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

   https://doi.org/10.1093/molbev/msaa139  

   Zhang, Chao; Scornavacca, Celine; Molloy, Erin K; Mirarab, Siavash (September 2020, Molecular Biology and Evolution)

   Thorne, Jeffrey (Ed.)

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

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2. INSTRAL: Discordance-Aware Phylogenetic Placement Using Quartet Scores

   https://doi.org/10.1093/sysbio/syz045  

   Rabiee, Maryam; Mirarab, Siavash; Posada, ed., David (August 2019, Systematic Biology)

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

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3. Resolving Marine–Freshwater Transitions by Diatoms Through a Fog of Gene Tree Discordance

   https://doi.org/10.1093/sysbio/syad038  

   Roberts, Wade R.; Ruck, Elizabeth C.; Downey, Kala M.; Pinseel, Eveline; Alverson, Andrew J.; Smith, ed., Stacey (June 2023, Systematic Biology)

   Abstract Despite the obstacles facing marine colonists, most lineages of aquatic organisms have colonized and diversified in freshwaters repeatedly. These transitions can trigger rapid morphological or physiological change and, on longer timescales, lead to increased rates of speciation and extinction. Diatoms are a lineage of ancestrally marine microalgae that have diversified throughout freshwater habitats worldwide. We generated a phylogenomic data set of genomes and transcriptomes for 59 diatom taxa to resolve freshwater transitions in one lineage, the Thalassiosirales. Although most parts of the species tree were consistently resolved with strong support, we had difficulties resolving a Paleocene radiation, which affected the placement of one freshwater lineage. This and other parts of the tree were characterized by high levels of gene tree discordance caused by incomplete lineage sorting and low phylogenetic signal. Despite differences in species trees inferred from concatenation versus summary methods and codons versus amino acids, traditional methods of ancestral state reconstruction supported six transitions into freshwaters, two of which led to subsequent species diversification. Evidence from gene trees, protein alignments, and diatom life history together suggest that habitat transitions were largely the product of homoplasy rather than hemiplasy, a condition where transitions occur on branches in gene trees not shared with the species tree. Nevertheless, we identified a set of putatively hemiplasious genes, many of which have been associated with shifts to low salinity, indicating that hemiplasy played a small but potentially important role in freshwater adaptation. Accounting for differences in evolutionary outcomes, in which some taxa became locked into freshwaters while others were able to return to the ocean or become salinity generalists, might help further distinguish different sources of adaptive mutation in freshwater diatoms. [hemiplasy; homoplasy; phylogenomics; salinity, Thalassiosirales.] 

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4. QuCo: quartet-based co-estimation of species trees and gene trees

   https://doi.org/10.1093/bioinformatics/btac265  

   Rabiee, Maryam; Mirarab, Siavash (June 2022, Bioinformatics)

   Abstract MotivationPhylogenomics faces a dilemma: on the one hand, most accurate species and gene tree estimation methods are those that co-estimate them; on the other hand, these co-estimation methods do not scale to moderately large numbers of species. The summary-based methods, which first infer gene trees independently and then combine them, are much more scalable but are prone to gene tree estimation error, which is inevitable when inferring trees from limited-length data. Gene tree estimation error is not just random noise and can create biases such as long-branch attraction. ResultsWe introduce a scalable likelihood-based approach to co-estimation under the multi-species coalescent model. The method, called quartet co-estimation (QuCo), takes as input independently inferred distributions over gene trees and computes the most likely species tree topology and internal branch length for each quartet, marginalizing over gene tree topologies and ignoring branch lengths by making several simplifying assumptions. It then updates the gene tree posterior probabilities based on the species tree. The focus on gene tree topologies and the heuristic division to quartets enables fast likelihood calculations. We benchmark our method with extensive simulations for quartet trees in zones known to produce biased species trees and further with larger trees. We also run QuCo on a biological dataset of bees. Our results show better accuracy than the summary-based approach ASTRAL run on estimated gene trees. Availability and implementationQuCo is available on https://github.com/maryamrabiee/quco. Supplementary informationSupplementary data are available at Bioinformatics online. 

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5. Phylogenomic comparative methods: Accurate evolutionary inferences in the presence of gene tree discordance

   https://doi.org/10.1073/pnas.2220389120  

   Hibbins, Mark S; Breithaupt, Lara C; Hahn, Matthew W (May 2023, Proceedings of the National Academy of Sciences)

   Phylogenetic comparative methods have long been a mainstay of evolutionary biology, allowing for the study of trait evolution across species while accounting for their common ancestry. These analyses typically assume a single, bifurcating phylogenetic tree describing the shared history among species. However, modern phylogenomic analyses have shown that genomes are often composed of mosaic histories that can disagree both with the species tree and with each other—so-called discordant gene trees. These gene trees describe shared histories that are not captured by the species tree, and therefore that are unaccounted for in classic comparative approaches. The application of standard comparative methods to species histories containing discordance leads to incorrect inferences about the timing, direction, and rate of evolution. Here, we develop two approaches for incorporating gene tree histories into comparative methods: one that constructs an updated phylogenetic variance–covariance matrix from gene trees, and another that applies Felsenstein's pruning algorithm over a set of gene trees to calculate trait histories and likelihoods. Using simulation, we demonstrate that our approaches generate much more accurate estimates of tree-wide rates of trait evolution than standard methods. We apply our methods to two clades of the wild tomato genusSolanumwith varying rates of discordance, demonstrating the contribution of gene tree discordance to variation in a set of floral traits. Our approaches have the potential to be applied to a broad range of classic inference problems in phylogenetics, including ancestral state reconstruction and the inference of lineage-specific rate shifts. 

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