The Paleoproterozoic fossil record: Implications for the evolution of the biosphere during Earth's middle-age

Javaux, Emmanuelle; Lepot, Kevin

doi:10.1016/j.earscirev.2017.10.001

Cited by 116 publications

(79 citation statements)

References 241 publications

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“…In terms of timing during Earth history, it is generally agreed that the first forms of life on Earth were prokaryotes, with isotopic evidence for the existence of bacterial and archaeal metabolic processes tracing back to rocks 3.5 billion years of age [10,11] or older [12]. The microfossil record indicates that eukaryotes arose later, about 1.4 to 1.6 billion years ago [13], hence that eukaryotes arose from prokaryotes. Though eukaryotes are younger than prokaryotes, the nature of their phylogenetic relationship(s) to bacteria and archaea remains debated because of differing views about the evolutionary origin of eukaryotic cells.…”

Section: Introductionmentioning

confidence: 99%

Bacterial genes outnumber archaeal genes in eukaryotic genomes

Bruckner

Martin

2019

Preprint

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AbstractThe origin of eukaryotes is one of evolution’s most important transitions, yet it is still poorly understood. Evidence for how it occurred should be preserved in eukaryotic genomes. Based on phylogenetic trees from ribosomal RNA and ribosomal proteins, eukaryotes are typically depicted as branching together with or within archaea. This ribosomal affiliation is widely interpreted as evidence for an archaeal origin of eukaryotes. However, the extent to which the archaeal ancestry of genes for the cytosolic ribosomes of eukaryotic cells is representative for the rest of the eukaryotic genome is unknown. Here we have clustered 19,050,992 protein sequences from 5,443 bacteria and 212 archaea with 3,420,731 protein sequences from 150 eukaryotes spanning six eukaryotic supergroups to identify genes that link eukaryotes exclusively to bacteria and archaea respectively. By downsampling the bacterial sample we obtain estimates for the bacterial and archaeal proportions of genes among 150 eukaryotic genomes. Eukaryotic genomes possess a bacterial majority of genes. On average, eukaryotic genes are 56% bacterial in origin. The majority drops to 53% in eukaryotes that never possessed plastids, and increases to 61% in photosynthetic eukaryotic lineages, where the cyanobacterial ancestor of plastids contributed additional genes to the eukaryotic genome, reaching 67% in higher plants. Intracellular parasites, which undergo reductive evolution in adaptation to the nutrient rich environment of the cells that they infect, relinquish bacterial genes for metabolic processes. In the current sample, this process of adaptive gene loss is most pronounced in the human parasite Encephalitozoon intestinalis with 86% archaeal and 14% bacterial derived genes. The most bacterial eukaryote genome sampled is rice, with 67% bacterial and 33% archaeal genes. The functional dichotomy, initially described for yeast, of archaeal genes being involved in genetic information processing and bacterial genes being involved in metabolic processes is conserved across all eukaryotic supergroups.

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Section: Introductionmentioning

confidence: 99%

Bacterial genes outnumber archaeal genes in eukaryotic genomes

Bruckner

Martin

2019

Preprint

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“…Current molecular clock estimates for the emergence of the last eukaryotic common ancestor (LECA) vary considerably depending on the models and fossil calibrations used, ranging from 1.9 to 1 billion years ago (Ga) [39]. Putative crown-group eukaryotic microfossils date back to the late Paleoproterozoic Era (2.5-1.6 Ga) [40,41], consistent with the older age estimate for the LECA provided by molecular clocks [39]. Recently, phosphatized microfossils from the Vindhyan Supergroup in India have been interpreted as ca.…”

Section: Animal Origins In Context: the Tonian Earth Systemmentioning

confidence: 99%

Animal origins and the Tonian Earth system

Mills

Francis

Canfield

2018

Emerging Topics in Life Sciences

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The Neoproterozoic Era (1000-541 million years ago, Ma) was characterized by dramatic environmental and evolutionary change, including at least two episodes of extensive, low-latitude glaciation, potential changes in the redox structure of the global ocean, and the origin and diversification of animal life. How these different events related to one another remains an active area of research, particularly how these environmental changes influenced, and were influenced by, the earliest evolution of animals. Animal multicellularity is estimated to have evolved in the Tonian Period (1000-720 Ma) and represents one of at least six independent acquisitions of complex multicellularity, characterized by cellular differentiation, three-dimensional body plans, and active nutrient transport. Compared with the other instances of complex multicellularity, animals represent the only clade to have evolved from wall-less, phagotrophic flagellates, which likely placed unique cytological and trophic constraints on the evolution of animal multicellularity. Here, we compare recent molecular clock estimates with compilations of the chromium isotope, micropaleontological, and organic biomarker records, suggesting that, as of now, the origin of animals was not obviously correlated to any environmental-ecological change in the Tonian Period. This lack of correlation is consistent with the idea that the evolution of animal multicellularity was primarily dictated by internal, developmental constraints and occurred independently of the known environmental-ecological changes that characterized the Neoproterozoic Era.

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“…These authors emphasized that linking fossils that are hundreds of millions to >1 billion years of age with modern representatives can be difficult, and also noted the potential for deposit contamination and for physical processes to mimic simple cyanobacterial morphologies. The difficulties of classifying Proterozoic remains as algae or even distinguishing prokaryotic fossils from eukaryotes were echoed by Javaux and Lepot (), who reviewed known Paleoproterozoic microfossils and provide an excellent primer on modern methods employed to evaluate such ancient remains.…”

Section: How Might More Proterozoic Fossils Aid Our Understanding Of mentioning

confidence: 99%

“…The common assumption that fossil akinetes indicate N‐fixation is based upon the potential for modern multicellular cyanobacteria that generate akinetes to also have the genetic capacity to produce structurally distinctive heterocytes (heterocysts) marking N‐fixation, but which may have lower preservation potential. Existing Proterozoic fossils interpreted as cyanobacterial akinetes have recently been reviewed (Javaux and Lepot ), but more fossil evidence would be helpful, because considerable skepticism surrounds the interpretation of putative akinete fossils. Benthic cyanobacterial filaments having cells interpreted as akinetes have recently been reported as compression fossils on the bedding surfaces of shales from the ~1,000–720 Ma Liulaobei Formation, North China (Pang et al.…”

Section: How Might More Proterozoic Fossils Aid Our Understanding Of mentioning

confidence: 99%

Digging deeper: why we need more Proterozoic algal fossils and how to get them

Graham

2018

Journal of Phycology

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Known Proterozoic algal fossils raise compelling questions about the origin and diversification of cyanobacteria and eukaryotic algae, and their ecological influence in deep time. This Perspectives article describes particular examples of persistent evolutionary and biogeochemical issues whose resolution would be aided by additional algal fossil evidence from Proterozoic deposits, which have been the subjects of recent intensive study. New Proterozoic geosciences literature relevant to the early diversification of algae is surveyed. Previously underappreciated algal traits that might improve taxonomic attributions of fossil remains are highlighted. Processes that phycologists could use to improve detection of algal fossils are recommended. Potential geological sources of new Proterozoic fossils are suggested.

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The Paleoproterozoic fossil record: Implications for the evolution of the biosphere during Earth's middle-age

Cited by 116 publications

References 241 publications

Bacterial genes outnumber archaeal genes in eukaryotic genomes

Bacterial genes outnumber archaeal genes in eukaryotic genomes

Animal origins and the Tonian Earth system

Digging deeper: why we need more Proterozoic algal fossils and how to get them

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