I'm pleased to introduce our new paper rooting the eukaryote Tree of Life (eToL) that resulted from a collaboration led by PhD student Kelsey Williamson and a large group of collaborators doi.orhttps://doi.org/10.1038/s41586-025-08709-5
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It depends on the group. Most jakobids and malawimonads are aerobic flagellates that can live in freshwater, marine or soil environments. Metamonad excavates are all low-oxygen adapted (have 'anaerobic mitochondria') and depending on the organism live in freshwater, marine or estuarine sediments.
No 'typical excavates' are photosynthetic and they are bacterivorous (i.e. eat Bacteria or Archaea), although it's possible some might eat other eukaryotes. They are all phagotrophs.
An important point is that LECA would be an "excavate" but for sure would be aerobically respiring because we know for sure that mitochondrial aerobic respiration is ancestral to extant eukaryotes. However, the amount of oxygen it 'needed' might have been relatively low.
🔬 Locating the root of the eToL has been a long-standing challenge due to limited signal because of its age (>1.2 Ga), phylogenetic artefacts from inadequate models of sequence evolution, poor taxonomics sampling and vast evolutionary distances from prokaryotic outgroups.
In this study, Kelsey assembled a much larger dataset of mitochondrial proteins (93) from representatives of all known eukaryotic supergroups. We applied state-of-the-art phylogenetic models to infer the optimal trees and extensively evaluated alternative root positions
🌱 The analyses robustly support a root lying between two multi-supergroup assemblages: ‘Opimoda+’ and ‘Diphoda+’. This position was consistently supported across different phylogenetic models and robustness analyses. We're calling this the 'OpiDip+' root
⛏️ Interestingly, flagellated protist lineages with 9 different shared ultrastructural features -- i.e. 'excavate’ flagellates -- are placed on both sides of this root. This suggests that the complex features of the ‘excavate’ cell architecture trace back to LECA
🔑 If excavate features on both sides of the root are indeed homologous, it implies that LECA itself might have been a ‘typical excavate-like’ cell giving us unprecedented insights into the nature and lifestyle of the common ancestor of all eukaryotes.
🎉 This study provides a crucial framework for investigating the origin and evolution of canonical eukaryotic features and sheds new light on the ancestral cells from which all extant eukaryotes arose and the 'endpoint' of eukaryogenesis.
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