in part because they are very fast to compute. We consider rate variation across species lineages, across genes, their lineage-by-gene interaction, and rate variation across gene-tree edges. We simulated species networks according to a birth-death-hybridization process, so as to capture a range of realistic species phylogenies. For all 3 methods tested, we found a marked increase in the false discovery of reticulation (type-1 error rate) when there is rate variation across species lineages. The D3 test was the most sensitive, with around 80% type-1 error, such that D3 appears to more sensitive to a departure from the clock than to the presence of reticulation. For all 3 tests, the power to detect hybridization events decreased as the number of hybridization events increased, indicating that multiple hybridization events can obscure one another if they occur within a small subset of taxa. Our study highlights the need to consider rate variation when using site-based summary statistics, and points to the advantages of methods that do not require assumptions on evolutionary rates across lineages or across genes.

Incongruence in the phylogenomics era

Genome-scale data and the development of novel statistical phylogenetic approaches have greatly aided the reconstruction of a broad sketch of the tree of life and resolved many of its branches. However, incongruence - the inference of conflicting evolutionary histories - remains pervasive in phylogenomic data, hampering our ability to reconstruct and interpret the tree of life. Biological factors, such as incomplete lineage sorting, horizontal gene transfer, hybridization, introgression, recombination and convergent molecular evolution, can lead to gene phylogenies that differ from the species tree. In addition, analytical factors, including stochastic, systematic and treatment errors, can drive incongruence. Here, we review these factors, discuss methodological advances to identify and handle incongruence, and highlight avenues for future research.

QR-STAR: A Polynomial-Time Statistically Consistent Method for Rooting Species Trees Under the Coalescent

We address the problem of rooting an unrooted species tree given a set of unrooted gene trees, under the assumption that gene trees evolve within the model species tree under the multispecies coalescent (MSC) model. Quintet Rooting (QR) is a polynomial time algorithm that was recently proposed for this problem, which is based on the theory developed by Allman, Degnan, and Rhodes that proves the identifiability of rooted 5-taxon trees from unrooted gene trees under the MSC. However, although QR had good accuracy in simulations, its statistical consistency was left as an open problem. We present QR-STAR, a variant of QR with an additional step and a different cost function, and prove that it is statistically consistent under the MSC. Moreover, we derive sample complexity bounds for QR-STAR and show that a particular variant of it based on "short quintets" has polynomial sample complexity. Finally, our simulation study under a variety of model conditions shows that QR-STAR matches or improves on the accuracy of QR. QR-STAR is available in open-source form on github.

Weighted ASTRID: fast and accurate species trees from weighted internode distances

BACKGROUND

Species tree estimation is a basic step in many biological research projects, but is complicated by the fact that gene trees can differ from the species tree due to processes such as incomplete lineage sorting (ILS), gene duplication and loss (GDL), and horizontal gene transfer (HGT), which can cause different regions within the genome to have different evolutionary histories (i.e., "gene tree heterogeneity"). One approach to estimating species trees in the presence of gene tree heterogeneity resulting from ILS operates by computing trees on each genomic region (i.e., computing "gene trees") and then using these gene trees to define a matrix of average internode distances, where the internode distance in a tree T between two species x and y is the number of nodes in T between the leaves corresponding to x and y. Given such a matrix, a tree can then be computed using methods such as neighbor joining. Methods such as ASTRID and NJst (which use this basic approach) are provably statistically consistent, very fast (low degree polynomial time) and have had high accuracy under many conditions that makes them competitive with other popular species tree estimation methods. In this study, inspired by the very recent work of weighted ASTRAL, we present weighted ASTRID, a variant of ASTRID that takes the branch uncertainty on the gene trees into account in the internode distance.

RESULTS

Our experimental study evaluating weighted ASTRID typically shows improvements in accuracy compared to the original (unweighted) ASTRID, and shows competitive accuracy against weighted ASTRAL, the state of the art. Our re-implementation of ASTRID also improves the runtime, with marked improvements on large datasets.

CONCLUSIONS

Weighted ASTRID is a new and very fast method for species tree estimation that typically improves upon ASTRID and has comparable accuracy to weighted ASTRAL, while remaining much faster. Weighted ASTRID is available at https://github.com/RuneBlaze/internode .

Comparative genomics reveals the hybrid origin of a macaque group

Although species can arise through hybridization, compelling evidence for hybrid speciation has been reported only rarely in animals. Here, we present phylogenomic analyses on genomes from 12 macaque species and show that the fascicularis group originated from an ancient hybridization between the sinica and silenus groups ~3.45 to 3.56 million years ago. The X chromosomes and low-recombination regions exhibited equal contributions from each parental lineage, suggesting that they were less affected by subsequent backcrossing and hence could have played an important role in maintaining hybrid integrity. We identified many reproduction-associated genes that could have contributed to the development of the mixed sexual phenotypes characteristic of the fascicularis group. The phylogeny within the silenus group was also resolved, and functional experimentation confirmed that all extant Western silenus species are susceptible to HIV-1 infection. Our study provides novel insights into macaque evolution and reveals a hybrid speciation event that has occurred only very rarely in primates.

Phylogenomics and biogeography of arid-adapted Chlamydogobius goby fishes

The progressive aridification of the Australian continent from ∼ 20 million years ago posed severe challenges for the persistence of its resident biota. A key question involves the role of refugial habitats - specifically, their ability to mediate the effects of habitat loss and fragmentation, and their potential to shape opportunities for allopatric speciation. With freshwater species, for example, the patchiness, or absence, of water will constrain distributions. However, aridity may not necessarily isolate populations if disjunct refugia experience frequent hydrological connections. To investigate this potential dichotomy, we explored the evolutionary history of the Chlamydogobius gobies (Gobiiformes: Gobiidae), an arid-adapted genus of six small, benthic fish species that exploit all types of waterbodies (i.e. desert springs, waterholes and bore-fed wetlands, coastal estuarine creeks and mangroves) across parts of central and northern Australia. We used Anchored Phylogenomics to generate a highly resolved phylogeny of the group from sequence data for 260 nuclear loci. Buttressed by companion allozyme and mtDNA datasets, our molecular findings infer the diversification of Chlamydogobius in arid Australia, and provide a phylogenetic structure that cannot be simply explained by invoking allopatric speciation events reflecting current geographic proximity. Our findings are generally consistent with the existing morphological delimitation of species, with one exception: at the shallowest nodes of phylogenetic reconstruction, the molecular data do not fully support the current dichotomous delineation of C. japalpa from C. eremius in Kati Thanda-Lake Eyre-associated waterbodies. Together these findings illustrate the ability of structural (hydrological) connections to generate patterns of connectivity and isolation for an ecologically moderate disperser in response to ongoing habitat aridification. Finally, we explore the implications of these results for the immediate management of threatened (C. gloveri) and critically endangered (C. micropterus, C. squamigenus) congeners.

A New Assessment of Robust Capuchin Monkey (Sapajus) Evolutionary History Using Genome-Wide SNP Marker Data and a Bayesian Approach to Species Delimitation

Robust capuchin monkeys, Sapajus genus, are among the most phenotypically diverse and widespread groups of primates in South America, with one of the most confusing and often shifting taxonomies. We used a ddRADseq approach to generate genome-wide SNP markers for 171 individuals from all putative extant species of Sapajus to access their evolutionary history. Using maximum likelihood, multispecies coalescent phylogenetic inference, and a Bayes Factor method to test for alternative hypotheses of species delimitation, we inferred the phylogenetic history of the Sapajus radiation, evaluating the number of discrete species supported. Our results support the recognition of three species from the Atlantic Forest south of the São Francisco River, with these species being the first splits in the robust capuchin radiation. Our results were congruent in recovering the Pantanal and Amazonian Sapajus as structured into three monophyletic clades, though new morphological assessments are necessary, as the Amazonian clades do not agree with previous morphology-based taxonomic distributions. Phylogenetic reconstructions for Sapajus occurring in the Cerrado, Caatinga, and northeastern Atlantic Forest were less congruent with morphology-based phylogenetic reconstructions, as the bearded capuchin was recovered as a paraphyletic clade, with samples from the Caatinga biome being either a monophyletic clade or nested with the blond capuchin monkey.

Phylotranscriptomic Analyses of Mycoheterotrophic Monocots Show a Continuum of Convergent Evolutionary Changes in Expressed Nuclear Genes From Three Independent Nonphotosynthetic Lineages

Mycoheterotrophy is an alternative nutritional strategy whereby plants obtain sugars and other nutrients from soil fungi. Mycoheterotrophy and associated loss of photosynthesis have evolved repeatedly in plants, particularly in monocots. Although reductive evolution of plastomes in mycoheterotrophs is well documented, the dynamics of nuclear genome evolution remains largely unknown. Transcriptome datasets were generated from four mycoheterotrophs in three families (Orchidaceae, Burmanniaceae, Triuridaceae) and related green plants and used for phylogenomic analyses to resolve relationships among the mycoheterotrophs, their relatives, and representatives across the monocots. Phylogenetic trees based on 602 genes were mostly congruent with plastome phylogenies, except for an Asparagales + Liliales clade inferred in the nuclear trees. Reduction and loss of chlorophyll synthesis and photosynthetic gene expression and relaxation of purifying selection on retained genes were progressive, with greater loss in older nonphotosynthetic lineages. One hundred seventy-four of 1375 plant benchmark universally conserved orthologous genes were undetected in any mycoheterotroph transcriptome or the genome of the mycoheterotrophic orchid Gastrodia but were expressed in green relatives, providing evidence for massively convergent gene loss in nonphotosynthetic lineages. We designate this set of deleted or undetected genes Missing in Mycoheterotrophs (MIM). MIM genes encode not only mainly photosynthetic or plastid membrane proteins but also a diverse set of plastid processes, genes of unknown function, mitochondrial, and cellular processes. Transcription of a photosystem II gene (psb29) in all lineages implies a nonphotosynthetic function for this and other genes retained in mycoheterotrophs. Nonphotosynthetic plants enable novel insights into gene function as well as gene expression shifts, gene loss, and convergence in nuclear genomes.

Identifiability of local and global features of phylogenetic networks from average distances

Phylogenetic networks extend phylogenetic trees to model non-vertical inheritance, by which a lineage inherits material from multiple parents. The computational complexity of estimating phylogenetic networks from genome-wide data with likelihood-based methods limits the size of networks that can be handled. Methods based on pairwise distances could offer faster alternatives. We study here the information that average pairwise distances contain on the underlying phylogenetic network, by characterizing local and global features that can or cannot be identified. For general networks, we clarify that the root and edge lengths adjacent to reticulations are not identifiable, and then focus on the class of zipped-up semidirected networks. We provide a criterion to swap subgraphs locally, such as 3-cycles, resulting in indistinguishable networks. We propose the "distance split tree", which can be constructed from pairwise distances, and prove that it is a refinement of the network's tree of blobs, capturing the tree-like features of the network. For level-1 networks, this distance split tree is equal to the tree of blobs refined to separate polytomies from blobs, and we prove that the mixed representation of the network is identifiable. The information loss is localized around 4-cycles, for which the placement of the reticulation is unidentifiable. The mixed representation combines split edges for 4-cycles, regular tree and hybrid edges from the semidirected network, and edge parameters that encode all information identifiable from average pairwise distances.

Weighting by Gene Tree Uncertainty Improves Accuracy of Quartet-based Species Trees

Phylogenomic analyses routinely estimate species trees using methods that account for gene tree discordance. However, the most scalable species tree inference methods, which summarize independently inferred gene trees to obtain a species tree, are sensitive to hard-to-avoid errors introduced in the gene tree estimation step. This dilemma has created much debate on the merits of concatenation versus summary methods and practical obstacles to using summary methods more widely and to the exclusion of concatenation. The most successful attempt at making summary methods resilient to noisy gene trees has been contracting low support branches from the gene trees. Unfortunately, this approach requires arbitrary thresholds and poses new challenges. Here, we introduce threshold-free weighting schemes for the quartet-based species tree inference, the metric used in the popular method ASTRAL. By reducing the impact of quartets with low support or long terminal branches (or both), weighting provides stronger theoretical guarantees and better empirical performance than the unweighted ASTRAL. Our simulations show that weighting improves accuracy across many conditions and reduces the gap with concatenation in conditions with low gene tree discordance and high noise. On empirical data, weighting improves congruence with concatenation and increases support. Together, our results show that weighting, enabled by a new optimization algorithm we introduce, improves the utility of summary methods and can reduce the incongruence often observed across analytical pipelines.

Quartet Based Gene Tree Imputation Using Deep Learning Improves Phylogenomic Analyses Despite Missing Data

Species tree estimation is frequently based on phylogenomic approaches that use multiple genes from throughout the genome. However, for a combination of reasons (ranging from sampling biases to more biological causes, as in gene birth and loss), gene trees are often incomplete, meaning that not all species of interest have a common set of genes. Incomplete gene trees can potentially impact the accuracy of phylogenomic inference. We, for the first time, introduce the problem of imputing the quartet distribution induced by a set of incomplete gene trees, which involves adding the missing quartets back to the quartet distribution. We present Quartet based Gene tree Imputation using Deep Learning (QT-GILD), an automated and specially tailored unsupervised deep learning technique, accompanied by cues from natural language processing, which learns the quartet distribution in a given set of incomplete gene trees and generates a complete set of quartets accordingly. QT-GILD is a general-purpose technique needing no explicit modeling of the subject system or reasons for missing data or gene tree heterogeneity. Experimental studies on a collection of simulated and empirical datasets suggest that QT-GILD can effectively impute the quartet distribution, which results in a dramatic improvement in the species tree accuracy. Remarkably, QT-GILD not only imputes the missing quartets but can also account for gene tree estimation error. Therefore, QT-GILD advances the state-of-the-art in species tree estimation from gene trees in the face of missing data.

Phylogenomic Coalescent Analyses of Avian Retroelements Infer Zero-Length Branches at the Base of Neoaves, Emergent Support for Controversial Clades, and Ancient Introgressive Hybridization in Afroaves

Retroelement insertions (RIs) are low-homoplasy characters that are ideal data for addressing deep evolutionary radiations, where gene tree reconstruction errors can severely hinder phylogenetic inference with DNA and protein sequence data. Phylogenomic studies of Neoaves, a large clade of birds (>9000 species) that first diversified near the Cretaceous−Paleogene boundary, have yielded an array of robustly supported, contradictory relationships among deep lineages. Here, we reanalyzed a large RI matrix for birds using recently proposed quartet-based coalescent methods that enable inference of large species trees including branch lengths in coalescent units, clade-support, statistical tests for gene flow, and combined analysis with DNA-sequence-based gene trees. Genome-scale coalescent analyses revealed extremely short branches at the base of Neoaves, meager branch support, and limited congruence with previous work at the most challenging nodes. Despite widespread topological conflicts with DNA-sequence-based trees, combined analyses of RIs with thousands of gene trees show emergent support for multiple higher-level clades (Columbea, Passerea, Columbimorphae, Otidimorphae, Phaethoquornithes). RIs express asymmetrical support for deep relationships within the subclade Afroaves that hints at ancient gene flow involving the owl lineage (Strigiformes). Because DNA-sequence data are challenged by gene tree-reconstruction error, analysis of RIs represents one approach for improving gene tree-based methods when divergences are deep, internodes are short, terminal branches are long, and introgressive hybridization further confounds species−tree inference.

The Tracking of Moist Habitats Allowed Aiphanes (Arecaceae) to Cover the Elevation Gradient of the Northern Andes

The topographic gradients of the Tropical Andes may have triggered species divergence by different mechanisms. Topography separates species' geographical ranges and offers climatic heterogeneity, which could potentially foster local adaptation to specific climatic conditions and result in narrowly distributed endemic species. Such a pattern is found in the Andean centered palm genus Aiphanes. To test the extent to which geographic barriers and climatic heterogeneity can explain distribution patterns in Aiphanes, we sampled 34 out of 36 currently recognized species in that genus and sequenced them by Sanger sequencing and/or sequence target capture sequencing. We generated Bayesian, likelihood, and species-tree phylogenies, with which we explored climatic trait evolution from current climatic occupation. We also estimated species distribution models to test the relative roles of geographical and climatic divergence in their evolution. We found that Aiphanes originated in the Miocene in Andean environments and possibly in mid-elevation habitats. Diversification is related to the occupation of the adjacent high and low elevation habitats tracking high annual precipitation and low precipitation seasonality (moist habitats). Different species in different clades repeatedly occupy all the different temperatures offered by the elevation gradient from 0 to 3,000 m in different geographically isolated areas. A pattern of conserved adaptation to moist environments is consistent among the clades. Our results stress the evolutionary roles of niche truncation of wide thermal tolerance by physical range fragmentation, coupled with water-related niche conservatism, to colonize the topographic gradient.

Species Tree Estimation and the Impact of Gene Loss Following Whole-Genome Duplication

Whole-genome duplication (WGD) occurs broadly and repeatedly across the history of eukaryotes and is recognized as a prominent evolutionary force, especially in plants. Immediately following WGD, most genes are present in two copies as paralogs. Due to this redundancy, one copy of a paralog pair commonly undergoes pseudogenization and is eventually lost. When speciation occurs shortly after WGD; however, differential loss of paralogs may lead to spurious phylogenetic inference resulting from the inclusion of pseudoorthologs–paralogous genes mistakenly identified as orthologs because they are present in single copies within each sampled species. The influence and impact of including pseudoorthologs versus true orthologs as a result of gene extinction (or incomplete laboratory sampling) are only recently gaining empirical attention in the phylogenomics community. Moreover, few studies have yet to investigate this phenomenon in an explicit coalescent framework. Here, using mathematical models, numerous simulated data sets, and two newly assembled empirical data sets, we assess the effect of pseudoorthologs on species tree estimation under varying degrees of incomplete lineage sorting (ILS) and differential gene loss scenarios following WGD. When gene loss occurs along the terminal branches of the species tree, alignment-based (BPP) and gene-tree-based (ASTRAL, MP-EST, and STAR) coalescent methods are adversely affected as the degree of ILS increases. This can be greatly improved by sampling a sufficiently large number of genes. Under the same circumstances, however, concatenation methods consistently estimate incorrect species trees as the number of genes increases. Additionally, pseudoorthologs can greatly mislead species tree inference when gene loss occurs along the internal branches of the species tree. Here, both coalescent and concatenation methods yield inconsistent results. These results underscore the importance of understanding the influence of pseudoorthologs in the phylogenomics era. [Coalescent method; concatenation method; incomplete lineage sorting; pseudoorthologs; single-copy gene; whole-genome duplication.]

Covariance of pairwise differences on a multi-species coalescent tree and implications for F ST

The multi-species coalescent (MSC) provides a theoretical foundation for modern phylogenetics and comparative population genetics. Its theoretical properties have been heavily studied but there are still aspects of the MSC that are largely unknown, including the covariances in pairwise coalescence times, which are fundamental for understanding the properties of statistics that combine data from multiple species, such as the fixation index (F_ST). The major contribution of this study is the derivation and implementation of exact expressions for the covariances of pairwise coalescence times under phylogenetic models with piecewise constant changes in population size, assuming no gene flow after species divergence. We use these expressions to derive the variance in average pairwise differences within and between populations. We then derive approximations for the expectation and bias of a sequence-based estimator of F_ST, a commonly used genetic measurement of population differentiation, when it is applied to a non-recombining region of the genome. We show that the estimator of F_ST is generally biased downward. A freely available software package is provided, STCov, to calculate the mean, variances and covariances in coalescence times presented here under user-defined piecewise-constant species trees.

This article is part of the theme issue ‘Celebrating 50 years since Lewontin's apportionment of human diversity’.

FrogCap: A modular sequence capture probe-set for phylogenomics and population genetics for all frogs, assessed across multiple phylogenetic scales

Despite the prevalence of high-throughput sequencing in phylogenetics, many relationships remain difficult to resolve because of conflicting signal among genomic regions. Selection of different types of molecular markers from different genomic regions is required to overcome these challenges. For evolutionary studies in frogs, we introduce the publicly available FrogCap suite of genomic resources, which is a large collection of ~15,000 markers that unifies previous genetic sequencing efforts. FrogCap is designed to be modular, such that subsets of markers and SNPs can be selected based on the desired phylogenetic scale. FrogCap uses a variety of marker types that include exons and introns, ultraconserved elements, and previously sequenced Sanger markers, which span up to 10,000 bp in alignment lengths; in addition, we demonstrate potential for SNP-based analyses. We tested FrogCap using 121 samples distributed across five phylogenetic scales, comparing probes designed using a consensus- or exemplar genome-based approach. Using the consensus design is more resilient to issues with sensitivity, specificity, and missing data than picking an exemplar genome sequence. We also tested the impact of different bait kit sizes (20,020 vs. 40,040) on depth of coverage and found triple the depth for the 20,020 bait  kit. We observed sequence capture success (i.e., missing data, sequenced markers/bases, marker length, and informative sites) across phylogenetic scales. The incorporation of different marker types is effective for deep phylogenetic relationships and shallow population genetics studies. Having demonstrated FrogCap's utility and modularity, we conclude that these new resources are efficacious for high-throughput sequencing projects across variable timescales.

Assembling a Reference Phylogenomic Tree of Bacteria and Archaea by Summarizing Many Gene Phylogenies

Phylogenomics is the inference of phylogenetic trees based on multiple marker genes sampled in the genomes of interest. An important challenge in phylogenomics is the potential incongruence among the evolutionary histories of individual genes, which can be widespread in microorganisms due to the prevalence of horizontal gene transfer. This protocol introduces the procedures for building a phylogenetic tree of a large number of microbial genomes using a broad sampling of marker genes that are representative of whole-genome evolution. The protocol highlights the use of a gene tree summary method, which can effectively reconstruct the species tree while accounting for the topological conflicts among individual gene trees. The pipeline described in this protocol is scalable to tens of thousands of genomes while retaining high accuracy. We discussed multiple software tools, libraries, and scripts to enable convenient adoption of the protocol. The protocol is suitable for microbiology and microbiome studies based on public genomes and metagenomic data.

Dispersal, not vicariance, explains the biogeographic origin of iguanas on Madagascar

Lizards of the clade Iguanidae (sensu lato) are primarily a New World group. Thus, the remarkable presence of an endemic lineage of iguanas (family Opluridae) on the isolated Indian Ocean island of Madagascar has long been considered a biogeographic anomaly. Previous work attributed this disjunct extant distribution to: (1) vicariance at about 140-165 Ma, caused by the breakup of Gondwana and the separation of South America, Africa, and Madagascar (with subsequent extinction of iguanas on Africa, and potentially other Gondwanan landmasses), (2) vicariance at about 80-90 Ma, caused by the sundering of hypothesized land-bridge connections between South America, Antarctica, India, and Madagascar, or (3) long-distance overwater dispersal from South America to Madagascar. Each hypothesis has been supported with molecular divergence dating analyses, and thus the biogeographic origin of the Opluridae is not yet well resolved. Here we utilize genetic sequences of ultraconserved elements for all Iguania families and the majority of Iguanidae (s.l.) genera, and morphological data for extant and fossil taxa (used for divergence dating analyses), to produce the most comprehensive dataset applied to date to test these origin hypotheses. We find strong support for a sister relationship between the Opluridae (Madagascar) and Leiosauridae (South America). Divergence of the Opluridae from Leiosauridae is dated to between the late Cretaceous and mid-Paleogene, at a time when Madagascar was already an island and was isolated from all other Gondwanan landmasses. Consequently, our results support a hypothesis of long-distance overwater dispersal of the Opluridae lineage, either directly from South America to Madagascar or potentially via Antarctica or Africa, leading to this radiation of iguanas in the Indian Ocean.

Multispecies Coalescent: Theory and Applications in Phylogenetics

Species tree estimation is a basic part of many biological research projects, ranging from answering basic evolutionary questions (e.g., how did a group of species adapt to their environments?) to addressing questions in functional biology. Yet, species tree estimation is very challenging, due to processes such as incomplete lineage sorting, gene duplication and loss, horizontal gene transfer, and hybridization, which can make gene trees differ from each other and from the overall evolutionary history of the species. Over the last 10–20 years, there has been tremendous growth in methods and mathematical theory for estimating species trees and phylogenetic networks, and some of these methods are now in wide use. In this survey, we provide an overview of the current state of the art, identify the limitations of existing methods and theory, and propose additional research problems and directions.

A Combined Morphological and Molecular Evolutionary Analysis of Karst-Environment Adaptation for the Genus Urophysa (Ranunculaceae)

The karst environment is characterized by low soil water content, periodic water deficiency, and poor nutrient availability, which provides an ideal natural laboratory for studying the adaptive evolution of its inhabitants. However, how species adapt to such a special karst environment remains poorly understood. Here, transcriptome sequences of two Urophysa species (Urophysa rockii and Urophysa henryi), which are Chinese endemics with karst-specific distribution, and allied species in Semiaquilegia and Aquilegia (living in non-karst habitat) were collected. Single-copy genes (SCGs) were extracted to perform the phylogenetic analysis using concatenation and coalescent methods. Positively selected genes (PSGs) and clusters of paralogous genes (Mul_genes) were detected and subsequently used to conduct gene function annotation. We filtered 2,271 SCGs and the coalescent analysis revealed that 1,930 SCGs shared the same tree topology, which was consistent with the topology detected from the concatenated tree. Total of 335 PSGs and 243 Mul_genes were detected, and many were enriched in stress and stimulus resistance, transmembrane transport, cellular ion homeostasis, calcium ion transport, calcium signaling regulation, and water retention. Both molecular and morphological evidences indicated that Urophysa species evolved complex strategies for adapting to hostile karst environments. Our findings will contribute to a new understanding of genetic and phenotypic adaptive mechanisms of karst adaptation in plants.

wQFM: Highly Accurate Genome-scale Species Tree Estimation from Weighted Quartets

MOTIVATION

Species tree estimation from genes sampled from throughout the whole genome is complicated due to the gene tree-species tree discordance. Incomplete lineage sorting (ILS) is one of the most frequent causes for this discordance, where alleles can coexist in populations for periods that may span several speciation events. Quartet-based summary methods for estimating species trees from a collection of gene trees are becoming popular due to their high accuracy and statistical guarantee under ILS. Generating quartets with appropriate weights, where weights correspond to the relative importance of quartets, and subsequently amalgamating the weighted quartets to infer a single coherent species tree can allow for a statistically consistent way of estimating species trees. However, handling weighted quartets is challenging.

RESULTS

We propose wQFM, a highly accurate method for species tree estimation from multi-locus data, by extending the quartet FM (QFM) algorithm to a weighted setting. wQFM was assessed on a collection of simulated and real biological datasets, including the avian phylogenomic dataset which is one of the largest phylogenomic datasets to date. We compared wQFM with wQMC, which is the best alternate method for weighted quartet amalgamation, and with ASTRAL, which is one of the most accurate and widely used coalescent-based species tree estimation methods. Our results suggest that wQFM matches or improves upon the accuracy of wQMC and ASTRAL.

AVAILABILITY

wQFM is available in open source form at https://github.com/Mahim1997/wQFM-2020.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Quartet-Based Inference is Statistically Consistent Under the Unified Duplication-Loss-Coalescence Model

Motivation

The classic multispecies coalescent (MSC) model provides the means for theoretical justification of incomplete lineage sorting-aware species tree inference methods. This has motivated an extensive body of work on phylogenetic methods that are statistically consistent under MSC. One such particularly popular method is ASTRAL, a quartet-based species tree inference method. Novel studies suggest that ASTRAL also performs well when given multi-locus gene trees in simulation studies. Further, Legried et al. recently demonstrated that ASTRAL is statistically consistent under the gene duplication and loss model (GDL). GDL is prevalent in evolutionary histories and is the first core process in the powerful duplication-loss-coalescence evolutionary model (DLCoal) by Rasmussen and Kellis.

Results

In this work, we prove that ASTRAL is statistically consistent under the general DLCoal model. Therefore, our result supports the empirical evidence from the simulation-based studies. More broadly, we prove that the quartet-based inference approach is statistically consistent under DLCoal.

Supplementary information

Supplementary data are available at Bioinformatics online.

Statistical inconsistency of the unrooted minimize deep coalescence criterion

Species trees, which describe the evolutionary relationships between species, are often inferred from gene trees, which describe the ancestral relationships between sequences sampled at different loci from the species of interest. A common approach to inferring species trees from gene trees is motivated by supposing that gene tree variation is due to incomplete lineage sorting, also known as deep coalescence. One of the earliest methods motivated by deep coalescence is to find the species tree that minimizes the number of deep coalescent events needed to explain discrepancies between the species tree and input gene trees. This minimize deep coalescence (MDC) criterion can be applied in both rooted and unrooted settings. where either rooted or unrooted gene trees can be used to infer a rooted species tree. Previous work has shown that MDC is statistically inconsistent in the rooted setting, meaning that under a probabilistic model for deep coalescence, the multispecies coalescent, for some species trees, increasing the number of input gene trees does not make the method more likely to return a correct species tree. Here, we obtain analogous results in the unrooted setting, showing conditions leading to inconsistency of the MDC criterion using the multispecies coalescent model with unrooted gene trees for four taxa and five taxa.

Species tree estimation from gene trees by minimizing deep coalescence and maximizing quartet consistency: a comparative study and the presence of pseudo species tree terraces

Species tree estimation from multi-locus datasets is extremely challenging, especially in the presence of gene tree heterogeneity across the genome due to incomplete lineage sorting (ILS). Summary methods have been developed which estimate gene trees and then combine the gene trees to estimate a species tree by optimizing various optimization scores. In this study, we have extended and adapted the concept of phylogenetic terraces to species tree estimation by "summarizing" a set of gene trees, where multiple species trees with distinct topologies may have exactly the same optimality score (i.e., quartet score, extra lineage score, etc.). We particularly investigated the presence and impacts of equally optimal trees in species tree estimation from multi-locus data using summary methods by taking ILS into account. We analyzed two of the most popular ILS-aware optimization criteria: maximize quartet consistency (MQC) and minimize deep coalescence (MDC). Methods based on MQC are provably statistically consistent, whereas MDC is not a consistent criterion for species tree estimation. We present a comprehensive comparative study of these two optimality criteria. Our experiments, on a collection of datasets simulated under ILS, indicate that MDC may result in competitive or identical quartet consistency score as MQC, but could be significantly worse than MQC in terms of tree accuracy - demonstrating the presence and impacts of equally optimal species trees. This is the first known study that provides the conditions for the datasets to have equally optimal trees in the context of phylogenomic inference using summary methods.

Heuristics for unrooted, unranked, and ranked anomaly zones under birth-death models

Species trees that can generate a nonmatching gene tree topology that is more probable than the topology matching the species tree are said to be in an anomaly zone. We introduce some heuristic approaches to infer whether species trees are in anomaly zones when it is difficult or impossible to compute the entire distribution of gene tree topologies. Here, probabilities of unrooted, unranked, and ranked gene tree topologies under the multispecies coalescent are used. A ranked tree can be viewed as an unranked tree with a temporal ordering of its internal nodes. Overall, considering probabilities of unrooted or unranked gene tree topologies within one nearest neighbor interchange from the species tree topology is a reasonable heuristic to infer the existence of anomalous unrooted or unranked gene trees, respectively. We investigated a test proposed by Linkem et al. (2016) which classifies a species tree as being in an unranked anomaly zone if there is a subset of four taxa in an unranked anomaly zone. We find this test to have high true positive rates, but it can also have high false positive rates. For ranked trees, because at least one of the most probable ranked gene tree topologies must have the same unranked topology as the species tree, we propose to use only those ranked gene trees that have topologies that match the unranked species tree topology. We find that the probability that the species tree is in unrooted and unranked anomaly zones tends to increase with the speciation rate, and the probability of all three types of anomaly zones increases rapidly with the number of taxa. We find that probabilities that species trees are in an anomaly zone can be quite high for moderately high speciation rates.

Phylogenomics of Porites from the Arabian Peninsula

The advent of high throughput sequencing technologies provides an opportunity to resolve phylogenetic relationships among closely related species. By incorporating hundreds to thousands of unlinked loci and single nucleotide polymorphisms (SNPs), phylogenomic analyses have a far greater potential to resolve species boundaries than approaches that rely on only a few markers. Scleractinian taxa have proved challenging to identify using traditional morphological approaches and many groups lack an adequate set of molecular markers to investigate their phylogenies. Here, we examine the potential of Restriction-site Associated DNA sequencing (RADseq) to investigate phylogenetic relationships and species limits within the scleractinian coral genus Porites. A total of 126 colonies were collected from 16 localities in the seas surrounding the Arabian Peninsula and ascribed to 12 nominal and two unknown species based on their morphology. Reference mapping was used to retrieve and compare nearly complete mitochondrial genomes, ribosomal DNA, and histone loci. De novo assembly and reference mapping to the P. lobata coral transcriptome were compared and used to obtain thousands of genome-wide loci and SNPs. A suite of species discovery methods (phylogenetic, ordination, and clustering analyses) and species delimitation approaches (coalescent-based, species tree, and Bayesian Factor delimitation) suggested the presence of eight molecular lineages, one of which included six morphospecies. Our phylogenomic approach provided a fully supported phylogeny of Porites from the Arabian Peninsula, suggesting the power of RADseq data to solve the species delineation problem in this speciose coral genus.

Population Genomics Reveals Incipient Speciation, Introgression, and Adaptation in the African Mona Monkey (Cercopithecus mona)

Guenons (tribe Cercopithecini) are the most widely distributed nonhuman primate in the tropical forest belt of Africa and show considerable phenotypic, taxonomic, and ecological diversity. However, genomic information for most species within this group is still lacking. Here, we present a high-quality de novo genome (total 2.90 Gb, contig N50 equal to 22.7 Mb) of the mona monkey (Cercopithecus mona), together with genome resequencing data of 13 individuals sampled across Nigeria. Our results showed differentiation between populations from East and West of the Niger River ∼84 ka and potential ancient introgression in the East population from other mona group species. The PTPRK, FRAS1, BNC2, and EDN3 genes related to pigmentation displayed signals of introgression in the East population. Genomic scans suggest that immunity genes such as AKT3 and IL13 (possibly involved in simian immunodeficiency virus defense), and G6PD, a gene involved in malaria resistance, are under positive natural selection. Our study gives insights into differentiation, natural selection, and introgression in guenons.

PRANC: ML species tree estimation from the ranked gene trees under coalescence

SUMMARY

PRANC computes the Probabilities of RANked gene tree topologies under the multispecies coalescent. A ranked gene tree is a gene tree accounting for the temporal ordering of internal nodes. PRANC can also estimate the maximum likelihood (ML) species tree from a sample of ranked or unranked gene tree topologies. It estimates the ML tree with estimated branch lengths in coalescent units.

AVAILABILITY AND IMPLEMENTATION

PRANC is written in C++ and freely available at github.com/anastasiiakim/PRANC.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Gene tree discord, simplex plots, and statistical tests under the coalescent

A simple graphical device, the simplex plot of quartet concordance factors, is introduced to aid in the exploration of a collection of gene trees on a common set of taxa. A single plot summarizes all gene tree discord, and allows for visual comparison to the expected discord from the multispecies coalescent model (MSC) of incomplete lineage sorting on a species tree. A formal statistical procedure is described that can quantify the deviation from expectation for each subset of four taxa, suggesting when the data is not in accord with the MSC, and thus that either gene tree inference error is substantial or a more complex model such as that on a network may be required. If the collection of gene trees is in accord with the MSC, the plots reveal when substantial incomplete lineage sorting is present. Applications to both simulated and empirical multilocus data sets illustrate the insights provided.

Collapsing dubiously resolved gene-tree branches in phylogenomic coalescent analyses

In two-step coalescent analyses of phylogenomic data, gene-tree topologies are treated as fixed prior to species-tree inference. Although all gene-tree conflict is assumed to be caused by lineage sorting when applying these methods, in empirical datasets much of the conflict can be caused by estimation error. Weakly supported and even arbitrarily resolved clades are important sources of this estimation error for gene trees inferred from few informative characters relative to the number of sampled terminals, and the resulting extraneous conflict among gene trees can negatively impact species-tree inference. In this study, we quantified the relative severity of alternative methods for collapsing gene-tree branches for seven empirical datasets and quantified their effects on species-tree inference. The branch-collapsing methods that we employed were based on the strict consensus of optimal topologies, various bootstrap thresholds, and 0% approximate likelihood ratio test (SH-like aLRT) support. Up to 86% of internal gene-tree branches are dubiously or arbitrarily resolved in reanalyses of these published phylogenomic datasets, and collapsing these branches increased inferred species-tree coalescent branch lengths by up to 455%. For two datasets, the longer inferred branch lengths sometimes impacted inference of anomaly-zone conditions. Although branch-collapsing methods did not consistently affect the species-tree topology, they often increased branch support. The more severe and clearly justified gene-tree branch-collapsing methods, which we recommend be broadly applied for two-step coalescent analyses, are use of the strict consensus in parsimony analyses and the collapse clades with 0% SH-like aLRT support in likelihood analyses. Collapsing dubiously or arbitrarily resolved branches in gene trees sometimes improved congruence between coalescent-based results and concatenation trees. In such cases, we contend that the resolution provided by concatenation should be preferred and that incomplete lineage sorting is a poor explanation for the initial conflict between phylogenetic approaches.

Complexity of the simplest species tree problem

The multispecies coalescent model provides a natural framework for species tree estimation accounting for gene-tree conflicts. Although a number of species tree methods under the multispecies coalescent have been suggested and evaluated using simulation, their statistical properties remain poorly understood. Here, we use mathematical analysis aided by computer simulation to examine the identifiability, consistency, and efficiency of different species tree methods in the case of three species and three sequences under the molecular clock. We consider four major species-tree methods including concatenation, two-step, independent-sites maximum likelihood, and maximum likelihood. We develop approximations that predict that the probit transform of the species tree estimation error decreases linearly with the square root of the number of loci. Even in this simplest case, major differences exist among the methods. Full-likelihood methods are considerably more efficient than summary methods such as concatenation and two-step. They also provide estimates of important parameters such as species divergence times and ancestral population sizes,whereas these parameters are not identifiable by summary methods. Our results highlight the need to improve the statistical efficiency of summary methods and the computational efficiency of full likelihood methods of species tree estimation.

Phylogenomics of white-eyes, a 'great speciator', reveals Indonesian archipelago as the center of lineage diversity

Archipelagoes serve as important 'natural laboratories' which facilitate the study of island radiations and contribute to the understanding of evolutionary processes. The white-eye genus Zosterops is a classical example of a 'great speciator', comprising c. 100 species from across the Old World, most of them insular. We achieved an extensive geographic DNA sampling of Zosterops by using historical specimens and recently collected samples. Using over 700 genome-wide loci in conjunction with coalescent species tree methods and gene flow detection approaches, we untangled the reticulated evolutionary history of Zosterops, which comprises three main clades centered in Indo-Africa, Asia, and Australasia, respectively. Genetic introgression between species permeates the Zosterops phylogeny, regardless of how distantly related species are. Crucially, we identified the Indonesian archipelago, and specifically Borneo, as the major center of diversity and the only area where all three main clades overlap, attesting to the evolutionary importance of this region.

Phylogenomics and the Genetic Architecture of the Placental Mammal Radiation

The genomes of placental mammals are being sequenced at an unprecedented rate. Alignments of hundreds, and one day thousands, of genomes spanning the rich living and extinct diversity of species offer unparalleled power to resolve phylogenetic controversies, identify genomic innovations of adaptation, and dissect the genetic architecture of reproductive isolation. We highlight outstanding questions about the earliest phases of placental mammal diversification and the promise of newer methods, as well as remaining challenges, toward using whole genome data to resolve placental mammal phylogeny. The next phase of mammalian comparative genomics will see the completion and application of finished-quality, gapless genome assemblies from many ordinal lineages and closely related species. Interspecific comparisons between the most hypervariable genomic loci will likely reveal large, but heretofore mostly underappreciated, effects on population divergence, morphological innovation, and the origin of new species.

Topological Metrizations of Trees, and New Quartet Methods of Tree Inference

Topological phylogenetic trees can be assigned edge weights in several natural ways, highlighting different aspects of the tree. Here, the rooted triple and quartet metrizations are introduced, and applied to formulate novel methods of inferring large trees from rooted triple and quartet data. These methods lead to new statistically consistent procedures for inference of a species tree from gene trees under the multispecies coalescent model.

ASTRAL-Pro: Quartet-Based Species-Tree Inference despite Paralogy

Phylogenetic inference from genome-wide data (phylogenomics) has revolutionized the study of evolution because it enables accounting for discordance among evolutionary histories across the genome. To this end, summary methods have been developed to allow accurate and scalable inference of species trees from gene trees. However, most of these methods, including the widely used ASTRAL, can only handle single-copy gene trees and do not attempt to model gene duplication and gene loss. As a result, most phylogenomic studies have focused on single-copy genes and have discarded large parts of the data. Here, we first propose a measure of quartet similarity between single-copy and multicopy trees that accounts for orthology and paralogy. We then introduce a method called ASTRAL-Pro (ASTRAL for PaRalogs and Orthologs) to find the species tree that optimizes our quartet similarity measure using dynamic programing. By studying its performance on an extensive collection of simulated data sets and on real data sets, we show that ASTRAL-Pro is more accurate than alternative methods.

Revisiting the phylogeny of the genus Lolliguncula Steenstrup 1881 improves understanding of their biogeography and proves the validity of Lolliguncula argus Brakoniecki & Roper, 1985

The biogeography of American loliginid squids has been improved in recent years, but certain key taxa have been missing. Given that the most accurate phylogenies and estimates of divergence times of common ancestors depend heavily on good taxonomic coverage we have reanalyzed the genus Lolliguncula in light of new samples that increase the geographic and taxonomic coverage. New sequences were produced using standard methods to update an existing dataset for COI, 16S and Rhodopsin markers. Data was analyzed using various species delimitation methods, rigorous phylogenetic analyses and estimates of divergence times between clades. Within Lolliguncula we recover five monophyletic lineages that relate to the known species L. argus, L. diomedeae, L. panamensis, L. brevis North Atlantic and L. brevis South Atlantic. Except when using low divergence thresholds in ABGD, species delimitation methods only identify four of these lineages as distinct species, grouping L. argus and L. diomedeae as a single species. However, considering the reciprocal monophyly, recent divergence time estimate and morphological diagnoses we refrain from synonymizing L. argus within L. diomedeae, considering them very recently diverged species. The biogeography of the American loliginids is discussed, wherein basal cladogenesis in both Lolliguncula and Doryteuthis occur between the Atlantic and Pacific about 45 mya, with subsequent speciation around 20 mya associated with seafloor changes during the formation of the Caribbean. The recent speciation between L. argus and L. diomedeae is associated to oceanic environmental changes associated with glaciation, deep sea cooling and tropical upwelling.

Machine learning based imputation techniques for estimating phylogenetic trees from incomplete distance matrices

BACKGROUND

With the rapid growth rate of newly sequenced genomes, species tree inference from genes sampled throughout the whole genome has become a basic task in comparative and evolutionary biology. However, substantial challenges remain in leveraging these large scale molecular data. One of the foremost challenges is to develop efficient methods that can handle missing data. Popular distance-based methods, such as NJ (neighbor joining) and UPGMA (unweighted pair group method with arithmetic mean) require complete distance matrices without any missing data.

RESULTS

We introduce two highly accurate machine learning based distance imputation techniques. These methods are based on matrix factorization and autoencoder based deep learning architectures. We evaluated these two methods on a collection of simulated and biological datasets. Experimental results suggest that our proposed methods match or improve upon the best alternate distance imputation techniques. Moreover, these methods are scalable to large datasets with hundreds of taxa, and can handle a substantial amount of missing data.

CONCLUSIONS

This study shows, for the first time, the power and feasibility of applying deep learning techniques for imputing distance matrices. Thus, this study advances the state-of-the-art in phylogenetic tree construction in the presence of missing data. The proposed methods are available in open source form at https://github.com/Ananya-Bhattacharjee/ImputeDistances .

Inferring Metric Trees from Weighted Quartets via an Intertaxon Distance

A metric phylogenetic tree relating a collection of taxa induces weighted rooted triples and weighted quartets for all subsets of three and four taxa, respectively. New intertaxon distances are defined that can be calculated from these weights, and shown to exactly fit the same tree topology, but with edge weights rescaled by certain factors dependent on the associated split size. These distances are analogs for metric trees of similar ones recently introduced for topological trees that are based on induced unweighted rooted triples and quartets. The distances introduced here lead to new statistically consistent methods of inferring a metric species tree from a collection of topological gene trees generated under the multispecies coalescent model of incomplete lineage sorting. Simulations provide insight into their potential.

Toward a Fully Resolved Fungal Tree of Life

In this review, we discuss the current status and future challenges for fully elucidating the fungal tree of life. In the last 15 years, advances in genomic technologies have revolutionized fungal systematics, ushering the field into the phylogenomic era. This has made the unthinkable possible, namely access to the entire genetic record of all known extant taxa. We first review the current status of the fungal tree and highlight areas where additional effort will be required. We then review the analytical challenges imposed by the volume of data and discuss methods to recover the most accurate species tree given the sea of gene trees. Highly resolved and deeply sampled trees are being leveraged in novel ways to study fungal radiations, species delimitation, and metabolic evolution. Finally, we discuss the critical issue of incorporating the unnamed and uncultured dark matter taxa that represent the vast majority of fungal diversity.

ASTRAL-MP: scaling ASTRAL to very large datasets using randomization and parallelization

MOTIVATION

Evolutionary histories can change from one part of the genome to another. The potential for discordance between the gene trees has motivated the development of summary methods that reconstruct a species tree from an input collection of gene trees. ASTRAL is a widely used summary method and has been able to scale to relatively large datasets. However, the size of genomic datasets is quickly growing. Despite its relative efficiency, the current single-threaded implementation of ASTRAL is falling behind the data growth trends is not able to analyze the largest available datasets in a reasonable time.

RESULTS

ASTRAL uses dynamic programing and is not trivially parallel. In this paper, we introduce ASTRAL-MP, the first version of ASTRAL that can exploit parallelism and also uses randomization techniques to speed up some of its steps. Importantly, ASTRAL-MP can take advantage of not just multiple CPU cores but also one or several graphics processing units (GPUs). The ASTRAL-MP code scales very well with increasing CPU cores, and its GPU version, implemented in OpenCL, can have up to 158× speedups compared to ASTRAL-III. Using GPUs and multiple cores, ASTRAL-MP is able to analyze datasets with 10 000 species or datasets with more than 100 000 genes in <2 days.

AVAILABILITY AND IMPLEMENTATION

ASTRAL-MP is available at https://github.com/smirarab/ASTRAL/tree/MP.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

A transcriptome-based study on the phylogeny and evolution of the taxonomically controversial subfamily Apioideae (Apiaceae)

BACKGROUND AND AIMS

A long-standing controversy in the subfamily Apioideae concerns relationships among the major lineages, which has prevented a comprehensive study of their fruits and evolutionary history. Here we use single copy genes (SCGs) generated from transcriptome datasets to generate a reliable species tree and explore the evolutionary history of Apioideae.

METHODS

In total, 3351 SCGs were generated from 27 transcriptome datasets and one genome, and further used for phylogenetic analysis using coalescent-based methods. Fruit morphology and anatomy were studied in combination with the species tree. Eleven SCGs were screened out for dating analysis with two fossils selected for calibration.

KEY RESULTS

A well-supported species tree was generated with a topology [Chamaesieae, (Bupleureae, (Pleurospermeae, (Physospermopsis Clade, (Group C, (Group A, Group B)))))] that differed from previous trees. Daucinae and Torilidinae were not in the tribe Scandiceae and existed as sister groups to the Acronema Clade. Five branches (I-V) of the species tree showed low quartet support but strong local posterior probabilities. Dating analysis suggested that Apioideae originated around 56.64 Mya (95 % highest posterior density interval, 45.18-73.53 Mya).

CONCLUSIONS

This study resolves a controversial phylogenetic relationship in Apioideae based on 3351 SCGs and coalescent-based species tree estimation methods. Gene trees that contributed to the species tree may undergoing rapid evolutionary divergence and incomplete lineage sorting. Fruits of Apioideae might have evolved in two directions, anemochorous and hydrochorous, with epizoochorous as a derived mode. Molecular and morphological evidence suggests that Daucinae and Torilidinae should be restored to the tribe level. Our results provide new insights into the morphological evolution of this subfamily, which may contribute to a better understanding of species diversification in Apioideae. Molecular dating analysis suggests that uplift of the Qinghai-Tibetan Plateau (QTP) and climate changes probably drove rapid speciation and diversification of Apioideae in the QTP region.

INSTRAL: Discordance-Aware Phylogenetic Placement Using Quartet Scores

Phylogenomic analyses have increasingly adopted species tree reconstruction using methods that account for gene tree discordance using pipelines that require both human effort and computational resources. As the number of available genomes continues to increase, a new problem is facing researchers. Once more species become available, they have to repeat the whole process from the beginning because updating species trees is currently not possible. However, the de novo inference can be prohibitively costly in human effort or machine time. In this article, we introduce INSTRAL, a method that extends ASTRAL to enable phylogenetic placement. INSTRAL is designed to place a new species on an existing species tree after sequences from the new species have already been added to gene trees; thus, INSTRAL is complementary to existing placement methods that update gene trees. [ASTRAL; ILS; phylogenetic placement; species tree reconstruction.].

Coalescent-based delimitation and species-tree estimations reveal Appalachian origin and Neogene diversification in Russula subsection Roseinae

Numerous lineages of mushroom-forming fungi have been subject to bursts of diversification throughout their evolutionary history, events that can impact our ability to infer well-resolved phylogenies. However, groups that have undergone quick genetic change may have the highest adaptive potential. As the second largest genus of mushroom-forming fungi, Russula provides an excellent model for studying hyper-diversification and processes in evolution that drives it. This study focuses on the morphologically defined group - Russula subsection Roseinae. Species hypotheses based on morphological differentiation and multi-locus phylogenetic analyses are tested in the Roseinae using different applications of the multi-species coalescent model. Based on this combined approach, we recognize fourteen species in Roseinae including the Albida and wholly novel Magnarosea clades. Reconstruction of biogeographic and host association history suggest that parapatric speciation in refugia during glacial cycles of the Pleistocene drove diversification within the Roseinae, which is found to have a Laurasian distribution with an evolutionary origin in the Appalachian Mountains of eastern North America. Finally, we detect jump dispersal at a continental scale that has driven diversification since the most recent glacial cycles.