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Research Article (Submitted to MBE 2005) Application of Phylogenetic Networks in Evolutionary Studies
Abstract
The evolutionary history of a set of taxa is usually represented by a phylogenetic tree, and this model has greatly facilitated the discus-sion and testing of hypotheses. However, it is well known that more complex evolutionary scenarios are poorly described by such models. Further, even when evolution proceeds in a tree-like manner, analysis of the data may not be best served by using methods that enforce a tree structure, but rather by a richer visualization of the data to evaluate its properties, at least as an essential first step. Thus, phylogenetic net-works should be employed when reticulate events such as hybridization, horizontal gene transfer, recombination, or gene duplication and-loss are believed to be involved, and, even in the absence of such events, phylogenetic networks have a useful role to play. This paper reviews the terminology used for phylogenetic networks and covers both split networks and reticulate networks, how they are defined and how they can be interpreted. Additionally, the paper outlines the beginnings of a comprehensive statistical framework for applying split network meth-ods. We show how split networks can represent confidence sets of trees and introduce a conservative statistical test for whether the conflicting signal in a network is treelike. Finally, this paper describes a new pro-gram SplitsTree4, an interactive and comprehensive tool for inferring different types of phylogenetic networks from sequences, distances and trees.
... Alignments of forward orientation pilA and downstream, inverted orientations of pilA were generated in Geneious and tested for recombination using a Phi test in SplitsTree (version 4.16.1) [61,69]. Translated pilA amino acid sequences produced from this study were aligned with pilA amino acid sequences of serogroup reference strains [25] in Geneious. ...
... Unique hemolysin gene sequences (n = 3) were tested for recombination using a Phi test in SplitsTree (version 4.16.1) [61,69]. ...
Background
Moraxella bovis and Moraxella bovoculi both associate with infectious bovine keratoconjunctivitis (IBK), an economically significant and painful ocular disease that affects cattle worldwide. There are two genotypes of M. bovoculi (genotypes 1 and 2) that differ in their gene content and potential virulence factors, although neither have been experimentally shown to cause IBK. M. bovis is a causative IBK agent, however, not all strains carry a complete assortment of known virulence factors. The goals of this study were to determine the population structure and depth of M. bovis genomic diversity, and to compare core and accessory genes and predicted outer membrane protein profiles both within and between M. bovis and M. bovoculi.
Results
Phylogenetic trees and bioinformatic analyses of 36 M. bovis chromosomes sequenced in this study and additional available chromosomes of M. bovis and both genotype 1 and 2 M. bovoculi, showed there are two genotypes (1 and 2) of M. bovis. The two M. bovis genotypes share a core of 2015 genes, with 121 and 186 genes specific to genotype 1 and 2, respectively. The two genotypes differ by their chromosome size and prophage content, encoded protein variants of the virulence factor hemolysin, and by their affiliation with different plasmids. Eight plasmid types were identified in this study, with types 1 and 6 observed in 88 and 56% of genotype 2 strains, respectively, and absent from genotype 1 strains. Only type 1 plasmids contained one or two gene copies encoding filamentous haemagglutinin-like proteins potentially involved with adhesion. A core of 1403 genes was shared between the genotype 1 and 2 strains of both M. bovis and M. bovoculi, which encoded a total of nine predicted outer membrane proteins.
Conclusions
There are two genotypes of M. bovis that differ in both chromosome content and plasmid profiles and thus may not equally associate with IBK. Immunological reagents specifically targeting select genotypes of M. bovis, or all genotypes of M. bovis and M. bovoculi together could be designed from the outer membrane proteins identified in this study.
... The ML trees were constructed using the same parameters described above. The Splits Tree analysis was performed to investigate conflicting phylogenetic signals and was performed on the ML tree alignment of the LUR using SplitsTree4 (54). The neighbor-net split network was constructed using uncorrected P character transforma tion and excluded gap sites. ...
Kaposi sarcoma (KS) is the most common cancer in people living with HIV (PLWH), particularly in sub-Saharan Africa (SSA), where Kaposi sarcoma herpesvirus (KSHV or human herpesvirus 8 [HHV-8]) is endemic. In KSHV endemic areas, the overall survival of KS patients has changed little over the past 20 years. A phylogenetic analysis of available full-length viral genomes (n = 164) identified two different virus lineages that co-circulate in KSHV endemic regions today. Their sequences differ from the GenBank reference sequence and those of common laboratory strains, which originated in the 1990s in the US and Europe. Targeted short-read sequencing accuracy was validated by PacBio-based long-read sequencing to resolve repeats. This analysis identified over 1,000 single nucleotide variants (SNV) in a new 14-member sequence collection from tumor biopsies and blood in Malawi with 127 ± 32 (median ± SD) SNV per genome. Most were private, i.e., specific to one individual’s virus. Within each of the two lineages, KSHV continues to evolve over time and across national borders by genetic drift and recombination. Analyses of shared SNVs by AlphaFold2 predicted some changes in the conformation of key viral proteins. These findings may help our understanding of herpesvirus evolution.
IMPORTANCE
To understand viruses, the field needs to know their genetic makeup. To develop mechanistic models, targeted therapies, and vaccines, we need comprehensive and up-to-date sequence information on the viral strains that circulate where the diseases appear today. Our knowledge of Kaposi sarcoma herpesvirus (KSHV) sequence distribution and evolution is behind that of other human herpesviruses and RNA viruses. Here, we add to community knowledge using new technologies and artificial intelligence.
... We visually checked alignments to ensure that insertion-deletions did not disrupt translation of coding regions. We constructed genetic networks from the separate mt and nu datasets to visualize patterns of genetic divergence using the NeighborNet algorithm implemented in SplitsTree v. 4.15.1 (Huson and Bryant 2006). ...
In recent years, hybridization has come into focus as a potent force with a myriad of evolutionary outcomes. Natural hybridization has been documented across the hylid treefrog genus Dryophytes, but few studies have demonstrated the origins of putative natural hybrids. Here, we use molecular and acoustical data to test the parentage of 2 putative D. chrysoscelis x D. femoralis hybrids found in the wild in Virginia and North Carolina. Using 1 mitochondrial and 4 nuclear loci, we demonstrate that these 2 individuals are genetically intermediate between D. chrysoscelis (Cope's Gray Treefrog) and D. femoralis (Pine Woods Treefrog), with differing maternal species. The mating calls of hybrids are consistent with those of previous studies and feature a breakdown in structure that may result from an intermediate phenotype between the unpulsed and pulsed notes of the respective parent species. While hybridization between the 2 species is apparently rare, our results combined with previous laboratory studies demonstrate the potential for introgressive hybridization, necessitating further work to identify the extent of hybridization in the system.
... In addition, to reexamine genetic recombination inferences, we also applied the SplitsTree (version 4.14.4) (Huson and Bryant 2006), and RDP4 (Beta 4.96) (Martin et al. 2015) software packages. In particular, we used the method of split decomposition method (Bandelt and Dress 1992), implemented in SplitsTree, to detect parallel nucleotide substitutions with con icting evolutionary signals in the targeted mtDNA region of the GMB haplotypes and its genetically most closely related conspeci cs. ...
An in-depth understanding of the biodiversity of Bos taurus is highly important to tackling global food security challenges partially via deciphering and preserving local breeds that demonstrate their potential to adapt to the growing global warming worldwide. In this study, we elucidate the population structures and mechanisms of evolutionary divergence of the Georgian Mountain Breed (GMB) of cow and its genetically most closely related conspecifics worldwide. We performed the sequencing and evolutionary analyses of the specific mitochondrial DNA (mtDNA) region involving cytb , two tRNAs-encoding genetic loci, and the D-loop of the GMB populations from the Khevsureti and Adjara regions of Georgia. A large panel of different evolutionary algorithms, implemented in the MEGA11 and DnaSP software packages, were applied in these analyses. A total of 25 haplotypes were determined among 82 individuals of GMB, belonging predominantly to the haplogroups T (T3, T1, T2, T4) or Q (Q1). 10 hitherto unique haplotypes, exhibited by singletons (SNGTs), could be also determined in the GMB populations from the above regions. In the maximum likelihood evolutionary analysis, a specific SNGT appeared to be most closely related to the Bos indicus sub-haplogroup I1a. The haplotype diversity (0.997), nucleotide diversity (0.00636), and the overall mean distance within their populations (0.01) were higher for GMB as compared to these estimates (0.930, 0.00482, and 0.00) calculated for its genetically most closely related conspecifics respectively. It is suggested that the evolution of the GMB populations has been driven via introgression, as well as by parallel and/or possible convergent evolution.
... 48 Phylogenetic analyses were performed using SplitsTree4 and MEGA11 software. 49,50 All sequences were aligned using ClustalW algorithm. Visualization of phylogenetic relationships between alleles for each individual loci was performed using Maximum Composite Likelihood model. ...
The major histocompatibility complex (MHC) with its class I and II genes plays a crucial role in the immune response to pathogens by presenting oligopeptide antigens to various immune response effector cells. In order to counteract the vast variability of infectious agents, MHC class I and II genes usually retain high levels of SNPs mainly concentrated in the exons encoding the antigen binding sites. The aim of the study was to reveal new variability of selected MHC genes with a special focus on MHC class I physical haplotypes. Long‐range NGS to was used to identify exon 2–exon 3 alleles in three genetically distinct horse breeds. A total of 116 allelic variants were found in the MHC class I genes Eqca‐1, Eqca‐2, Eqca‐7 and Eqca‐Ψ, 112 of which were novel. The MHC class II DRA locus was confirmed to comprise five exon 2 alleles, and no new sequences were observed. Additional variability in terms of 15 novel exon 2 alleles was identified in the DQA1 locus. Extensive overall variability across the entire MHC region was confirmed by an analysis of MHC‐linked microsatellite loci. Both diversifying and purifying selection were detected within the MHC class I and II loci analyzed.
Cryptic diversity in evolutionary radiation offers an excellent system for investigating the intricacies of evolutionary progress. Understanding the evolution of cryptic diversity is imperative for unraveling the hidden complexities of biodiversity. However, empirical evidence elucidating the mechanisms behind cryptic radiation remains limited, particularly in plants. Here, we focus on a monophyletic group of Aquilegia species mainly distributed in the mountains of Southwest China, one of the world’s biodiversity hotspots. Using whole-genome resequencing of 158 individuals from 23 natural populations, we identify three to four paraphyletic lineages within each morphological species. Our findings reveal that 39 out of 43 detected instances of introgression occurred post-lineage formation. Identifying shared genomic regions indicates that the divergence of fixed singletons in lineages from morphological species A. kansuensis and A. rockii predates lineage formation, supporting a scenario where incomplete lineage sorting of standing variation contributes to morphological parallelism. Furthermore, strong positive correlations among genomic differentiation, divergence, and introgression suggest that standing variations and introgression from non-sister lineages contribute to the rapid genetic divergence. Our study illuminates the important roles of standing variations and introgression in plant cryptic radiation, advancing our understanding of the complex mechanisms behind the evolution of biodiversity in recent radiation events.
The genus Begomovirus (family Geminiviridae) includes plant viruses that have a negative impact on the production of several economically important crops worldwide. Begomoviruses infect a wide range of non-cultivated plants, which may serve as alternative hosts or inoculum sources for epidemics in crops. In this study, we evaluated the genetic variability and population structure of Macroptilium yellow vein virus (MacYVV; Begomovirus macroptilivenae), associated with non-cultivated Macroptilium spp. in the state of Alagoas (AL), northeastern Brazil. Complete DNA-A sequences (n = 29) were obtained from symptomatic plants collected in different municipalities of AL during 2019 and 2020. Pairwise sequence comparisons indicated a low degree of genetic variability, with 93.9–100% identity to 18 previously characterized sequences. To better understand the population structuring of MacYVV in AL, the complete DNA-A data set (n = 47) was analyzed. Although the DAPC and STRUCTURE approaches yielded slightly divergent numbers of putative MacYVV subpopulations, the results are consistent with the phylogenetic relationships among MacYVV isolates, where five well-supported subgroups correlated with geographic location were observed. The low variability of the MacYVV population could be related to the small number of recombination events detected and be reflective of a long-term virus-host relationship in which the virus is very well adapted to the host.
Seagrass beds are increasingly degraded; however, their protection and restoration are still confined to localized marine areas, making it difficult to establish connectivity between differently protected and restored areas. One limiting factor is the lack of understanding of the processes and mechanisms contributing to seagrass population expansion at the ocean area scale, which is the main driver of seagrass dispersal via oceanic circulation. Coastal China. Taxon: Eelgrass (Zostera marina)Using eelgrass as a model species, we propose a strategy to resequence seagrass samples from different geographical populations, analyze the genetic structure of seagrasses by combining genomics and population evolution, construct and screen an optimal model of seagrass colonization history, calibrate the timing of colonization events, and thereby deduce the evolutionary history of seagrass populations. We constructed a three‐dimensional hydrodynamic model based on the FVCOM numerical model to clarify the seasonal changes in the surface circulation patterns of seagrasses in their natural distribution areas and to precisely locate the colonization pathways of seagrass populations by combining the history of population differentiation. This study elucidated the main proliferation pathways of the target seagrass populations and their physical driving mechanisms and provides a theoretical basis for the study of seagrass population evolution and their protection and restoration.
Background
Invasive meningococcal disease (IMD) of serogroup B is preventable by protein-based vaccines targeting one (Bivalent rLP2086 vaccine) or several variable proteins (4CMenB vaccine) at the bacterial surface. The 4CMenB was licensed in Europe in 2013 but has been recommended and reimbursed in France for infants over 2 months old since April 2022. The bivalent rLP2086 vaccine was licensed in Europe in 2017 for subjects of 10 years and older. Evaluating strain coverage and fluctuations prior to large scale vaccine use is highly informative.
Methods
We analysed invasive isolates at the French National Reference Centre for meningococci between 1975 and 2022. The 1691 recovered isolates were sequenced. We scored sex, and age groups of subjects. We also scored clonal complexes (CC) and the predicted coverage rates of the corresponding isolates using the genetic Meningococcal Antigen Typing System (gMATS) and the Meningococcal Deduced Vaccine Antigen Reactivity (MenDeVAR).
Results
The period was divided into four periods 1975–1986, 1987–1998–1999–2010 and 2011–2022. Our data clearly show significant differences in the distribution of alleles encoding the vaccine-covered antigens between these four periods. The clonal complex (CC) distribution also differed between the two periods with the disappearance of CC8 since 2011 and drastic decreases in CC11 since 1999. MenDeVar-predicted coverage fluctuated between 46.8% and 60.6% during the four periods for the 4CMenB and between 63.4% and 81.3% for rLP2086. For 4CMenB, coverage was higher using gMATS and varied between 74.5% and 85.0%. Fluctuations were also observed for all age groups.
Conclusions
IMD epidemiology is continuously changing with fluctuation in vaccine strain coverage over the 48 years prior to the routine implementation of the vaccines.
Assessing how genetic diversity is spatially structured underlies many research questions in evolutionary ecology and contributes to understanding the factors implicated in population declines and extirpations, facilitating identification of conservation priorities and decision-making. In this study, we surveyed genomic diversity using genotyping by sequencing in the six subspecies of the midwife toad Alytes obstetricans/almogavarii complex, a group of amphibians from southwestern Europe threatened by habitat loss, climate change and chytridiomycosis. We first illustrate how the structure evident in mitochondrial DNA (mtDNA) and nuclear DNA microsatellites is discordant with the respective distributions of subspecies and patterns of admixture between them. We further document a deeply-divergent mtDNA haplogroup unique to Central Spain that is not reflected by the nuclear diversity, likely corresponding to a ghost mtDNA lineage. Patterns of genetic diversity and structure differ among and within subspecies. The Pyrenean endemics A. a. almogavarii and A. a. inigoi form homogenous genetic groups with high levels of heterozygosity, while the more widespread A. o. pertinax, A. o. boscai and A. o. lusitanicus are geographically structured across the Iberian Peninsula, comprising both genetically diverse and impoverished populations. Finally, A. o. obstetricans probably persisted in a composite glacial refugium north of the Pyrenees, from which it recently expanded across Western Europe, losing much of its genetic variation. Our results should be considered in future red list assessments, management unit delimitation, and ex-situ conservation efforts, and are also relevant to study chytrid epidemiology, for which A. obstetricans has been a model organism for nearly three decades.
Ongoing efforts to improve sheep reference genome assemblies still leave many gaps and incomplete regions, resulting in a few common failures and errors in genomic studies. Here, we report a 2.85-Gb gap-free telomere-to-telomere genome of a ram (T2T-sheep1.0), including all autosomes and the X and Y chromosomes. This genome adds 220.05 Mb of previously unresolved regions and 754 new genes to the most updated reference assembly ARS-UI_Ramb_v3.0; it contains four types of repeat units (SatI, SatII, SatIII and CenY) in centromeric regions. T2T-sheep1.0 has a base accuracy of more than 99.999%, corrects several structural errors in previous reference assemblies and improves structural variant detection in repetitive sequences. Alignment of whole-genome short-read sequences of global domestic and wild sheep against T2T-sheep1.0 identifies 2,664,979 new single-nucleotide polymorphisms in previously unresolved regions, which improves the population genetic analyses and detection of selective signals for domestication (for example, ABCC4) and wool fineness (for example, FOXQ1).
The genus Camellia is widely distributed, primarily in East Asia. Camellia japonica is located at the northern limit of this genus distribution, and understanding changes in its distribution is crucial for understanding the evolution of plants in this region, as well as their relationship with geological history and climate change. Moreover, the classification of sect. Camellia in Japan has not been clarified. Therefore, this study aims to understand the evolutionary history of the Japanese sect. Camellia. The genetic population structure was analysed using SNP data and MIG‐seq. The relationship between the Japanese sect. Camellia, including the related species in China, was further inferred from the phylogeny generated by RA x ML, SplitsTree and PCA. Population genetic structure was inferred using a Bayesian clustering method (ADMIXTURE). We subsequently employed approximate Bayesian computation, which was further supported by the coalescent simulations (DIYABC, fastsimcoal and Bayesian Skyline Plots) to explore the changes in population, determining which events appropriately explain the phylogeographical signature. Ecological niche modelling was combined with genetic analyses to compare current and past distributions. The analyses consistently showed that C. japonica and C. rusticana are distinct, having diverged from each other during the Middle to Late Miocene period. Furthermore, C. japonica differentiated into four major populations (North, South, Ryukyu‐Taiwan and Continent). The Japanese sect. Camellia underwent speciation during archipelago formation, reflecting its ancient evolutionary history compared with other native Japanese plants. C. rusticana did not diverge from C. japonica in snow‐rich environments during the Quaternary period. Our results suggest that both species have been independent since ancient times and that ancestral populations of C. japonica have persisted in northern regions. Furthermore, the C. japonica population on the continent is hypothesised to have experienced a reverse‐colonisation event from southern Japan during the late Pleistocene glaciation.
In a hybrid zone between two tropical lekking birds, yellow male plumage of one species has introgressed asymmetrically replacing white plumage of another via sexual selection. Here, we present a detailed analysis of the plumage trait to uncover its physical and genetic bases and trace its evolutionary history. We determine that the carotenoid lutein underlies the yellow phenotype and describe microstructural feather features likely to enhance color appearance. These same features reduce predicted water shedding capacity of feathers, a potential liability in the tropics. Through genome-scale DNA sequencing of hybrids and each species in the genus, we identify BCO2 as the major gene responsible for the color polymorphism. The BCO2 gene tree and genome-wide allele frequency patterns suggest that carotenoid-pigmented collars initially arose in a third species and reached the hybrid zone through historical gene flow. Complex interplay between sexual selection and hybridization has thus shaped phenotypes of these species, where conspicuous sexual traits are key to male reproductive success.
It is normally supposed that populations of the same species should evolve shared mechanisms of adaptation to common stressors due to evolutionary constraint. Here, we describe a system of within-species local adaptation to coastal habitats, Brassica fruticulosa, and detail surprising strategic variability in adaptive responses to high salinity. These different adaptive responses in neighboring populations are evidenced by transcriptomes, diverse physiological outputs, and distinct genomic selective landscapes. In response to high salinity Northern Catalonian populations restrict root-to-shoot Na ⁺ transport, favoring K ⁺ uptake. Contrastingly, Central Catalonian populations accumulate Na ⁺ in leaves and compensate for the osmotic imbalance with compatible solutes such as proline. Despite contrasting responses, both metapopulations were salinity tolerant relative to all inland accessions. To characterize the genomic basis of these divergent adaptive strategies in an otherwise non-saline-tolerant species, we generate a long-read-based genome and population sequencing of 18 populations (nine inland, nine coastal) across the B. fruticulosa species range. Results of genomic and transcriptomic approaches support the physiological observations of distinct underlying mechanisms of adaptation to high salinity and reveal potential genetic targets of these two very recently evolved salinity adaptations. We therefore provide a model of within-species salinity adaptation and reveal cryptic variation in neighboring plant populations in the mechanisms of adaptation to an important natural stressor highly relevant to agriculture.
Fusobacteria have been associated to different diseases, including colorectal cancer (CRC), but knowledge of which taxonomic groups contribute to specific conditions is incomplete. We analyzed the genetic diversity and relationships within the Fusobacterium genus. We report recent and ancestral recombination in core genes, indicating that fusobacteria have mosaic genomes and emphasizing that taxonomic demarcation should not rely on single genes/gene regions. Across databases, we found ample evidence of species miss-classification and of undescribed species, which are both expected to complicate disease association. By focusing on a lineage that includes F. periodonticum/pseudoperiodonticum and F. nucleatum, we show that genomes belong to four modern populations, but most known species/subspecies emerged from individual ancestral populations. Of these, the F. periodonticum/pseudoperiodonticum population experienced the lowest drift and displays the highest genetic diversity, in line with the less specialized distribution of these bacteria in oral sites. A highly drifted ancestral population instead contributed genetic ancestry to a new species, which includes genomes classified within the F. nucleatum animalis diversity in a recent CRC study. Thus, evidence herein calls for further evolutionary and phylogenomic analyses based on more Flavobacterium nucleatum genome sequences. More generally, our data inform future molecular profiling approaches to investigate the epidemiology of Fusobacterium-associated diseases.
Background and Aims
Biological aspects of haustorial parasitism have significant effects on the configuration of the plastid genome. Approximately half the diversity of haustorial parasites belongs to the order Santalales, where a clearer picture of plastome evolution in relation to parasitism is starting to emerge. However, in previous studies of plastome evolution there is still a notable under-representation of members from non-parasitic and deep-branching hemiparasitic lineages, limiting evolutionary inference around the time of transition to a parasitic lifestyle. To expand taxon sampling relevant to this transition we therefore targeted three families of non-parasites (Erythropalaceae, Strombosiaceae and Coulaceae), two families of root-feeding hemiparasites (Ximeniaceae and Olacaceae) and two families of uncertain parasitic status (Aptandraceae and Octoknemaceae). With data from these lineages we aimed to explore plastome evolution in relation to the evolution of parasitism.
Methods
From 29 new samples we sequenced and annotated plastomes and the nuclear ribosomal cistron. We examined phylogenetic patterns, plastome evolution, and patterns of relaxed or intensified selection in plastid genes. Available transcriptome data were analysed to investigate potential transfer of infA to the nuclear genome.
Results
Phylogenetic relationships indicate a single functional loss of all plastid ndh genes (ndhA–K) in a clade formed by confirmed parasites and Aptandraceae, and the loss coincides with major size and boundary shifts of the inverted repeat (IR) region. Depending on an autotrophic or heterotrophic lifestyle in Aptandraceae, plastome changes are either correlated with or pre-date the evolution of parasitism. Phylogenetic patterns also indicate repeated loss of infA from the plastome, and based on the presence of transcribed sequences with presequences corresponding to thylakoid luminal transit peptides, we infer that the genes were transferred to the nuclear genome.
Conclusions
Except for the loss of the ndh complex, relatively few genes have been lost from the plastome in deep-branching root parasites in Santalales. Prior to loss of the ndh genes, they show signs of relaxed selection indicative of their dispensability. To firmly establish a potential correlation between ndh gene loss, plastome instability and evolution of parasitism, it is pertinent to refute or confirm a parasitic lifestyle in all Santalales clades.
Phylogenetic inference of polyploid species is the first step towards understanding their patterns of diversification. In this paper, we review the challenges and limitations of inferring species relationships of polyploid plants using traditional phylogenetic sequencing approaches, as well as the mischaracterization of the species tree from single or multiple gene trees. We provide a roadmap to infer interspecific relationships among polyploid lineages by comparing and evaluating the application of current phylogenetic, phylogenomic, transcriptomic, and whole‐genome approaches using different sequencing platforms. For polyploid species tree reconstruction, we assess the following criteria: (1) the amount of prior information or tools required to capture the genetic region(s) of interest; (2) the probability of recovering homeologs for polyploid species; and (3) the time efficiency of downstream data analysis. Moreover, we discuss bioinformatic pipelines that can reconstruct networks of polyploid species relationships. In summary, although current phylogenomic approaches have improved our understanding of reticulate species relationships in polyploid‐rich genera, the difficulties of recovering reliable orthologous genes and sorting all homeologous copies for allopolyploids remain a challenge. In the future, assembled long‐read sequencing data will assist the recovery and identification of multiple gene copies, which can be particularly useful for reconstructing the multiple independent origins of polyploids.
This study delves into the cytogenetic, molecular, and ecological aspects of the Alstroemeria pulchra complex, emphasizing the role of prior morpho-colorimetric analyses in differentiating the infraspecific taxa of A. pulchra. The integration of advanced morpho-colorimetric analyses provided a quantitative basis for this differentiation, showcasing significant variations in flower morphology and coloration that precede and complement the cytogenetic, molecular, and ecological findings presented herein. Cytogenetic studies unveiled chromosomal disparities, and differentiated genetic clusters support the taxonomic separation of A. pulchra var. maxima from A. pulchra var. pulchra and A. pulchra subsp. lavandulacea. Additionally, updated morphometric descriptions, observations, and a differentiation key for the subspecies of A. pulchra are provided. This integrative approach not only deepens the understanding of biodiversity and adaptation in Alstroemeria but also underscores the synergy between various scientific disciplines to unravel taxonomic complexities. The obtained results pose new questions about the evolution and adaptation in related Alstroemeria species, the methodologies utilized can serve as a significant contribution to future research and conservation of this botanical genus with ornamental and ecological value.
The Han Chinese history is shaped by substantial demographic activities and sociocultural transmissions. However, it remains challenging to assess the contributions of demic and cultural diffusion to Han culture and language, primarily due to the lack of rigorous examination of genetic–linguistic congruence. Here we digitized a large-scale linguistic inventory comprising 1,018 lexical traits across 926 dialect varieties. Using phylogenetic analysis and admixture inference, we revealed a north–south gradient of lexical differences that probably resulted from historical migrations. Furthermore, we quantified extensive horizontal language transfers and pinpointed central China as a dialectal melting pot. Integrating genetic data from 30,408 Han Chinese individuals, we compared the lexical and genetic landscapes across 26 provinces. Our results support a hybrid model where demic diffusion predominantly impacts central China, while cultural diffusion and language assimilation occur in southwestern and coastal regions, respectively. This interdisciplinary study sheds light on the complex social-genetic history of the Han Chinese.
Background
The persistence of tuberculosis today and its global disparity send a powerful message that effective tuberculosis control must respond to its regional epidemiology. Active case finding through contact investigation is a standard protocol used for tuberculosis control, but its effectiveness has not been established, especially in endemic areas.
Methods
To quantify the potential effectiveness of contact investigation in Kampala, Uganda, we used a cross-sectional design to evaluate the social networks of 123 tuberculosis index cases and 124 controls without tuberculosis.
Results
Tuberculous infection was present in 515 of 989 tuberculosis case contacts (52.1%) and 396 of 1026 control contacts (38.6%; adjusted prevalence ratio, 1.4; 95% CI, 1.3–1.6). The proportion of infected participants with known exposure within the social network of the tuberculosis case was 35%. The population-attributable fraction was 11.1% for any known exposure, with 7.3% attributable to household exposure and 3.4% attributable to extrahousehold exposure.
Conclusions
This low population-attributable fraction indicates that contact tracing in the social networks of index cases will have only a modest effect in reducing tuberculous infection in a community. New approaches to community-level active case finding are needed.
Background and Aims
Polyploidy is considered one of the main mechanisms of plant evolution and speciation. In the Mediterranean Basin, polyploidy has contributed to making this region a biodiversity hotspot, along with its geological and climatic history and other ecological and biogeographical factors. The Mediterranean genus Centaurium (Gentianaceae) comprises ~25 species, of which 60 % are polyploids, including tetraploids and hexaploids. To date, the evolutionary history of centauries has been studied using Sanger sequencing phylogenies, which have been insufficient to fully understand the phylogenetic relationships in this lineage. The goal of this study is to gain a better understanding of the evolutionary history of Centaurium by exploring the mechanisms that have driven its diversification, specifically hybridization and polyploidy. We aim to identify the parentage of hybrid species, at the species or clade level, as well as assessing whether morphological traits are associated with particular ploidy levels.
Methods
We sequenced RADseq markers from 42 samples of 28 Centaurium taxa, and performed phylogenomic analyses using maximum likelihood, summary coalescent SVDquartets and Neighbor-Net approaches. To identify hybrid taxa, we used PhyloNetworks and the fastSTRUCTURE algorithm. To infer the putative parental species of the allopolyploids, we employed genomic analyses (SNIPloid). The association between different traits and particular ploidy levels was explored with non-metric multidimensional scaling.
Key Results
Our phylogenetic analyses confirmed the long-suspected occurrence of recurrent hybridization. The allopolyploid origin of the tetraploid C. serpentinicola and the hexaploids C. mairei, C. malzacianum and C. centaurioides was also confirmed, unlike that of C. discolor. We inferred additional signatures of hybridization events within the genus and identified morphological traits differentially distributed in different ploidy levels.
Conclusions
This study highlights the important role that hybridization has played in the evolution of a Mediterranean genus such as Centaurium, leading to a polyploid complex, which facilitated its diversification and may exemplify that of other Mediterranean groups.
Phylogenetic inference and reconstruction methods generate hypotheses on evolutionary history. Competing inference methods are frequently used, and the evaluation of the generated hypotheses is achieved using tree comparison costs. The Robinson-Foulds (RF) distance is a widely used cost to compare the topology of two trees, but this cost is sensitive to tree error and can overestimate tree differences. To overcome this limitation, a refined version of the RF distance called the Cluster Affinity (CA) distance was introduced. However, CA distances are symmetric and cannot compare different types of trees. These asymmetric comparisons occur when gene trees are compared with species trees, when disparate datasets are integrated into a supertree, or when tree comparison measures are used to infer a phylogenetic network. In this study, we introduce a relaxation of the original Affinity distance to compare heterogeneous trees called the asymmetric CA cost. We also develop a biologically interpretable cost, the Cluster Support cost that normalizes by cluster size across gene trees. The characteristics of these costs are similar to the symmetric CA cost. We describe efficient algorithms, derive the exact diameters, and use these to standardize the cost to be applicable in practice. These costs provide objective, fine-scale, and biologically interpretable values that can assess differences and similarities between phylogenetic trees.
Elymus sensu stricto includes tetraploid species in the tribe Triticeae with a StH genome combination derived from Hordeum (H) and Pseudoroegneria (St). The group is related to many important cereals and forage grasses and is considered an important wild genetic resource for crop breeding. The relationships within Elymus s.s. have been difficult to resolve due to the large number of widely distributed species, a high degree of morphological diversity, introgression between species, and potential multiple origins. Using genome-wide DArTseqLD data from 57 taxa, including the StH group and associated species, it is possible to gain representative information about the genetic structure of the genus. SplitsTree, STRUCTURE and principal component analysis (PCoA) show that Elymus s.s. is divided into two major clades highly correlating with geographical origin separating American species from Eurasians. These findings, together with the contribution of different Pseudoroegneria and Hordeum species to the two clades, support the conclusion that Elymus s.s. has at least two independent origins. The Eurasian and American clades are further divided into three and two subclades, respectively. The results show that Elymus species have migrated multiple times from North to South America and between America and Eurasia. The new findings could be used to develop a new classification of Elymus s.s. with sections based on phylogenetic data.
Introgression allows polyploid species to acquire new genomic content from diploid progenitors or from other unrelated diploid or polyploid lineages, contributing to genetic diversity and facilitating adaptive allele discovery. In some cases, high levels of introgression elicit the replacement of large numbers of alleles inherited from the polyploid's ancestral species, profoundly reshaping the polyploid's genomic composition. In such complex polyploids it is often difficult to determine which taxa were the progenitor species and which taxa provided additional introgressive blocks through subsequent hybridization. Here, we use population-level genomic data to reconstruct the phylogenetic history of Betula pubescens (downy birch), a tetraploid species often assumed to be of allopolyploid origin and which is known to hybridize with at least four other birch species. This was achieved by modeling of polyploidization and introgression events under the multispecies coalescent and then using an approximate Bayesian computation (ABC) rejection algorithm to evaluate and compare competing polyploidization models. We provide evidence that B. pubescens is the outcome of an autoploid genome doubling event in the common ancestor of B. pendula and its extant sister species, B. platyphylla, that took place approximately 178,000-188,000 generations ago. Extensive hybridization with B. pendula, B. nana, and B. humilis followed in the aftermath of autopolyploidization, with the relative contribution of each of these species to the B. pubescens genome varying markedly across the species' range. Functional analysis of B. pubescens loci containing alleles introgressed from B. nana identified multiple genes involved in climate adaptation, while loci containing alleles derived from B. humilis revealed several genes involved in the regulation of meiotic stability and pollen viability in plant species.
The article and supplementary files are open access and can be downloaded from:
https://bsppjournals.onlinelibrary.wiley.com/doi/10.1111/mpp.13450
Phytophthora pseudosyringae is a self-fertile pathogen of woody plants, particularly associated with tree species from the genera Fagus, Notholithocarpus, Nothofagus and Quercus, which is found across Europe and in parts of North America and Chile. It can behave as a soil pathogen infecting roots and the stem collar region, as well as an aerial pathogen infecting leaves, twigs and stem barks, causing particular damage in the United Kingdom and western North America. The population structure, migration and potential outcrossing of a worldwide collection of isolates were investigated
using genotyping-by-sequencing. Coalescent-based migration analysis revealed that the North American population originated from Europe. Historical gene flow has occurred between the continents in both directions to some extent, yet contemporary
migration is overwhelmingly from Europe to North America. Two broad population clusters dominate the global population of the pathogen, with a subgroup derived from one of the main clusters found only in western North America. Index of association
and network analyses indicate an influential level of outcrossing has occurred in this preferentially inbreeding, homothallic oomycete. Outcrossing between the two main population clusters has created distinct subgroups of admixed individuals that are, however, less common than the main population clusters. Differences in life history
traits between the two main population clusters should be further investigated together with virulence and host range tests to evaluate the risk each population poses to natural environments worldwide.
Fungal pathogens pose threats to crop productivity and food security. Management of fungal diseases can be achieved through an integrated disease management approach, including accurate identification of the causative agents. Diaporthe blight is a common disease of eggplant (Solanum melongena). Although Diaporthe vexans has been implicated as the causative agent, it was unclear until this study whether other Diaporthe species also contribute to this disease. In this study, leaf and fruit blights of eggplants were collected from different provinces in the Philippines. Through a polyphasic approach—morphological, cultural, pathogenicity, and multi-locus phylogenetic analyses of ITS, TEF1-α, TUB2, CAL, and HIS3 coupled with genealogical concordance phylogenetic species recognition analyses—we identified six Diaporthe speciesfrom the D. sojae species complex and D. arecae species complex. Two novel species, D. solani-melongenae and D. talong, along with the re-validated D. melongenae, and known species, viz., D. arecae, D. passifloricola, and D. vexans were identified as the causative agents of Diaporthe leaf and fruit blight of eggplant in the Philippines. Additionally, we also provide evidence supporting the synonymization of D. etinsidea with D. tulliensis, D. durionigena with D. rosae, and D. griceae with D. vexans. Our study confirmed that D. vexans is the major causative agent of eggplant blight in the country. All Diaporthe species were found to be pathogenic to eggplant. The results of this study contribute to the understanding of the eggplant blight disease, its potential spread, and the development of more targeted management strategies.
Integrative and conjugative elements (ICEs) are self-transmissible mobile elements that transfer functional genetic units across broad phylogenetic distances. Accessory genes shuttled by ICEs can make significant contributions to bacterial fitness. Most ICEs characterized to date encode readily observable phenotypes contributing to symbiosis, pathogenicity, and antimicrobial resistance, yet the majority of ICEs carry genes of unknown function. Recent observations of rapid acquisition of ICEs in a pandemic lineage of Pseudomonas syringae pv. actinidae led to investigation of the structural and functional diversity of these elements. Fifty-three unique ICE types were identified across the P. syringae species complex. Together they form a distinct family of ICEs (PsICEs) that share a distant relationship to ICEs found in Pseudomonas aeruginosa . PsICEs are defined by conserved backbone genes punctuated by an array of accessory cargo genes, are highly recombinogenic, and display distinct evolutionary histories compared to their bacterial hosts. The most common cargo is a recently disseminated 16-kb mobile genetic element designated Tn 6212 . Deletion of Tn 6212 did not alter pathogen growth in planta, but mutants displayed fitness defects when grown on tricarboxylic acid (TCA) cycle intermediates. RNA-seq analysis of a set of nested deletion mutants showed that a Tn 6212 -encoded LysR regulator has global effects on chromosomal gene expression. We show that Tn 6212 responds to preferred carbon sources and manipulates bacterial metabolism to maximize growth.
Motivation
The abundance of gene flow in the Tree of Life challenges the notion that evolution can be represented with a fully bifurcating process which cannot capture important biological realities like hybridization, introgression, or horizontal gene transfer. Coalescent-based network methods are increasingly popular, yet not scalable for big data, because they need to perform a heuristic search in the space of networks as well as numerical optimization that can be NP-hard. Here, we introduce a novel method to reconstruct phylogenetic networks based on algebraic invariants. While there is a long tradition of using algebraic invariants in phylogenetics, our work is the first to define phylogenetic invariants on concordance factors (frequencies of four-taxon splits in the input gene trees) to identify level-1 phylogenetic networks under the multispecies coalescent model.
Results
Our novel hybrid detection methodology is optimization-free as it only requires the evaluation of polynomial equations, and as such, it bypasses the traversal of network space, yielding a computational speed at least 10 times faster than the fastest-to-date network methods. We illustrate our method’s performance on simulated and real data from the genus Canis.
Availability and implementation
We present an open-source publicly available Julia package PhyloDiamond.jl available at https://github.com/solislemuslab/PhyloDiamond.jl with broad applicability within the evolutionary community.
Objectives
Taxonomic assignment based on whole-genome sequencing data facilitates clear demarcation of species within a complex genus. Here, we applied a unique pan-genome phylogenetic method, open reading frame (ORF)-based binarized structure network analysis (OSNA), for taxonomic inference of Aeromonas spp., a complex taxonomic group consisting of 30 species.
Methods
Data from 335 publicly available Aeromonas genomes, including the reference genomes of 30 species, were used to build a phylogenetic tree using OSNA. In OSNA, whole-genome structures are expressed as binary sequences based on the presence or absence of ORFs, and a tree is generated using neighbor-net, a distance-based method for constructing phylogenetic networks from binary sequences. The tree built by OSNA was compared to that constructed by a core-genome single-nucleotide polymorphism (SNP)-based analysis. Furthermore, the orthologous average nucleotide identity (OrthoANI) values of the sequences that clustered in a single clade in the OSNA-based tree were calculated.
Results
The phylogenetic tree constructed with OSNA successfully delineated the majority of species of the genus Aeromonas forming conspecific clades for individual species, which was corroborated by OrthoANI values. Moreover, the OSNA-based phylogenetic tree demonstrated high compositional similarity to the core-genome SNP-based phylogenetic tree, supported by the Fowlkes–Mallows index.
Conclusions
We propose that OSNA is a useful tool in predicting the taxonomic classification of complex bacterial genera.
Purpose
To sequence, identify, and perform phylogenetic and recombination analysis on three clinical adenovirus samples taken from the vitreous humor at the Bascom Palmer Eye Institute.
Methods
The PacBio Sequel II was used to sequence the genomes of the three clinical adenovirus isolates. To identify the isolates, a full genome-based multiple sequence alignment (MSA) of 722 mastadenoviruses was generated using multiple alignment using fast Fourier transform (MAFFT). MAFFT was also used to generate genome-based human adenovirus B (HAdV-B) MSAs, as well as HAdV-B fiber, hexon, and penton protein-based MSAs. To examine recombination within HAdV-B, RF-Net 2 and Bootscan software programs were used.
Results
In the course of classifying three new atypical ocular adenovirus samples, taken from the vitreous humor, we found that all three isolates were HAdV-B species. The three Bascom Palmer HAdV-B genomes were then combined with over 300 HAdV-B genome sequences, including nine ocular HAdV-B genome sequences. Attempts to categorize the penton, hexon, and fiber serotypes using phylogeny of the three Bascom Palmer samples were inconclusive due to incongruence between serotype and phylogeny in the dataset. Recombination analysis using a subset of HAdV-B strains to generate a hybridization network detected recombination between nonhuman primate and human-derived strains, recombination between one HAdV-B strain and the HAdV-E outgroup, and limited recombination between the B1 and B2 clades.
Conclusions
The discordance between serotype and phylogeny detected in this study suggests that the current classification system does not accurately describe the natural history and phylogenetic relationships among adenoviruses.
Taxonomic entities below the species level often pose difficulties for conservation practice, especially when they are ecologically distinct from the nominal species. Genomic tools provide the opportunity to study and potentially resolve such cryptic diversity. The Alcon blue butterfly Phengaris alcon species complex is such a cryptic example, comprising different ecotypes or even subspecies, one of them is the high elevation taxon P. rebeli from the European Alps. We sequenced a first reference genome for Phengaris alcon. Furthermore, we generated whole genome resequence data for individuals of three Swiss ecotypes, i.e., the low elevation P. alcon, the mid elevation and high elevation alpine P. rebeli and integrated genomic data from across Europe to study the relationship among these ecotypes. At a European scale, our results suggest that for the P. alcon complex, biogeography and the evolutionary context of diversification is more multifaceted than previously suggested, falling in the range of more recent ecological speciation. In Switzerland, the three ecotypes were genetically isolated with only limited current gene flow between them. Past gene flow, however, could have given rise to the mid elevation ecotype. Our findings emphasise that high elevation P. rebeli in the Alps should be treated as a distinct species. Our study highlights how the availability of reference genome assemblies allows to address so far open taxonomic questions in conservation research and that broadscale studies are needed to understand the biogeographic history of apparent diversification.
Trichophyton erinacei is a main cause of dermatophytosis in hedgehogs and is increasingly reported from human infections worldwide. This pathogen was originally described in the European hedgehog (Erinaceus europaeus) but is also frequently found in the African four-toed hedgehog (Atelerix albiventris), a popular pet animal worldwide. Little is known about the taxonomy and population genetics of this pathogen despite its increasing importance in clinical practice. Notably, whether there are different populations or even cryptic species associated with different hosts or geographic regions is not known. To answer these questions, we collected 161 isolates, performed phylogenetic and population-genetic analyses, determined mating-type, and characterised morphology and physiology. Multigene phylogeny and microsatellite analysis supported T. erinacei as a monophyletic species, in contrast to highly incongruent single-gene phylogenies. Two main subpopulations, one specific mainly to Atelerix and second to Erinaceus hosts, were identified inside T. erinacei, and slight differences in the size of microconidia and antifungal susceptibilities were observed among them. Although the process of speciation into two lineages is ongoing in T. erinacei, there is still gene flow between these populations. Thus, we present T. erinacei as a single species, with notable intraspecies variability in genotype and phenotype. The data from wild hedgehogs indicated that sexual reproduction in T. erinacei and de novo infection of hedgehogs from soil are probably rare events and that clonal horizontal spread strongly dominates. The molecular typing approach used in this study represents a suitable tool for further epidemiological surveillance of this emerging pathogen in both animals and humans. The results of this study also highlighted the need to use a multigene phylogeny ideally in combination with other independent molecular markers to understand the species boundaries of dermatophytes.
Citation: Čmoková A, Kolařík M, Guillot J, et al. 2022. Host-driven subspeciation in the hedgehog fungus, Trichophyton erinacei, an emerging cause of human dermatophytosis. Persoonia 48: 203–218. https://doi.org/10.3767/persoonia.2022.48.06.
Hybridisation is a common event in yeasts often leading to genomic variability and adaptation. The yeast Candida orthopsilosis is a human-associated opportunistic pathogen belonging to the Candida parapsilosis species complex. Most C. orthopsilosis clinical isolates are hybrids resulting from at least four independent crosses between two parental lineages, of which only one has been identified. The rare presence or total absence of parentals amongst clinical isolates is hypothesised to be a consequence of a reduced pathogenicity with respect to their hybrids. Here, we sequence and analyse the genomes of environmental C. orthopsilosis strains isolated from warm marine ecosystems. We find that a majority of environmental isolates are hybrids, phylogenetically closely related to hybrid clinical isolates. Furthermore, we identify the missing parental lineage, thus providing a more complete overview of the genomic evolution of this species. Additionally, we discover phenotypic differences between the two parental lineages, as well as between parents and hybrids, under conditions relevant for pathogenesis. Our results suggest a marine origin of C. orthopsilosis hybrids, with intrinsic pathogenic potential, and pave the way to identify pre-existing environmental adaptations that rendered hybrids more prone than parental lineages to colonise and infect the mammalian host.
Circumscribing species boundries is necessary in systematic plant biology. Even a mistake
in delimiting taxa may lead to incorrect scientific interpretations. Draba rimarum (Rech.f.) A.R.
Khosravi & A. Eslami-Farouji is an endemic Iranian species with a narrow geographic
distribution, and is genetically close to D. aucheri. The present study provided a phylogenetic
review, time divergence, and planar network of both species to unravel the distinct position of
both species along with the prediction of any conflicting or ambiguous signals. Regarding this
purpose, here we represent that phylogenetic trees may fail to show reliable results toward the
distinct position of genetically close species.
Background Explaining contrasting patterns of distribution between related species is crucial for understanding
the dynamics of biodiversity. Despite instances where hybridization and whole genome duplication (WGD) can yield
detrimental outcomes, a role in facilitating the expansion of distribution range has been proposed. The Vitaceae
genus Causonis exhibits great variations in species’ distribution ranges, with most species in the derived lineages
having a much wider range than those in the early-diverged lineages. Hybridization and WGD events have been
suggested to occur in Causonis based on evidence of phylogenetic discordance. The genus, therefore, provides us
with an opportunity to for explore different hybridization and polyploidization modes in lineages with contrasting
species’ distribution ranges. However, the evolutionary history of Causonis incorporating potential hybridization
and WGD events remains to be explored.
Results With plastid and nuclear data from dense sampling, this study resolved the phylogenetic relationships
within Causonis and revealed significant cyto-nuclear discordance. Nuclear gene tree conflicts were detected
across the genus, especially in the japonica-corniculata clade, which were mainly attributed to gene flow. This study
also inferred the allopolyploid origin of the core Causonis species, which promoted the accumulation of stress-related
genes. Causonis was estimated to have originated in continental Asia in the early Eocene, and experienced glaciation
in the early Oligocene, shortly after the divergence of the early-divergent lineages. The japonica-corniculata clade
mainly diversified in the Miocene, followed by temperature declines that may have facilitated secondary contact.
Species distribution modeling based on current climate change predicted that the widespread C. japonica tends to be
more invasive, while the endemic C. ciliifera may be at risk of extinction.
Conclusions This study presents Causonis, a genus with complex reticulate evolutionary history, as a model
of how hybridization and WGD modes differ in lineages of contrasting species’ geographic ranges. It is important
to consider specific evolutionary histories and genetic properties of the focal species within conservation strategies.
Keywords Distribution range, Causonis, Hybridization, Whole genome duplication, Allopolyploidization, Reticulate
evolution
Protein structures carry signal of common ancestry and can therefore aid in reconstructing their evolutionary histories. To expedite the structure-informed inference process, a web server, Structome, has been developed that allows users to rapidly identify protein structures similar to a query protein and to assemble datasets useful for structure-based phylogenetics. Structome was created by clustering ∼94% of the structures in RCSB PDB using 90% sequence identity and representing each cluster by a centroid structure. Structure similarity between centroid proteins was calculated, and annotations from PDB, SCOP, and CATH were integrated. To illustrate utility, an H3 histone was used as a query, and results show that the protein structures returned by Structome span both sequence and structural diversity of the histone fold. Additionally, the pre-computed nexus-formatted distance matrix, provided by Structome, enables analysis of evolutionary relationships between proteins not identifiable using searches based on sequence similarity alone. Our results demonstrate that, beginning with a single structure, Structome can be used to rapidly generate a dataset of structural neighbours and allows deep evolutionary history of proteins to be studied.
Availability and Implementation
Structome is available at: https://structome.bii.a-star.edu.sg.
Understanding processes leading to disease emergence is important for effective disease management and prevention of future epidemics. Utilizing whole genome sequencing, we studied the phylogenetic relationship and diversity of two populations of the bacterial oak pathogen Lonsdalea quercina from western North America (Colorado and California) and compared these populations to other Lonsdalea species found worldwide. Phylogenetic analysis separated Colorado and California populations into two Lonsdalea clades, with genetic divergence near species boundaries, suggesting long isolation and populations that differ in genetic structure and distribution and possibly their polyphyletic origin. Genotypes collected from different host species and habitats were randomly distributed within the California cluster. Most Colorado isolates from introduced planted trees, however, were distinct from three isolates collected from a natural stand of Colorado native Quercus gambelii, indicating cryptic population structure. The California identical core genotypes distribution varied, while Colorado identical core genotypes were always collected from neighboring trees. Despite its recent emergence, the Colorado population had higher nucleotide diversity, possibly due to its long presence in Colorado or due to migrants moving with nursery stock. Overall, results suggest independent pathogen emergence in two states likely driven by changes in host-microbe interactions due to ecosystems changes. Further studies are warranted to understand evolutionary relationships among L. quercina from different areas, including the red oak native habitat in northeastern USA.
Hybrid zones occur where genetically distinct populations meet, mate and produce offspring with mixed ancestry. In Plethodontid salamanders, introgressive hybridization is a common phenomenon, where hybrids backcross with parental populations leading to the spread of new alleles into the parental genomes. Whereas many hybrid zones have been reported in American Plethodontid salamanders, only a single hybrid zone has been documented in European plethodontids so far, which is located at the Apuan Alps in the Italian Peninsula. Here, we describe a previously unreported hybrid zone in the Northern Apennines involving all the three Plethodontid salamander species inhabiting the Italian Peninsula. We found 21 new Speleomantes sites of occurrence, from a hitherto unexplored area located at the boundaries between three Speleomantes species ranges. Using mitochondrial (Cytb and ND2 genes) and nuclear markers (two diagnostic SNPs at the NCX1 gene), we revealed a three‐way contact zone where all the three mainland species hybridize: S. strinatii , S. ambrosii and S. italicus . We observed a strong mitonuclear discordance, with mitochondrial markers showing a conspicuous geographic pattern, while diagnostic nuclear SNPs coexisted in both the same populations and individuals, providing evidence of hybridization in many possible combinations. The introgression is asymmetric, with S. italicus mitogenome usually associated with S. a. ambrosii and, to a lesser extent, to S. strinatii nuclear alleles. This finding confirms that Plethodontid are a group of choice to investigate hybridization mechanisms and suggests that behavioural, genetic and ecological components may concur in determining the direction and extent of introgression.
Endogenous retroviruses (ERVs) record past retroviral infections, providing molecular archives for interrogating the evolution of retroviruses and retrovirus-host interaction. However, the vast majority of ERVs are not active anymore due to various disruptive mutations, and ongoing retroviral invasion of vertebrate genomes has been rarely documented. Here we analyze genomics data from 2004 vertebrates for mining invading ERVs (ERVi). We find that at least 412 ERVi elements representing 217 viral operational taxonomic units are invading the genomes of 123 vertebrates, 18 of which have been assessed to be threatened species. Our results reveal an unexpected prevalence of ongoing retroviral invasion in vertebrates and expand the diversity of retroviruses recently circulating in the wild. We characterize the pattern and nature of ERVi in the historical and biogeographical context of their hosts, for instance, the generation of model organisms, sympatric speciation, and domestication. We suspect that these ERVi are relevant to conservation of threatened species, zoonoses in the wild, and emerging infectious diseases in humans.
A transition to selfing can be beneficial when mating partners are scarce, for example, due to ploidy changes or at species range edges. Here, we explain how self-compatibility evolved in diploid Siberian Arabidopsis lyrata, and how it contributed to the establishment of allotetraploid Arabidopsis kamchatica. First, we provide chromosome-level genome assemblies for two self-fertilizing diploid A. lyrata accessions, one from North America and one from Siberia, including a fully assembled S-locus for the latter. We then propose a sequence of events leading to the loss of self-incompatibility in Siberian A. lyrata, date this independent transition to ∼90 Kya, and infer evolutionary relationships between Siberian and North American A. lyrata, showing an independent transition to selfing in Siberia. Finally, we provide evidence that this selfing Siberian A. lyrata lineage contributed to the formation of the allotetraploid A. kamchatica and propose that the selfing of the latter is mediated by the loss-of-function mutation in a dominant S-allele inherited from A. lyrata.
Domestication is an excellent case study for understanding adaptation and multiple fungal lineages have been domesticated for fermenting food products. Studying domestication in fungi has thus both fundamental and applied interest. Genomic studies have revealed the existence of four populations within the blue‐cheese‐making fungus Penicillium roqueforti. The two cheese populations show footprints of domestication, but the adaptation of the two non‐cheese populations to their ecological niches (i.e., silage/spoiled food and lumber/spoiled food) has not been investigated yet. Here, we reveal the existence of a new P. roqueforti population, specific to French Termignon cheeses, produced using small‐scale traditional practices, with spontaneous blue mould colonisation. This Termignon population is genetically differentiated from the four previously identified populations, providing a novel source of genetic diversity for cheese making. The Termignon population indeed displayed substantial genetic diversity, both mating types, horizontally transferred regions previously detected in the non‐Roquefort population, and intermediate phenotypes between cheese and non‐cheese populations. Phenotypically, the non‐Roquefort cheese population was the most differentiated, with specific traits beneficial for cheese making, in particular higher tolerance to salt, to acidic pH and to lactic acid. Our results support the view that this clonal population, used for many cheese types in multiple countries, is a domesticated lineage on which humans exerted strong selection. The lumber/spoiled food and silage/spoiled food populations were not more tolerant to crop fungicides but showed faster growth in various carbon sources (e.g., dextrose, pectin, sucrose, xylose and/or lactose), which can be beneficial in their ecological niches. Such contrasted phenotypes between P. roqueforti populations, with beneficial traits for cheese‐making in the cheese populations and enhanced ability to metabolise sugars in the lumber/spoiled food population, support the inference of domestication in cheese fungi and more generally of adaptation to anthropized environments.
Paeonia decomposita, Paeonia rotundiloba, and Paeonia rockii are three closely related species of Sect. Moutan is distributed in the montane area of the Eastern Hengduan Mountain region. Understanding the population history of these three tree peony species could contribute to unraveling the evolutionary patterns of undergrowth species in this hotspot area. We used one nuclear DNA marker (internal transcribed spacer region, ITS) and two chloroplast DNA markers (matK, ycf1) to reconstruct the phylogeographic pattern of the populations. In total, 228 individuals from 17 populations of the three species were analyzed in this study. Three nuclear clades (Clade I - Clade III) and four maternal clades (Clade A - Clade D) were reconstructed. Molecular dating suggested that young lineages diverged during the late Pliocene and early Pleistocene, younger than the uplift of the Hengduan Mountains but older than the last glacial maximum (LGM). Significant population and phylogeographic structures were detected at both markers. Furthermore, the populations of these tree peonies were overall at equilibrium during the climatic oscillations of the Pleistocene. The simulated palaeoranges of the three species during the LGM period mostly overlapped, which could have led to cross-breeding events. We propose an evolutionary scenario in which mountain orogenesis around the Hengduan Mountain area triggered parapatric isolation between maternal lineages of tree peonies. Subsequent climatic fluctuations drove migration and range recontact of these populations along the valleys. This detailed evolutionary history provides new insights into the phylogeographic pattern of species from mountain-valley systems.
Leishmania aethiopica is a zoonotic Old World parasite transmitted by Phlebotomine sand flies and causing cutaneous leishmaniasis in Ethiopia and Kenya. Despite a range of clinical manifestations and a high prevalence of treatment failure, L. aethiopica is one of the most neglected species of the Leishmania genus in terms of scientific attention. Here, we explored the genome diversity of L. aethiopica by analyzing the genomes of twenty isolates from Ethiopia. Phylogenomic analyses identified two strains as interspecific hybrids involving L. aethiopica as one parent and L. donovani and L. tropica respectively as the other parent. High levels of genome-wide heterozygosity suggest that these two hybrids are equivalent to F1 progeny that propagated mitotically since the initial hybridization event. Analyses of allelic read depths further revealed that the L. aethiopica - L. tropica hybrid was diploid and the L. aethiopica - L. donovani hybrid was triploid, as has been described for other interspecific Leishmania hybrids. When focusing on L. aethiopica, we show that this species is genetically highly diverse and consists of both asexually evolving strains and groups of recombining parasites. A remarkable observation is that some L. aethiopica strains showed an extensive loss of heterozygosity across large regions of the nuclear genome, which likely arose from gene conversion/mitotic recombination. Hence, our prospection of L. aethiopica genomics revealed new insights into the genomic consequences of both meiotic and mitotic recombination in Leishmania.
The fishes of the Chiasmodontidae family, known as swallower fishes, are species adapted to live in deep seas. Several studies have shown the proximity of this family to Tetragonuridae and Amarsipidae. However, the phylogenetic position of this clade related to other Pelagiaria groups remains uncertain even when phylogenomic studies are employed. Since the low number of published mitogenomes, our study aimed to assemble six new mitochondrial genomes of Chiasmodontidae from database libraries to expand the discussion regarding the phylogeny of this group within Scombriformes. As expected, the composition and organization of mitogenomes were stable among the analyzed species, although we detected repetitive sequences in the D-loop of species of the genus Kali not seen in Chiasmodon, Dysalotus, and Pseudoscopelus. Our phylogeny incorporating 51 mitogenomes from several families of Scombriformes, including nine chiasmodontids, recovered interfamilial relationships well established in previous studies, including a clade containing Chiasmodontidae, Amarsipidae, and Tetragonuridae. However, phylogenetic relationships between larger clades remain unclear, with disagreements between different phylogenomic studies. We argue that such inconsistencies are not only due to biases and limitations in the data but mainly to complex biological events in the adaptive irradiation of Scombriformes after the Cretaceous-Paleogene extinction event.
How species diverge into different lineages is a central issue in evolutionary biology. Despite the increasing evidence indicating that such divergences do not need geographic isolation, the correlation between the lineage divergence and the adaptive ecological divergence of phenotype corresponding to distributional is still unknown. In addition, gene flow has been widely detected during and through such diverging processes. We used one widely distributed Aquilegia viridiflora complex as a model system to examine genomic differentiation and corresponding phenotypic variations along geographic gradients. Our phenotypic analyses 20 populations from northwest to northeast China identified two phenotypic groups along the geographic cline. All examined traits are distinct between them although a few intermediate individuals occur in their contacting regions. We further sequenced the genomes of the representative individuals of each population. However, four distinct genetic lineages were detected based on nuclear genomes. In particular, we recovered numerous genetic hybrids in the contact regions of four lineages were recovered. Gene flow is widespread and continuous between four lineages but much higher between contacting lineages than geographically isolated lineages. Gene flow and natural selection might result in the inconsistency between heredity and phenotype. Moreover, many genes with fast lineage-specific mutations were identified to be involved in local adaptation. Our results suggest that both geographic isolation and local selection exerted by the environment and pollinators may together create geographic distributions of phenotypic variations as well as the underlying genomic divergences in numerous lineages.
Genetic structure analyses have yielded some examples of inconsistencies between genetic and morphological information. Here, eleven nuclear microsatellite markers and mitochondrial haplotypes were used to examine the genetic structure and gene flow among Japanese Undaria pinnatifida populations and the congeneric species U. undarioides and U. peterseniana . Undaria pinnatifida was subdivided into four “Groups” of populations based on Bayesian clustering analysis, Neighbor-net analysis and Principal coordinate analysis (PCoA). Undaria undarioides samples formed a unique Group. In contrast, U. peterseniana samples either grouped with a mixture of U. pinnatifida and U. undarioides clusters or were included within one of the U. pinnatifida clusters. More significantly, Groups of populations shared alleles with geographically adjacent Groups even between different morphospecies. No clear differences between the inter-and intra-specific genetic divergence were observed in either nuclear or mitochondrial markers. As a result, U. undarioides and U. peterseniana were synonymized with U. pinnatifida . Isolation-by-distance suggested the significance of geographical isolation for maintaining the observed divergence.
Consisting of approximately 320 species, Macrocheles is the most widely distributed genus in the family Macrochelidae. Though some studies have focused on the description of Macrochelidae using molecular techniques (e.g., RAPD) and sequencing of some genes, the interspecies relationships within Macrocheles still remain uncertain. As such, in the present study, we examine all publicly available data in GenBank to explore the evolutionary relationships, divergence times, and amino acid variations within Macrocheles. Exploring the patterns of variation in the secondary protein structure shows high levels of conservation in the second and last helices, emphasizing their involvement in the energy metabolism function of the cytochrome oxidase subunit I enzyme. According to our phylogenetic analysis, all available Macrocheles species are clustered in a monophyletic group. However, in the reconstructed trees, we subdivided M. merdarius and M. willowae into two well-supported intraspecific clades that are driven by geographic separation and host specificity. We also estimate the divergence time of selected species using calibration evidence from available fossils and previous studies. Thus, we estimate that the age of the Parasitiformes is 320.4 (273.3-384.3) Mya (Permian), and the Mesostigmata is 285.1 (270.8-286.4) Mya (Carboniferous), both with likely origins in the Paleozoic era. We also estimate that Macrocheles diverged from other Mesostigmata mites during the Mesozoic, approximately 222.9 Mya.
The Euro-Siberian steppe flora consists of warm- and cold-adapted species, which may have responded differently to Pleistocene glacials and interglacials. Genotyping-by-sequencing individuals from across the distribution range of the pheasant’s eye (Adonis vernalis), we aimed to gain insight into steppe florogenesis based on the species’ evolutionary history. Although the primary area of origin of the species group comprising A. vernalis, A. villosa and A. volgensis is in Asia, our results indicate that recent populations of A. vernalis are not of Asian origin but evolved in the southern part of Europe during the Pleistocene, with Spanish populations clearly genetically distinct from the Southeastern European populations. We inferred that A. vernalis migrated eastwards from the sub-Mediterranean forest-steppes of Southeastern Europe into the continental forest-steppe zone. Eastern European populations had the highest private allelic richness, indicating long-term large population sizes in this region. As a thermophilic species, A. vernalis seems unlikely to have survived in the cold deserts of the Last Glacial Maximum in Western Siberia, so this region was likely (re)colonized postglacially. Overall, our results reinforce the importance of identifying the area of origin and the corresponding ecological requirements of steppe plants in order to understand the composition of today’s steppe flora.
Studies on phylogeography and population structure of Ixodes ricinus have been carried out in Europe for decades, but the number of specimens from the Middle East included in these analyses is relatively small, despite the wide distribution of the species in this area. This study aimed to clarify the phylogenetic positions of I. ricinus from Turkey as well as to investigate the presence of Ixodes inopinatus in Anatolia. For this purpose, one mitochondrial (mt 16S rDNA) and one nuclear gene (defensin) were used to generate molecular data from I. ricinus samples, which were collected from 17 locations across the species’ distributional range in Turkey. Bayesian inference was used to investigate phylogenetic relationships. Globally, the mt 16S rDNA lineages correspond to the lineages revealed by defensin; I. ricinus and I. inopinatus sequences clustered separately. However, a discordant genetic pattern was observed between the phylogenetic position of turkish I. ricinus revealed by nuclear versus mitochondrial genes. All Turkish haplotypes of mt 16SrDNA clustered with I. ricinus samples from Europe, which might be the result of extensive gene flow between populations of Europe and the Middle East. On the other hand, a sample from Thrace Region grouped within I. inopinatus clade. Thus, the occurrence of I. inopinatus in Turkey was demonstrated for the first time using molecular data. Moreover, four individuals were found to be heterozygous for the defensin. The potential evolutionary processes that underlie this observed discrepancy between the phylogenetic trees of two genes have been discussed.
Background
The great diversity of lifestyles and survival strategies observed in fungi is reflected in the many ways in which they reproduce and recombine. Although a complete absence of recombination is rare, it has been reported for some species, among them 2 extremotolerant black yeasts from Dothideomycetes: Hortaea werneckii and Aureobasidium melanogenum. Therefore, the presence of diploid strains in these species cannot be explained as the product of conventional sexual reproduction.
Results
Genome sequencing revealed that the ratio of diploid to haploid strains in both H. werneckii and A. melanogenum is about 2:1. Linkage disequilibrium between pairs of polymorphic loci and a high degree of concordance between the phylogenies of different genomic regions confirmed that both species are clonal. Heterozygosity of diploid strains is high, with several hybridizing genome pairs reaching the intergenomic distances typically seen between different fungal species. The origin of diploid strains collected worldwide can be traced to a handful of hybridization events that produced diploids, which were stable over long periods of time and distributed over large geographic areas.
Conclusions
Our results, based on the genomes of over 100 strains of 2 black yeasts, show that although they are clonal, they occasionally form stable and highly heterozygous diploid intraspecific hybrids. The mechanism of these apparently rare hybridization events, which are not followed by meiosis or haploidization, remains unknown. Both extremotolerant yeasts, H. werneckii and even more so A. melanogenum, a close relative of the intensely recombining and biotechnologically relevant Aureobasidium pullulans, provide an attractive model for studying the role of clonality and ploidy in extremotolerant fungi.
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