Merging Arcs to Produce Acyclic Phylogenetic Networks and Normal Networks

As phylogenetic networks grow increasingly complicated, systematic methods for simplifying them to reveal properties will become more useful. This paper considers how to modify acyclic phylogenetic networks into other acyclic networks by contracting specific arcs that include a set D. The networks need not be binary, so vertices in the networks may have more than two parents and/or more than two children. In general, in order to make the resulting network acyclic, additional arcs not in D must also be contracted. This paper shows how to choose D so that the resulting acyclic network is “pre-normal”. As a result, removal of all redundant arcs yields a normal network. The set D can be selected based only on the geometry of the network, giving a well-defined normal phylogenetic network depending only on the given network. There are CSD maps relating most of the networks. The resulting network can be visualized as a “wired lift” in the original network, which appears as the original network with each arc drawn in one of three ways.

Comparing the topology of phylogenetic network generators

Phylogenetic networks represent evolutionary history of species and can record natural reticulate evolutionary processes such as horizontal gene transfer and gene recombination. This makes phylogenetic networks a more comprehensive representation of evolutionary history compared to phylogenetic trees. Stochastic processes for generating random trees or networks are important tools in evolutionary analysis, especially in phylogeny reconstruction where they can be utilized for validation or serve as priors for Bayesian methods. However, as more network generators are developed, there is a lack of discussion or comparison for different generators. To bridge this gap, we compare a set of phylogenetic network generators by profiling topological summary statistics of the generated networks over the number of reticulations and comparing the topological profiles.

Applicability of several rooted phylogenetic network algorithms for representing the evolutionary history of SARS-CoV-2

Background Rooted phylogenetic networks are used to display complex evolutionary history involving so-called reticulation events, such as genetic recombination. Various methods have been developed to construct such networks, using for example a multiple sequence alignment or multiple phylogenetic trees as input data. Coronaviruses are known to recombine frequently, but rooted phylogenetic networks have not yet been used extensively to describe their evolutionary history. Here, we created a workflow to compare the evolutionary history of SARS-CoV-2 with other SARS-like viruses using several rooted phylogenetic network inference algorithms. This workflow includes filtering noise from sets of phylogenetic trees by contracting edges based on branch length and bootstrap support, followed by resolution of multifurcations. We explored the running times of the network inference algorithms, the impact of filtering on the properties of the produced networks, and attempted to derive biological insights regarding the evolution of SARS-CoV-2 from them. Results The network inference algorithms are capable of constructing rooted phylogenetic networks for coronavirus data, although running-time limitations require restricting such datasets to a relatively small number of taxa. Filtering generally reduces the number of reticulations in the produced networks and increases their temporal consistency. Taxon bat-SL-CoVZC45 emerges as a major and structural source of discordance in the dataset. The tested algorithms often indicate that SARS-CoV-2/RaTG13 is a tree-like clade, with possibly some reticulate activity further back in their history. A smaller number of constructed networks posit SARS-CoV-2 as a possible recombinant, although this might be a methodological artefact arising from the interaction of bat-SL-CoVZC45 discordance and the optimization criteria used. Conclusion Our results demonstrate that as part of a wider workflow and with careful attention paid to running time, rooted phylogenetic network algorithms are capable of producing plausible networks from coronavirus data. These networks partly corroborate existing theories about SARS-CoV-2, and partly produce new avenues for exploration regarding the location and significance of reticulate activity within the wider group of SARS-like viruses. Our workflow may serve as a model for pipelines in which phylogenetic network algorithms can be used to analyse different datasets and test different hypotheses.

Phylogenomic analyses using genomes and transcriptomes do not resolve relationships among major clades in Phrymaceae

Premise of the study: Phylogenomic datasets using genomes and transcriptomes provide rich opportunities beyond resolving bifurcating phylogenetic relationships. Monkeyflower (Phrymaceae) is a model system for evolutionary ecology. However, it lacks a well-supported phylogeny for a stable taxonomy and for macroevolutionary comparisons. Methods: We sampled 24 genomes and transcriptomes in Phrymaceae and closely related families, including eight newly sequenced transcriptomes. We reconstructed the phylogeny using IQ-TREE and ASTRAL, evaluated gene tree discordance using PhyParts, Quartet Sampling, and cloudogram, and carried out phylogenetic network analyses using PhyloNet and HyDe. We searched for whole genome duplication (WGD) events using chromosome numbers, synonymous distance, and gene duplication events. Key results: Most gene trees support the monophyly of Phrymaceae and each of its tribes. Most gene trees also support the tribe Mimuleae being sister to Phrymeae + Diplaceae + Leucocarpeae, with extensive gene tree discordance among the latter three. Despite the discordance, polyphyly of Mimulus s.l. is strongly supported, and no particular reticulation event among the Phrymaceae tribes is well supported. Reticulation likely occurred among Erythranthe bicolor and close relatives. No ancient WGD event was detected in Phrymaceae. Instead, small-scale duplications are among potential drivers of macroevolutionary diversification of Phrymaceae. Conclusions: We show that analysis of reticulate evolution is sensitive to taxon sampling and methods used. We also demonstrate that genome-scale data do not always fully "resolve" phylogenetic relationships. They present rich opportunities to investigate reticulate evolution, and gene and genome evolution involved in lineage diversification and adaptation.

Phylogeny of Pyrus and their relationships inferred from sequences of nuclear NIA-i3 intron and chloroplast ndhC-trnV and trnR-atpA

Background: Pear (Pyrus L.) belongs to subtribe Malinae, tribe Maleae, family Rosaceae. According to the geography distribution, it could be divided into Oriental pear and Occidental pear. Though the phylogeny of Pyrus was complicate, previous study referring to morphology, nuclear genes and chloroplast genes made the relationships clear gradually. However, they had lower sequence divergence and less information, therefore it hardly solved the phylogeny of Pyrus. Results: A total of 100 accessions from Oriental and Occidental pears were used to elucidate the phylogeny of Pyrus by one nuclear NIA-i3 intron and two chloroplast regions (ndhC-trnV and trnR-atpA) with higher polymorphism. The Neighbor-Net phylogenetic network indicated that the phylogenetic relationships were complicate based on ndhC-trnV and trnR-atpA. Oriental pear and Occidental pear were separated in the tree of NIA-i3, P. betulaforlia, P. pashia (except P. pashia ‘P10-3’_1 and P. pashia ‘P23-4’_1) were monophyly; several P. ussuriensis were closely related with P. xerophila. However, the phylogenetic relationships of Chinese White Pear, P. pyrifolia and some P. ussuriensis still could not be well solved; West Asian species and European species were mingled together. Occidental pear P. caucasica 684，P. pyraster 989，P. elaeagrifolia 2817 might be hybrids between Oriental pear and Occidental pear.Conclusions: The phylogenetic relationships of Pyrus were still complicate because interspecies and intraspecies of Oriental pear and Occidental pear respectively were intercrossed. More genes and more accessions were needed to solve the phylogenetic relationships in Pyrus and to explore the possible parents.

Social entrenchment influences the amount of areal borrowing in contact languages

Aims and objectives: Social factors in language contact are not well understood. This study seeks to establish and explain the role of social entrenchment in the evolution of contact languages. It also aims to contribute to a broader perspective on areality that can account for social and linguistic factors in contact outcomes involving all languages present in multilingual ecologies, including contact languages. Methodology: The copula system was singled out for a detailed analysis. A corpus of primary data of the three African English-lexifier contact languages, Pichi, Cameroon Pidgin, and Ghanaian Pidgin, their ancestor Krio, and of their African adstrates (Bube, Mokpe, Akan) and European superstrates (Spanish, English) was investigated and compared. Data and analysis: Relevant features were selected for a dissimilarity matrix. A quantitative analysis was done with SplitsTree4. The resulting distance matrix and phylogenetic network were investigated for signals of genealogical transmission and areal diffusion and interpreted on their social background. Findings/conclusions: The copula systems of the three contact languages carry a genealogical signal of their ancestor Krio as well as an areal signal from the adstrates and superstrates spoken in their respective ecologies. The amount of areal borrowing increases in the order Pichi < Cameroon Pidgin < Ghanaian Pidgin, reflective of the depth of social entrenchment of each variety from left to right. Originality: Previous studies do not describe the copula systems of the English-lexifier contact languages of Africa and the Caribbean at a similar level of granularity and mostly focus on their emergence during creolization. This study attempts to explain their subsequent areal differentiation and links it to differences in social ecologies. Significance/implications: Areal borrowing can lead to significant departures from genealogically inherited structures within a short time if social entrenchment is shallow. Conversely, even languages of wider communication can remain remarkably stable if social entrenchment is deep.

Species Phylogeny versus Gene Trees: A Case Study of an Incongruent Data Matrix Based on Paphiopedilum Pfitz. (Orchidaceae)

The phylogeny of the genus Paphiopedilum based on the plastome is consistent with morphological analysis. However, to date, none of the analyzed nuclear markers has confirmed this. Topology incongruence among the trees of different nuclear markers concerns entire sections of the subgenus Paphiopedilum. The low-copy nuclear protein-coding gene PHYC was obtained for 22 species representing all sections and subgenera of Paphiopedilum. The nuclear-based phylogeny is supported by morphological characteristics and plastid data analysis. We assumed that an incongruence in nuclear gene trees is caused by ancestral homoploid hybridization. We present a model for inferring the phylogeny of the species despite the incongruence of the different tree topologies. Our analysis, based on six low-copy nuclear genes, is congruent with plastome phylogeny and has been confirmed by phylogenetic network analysis.

On the Species Delimitation of the Maddenia Group of Prunus (Rosaceae): Evidence From Plastome and Nuclear Sequences and Morphology

The recognition, identification, and differentiation of closely related plant species present significant and notorious challenges to taxonomists. The Maddenia group of Prunus, which comprises four to seven species, is an example of a group in which species delimitation and phylogenetic reconstruction have been difficult, due to the lack of clear morphological distinctions, limited sampling, and low informativeness of molecular evidence. Thus, the precise number of species in the group and the relationships among them remain unclear. Here, we used genome skimming to generate the DNA sequence data for 22 samples, including 17 Maddenia individuals and five outgroups in Amygdaloideae of Rosaceae, from which we assembled the plastome and 446 single-copy nuclear (SCN) genes for each sample. The phylogenetic relationships of the Maddenia group were then reconstructed using both concatenated and coalescent-based methods. We also identified eight highly variable regions and detected simple sequence repeats (SSRs) and repeat sequences in the Maddenia species plastomes. The phylogenetic analysis based on the complete plastomes strongly supported three main subclades in the Maddenia group of Prunus, while five subclades were recognized based on the nuclear tree. The phylogenetic network analysis detected six hybridization events. Integrating the nuclear and morphological evidence, we proposed to recognize five species within the Maddenia group, i.e., Prunus fujianensis, P. himalayana, P. gongshanensis, P. hypoleuca, and P. hypoxantha. Within this group, the first three species are well-supported, while the gene flow occurring throughout the Maddenia group seems to be especially frequent between P. hypoleuca and P. hypoxantha, eroding the barrier between them. The phylogenetic trees based on eight concatenated hypervariable regions had a similar topology with the complete plastomes, showing their potential as molecular markers and effective barcodes for further phylogeographic studies on Maddenia.

Lpnet: Reconstructing Phylogenetic Networks from Distances Using Integer Linear Programming

We present Lpnet, a variant of the widely used Neighbor-net method that approximates pairwise distances between taxa by a circular phylogenetic network. We use integer linear programming to replace a heurisristic part of the agglomeration procedure based on local information by an exact global solution. This approach achieves an improved approximation of the input distance for the clear majority of experiments that we have run for simulated and real data. We release an implementation in R that can handle up to 94 taxa and usually needs about one minute on a standard computer for 80 taxa.

Maximum Parsimony Inference of Phylogenetic Networks in the Presence of Polyploid Complexes

Phylogenetic networks provide a powerful framework for modeling and analyzing reticulate evolutionary histories. While polyploidy has been shown to be prevalent not only in plants but also in other groups of eukaryotic species, most work done thus far on phylogenetic network inference assumes diploid hybridization. These inference methods have been applied, with varying degrees of success, to data sets with polyploid species, even though polyploidy violates the mathematical assumptions underlying these methods. Statistical methods were developed recently for handling specific types of polyploids and so were parsimony methods that could handle polyploidy more generally yet while excluding processes such as incomplete lineage sorting. In this paper, we introduce a new method for inferring most parsimonious phylogenetic networks on data that include polyploid species. Taking gene tree topologies as input, the method seeks a phylogenetic network that minimizes deep coalescences while accounting for polyploidy. We demonstrate the performance of the method on both simulated and biological data. The inference method as well as a method for evaluating evolutionary hypotheses in the form of phylogenetic networks are implemented and publicly available in the PhyloNet software package.