Biology subjects

Delwiche, C. F.

Publications and source records attributed to Delwiche, C. F..

7 recordsLinked to original sources

bioRxiv2026

OmegaSwitch: Bayesian Markov-Modulated Codon Models for Estimating dN/dS

Selective pressures can vary across both sites and evolutionary lineages; however, most codon models accommodate heterogeneity along only one of these dimensions and require the number of selective regimes to be specified in advance. Here, we introduce OmegaSwitch, a Bayesian phylogenetic software framework for inferring changes in the nonsynonymous-to-synonymous substitution-rate ratio (dN/dS) across sites and through evolutionary time. We implement a Markov-modulated codon model in which lineages transition among discrete dN/dS regimes and use reversible-jump Markov chain Monte Carlo to infer the number of regimes simultaneously. We further develop a Dirichlet-process mixture extension that allows the parameters governing these time-heterogeneous processes to vary among sites. Ancestral sampling produces joint posterior distributions of dN/dS across sites and nodes of the phylogeny, enabling lineage- and site-specific summaries with quantified uncertainty. Simulation analyses showed that both the posterior intervals for dN/dS and the number of evolutionary regimes were well calibrated under both models. We demonstrate OmegaSwitch using vertebrate alpha- and beta-globins. OmegaSwitch therefore provides a flexible Bayesian framework for investigating how selective pressures vary across protein-coding sequences and phylogenetic history.

evolutionary biology↗

bioRxiv2026

Spliceosome loss in the red tide ciliate Mesodinium rubrum presents a symbiotic cul-de-sac

Mesodinium rubrum, a marine microbial eukaryote associated with some of the largest red tides on Earth, has the remarkable ability to commandeer the plastids, mitochondria and nuclei from the alga Teleaulax amphioxeia for photosynthesis. Here we report analyses of assemblies of M. rubrums two nuclear genomes. Unexpectedly, M. rubrum appears to have completely lost its spliceosomal introns, most spliceosomal molecules, and the key genes for an intron splicing-associated process, Nonsense-mediated mRNA Decay (NMD). In contrast, non-spliceosomal tRNA introns have been retained, as have thousands of intron analogs spliced out of DNA during ciliate somatic genome development (internal eliminated sequences - IESs). Intron-containing genes, especially from intron-rich species like T. amphioxeia, would likely be defunct if horizontally transferred to a host without a spliceosome like M. rubrum, and thus we propose that introns can be a roadblock to progressive endosymbiotic genomic integration.

genomics↗

bioRxiv2026

Inferring Gene Presence in Incomplete Data via Phylogenetic Occupancy Modeling

Increasing access to genomic data has revolutionized our understanding of biology. Organisms that were previously unculturable or otherwise difficult to study have been investigated using metagenomic sequencing and bioinformatic assemblies, illuminating biological diversity that was previously invisible. However, as the availability of genomic data has grown, so has the challenge posed by incomplete genomes. Many genomes obtained from metagenomic assemblies or mixed cultures are of poor quality and establishing fully complete genomes requires substantial effort. Incomplete genomes pose difficulties for several common analyses, particularly gene-inventory and core-genome analyses. When genomes are incomplete, distinguishing true gene absence from non-detection becomes difficult. For relatively complete genomes, gene absences are inferred to be true absences, but for highly incomplete genomes, researchers often exclude such data entirely. Probabilistic models have attempted to address this issue in core genome analyses. In particular, mO-TUpan utilizes an iterative algorithm to infer genome completeness and categorize genes as core or accessory. In this work, we substantially improve upon this approach by integrating a well-established class of ecological models, called occupancy models, with evolutionary modeling. Our "phylogenetic occupancy model" defines a probability distribution over gene presence that accounts for shared information across related genomes. This framework simultaneously estimates genome completeness and the probability that a gene is present but unobserved. This model substantially outperforms competing methods for core genome inference and enables inference of single-gene presence/absence and ancestral-state reconstruction. Alongside this paper, we provide our model as a Python package.

evolutionary biology↗

bioRxiv2024

Group II Introns in Archaeal Genomes and the Evolutionary Origin of Eukaryotic Spliceosomal Introns

A key attribute of eukaryotic genomes is the presence of abundant spliceosomal introns that break up many protein-coding genes into multiple exons and must be spliced out during the process of gene expression. These introns are believed to be evolutionarily derived from group II introns, which are known to be widespread in bacteria. One prominent hypothesis is that the spliceosomal intron arose after the endosymbiotic origin of the mitochondrion, as a consequence of transfer of genes containing group II introns from the organelle to nuclear genome; in this model, transfer of group II introns into the ancestral eukaryotic genome set the stage for evolution of the spliceosomal form. However, the recent discovery and sequencing of asgard archaea -- the closest archaeal relatives of extant eukaryotes -- has shed significant light on the composition of the early eukaryotic genome and calls that model into question. Using sequence analysis and structural modeling, we show here the presence of group II intron maturases in the genomes of Heimdallarchaeia and other asgard archaea, and demonstrate by phylogenetic inference that these are closely related to both eukaryotic mitochondrial group II intron maturases and the spliceosome protein PRP8. This suggests that the first intron-containing eukaryotic common ancestor (FIECA) inherited selfish group II introns from its ancestral archaeal genome - the progenitor of the nuclear genome - rather than from the mitochondrial endosymbiont. These observations suggest that the spread and diversification of introns may have occurred independently of the acquisition of the mitochondrion. To better understand the context for intron evolution, we investigate the broader occurrence of group II introns in archaea, identify archaeal clades enriched in group II introns, and perform structural modeling to examine the relationship between the archaeal group II intron maturase and the eukaryotic spliceosome. We propose a model of intron acquisition and expansion during early eukaryotic evolution that places the spread of introns prior to the acquisition of mitochondria, possibly facilitated by the separation of transcription and translation afforded by the nucleus.

evolutionary biology↗

bioRxiv2024

Investigating the Evolution of Green Algae with a Large Transcriptomic Dataset

The colonization of land by plants, thought to have occurred approximately 450-500 million years ago (Ma) is one of the most important events in the history of life on Earth. Land plants, hereafter referred to as "embryophytes," comprise the foundation of every terrestrial biome, making them an essential lineage for the origin and maintenance of biodiversity. The embryophytes form a monophyletic clade within one of the two major phyla of the green algae, the Streptophyta. Estimates from fossil data and molecular clock analyses suggest the charophytes diverged from the other main phylum of green algae, the Chlorophyta, as much as 1500 Ma. Here we present a phylogenetic analysis using transcriptomic and genomic data of 62 green algae and embryophyte operational taxonomic units, 31 of which were assembled de novo for this project. We focus on identifying the charophyte lineage that is sister to embryophytes, and show that the Zygnematophyceae have the strongest support, followed by the Charophyceae. We demonstrate that this phylogenetic tree topology is robust across different phylogenetic models and methods. Furthermore, we examine amino acid and codon usage across the tree and find these data broadly follow the phylogenetic tree. We conclude by searching the dataset for several protein domains and gene families known to be important in embryophytes, including the ethylene signaling pathway and various ion transporters. Many of these domains and genes have homologous sequences in the charophyte lineages, giving insight into the processes that underlay the colonization of the land by plants.

evolutionary biology↗

bioRxiv2022

A phylogenomically informed five-order system for the closest relatives of land plants

The evolution of streptophytes had a profound impact on life on Earth. They brought forth those photosynthetic eukaryotes that today dominate the macroscopic flora: the land plants (Embryophyta) [1]. There is convincing evidence that the unicellular/filamentous Zygnematophyceae--and not the morphologically more elaborate Coleochaetophyceae or Charophyceae--are the closest algal relatives of land plants [2, 3, 4, 5, 6]. Despite the species richness (>4,000), wide distribution, and key evolutionary position of the zygnematophytes, their internal phylogeny remains largely unresolved [7, 8]. There are also putative zygnematophytes with interesting body plan modifications (e.g., filamentous growth) whose phylogenetic affiliations remain unknown. Here, we studied a filamentous green alga (strain MZCH580) from an Austrian peat bog with central or parietal chloroplasts that lack discernible pyrenoids. It represents Mougeotiopsis calospora PALLA, an enigmatic alga that was described more than 120 years ago [9], but never subjected to molecular analyses. We generated transcriptomic data of M. calospora strain MZCH580, and conducted comprehensive phylogenomic analyses (326 nuclear loci) for 46 taxonomically diverse zygnematophytes. Strain MZCH580 falls in a deep-branching zygnematophycean clade together with some unicellular species, and thus represents a formerly unknown zygnematophycean lineage with filamentous growth. Our well-supported phylogenomic tree lets us propose a new five-order system for the Zygnematophyceae, and provides evidence for at least five independent origins of true filamentous growth in the closest algal relatives of land plants. This phylogeny provides a robust and comprehensive framework for performing comparative analyses and inferring the evolution of cellular traits and body plans in the closest relatives of land plants.

evolutionary biology↗

bioRxiv2020

A mobile genetic element in the SARS-CoV-2 genome is shared with multiple insect species

Unprecedented quantities of sequence data have been generated from the newly emergent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causative agent of COVID-19. We document here the presence of s2m, a highly conserved, mobile genetic element with unknown function, in both the SARS-CoV-2 genome and a large number of insect genomes. Although s2m is not universally present among coronaviruses and appears to undergo horizontal transfer, the high sequence conservation and universal presence of s2m among isolates of SARS-CoV-2 indicate that, when present, the element is essential for viral function.

genetics↗