Testing Congruence in Phylogenomic Analysis

Traditional multilocus phylogeny fails to fully resolve Palearctic ground squirrels (Spermophilus) relationships but reveals a new species endemic to West Siberia

Previous efforts to reconstruct evolutionary history of Palearctic ground squirrels within the genus Spermophilus have primarily relied on a single mitochondrial marker for phylogenetic data. In this study, we present the first phylogeny with comprehensive taxon sampling of Spermophilus via a conventional multilocus approach utilizing five mitochondrial and five nuclear markers. Through application of the multispecies coalescent model, we constructed a species tree revealing four distinct clades that diverged during the Late Miocene. These clades are 1) S. alaschanicus and S. dauricus from East Asia; 2) S. musicus and S. pygmaeus from East Europe and northwestern Central Asia; 3) the subgenus Colobotis found across Central Asia and its adjacent regions and encompassing S. brevicauda, S. erythrogenys, S. fulvus, S. major, S. pallidicauda, S. ralli, S. relictus, S. selevini, and S. vorontsovi sp. nov.; and 4) a Central/Eastern Europe and Asia Minor clade comprising S. citellus, S. taurensis, S. xanthoprymnus, S. suslicus, and S. odessanus. The latter clade lacked strong support owing to uncertainty of taxonomic placement of S. odessanus and S. suslicus. Resolving relationships within the subgenus Colobotis, which radiated rapidly, remains challenging likely because of incomplete lineage sorting and introgressive hybridization. Most of modern Spermophilus species diversified during the Early-Middle Pleistocene (2.2-1.0 million years ago). We propose a revised taxonomic classification for the genus Spermophilus by recognizing 18 species including a newly identified one (S. vorontsovi sp. nov.), which is found only in a limited area in the southeast of West Siberia. Employing genome-wide single-nucleotide polymorphism genotyping, we substantiated the role of the Ob River as a major barrier ensuring robust isolation of this taxon from S. erythrogenys. Despite its inherent limitations, the traditional multilocus approach remains a valuable tool for resolving relationships and can provide important insights into otherwise poorly understood groups. It is imperative to recognize that additional efforts are needed to definitively determine phylogenetic relationships between certain species of Palearctic ground squirrels.

Mucor thermorhizoides-A New Species from Post-mining Site in Sudety Mountains (Poland)

Mucor representatives are mostly rapidly growing cosmopolitan soil saprotrophs of early diverged Mucoromycotina subphylum. Although this is the most speciose genus within the group, some lineages are still understudied. In this study, new species of Mucor was isolated from the post-mining area in southwestern Poland, where soil chemical composition analysis revealed high concentration of hydrocarbons and heavy metals. Phylogenetic analysis based on multigene phylogeny showed that the new isolate clusters distinctly from other Mucor species as a sister group to Mucor microsporus. New species Mucor thermorhizoides Abramczyk (Mucorales, Mucoromycota) is characterized by the extensive rhizoid production in elevated temperatures and formation of two layers of sporangiophores. It also significantly differs from M. microsporus in the shape of spores and the size of sporangia. M. thermorhizoides was shown to be able to grow in oligotrophic conditions at low temperatures. Together with M. microsporus they represent understudied and highly variable lineage of the Mucor genus.

Phylogenomics and topological conflicts in the tribe Anthospermeae (Rubiaceae)

Genome skimming (shallow whole-genome sequencing) offers time- and cost-efficient production of large amounts of DNA data that can be used to address unsolved evolutionary questions. Here we address phylogenetic relationships and topological incongruence in the tribe Anthospermeae (Rubiaceae), using phylogenomic data from the mitochondrion, the nuclear ribosomal cistron, and the plastome. All three genomic compartments resolve relationships in the Anthospermeae; the tribe is monophyletic and consists of three major subclades. Carpacoce Sond. is sister to the remaining clade, which comprises an African subclade and a Pacific subclade. Most results, from all three genomic compartments, are statistically well supported; however, not fully consistent. Intergenomic topological incongruence is most notable in the Pacific subclade but present also in the African subclade. Hybridization and introgression followed by organelle capture may explain these conflicts but other processes, such as incomplete lineage sorting (ILS), can yield similar patterns and cannot be ruled out based on the results. Whereas the null hypothesis of congruence among all sequenced loci in the individual genomes could not be rejected for nuclear and mitochondrial data, it was rejected for plastid data. Phylogenetic analyses of three subsets of plastid loci identified using the hierarchical likelihood ratio test demonstrated statistically supported intragenomic topological incongruence. Given that plastid genes are thought to be fully linked, this result is surprising and may suggest modeling or sampling error. However, biological processes such as biparental inheritance and inter-plastome recombination have been reported and may be responsible for the observed intragenomic incongruence. Mitochondrial insertions into the plastome are rarely documented in angiosperms. Our results indicate that a mitochondrial insertion event in the plastid trnS GGA - rps4 IGS region occurred in the common ancestor of the Pacific clade of Anthospermeae. Exclusion/inclusion of this locus in phylogenetic analyses had a strong impact on topological results in the Pacific clade.

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.

Ciliary transition zone evolution and the root of the eukaryote tree: implications for opisthokont origin and classification of kingdoms Protozoa, Plantae, and Fungi

I thoroughly discuss ciliary transition zone (TZ) evolution, highlighting many overlooked evolutionarily significant ultrastructural details. I establish fundamental principles of TZ ultrastructure and evolution throughout eukaryotes, inferring unrecognised ancestral TZ patterns for Fungi, opisthokonts, and Corticata (i.e., kingdoms Plantae and Chromista). Typical TZs have a dense transitional plate (TP), with a previously overlooked complex lattice as skeleton. I show most eukaryotes have centriole/TZ junction acorn-V filaments (whose ancestral function was arguably supporting central pair microtubule-nucleating sites; I discuss their role in centriole growth). Uniquely simple malawimonad TZs (without TP, simpler acorn) pinpoint the eukaryote tree's root between them and TP-bearers, highlighting novel superclades. I integrate TZ/ciliary evolution with the best multiprotein trees, naming newly recognised major eukaryote clades and revise megaclassification of basal kingdom Protozoa. Recent discovery of non-photosynthetic phagotrophic flagellates with genome-free plastids (Rhodelphis), the sister group to phylum Rhodophyta (red algae), illuminates plant and chromist early evolution. I show previously overlooked marked similarities in cell ultrastructure between Rhodelphis and Picomonas, formerly considered an early diverging chromist. In both a nonagonal tube lies between their TP and an annular septum surrounding their 9+2 ciliary axoneme. Mitochondrial dense condensations and mitochondrion-linked smooth endomembrane cytoplasmic partitioning cisternae further support grouping Picomonadea and Rhodelphea as new plant phylum Pararhoda. As Pararhoda/Rhodophyta form a robust clade on site-heterogeneous multiprotein trees, I group Pararhoda and Rhodophyta as new infrakingdom Rhodaria of Plantae within subkingdom Biliphyta, which also includes Glaucophyta with fundamentally similar TZ, uniquely in eukaryotes. I explain how biliphyte TZs generated viridiplant stellate-structures.

Conflict over the eukaryote root resides in strong outliers, mosaics and missing data sensitivity of site-specific (CAT) mixture models

Phylogenetic reconstruction using concatenated loci ("phylogenomics" or "supermatrix phylogeny") is a powerful tool for solving evolutionary splits that are poorly resolved in single gene/protein trees (SGTs). However, recent phylogenomic attempts to resolve the eukaryote root have yielded conflicting results, along with claims of various artefacts hidden in the data. We have investigated these conflicts using two new methods for assessing phylogenetic conflict. ConJak uses whole marker (gene or protein) jackknifing to assess deviation from a central mean for each individual sequence, while ConWin uses a sliding window to screen for incongruent protein fragments (mosaics). Both methods allow selective masking of individual sequences or sequence fragments in order to minimize missing data, an important consideration for resolving deep splits with limited data. Analyses focused on a set of 76 eukaryotic proteins of bacterial-ancestry previously used in various combinations to assess the branching order among the three major divisions of eukaryotes: Amorphea (mainly animals, fungi and Amoebozoa), Diaphoretickes (most other well-known eukaryotes and nearly all algae) and Excavata, represented here by Discoba (Jakobida, Heterolobosea, and Euglenozoa). ConJak analyses found strong outliers to be concentrated in under-sampled lineages, while ConWin analyses of Discoba, the most under-sampled of the major lineages, detected potentially incongruent fragments scattered throughout. Phylogenetic analyses of the full data using an LG-gamma model support a Discoba sister scenario (neozoan-excavate root), which rises to 99-100% bootstrap support with data masked according to either protocol. However, analyses with two site-specific (CAT) mixture models yielded widely inconsistent results and a striking sensitivity to missing data. The neozoan-excavate root places Amorphea and Diaphoretickes as more closely related to each other than either is to Discoba, a fundamental relationship that should remain unaffected by additional taxa.

Supergene origin and maintenance in Atlantic cod

Supergenes are sets of genes that are inherited as a single marker and encode complex phenotypes through their joint action. They are identified in an increasing number of organisms, yet their origins and evolution remain enigmatic. In Atlantic cod, four megabase-scale supergenes have been identified and linked to migratory lifestyle and environmental adaptations. Here we investigate the origin and maintenance of these four supergenes through analysis of whole-genome-sequencing data, including a new long-read-based genome assembly for a non-migratory Atlantic cod individual. We corroborate the finding that chromosomal inversions underlie all four supergenes, and we show that they originated at different times between 0.40 and 1.66 million years ago. We reveal gene flux between supergene haplotypes where migratory and stationary Atlantic cod co-occur and conclude that this gene flux is driven by gene conversion, on the basis of an increase in GC content in exchanged sites. Additionally, we find evidence for double crossover between supergene haplotypes, leading to the exchange of an ~275 kilobase fragment with genes potentially involved in adaptation to low salinity in the Baltic Sea. Our results suggest that supergenes can be maintained over long timescales in the same way as hybridizing species, through the selective purging of introduced genetic variation.

Atlantic cod carries four supergenes linked to migratory lifestyle and environmental adaptations. Using whole-genome sequencing, the authors show that the genome inversions that underlie the supergenes originated at different times and show gene flux between supergene haplotypes.

Derived woodiness and annual habit evolved in African umbellifers as alternative solutions for coping with drought

BACKGROUND

One of the major trends in angiosperm evolution was the shift from woody to herbaceous habit. However, reversals known as derived woodiness have also been reported in numerous, distantly related clades. Among theories evoked to explain the factors promoting the evolution of derived woodiness are moderate climate theory and cavitation theory. The first assumes that woody habit evolves in response to mild climate allowing for prolonged life span, which in turn leads to bigger and woodier bodies. The second sees woodiness as a result of natural selection for higher cavitation resistance in seasonally dry environments. Here, we compare climatic niches of woody and herbaceous, mostly southern African, umbellifers from the Lefebvrea clade to assess whether woody taxa in fact occur in markedly drier habitats. We also calibrate their phylogeny to estimate when derived woodiness evolved. Finally, we describe the wood anatomy of selected woody and herbaceous taxa to see if life forms are linked to any particular wood traits.

RESULTS

The evolution of derived woodiness in chamaephytes and phanerophytes as well as the shifts to short-lived annual therophytes in the Lefebvrea clade took place at roughly the same time: in the Late Miocene during a trend of global climate aridification. Climatic niches of woody and herbaceous genera from the Cape Floristic Region overlap. There are only two genera with distinctly different climatic preferences: they are herbaceous and occur outside of the Cape Floristic Region. Therefore, studied herbs have an overall climatic niche wider than their woody cousins. Woody and herbaceous species do not differ in qualitative wood anatomy, which is more affected by stem architecture and, probably, reproductive strategy than by habit.

CONCLUSIONS

Palaeodrought was likely a stimulus for the evolution of derived woodiness in the Lefebvrea clade, supporting the cavitation theory. The concurrent evolution of short-lived annuals withering before summer exemplifies an alternative solution to the same problem of drought-induced cavitation. Changes of the life form were most likely neither spurred nor precluded by any qualitative wood traits, which in turn are more affected by internode length and probably also reproductive strategy.

An efficient, non-phylogenetic method for detecting genes sharing evolutionary signals in phylogenomic datasets

Assessing the compatibility between gene family phylogenies is a crucial and often computationally demanding step in many phylogenomic analyses. Here, we describe the Evolutionary Similarity Index (IES), a means to assess shared evolution between gene families using a weighted orthogonal distance regression model applied to sequence distances. The utilization of pairwise distance matrices circumvents comparisons between gene tree topologies, which are inherently uncertain and sensitive to evolutionary model choice, phylogenetic reconstruction artifacts, and other sources of error. Furthermore, IES enables the many-to-many pairing of multiple copies between similarly evolving gene families. This is done by selecting non-overlapping pairs of copies, one from each assessed family, and yielding the least sum of squared residuals. Analyses of simulated gene family data sets show that IES’s accuracy is on par with popular tree-based methods while also less susceptible to noise introduced by sequence alignment and evolutionary model fitting. Applying IES to an empirical data set of 1,322 genes from 42 archaeal genomes identified eight major clusters of gene families with compatible evolutionary trends. The most cohesive cluster consisted of 62 genes with compatible evolutionary signal, which occur as both single-copy and multiple homologs per genome; phylogenetic analysis of concatenated alignments from this cluster produced a tree closely matching previously published species trees for Archaea. Four other clusters are mainly composed of accessory genes with limited distribution among Archaea and enriched toward specific metabolic functions. Pairwise evolutionary distances obtained from these accessory gene clusters suggest patterns of interphyla horizontal gene transfer. An IES implementation is available at https://github.com/lthiberiol/evolSimIndex.

PhyloWGA: chromosome-aware phylogenetic interrogation of whole genome alignments

SUMMARY

Here, we present PhyloWGA, an open source R package for conducting phylogenetic analysis and investigation of whole genome data.

AVAILABILITYAND IMPLEMENTATION

Available at Github (https://github.com/radamsRHA/PhyloWGA).

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Significance of incongruent DNA loci in the taxonomy of wood-decaying Basidioradulum radula

Modern taxonomic studies of Agaricomycetes rely on the integrative analyses of morphology, environmental data, geographic distribution, and usually several DNA loci. However, sampling and selection of DNA loci for the analyses are commonly shallow. In this study, we suggest minimal numbers of necessary specimens to sample and DNA loci to analyze in order to prevent inadequate taxonomic decisions in species groups with minor morphological and genealogical differences. We sampled four unlinked nuclear DNA gene regions (nuc rDNA ITS1-5.8S-ITS2, gh63, rpb2, and tef1) to revise the systematics of a common wood-decaying species Basidioradulum radula (Hymenochaetales) on an intercontinental set of specimens collected in the Northern Hemisphere. The DNA loci analyzed violate the genealogical concordance phylogenetic species recognition principles, thus confirming a single-species interpretation. We conclude that Hyphodontia syringae is a younger synonym of B. radula.

cognac: rapid generation of concatenated gene alignments for phylogenetic inference from large, bacterial whole genome sequencing datasets

Background

The quantity of genomic data is expanding at an increasing rate. Tools for phylogenetic analysis which scale to the quantity of available data are required. To address this need, we present cognac, a user-friendly software package to rapidly generate concatenated gene alignments for phylogenetic analysis.

Results

We illustrate that cognac is able to rapidly identify phylogenetic marker genes using a data driven approach and efficiently generate concatenated gene alignments for very large genomic datasets. To benchmark our tool, we generated core gene alignments for eight unique genera of bacteria, including a dataset of over 11,000 genomes from the genus Escherichia producing an alignment with 1353 genes, which was constructed in less than 17 h.

Conclusions

We demonstrate that cognac presents an efficient method for generating concatenated gene alignments for phylogenetic analysis. We have released cognac as an R package (https://github.com/rdcrawford/cognac) with customizable parameters for adaptation to diverse applications.

The genomic timeline of cichlid fish diversification across continents

Cichlid fishes are celebrated for their vast taxonomic, phenotypic, and ecological diversity; however, a central aspect of their evolution - the timeline of their diversification - remains contentious. Here, we generate draft genome assemblies of 14 species representing the global cichlid diversity and integrate these into a new phylogenomic hypothesis of cichlid and teleost evolution that we time-calibrate with 58 re-evaluated fossil constraints and a new Bayesian model accounting for fossil-assignment uncertainty. Our results support cichlid diversification long after the breakup of the supercontinent Gondwana and lay the foundation for precise temporal reconstructions of the exceptional continental cichlid adaptive radiations.

Total evidence or taxonomic congruence? A comparison of methods for combining biological evidence

Phylogenetic inference proposes an evolutionary hypothesis for a group of taxa which is usually represented as a phylogenetic tree. The use of several distinct biological evidence has shown to produce more resolved phylogenies than single evidence approaches. Currently, two conflicting paradigms are applied to combine biological evidence: taxonomic congruence (TC) and total evidence (TE). Although the literature recommends the application of these paradigms depending on the congruence of the input data, the resultant evolutionary hypotheses could vary according to the strategy used to combine the biological evidence biasing the resultant topologies of the trees. In this work, we evaluate the ability of different strategies associated with both paradigms to produce integrated evolutionary hypotheses by considering different features of the data: missing biological evidence, diversity among sequences, complexity, and congruence. Using datasets from the literature, we compare the resultant trees with reference hypotheses obtained by applying two inference criteria: maximum parsimony and likelihood. The results show that methods associated with TE paradigm are more robust compared to TC methods, obtaining trees with more similar topologies in relation to reference trees. These results are obtained regardless of (1) the features of the data, (2) the estimated evolutionary rates, and (3) the criteria used to infer the reference evolutionary hypotheses.

Parallel evolution of arborescent carrots (Daucus) in Macaronesia

PREMISE

Despite intensive research, the pathways and driving forces behind the evolution of derived woodiness on oceanic islands remain obscure. The genus Daucus comprises mostly herbs (therophytes, hemicryptophytes) with few rosette treelets (chamaephytes) endemic to various Macaronesian archipelagos, suggesting their independent evolution. To elucidate the evolutionary pathways to derived woodiness, we examined phylogenetic relationships and the habit and secondary xylem evolution in Daucus and related taxa.

METHODS

Sixty taxa were surveyed for molecular markers, life history, and habit traits. Twenty-one species were considered for wood anatomical characters. A dated phylogeny was estimated using Bayesian methods. The evolution of selected traits was reconstructed using parsimony and maximum likelihood.

RESULTS

Daucus dispersed independently to the Canary Islands (and subsequently to Madeira), Cape Verde, and the Azores in the late Miocene and Pleistocene. Life span, reproductive strategy, and life form were highly homoplastic; the ancestor of Daucus was probably a monocarpic, biennial hemicryptophyte. Rosette treelets evolved independently in the Canarian-Madeiran lineage and in Cape Verde, the latter within the last 0.13 Myr. Treelets and hemicryptophytes did not differ in wood anatomy. Pervasive axial parenchyma in wood occurred more often in polycarpic rather than monocarpic species.

CONCLUSIONS

Life span and life form in Daucus are evolutionarily labile and may change independently of wood anatomy, which is related to plant reproductive strategy rather than to life form. Insular woodiness may evolve rapidly (as demonstrated in D. bischoffii), and in Daucus, it does not seem to be an adaptation to lower the risk of xylem embolism.

PhyloToL: A Taxon/Gene-Rich Phylogenomic Pipeline to Explore Genome Evolution of Diverse Eukaryotes

Estimating multiple sequence alignments (MSAs) and inferring phylogenies are essential for many aspects of comparative biology. Yet, many bioinformatics tools for such analyses have focused on specific clades, with greatest attention paid to plants, animals, and fungi. The rapid increase in high-throughput sequencing (HTS) data from diverse lineages now provides opportunities to estimate evolutionary relationships and gene family evolution across the eukaryotic tree of life. At the same time, these types of data are known to be error-prone (e.g., substitutions, contamination). To address these opportunities and challenges, we have refined a phylogenomic pipeline, now named PhyloToL, to allow easy incorporation of data from HTS studies, to automate production of both MSAs and gene trees, and to identify and remove contaminants. PhyloToL is designed for phylogenomic analyses of diverse lineages across the tree of life (i.e., at scales of >100 My). We demonstrate the power of PhyloToL by assessing stop codon usage in Ciliophora, identifying contamination in a taxon- and gene-rich database and exploring the evolutionary history of chromosomes in the kinetoplastid parasite Trypanosoma brucei, the causative agent of African sleeping sickness. Benchmarking PhyloToL’s homology assessment against that of OrthoMCL and a published paper on superfamilies of bacterial and eukaryotic organellar outer membrane pore-forming proteins demonstrates the power of our approach for determining gene family membership and inferring gene trees. PhyloToL is highly flexible and allows users to easily explore HTS data, test hypotheses about phylogeny and gene family evolution and combine outputs with third-party tools (e.g., PhyloChromoMap, iGTP).

Assessing Combinability of Phylogenomic Data Using Bayes Factors

With the rapid reduction in sequencing costs of high-throughput genomic data, it has become commonplace to use hundreds of genes to infer phylogeny of any study system. While sampling a large number of genes has given us a tremendous opportunity to uncover previously unknown relationships and improve phylogenetic resolution, it also presents us with new challenges when the phylogenetic signal is confused by differences in the evolutionary histories of sampled genes. Given the incorporation of accurate marginal likelihood estimation methods into popular Bayesian software programs, it is natural to consider using the Bayes Factor (BF) to compare different partition models in which genes within any given partition subset share both tree topology and edge lengths. We explore using marginal likelihood to assess data subset combinability when data subsets have varying levels of phylogenetic discordance due to deep coalescence events among genes (simulated within a species tree), and compare the results with our recently described phylogenetic informational dissonance index (D) estimated for each data set. BF effectively detects phylogenetic incongruence and provides a way to assess the statistical significance of D values. We use BFs to assess data combinability using an empirical data set comprising 56 plastid genes from the green algal order Volvocales. We also discuss the potential need for calibrating BFs and demonstrate that BFs used in this study are correctly calibrated.

Polyploidy promotes species diversification of Allium through ecological shifts

Despite the role of polyploidy in multiple evolutionary processes, its impact on plant diversification remains controversial. An increased polyploid frequency may facilitate speciation through shifts in ecology, morphology or both. Here we used Allium to evaluate: (1) the relationship between intraspecific polyploid frequency and species diversification rate; and (2) whether this process is associated with habitat and/or trait shifts. Using eight plastid and nuclear ribosomal markers, we built a phylogeny of 448 Allium species, representing 46% of the total. We quantified intraspecific ploidy diversity, heterogeneity in diversification rates and their relationship along the phylogeny using trait-dependent diversification models. Finally, we evaluated the association between polyploidisation and habitat or trait shifts. We detected high ploidy diversity in Allium and a polyploidy-related diversification rate shift with a probability of 95% in East Asia. Allium lineages with high polyploid frequencies had higher species diversification rates than those of diploids or lineages with lower polyploid frequencies. Shifts in speciation rates were strongly correlated with habitat shifts linked to particular soil conditions; 81.7% of edaphic variation could be explained by polyploidisation. Our study emphasises the role of intraspecific polyploid frequency combined with ecological drivers on Allium diversification, which may explain plant radiations more generally.

Phylogenetic Conflicts, Combinability, and Deep Phylogenomics in Plants

Studies have demonstrated that pervasive gene tree conflict underlies several important phylogenetic relationships where different species tree methods produce conflicting results. Here, we present a means of dissecting the phylogenetic signal for alternative resolutions within a data set in order to resolve recalcitrant relationships and, importantly, identify what the data set is unable to resolve. These procedures extend upon methods for isolating conflict and concordance involving specific candidate relationships and can be used to identify systematic error and disambiguate sources of conflict among species tree inference methods. We demonstrate these on a large phylogenomic plant data set. Our results support the placement of Amborella as sister to the remaining extant angiosperms, Gnetales as sister to pines, and the monophyly of extant gymnosperms. Several other contentious relationships, including the resolution of relationships within the bryophytes and the eudicots, remain uncertain given the low number of supporting gene trees. To address whether concatenation of filtered genes amplified phylogenetic signal for relationships, we implemented a combinatorial heuristic to test combinability of genes. We found that nested conflicts limited the ability of data filtering methods to fully ameliorate conflicting signal amongst gene trees. These analyses confirmed that the underlying conflicting signal does not support broad concatenation of genes. Our approach provides a means of dissecting a specific data set to address deep phylogenetic relationships while also identifying the inferential boundaries of the data set. [Angiosperms; coalescent; gene-tree conflict; genomics; phylogenetics; phylogenomics.]

Phylogeny of certain members of Hyrcanus group (Diptera: Culicidae) in China based on mitochondrial genome fragments

Background

Species of the Anopheles hyrcanus group are widely distributed in Palearctic and Oriental regions and some of them are important malaria vectors. The cryptic species of An. hyrcanus group was almost impossible to identify based only on their morphology. The phylogenetic relationship of An. hyrcanus group was also not clear.

Methods

Five members of An. hyrcanus group were identified by rDNA ITS2 sequencing as An. yatsushiroensis, An. belenrae, An. kleini, An. lesteri and An. sineroides. The mitochondrial genome fragments were sequenced and annotated using the mitochondrial genome of An. sinensis as reference. Based on the four segments and Joint Data sequences of these species, and other four anopheline species downloaded from GenBank, intraspecific as well as interspecific genetic distances were calculated and the phylogenetic trees were reconstructed by the methods of neighbor joining, maximum parsimony, minimum evolution and maximum likelihood.

Findings

Four parts of mitochondrial genomes, which were partial fragments COI + tRNA + COII (F5), ATP6 + COIII(F7 + F8), ND1(F19) and lrRNA (F21), were obtained. All fragments were connected as one sequence (referred as Joint Data), which had a total length of 3393 bp. All fragment sequences were highly conservative within species, with the maximum p distance (0.026) calculated by F19 of An. belenrae. The pairwise interspecific p distance calculated by each fragment showed minor or even no difference among An. sinensis, An. kleini and An. belenrae. However, interspecific p distances calculated by the Joint Data sequence ranged from 0.004 (An. belenrae vs An. kleini) to 0.089 (An. sineroides vs An. minimus), and the p distances of the six members of An. hyrcanus group were all less than 0.029. The phylogenetic tree showed two major clades: all subgenus Anopheles species (including six members of An. hyrcanus group, An. atroparvus and An. quadrimaculatus A) and subgenus Cellia (including An. dirus and An. minimus). The An. hyrcanus group was divided into two clusters as ((An. lesteri, An. sineroides) An. yatsushiroensis) and ((An. belenrae, An. sinensis) An. kleini)).

Conclusions

The An. hyrcanus group in this study could be divided into two clusters, in one of which An. belenrae, An. sinensis and An. kleini were most closely related. More molecular markers would make greater contribution to phylogenetic analysis.

Identification and assessment of variable single-copy orthologous (SCO) nuclear loci for low-level phylogenomics: a case study in the genus Rosa (Rosaceae)

BACKGROUND

With an ever-growing number of published genomes, many low levels of the Tree of Life now contain several species with enough molecular data to perform shallow-scale phylogenomic studies. Moving away from using just a few universal phylogenetic markers, we can now target thousands of other loci to decipher taxa relationships. Making the best possible selection of informative sequences regarding the taxa studied has emerged as a new issue. Here, we developed a general procedure to mine genomic data, looking for orthologous single-copy loci capable of deciphering phylogenetic relationships below the generic rank. To develop our strategy, we chose the genus Rosa, a rapid-evolving lineage of the Rosaceae family in which several species genomes have recently been sequenced. We also compared our loci to conventional plastid markers, commonly used for phylogenetic inference in this genus.

RESULTS

We generated 1856 sequence tags in putative single-copy orthologous nuclear loci. Associated in silico primer pairs can potentially amplify fragments able to resolve a wide range of speciation events within the genus Rosa. Analysis of parsimony-informative site content showed the value of non-coding genomic regions to obtain variable sequences despite the fact that they may be more difficult to target in less related species. Dozens of nuclear loci outperform the conventional plastid phylogenetic markers in terms of phylogenetic informativeness, for both recent and ancient evolutionary divergences. However, conflicting phylogenetic signals were found between nuclear gene tree topologies and the species-tree topology, shedding light on the many patterns of hybridization and/or incomplete lineage sorting that occur in the genus Rosa.

CONCLUSIONS

With recently published genome sequence data, we developed a set of single-copy orthologous nuclear loci to resolve species-level phylogenomics in the genus Rosa. This genome-wide scale dataset contains hundreds of highly variable loci which phylogenetic interest was assessed in terms of phylogenetic informativeness and topological conflict. Our target identification procedure can easily be reproduced to identify new highly informative loci for other taxonomic groups and ranks.

Supergene validation: A model-based protocol for assessing the accuracy of non-model-based supergene methods

Genome-scale species tree inference is largely restricted to heuristic approaches that use estimated gene trees to reconstruct species-level relationships. Central to these heuristic species tree methods is the assumption that the gene trees are estimated without error. To increase the accuracy of input gene trees used to infer species trees, several techniques have recently been developed for constructing longer “supergenes” that represent sets of loci inferred to share the same genealogical history. While these supergene methods are designed to increase the amount of data for gene tree estimation by concatenating several loci into “supergenes” to increase gene tree accuracy, no formal protocols have been proposed to validate this key “supergene” concatenation step. In a recent study, we developed several supergene validation strategies for assessing the accuracy of a popular supergene method: the so-called “statistical binning” pipeline. In this article, we describe a more generalizable and model-based “supergene validation” protocol for assessing the accuracy of supergenes and supergene methods using model-based tests of phylogenetic congruency.

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Supergenes are validated by adopting model-based tests of topological congruence

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These model-based procedures out preform non-model based methods for supergene construction

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The results of this protocol can be used to assess the overall performance of a supergene method across a phylogenomic dataset

Intraspecific phylogeny of Anopheles (Kerteszia) neivai Howard, Dyar & Knab 1913, based on mitochondrial and nuclear ribosomal genes

Three mitochondrial regions and a fragment of a large nuclear ribosomal subunit was used to study the evolutionary patterns of An. neivai, a mosquito inhabiting mangroves and tropical forest in the lowland and coastal areas of the Yucatan Peninsula through the Pacific Ecuadorian coast. This species exhibits epidemiological importance regarding Malaria transmission in natural ecosystems, particularly in rural areas of the Pacific Colombian coast. The results based on phylogenetic networks and Bayesian inference showed no robust evidence supporting the existence of previously suggested cryptic species. Diversification patterns in geographically widespread species such as this one, are complex and therefore could impact malaria control strategies. Further studies focused on behavior, morphology, and phylogenomics will improve the understanding of the evolutionary patterns within An. neivai and its role as a disease vector.

OneTwoTree: An online tool for phylogeny reconstruction

Phylogeny reconstruction is a key instrument in numerous biological analyses, ranging from evolutionary and ecology research, to conservation and systems biology. The increasing accumulation of genomic data makes it possible to reconstruct phylogenies with both high accuracy and at increasingly finer resolution. Yet, taking advantage of the enormous amount of sequence data available requires the use of computational tools for efficient data retrieval and processing, or else the process could quickly become an error-prone endeavour. Here, we present OneTwoTree (http://onetwotree.tau.ac.il/), a Web-based tool for tree reconstruction based on the supermatrix paradigm. Given a list of taxa names of interest as the sole input requirement, OneTwoTree retrieves all available sequence data from NCBI GenBank, clusters these into orthology groups, identifies the most informative set of markers, searches for an appropriate outgroup, and assembles a partitioned sequence matrix that is then used for the final phylogeny reconstruction step. OneTwoTree further allows users to control various steps of the process, such as the merging of sequences from similar clusters, or phylogeny reconstruction based on markers from a specific genome type. By comparing the performance of OneTwoTree to a manually reconstructed phylogeny of the Antirrhineae tribe, we show that the use of OneTwoTree resulted in substantially higher data coverage in terms of both taxon sampling and the number of informative markers assembled. OneTwoTree provides a flexible online tool for species-tree reconstruction, aimed to assist researchers ranging in their level of prior expertise in the task of phylogeny reconstruction.

Phylogeny and biogeography of the pantropical genus Zanthoxylum and its closest relatives in the proto-Rutaceae group (Rutaceae)

Zanthoxylum L. (prickly ash) is the only genus in the Citrus L. family (Rutaceae) with a pantropical distribution. We present the first detailed phylogenetic and biogeographic study of the genus and its close relatives in the proto-Rutaceae group. Our phylogenetic analyses based on two plastid and two nuclear markers show that the genus Toddalia Juss. is nested within Zanthoxylum, that earlier generic and intrageneric classifications need revision, and that the homochlamydeous flowers of the temperate species of Zanthoxylum are the result of a reduction from heterochlamydeous flowers. The biogeographic analyses reveal a Eurasian origin of Zanthoxylum in the Paleocene or Eocene with successive intercontinental or long-range migrations. Zanthoxylum likely crossed the North Atlantic Land Bridges to colonize the Americas in the Eocene, and migrated back to the Old World probably via the Bering Land Bridge in the Oligocene or Miocene. Zanthoxylum also colonized several Pacific Islands and the Hawaiian clade shows phylogenetic incongruence between the plastid and nuclear datasets, suggesting hybridization. The Hawaiian species are one of the rare examples of endemic Hawaiian lineages that are older than the current main islands.

Missing data, clade support and "reticulation": the molecular systematics of Heliconius and related genera (Lepidoptera: Nymphalidae) re-examined

Kozak et al. (2015, Syst. Biol., 64: 505) portrayed the inference of evolutionary history among Heliconius and allied butterfly genera as a particularly difficult problem for systematics due to prevalent gene conflict caused by interspecific reticulation. To control for this, Kozak et al. conducted a series of multispecies coalescent phylogenetic analyses that they claimed revealed pervasive conflict among markers, but ultimately chose as their preferred hypothesis a phylogenetic tree generated by the traditional supermatrix approach. Intrigued by this seemingly contradictory set of conclusions, we conducted further analyses focusing on two prevalent aspects of the data set: missing data and the uneven contribution of phylogenetic signal among markers. Here, we demonstrate that Kozak et al. overstated their findings of reticulation and that evidence of gene-tree conflict is largely lacking. The distribution of intrinsic homoplasy and incongruence homoplasy in their data set does not follow the pattern expected if phylogenetic history had been obscured by pervasive horizontal gene flow; in fact, noise within individual gene partitions is ten times higher than the incongruence among gene partitions. We show that the patterns explained by Kozak et al. as a result of reticulation can be accounted for by missing data and homoplasy. We also find that although the preferred topology is resilient to missing data, measures of support are sensitive to, and strongly eroded by too many empty cells in the data matrix. Perhaps more importantly, we show that when some taxa are missing almost all characters, adding more genes to the data set provides little or no increase in support for the tree.

Genotypic and Lipid Analyses of Strains From the Archaeal Genus Halorubrum Reveal Insights Into Their Taxonomy, Divergence, and Population Structure

To gain a better understanding of how divergence occurs, and how taxonomy can benefit from studying natural populations, we isolated and examined 25 closely related Halorubrum strains obtained from different hypersaline communities and compared them to validly named species and other reference strains using five taxonomic study approaches: phylogenetic analysis using the 16S rRNA gene and multilocus sequencing analysis (MLSA), polar lipid profiles (PLP), average nucleotide identity (ANI) and DNA-DNA hybridization (DDH). 16S rRNA gene sequence could not differentiate the newly isolated strains from described species, while MLSA grouped strains into three major clusters. Two of those MLSA clusters distinguished candidates for new species. The third cluster with concatenated sequence identity equal to or greater than 97.5% was comprised of strains from Aran-Bidgol Lake (Iran) and solar salterns in Namibia and Spain, and two previously described species isolated from Mexico and Algeria. PLP and DDH analyses showed that Aran-Bidgol strains formed uniform populations, and that strains isolated from other geographic locations were heterogeneous and divergent, indicating that they may constitute different species. Therefore, applying only sequencing approaches and similarity cutoffs for circumscribing species may be too conservative, lumping concealed diversity into a single taxon. Further, our data support the interpretation that local populations experience unique evolutionary homogenization pressures, and once relieved of insular constraints (e.g., through migration) are free to diverge.

From cacti to carnivores: Improved phylotranscriptomic sampling and hierarchical homology inference provide further insight into the evolution of Caryophyllales

PREMISE OF THE STUDY

The Caryophyllales contain ~12,500 species and are known for their cosmopolitan distribution, convergence of trait evolution, and extreme adaptations. Some relationships within the Caryophyllales, like those of many large plant clades, remain unclear, and phylogenetic studies often recover alternative hypotheses. We explore the utility of broad and dense transcriptome sampling across the order for resolving evolutionary relationships in Caryophyllales.

METHODS

We generated 84 transcriptomes and combined these with 224 publicly available transcriptomes to perform a phylogenomic analysis of Caryophyllales. To overcome the computational challenge of ortholog detection in such a large data set, we developed an approach for clustering gene families that allowed us to analyze >300 transcriptomes and genomes. We then inferred the species relationships using multiple methods and performed gene-tree conflict analyses.

KEY RESULTS

Our phylogenetic analyses resolved many clades with strong support, but also showed significant gene-tree discordance. This discordance is not only a common feature of phylogenomic studies, but also represents an opportunity to understand processes that have structured phylogenies. We also found taxon sampling influences species-tree inference, highlighting the importance of more focused studies with additional taxon sampling.

CONCLUSIONS

Transcriptomes are useful both for species-tree inference and for uncovering evolutionary complexity within lineages. Through analyses of gene-tree conflict and multiple methods of species-tree inference, we demonstrate that phylogenomic data can provide unparalleled insight into the evolutionary history of Caryophyllales. We also discuss a method for overcoming computational challenges associated with homolog clustering in large data sets.

The Mediterranean: the cradle of Anthoxanthum (Poaceae) diploid diversity

Background and Aims

Knowledge of diploid phylogeny and ecogeography provide a foundation for understanding plant evolutionary history, diversification patterns and taxonomy. The genus Anthoxanthum (vernal grasses, Poaceae) represents a taxonomically intricate polyploid complex with large phenotypic variation and poorly resolved evolutionary relationships. The aims of the study were to reveal: (1) evolutionary lineages of the diploid taxa and their genetic differentiation; (2) the past distribution of the rediscovered 'Mediterranean diploid'; and (3) possible migration routes of diploids in the Mediterranean.

Methods

A combined approach involving sequencing of two plastid regions ( trnL-trnF and rpl32-trnL ), nrDNA ITS, rDNA FISH analyses, climatic niche characterization and spatio-temporal modelling was used.

Key Results

Among the examined diploid species, only two well-differentiated evolutionary lineages were recognized: Anthoxanthum gracile and A. alpinum . The other taxa - A. aristatum, A. ovatum, A. maderense and the 'Mediterranean diploid' - form a rather intermixed group based on the examined molecular data. In situ rDNA localization enabled identification of the ancestral Anthoxanthum karyotype, shared by A. gracile and two taxa from the crown group. For the studied taxa, ancestral location probabilities for six discrete geographical regions in the Mediterranean were proposed and likely scenarios of gradual expansion from them were suggested. Modelling past and present distributions shows that the 'Mediterranean diploid' has already been occurring in the same localities for 120 000 years.

Conclusions

Highly congruent results were obtained and dated the origin and first diversification of Anthoxanthum to the Miocene. The later divergence probably took place in the Pleistocene and started polyploid evolution within the genus. The most recent diversification event is still occurring, and incomplete lineage sorting prevents full diversification of taxa at the molecular level, despite clear separation based on climatic niches. The 'Mediterranean diploid' is hypothesized to be a possible relic of the most recent common ancestor of Anthoxanthum due to their sharing of ancestral features.

Conflicting phylogenomic signals reveal a pattern of reticulate evolution in a recent high-Andean diversification (Asteraceae: Astereae: Diplostephium)

High-throughput sequencing is helping biologists to overcome the difficulties of inferring the phylogenies of recently diverged taxa. The present study analyzes the phylogenetic signal of genomic regions with different inheritance patterns using genome skimming and ddRAD-seq in a species-rich Andean genus (Diplostephium) and its allies. We analyzed the complete nuclear ribosomal cistron, the complete chloroplast genome, a partial mitochondrial genome, and a nuclear-ddRAD matrix separately with phylogenetic methods. We applied several approaches to understand the causes of incongruence among datasets, including simulations and the detection of introgression using the D-statistic (ABBA-BABA test). We found significant incongruence among the nuclear, chloroplast, and mitochondrial phylogenies. The strong signal of hybridization found by simulations and the D-statistic among genera and inside the main clades of Diplostephium indicate reticulate evolution as a main cause of phylogenetic incongruence. Our results add evidence for a major role of reticulate evolution in events of rapid diversification. Hybridization and introgression confound chloroplast and mitochondrial phylogenies in relation to the species tree as a result of the uniparental inheritance of these genomic regions. Practical implications regarding the prevalence of hybridization are discussed in relation to the phylogenetic method.

Chimeric origins of ochrophytes and haptophytes revealed through an ancient plastid proteome

Plastids are supported by a wide range of proteins encoded within the nucleus and imported from the cytoplasm. These plastid-targeted proteins may originate from the endosymbiont, the host, or other sources entirely. Here, we identify and characterise 770 plastid-targeted proteins that are conserved across the ochrophytes, a major group of algae including diatoms, pelagophytes and kelps, that possess plastids derived from red algae. We show that the ancestral ochrophyte plastid proteome was an evolutionary chimera, with 25% of its phylogenetically tractable nucleus-encoded proteins deriving from green algae. We additionally show that functional mixing of host and plastid proteomes, such as through dual-targeting, is an ancestral feature of plastid evolution. Finally, we detect a clear phylogenetic signal from one ochrophyte subgroup, the lineage containing pelagophytes and dictyochophytes, in plastid-targeted proteins from another major algal lineage, the haptophytes. This may represent a possible serial endosymbiosis event deep in eukaryotic evolutionary history.

DOI:http://dx.doi.org/10.7554/eLife.23717.001

The cells of most plants and algae contain compartments called chloroplasts that enable them to capture energy from sunlight in a process known as photosynthesis. Chloroplasts are the remnants of photosynthetic bacteria that used to live freely in the environment until they were consumed by a larger cell. “Complex” chloroplasts can form if a cell that already has a chloroplast is swallowed by another cell.

The most abundant algae in the oceans are known as diatoms. These algae belong to a group called the stramenopiles, which also includes giant seaweeds such as kelp. The stramenopiles have a complex chloroplast that they acquired from a red alga (a relative of the seaweed used in sushi). However, some of the proteins in their chloroplasts are from other sources, such as the green algal relatives of plants, and it was not clear how these chloroplast proteins have contributed to the evolution of this group.

Many of the proteins that chloroplasts need to work properly are produced by the host cell and are then transported into the chloroplasts. Dorrell et al. studied the genetic material of many stramenopile species and identified 770 chloroplast-targeted proteins that are predicted to underpin the origins of this group. Experiments in a diatom called Phaeodactylum confirmed these predictions and show that many of these chloroplast-targeted proteins have been recruited from green algae, bacteria, and other compartments within the host cell to support the chloroplast.

Further experiments suggest that another major group of algae called the haptophytes once had a stramenopile chloroplast. The current haptophyte chloroplast does not come from the stramenopiles so the haptophytes appear to have replaced their chloroplasts at least once in their evolutionary history.

The findings show that algal chloroplasts are mosaics, supported by proteins from many different species. This helps us understand why certain species succeed in the wild and how they may respond to environmental changes in the oceans. In the future, these findings may help researchers to engineer new species of algae and plants for food and fuel production.

DOI:http://dx.doi.org/10.7554/eLife.23717.002

Clusterflock: a flocking algorithm for isolating congruent phylogenomic datasets

BACKGROUND

Collective animal behavior, such as the flocking of birds or the shoaling of fish, has inspired a class of algorithms designed to optimize distance-based clusters in various applications, including document analysis and DNA microarrays. In a flocking model, individual agents respond only to their immediate environment and move according to a few simple rules. After several iterations the agents self-organize, and clusters emerge without the need for partitional seeds. In addition to its unsupervised nature, flocking offers several computational advantages, including the potential to reduce the number of required comparisons.

FINDINGS

In the tool presented here, Clusterflock, we have implemented a flocking algorithm designed to locate groups (flocks) of orthologous gene families (OGFs) that share an evolutionary history. Pairwise distances that measure phylogenetic incongruence between OGFs guide flock formation. We tested this approach on several simulated datasets by varying the number of underlying topologies, the proportion of missing data, and evolutionary rates, and show that in datasets containing high levels of missing data and rate heterogeneity, Clusterflock outperforms other well-established clustering techniques. We also verified its utility on a known, large-scale recombination event in Staphylococcus aureus. By isolating sets of OGFs with divergent phylogenetic signals, we were able to pinpoint the recombined region without forcing a pre-determined number of groupings or defining a pre-determined incongruence threshold.

CONCLUSIONS

Clusterflock is an open-source tool that can be used to discover horizontally transferred genes, recombined areas of chromosomes, and the phylogenetic 'core' of a genome. Although we used it here in an evolutionary context, it is generalizable to any clustering problem. Users can write extensions to calculate any distance metric on the unit interval, and can use these distances to 'flock' any type of data.

Architecture of a Species: Phylogenomics of Staphylococcus aureus

A deluge of whole-genome sequencing has begun to give insights into the patterns and processes of microbial evolution, but genome sequences have accrued in a haphazard manner, with biased sampling of natural variation that is driven largely by medical and epidemiological priorities. For instance, there is a strong bias for sequencing epidemic lineages of methicillin-resistant Staphylococcus aureus (MRSA) over sensitive isolates (methicillin-sensitive S. aureus: MSSA). As more diverse genomes are sequenced the emerging picture is of a highly subdivided species with a handful of relatively clonal groups (complexes) that, at any given moment, dominate in particular geographical regions. The establishment of hegemony of particular clones appears to be a dynamic process of successive waves of replacement of the previously dominant clone. Here we review the phylogenomic structure of a diverse range of S. aureus, including both MRSA and MSSA. We consider the utility of the concept of the 'core' genome and the impact of recombination and horizontal transfer. We argue that whole-genome surveillance of S. aureus populations could lead to better forecasting of antibiotic resistance and virulence of emerging clones, and a better understanding of the elusive biological factors that determine repeated strain replacement.

Expected pairwise congruence among gene trees under the coalescent model

Although it is widely appreciated that gene trees may differ from the overall species tree and from one another due to various evolutionary processes (e.g., incomplete lineage sorting (ILS), horizontal gene transfer, etc.), the extent of this incongruence is rarely quantified and discussed. Here we consider the expected amount of incongruence arising from ILS, as modeled by the coalescent process. In particular, we compute the probability that two gene trees randomly sampled from the same species tree agree with one another as well as the distribution of the Robinson-Foulds distance between them, for species trees with three to eight taxa. We demonstrate that, as expected under the coalescent model, the amount of discordance is affected by species tree-specific factors such as speciation times and effective population sizes for the species under consideration. Our results highlight the fact that substantial discordance may occur, even when the number of species is very small, which has implications both for larger taxon samples and for any method that uses estimated gene trees as the basis for further statistical inference. The amount of incongruence is substantial enough that such methods may need to be modified to account for variability in the underlying gene trees.

Evolution of the immune system influences speciation rates in teleost fishes

Teleost fishes constitute the most species-rich vertebrate clade and exhibit extensive genetic and phenotypic variation, including diverse immune defense strategies. The genomic basis of a particularly aberrant strategy is exemplified by Atlantic cod, in which a loss of major histocompatibility complex (MHC) II functionality coincides with a marked expansion of MHC I genes. Through low-coverage genome sequencing (9-39×), assembly and comparative analyses for 66 teleost species, we show here that MHC II is missing in the entire Gadiformes lineage and thus was lost once in their common ancestor. In contrast, we find that MHC I gene expansions have occurred multiple times, both inside and outside this clade. Moreover, we identify an association between high MHC I copy number and elevated speciation rates using trait-dependent diversification models. Our results extend current understanding of the plasticity of the adaptive immune system and suggest an important role for immune-related genes in animal diversification.

A Recent Whole-Genome Duplication Divides Populations of a Globally Distributed Microsporidian

The Microsporidia are a major group of intracellular fungi and important parasites of animals including insects, fish, and immunocompromised humans. Microsporidian genomes have undergone extreme reductive evolution but there are major differences in genome size and structure within the group: some are prokaryote-like in size and organisation (<3 Mb of gene-dense sequence) while others have more typically eukaryotic genome architectures. To gain fine-scale, population-level insight into the evolutionary dynamics of these tiny eukaryotic genomes, we performed the broadest microsporidian population genomic study to date, sequencing geographically isolated strains of Spraguea, a marine microsporidian infecting goosefish worldwide. Our analysis revealed that population structure across the Atlantic Ocean is associated with a conserved difference in ploidy, with American and Canadian isolates sharing an ancestral whole genome duplication that was followed by widespread pseudogenisation and sorting-out of paralogue pairs. While past analyses have suggested de novo gene formation of microsporidian-specific genes, we found evidence for the origin of new genes from noncoding sequence since the divergence of these populations. Some of these genes experience selective constraint, suggesting the evolution of new functions and local host adaptation. Combining our data with published microsporidian genomes, we show that nucleotide composition across the phylum is shaped by a mutational bias favoring A and T nucleotides, which is opposed by an evolutionary force favoring an increase in genomic GC content. This study reveals ongoing dramatic reorganization of genome structure and the evolution of new gene functions in modern microsporidians despite extensive genomic streamlining in their common ancestor.

Assessing parallel gene histories in viral genomes

BACKGROUND

The increasing abundance of sequence data has exacerbated a long known problem: gene trees and species trees for the same terminal taxa are often incongruent. Indeed, genes within a genome have not all followed the same evolutionary path due to events such as incomplete lineage sorting, horizontal gene transfer, gene duplication and deletion, or recombination. Considering conflicts between gene trees as an obstacle, numerous methods have been developed to deal with these incongruences and to reconstruct consensus evolutionary histories of species despite the heterogeneity in the history of their genes. However, inconsistencies can also be seen as a source of information about the specific evolutionary processes that have shaped genomes.

RESULTS

The goal of the approach here proposed is to exploit this conflicting information: we have compiled eleven variables describing phylogenetic relationships and evolutionary pressures and submitted them to dimensionality reduction techniques to identify genes with similar evolutionary histories. To illustrate the applicability of the method, we have chosen two viral datasets, namely papillomaviruses and Turnip mosaic virus (TuMV) isolates, largely dissimilar in genome, evolutionary distance and biology. Our method pinpoints viral genes with common evolutionary patterns. In the case of papillomaviruses, gene clusters match well our knowledge on viral biology and life cycle, illustrating the potential of our approach. For the less known TuMV, our results trigger new hypotheses about viral evolution and gene interaction.

CONCLUSIONS

The approach here presented allows turning phylogenetic inconsistencies into evolutionary information, detecting gene assemblies with similar histories, and could be a powerful tool for comparative pathogenomics.

The effects of subsampling gene trees on coalescent methods applied to ancient divergences

Gene-tree-estimation error is a major concern for coalescent methods of phylogenetic inference. We sampled eight empirical studies of ancient lineages with diverse numbers of taxa and genes for which the original authors applied one or more coalescent methods. We found that the average pairwise congruence among gene trees varied greatly both between studies and also often within a study. We recommend that presenting plots of pairwise congruence among gene trees in a dataset be treated as a standard practice for empirical coalescent studies so that readers can readily assess the extent and distribution of incongruence among gene trees. ASTRAL-based coalescent analyses generally outperformed MP-EST and STAR with respect to both internal consistency (congruence between analyses of subsamples of genes with the complete dataset of all genes) and congruence with the concatenation-based topology. We evaluated the approach of subsampling gene trees that are, on average, more congruent with other gene trees as a method to reduce artifacts caused by gene-tree-estimation errors on coalescent analyses. We suggest that this method is well suited to testing whether gene-tree-estimation error is a primary cause of incongruence between concatenation- and coalescent-based results, to reconciling conflicting phylogenetic results based on different coalescent methods, and to identifying genes affected by artifacts that may then be targeted for reciprocal illumination. We provide scripts that automate the process of calculating pairwise gene-tree incongruence and subsampling trees while accounting for differential taxon sampling among genes. Finally, we assert that multiple tree-search replicates should be implemented as a standard practice for empirical coalescent studies that apply MP-EST.

Whole-Genome Sequencing Allows for Improved Identification of Persistent Listeria monocytogenes in Food-Associated Environments

While the food-borne pathogen Listeria monocytogenes can persist in food associated environments, there are no whole-genome sequence (WGS) based methods to differentiate persistent from sporadic strains. Whole-genome sequencing of 188 isolates from a longitudinal study of L. monocytogenes in retail delis was used to (i) apply single-nucleotide polymorphism (SNP)-based phylogenetics for subtyping of L. monocytogenes, (ii) use SNP counts to differentiate persistent from repeatedly reintroduced strains, and (iii) identify genetic determinants of L. monocytogenes persistence. WGS analysis revealed three prophage regions that explained differences between three pairs of phylogenetically similar populations with pulsed-field gel electrophoresis types that differed by ≤3 bands. WGS-SNP-based phylogenetics found that putatively persistent L. monocytogenes represent SNP patterns (i) unique to a single retail deli, supporting persistence within the deli (11 clades), (ii) unique to a single state, supporting clonal spread within a state (7 clades), or (iii) spanning multiple states (5 clades). Isolates that formed one of 11 deli-specific clades differed by a median of 10 SNPs or fewer. Isolates from 12 putative persistence events had significantly fewer SNPs (median, 2 to 22 SNPs) than between isolates of the same subtype from other delis (median up to 77 SNPs), supporting persistence of the strain. In 13 events, nearly indistinguishable isolates (0 to 1 SNP) were found across multiple delis. No individual genes were enriched among persistent isolates compared to sporadic isolates. Our data show that WGS analysis improves food-borne pathogen subtyping and identification of persistent bacterial pathogens in food associated environments.

Species Tree Inference Using a Mixture Model

Species tree reconstruction has been a subject of substantial research due to its central role across biology and medicine. A species tree is often reconstructed using a set of gene trees or by directly using sequence data. In either of these cases, one of the main confounding phenomena is the discordance between a species tree and a gene tree due to evolutionary events such as duplications and losses. Probabilistic methods can resolve the discordance by coestimating gene trees and the species tree but this approach poses a scalability problem for larger data sets. We present MixTreEM-DLRS: A two-phase approach for reconstructing a species tree in the presence of gene duplications and losses. In the first phase, MixTreEM, a novel structural expectation maximization algorithm based on a mixture model is used to reconstruct a set of candidate species trees, given sequence data for monocopy gene families from the genomes under study. In the second phase, PrIME-DLRS, a method based on the DLRS model (Åkerborg O, Sennblad B, Arvestad L, Lagergren J. 2009. Simultaneous Bayesian gene tree reconstruction and reconciliation analysis. Proc Natl Acad Sci U S A. 106(14):5714-5719), is used for selecting the best species tree. PrIME-DLRS can handle multicopy gene families since DLRS, apart from modeling sequence evolution, models gene duplication and loss using a gene evolution model (Arvestad L, Lagergren J, Sennblad B. 2009. The gene evolution model and computing its associated probabilities. J ACM. 56(2):1-44). We evaluate MixTreEM-DLRS using synthetic and biological data, and compare its performance with a recent genome-scale species tree reconstruction method PHYLDOG (Boussau B, Szöllősi GJ, Duret L, Gouy M, Tannier E, Daubin V. 2013. Genome-scale coestimation of species and gene trees. Genome Res. 23(2):323-330) as well as with a fast parsimony-based algorithm Duptree (Wehe A, Bansal MS, Burleigh JG, Eulenstein O. 2008. Duptree: a program for large-scale phylogenetic analyses using gene tree parsimony. Bioinformatics 24(13):1540-1541). Our method is competitive with PHYLDOG in terms of accuracy and runs significantly faster and our method outperforms Duptree in accuracy. The analysis constituted by MixTreEM without DLRS may also be used for selecting the target species tree, yielding a fast and yet accurate algorithm for larger data sets. MixTreEM is freely available at http://prime.scilifelab.se/mixtreem/.