Cyanobacteria and the Great Oxidation Event:Evidence from genes and fossils

This article is corrected by:Errata: Cyanobacteria and the Great Oxidation Event: evidence from genes and fossils Volume 58, Issue 5, 935–936, Article first published online: 14 August 2015International audienceCyanobacteria are among the most ancient of evolutionary lineages, oxygenic photosynthesizers that may have originated before 3.0 Ga, as evidenced by free oxygen levels. Throughout the Precambrian, cyanobacteria were one of the most important drivers of biological innovations, strongly impacting early Earth's environments. At the end of the Archean Eon, they were responsible for the rapid oxygena-tion of Earth's atmosphere during an episode referred to as the Great Oxidation Event (GOE). However, little is known about the origin and diversity of early cyanobacterial taxa, due to: (1) the scarceness of Precambrian fossil deposits; (2) limited characteristics for the identification of taxa; and (3) the poor preservation of ancient microfossils. Previous studies based on 16S rRNA have suggested that the origin of multi-cellularity within cyanobacteria might have been associated with the GOE. However, single-gene analyses have limitations, particularly for deep branches. We reconstructed the evolutionary history of cyanobacteria using genome scale data and re-evaluated the Precambrian fossil record to get more precise calibrations for a relaxed clock analysis. For the phylogenomic reconstructions, we identified 756 conserved gene sequences in 65 cyanobacterial taxa, of which eight genomes have been sequenced in this study. Character state reconstructions based on maximum likelihood and Bayesian phylogenetic inference confirm previous findings, of an ancient multicellular cyanobacterial lineage ancestral to the majority of modern cyanobacteria. Relaxed clock analyses provide firm support for an origin of cyanobacteria in the Archean and a transition to multicellularity before the GOE. It is likely that multicellu-larity had a greater impact on cyanobacterial fitness and thus abundance, than previously assumed. Multicellularity, as a major evolutionary innovation, forming a novel unit for selection to act upon, may have served to overcome evolutionary constraints and enabled diversification of the variety of mor-photypes seen in cyanobacteria today

Romundina and the evolutionary origin of teeth

Theories on the origin of vertebrate teeth have long focused on chondrichthyans as reflecting a primitive condition—but this is better informed by the extinct placoderms, which constitute a sister clade or grade to the living gnathostomes. Here, we show that ‘supragnathal’ toothplates from the acanthothoracid placoderm Romundina stellina comprise multi-cuspid teeth, each composed of an enameloid cap and core of dentine. These were added sequentially, approximately circumferentially, about a pioneer tooth. Teeth are bound to a bony plate that grew with the addition of marginal teeth. Homologous toothplates in arthrodire placoderms exhibit a more ordered arrangement of teeth that lack enameloid, but their organization into a gnathal, bound by layers of cellular bone associated with the addition of each successional tooth, is the same. The presence of enameloid in the teeth of Romundina suggests that it has been lost in other placoderms. Its covariation in the teeth and dermal skeleton of placoderms suggests a lack of independence early in the evolution of jawed vertebrates. It also appears that the dentition—manifest as discrete gnathal ossifications—was developmentally discrete from the jaws during this formative episode of vertebrate evolution

Evolution of fungal phenotypic disparity

Organismal grade multicellularity has been achieved only in animals, plants, and fungi. All three kingdoms manifest phenotypically disparate body plans, but their evolution has only been considered in detail for animals. Here we seek to test the general relevance of hypotheses on the evolution of animal body plans by characterising the evolution of fungal phenotypic variety (disparity). The distribution of living fungal form is defined by four distinct morphotypes: flagellated, zygomycetous, sac-bearing, and club-bearing. The discontinuity between morphotypes is a consequence of the extinction of phylogenetic intermediates, indicating that a complete record of fungal disparity would present a much more homogeneous distribution of form. Fungal phenotypic variety gradually expands through time for the most part but sharply increases with the emergence of multicellular body plans. Simulations show these temporal trends to be decidedly non-random, and at least partially shaped by hierarchical contingency. Fungal phenotypic distance is decoupled from changes in gene number, genome size, and taxonomic diversity. Only differences in organismal complexity, the number of traits that constitute an organism, at the cellular and multicellular levels present a meaningful relationship with fungal disparity. Both animals and fungi exhibit a gradual increase in disparity through time, resulting in distributions of form made discontinuous by the extinction of phylogenetic intermediates. These congruences hint at a common mode of multicellular body plan evolution.Follow ReadMe files for explanation. Funding provided by: Natural Environment Research Council GW4+ Doctoral Training Programme*Crossref Funder Registry ID: Award Number: Funding provided by: Natural Environment Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000270Award Number: NE/P013678/1Funding provided by: Biotechnology and Biological Sciences Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000268Award Number: BB/T012773/1Funding provided by: Biotechnology and Biological Sciences Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000268Award Number: BB/N000919/1See linked manuscript

SU(3) Breaking in Hyperon Beta Decays: a Prediction for Xi0 -> Sigma+ e anti-neutrino

SU(3) breaking in hyperon semi-leptonic decays is discussed. The SU(3) parameters $F$ and $D$, relevant to the ``proton-spin puzzle'', are extracted and a prediction is presented for the decay Xi0 -> Sigma+ e anti-neutrino, currently under study by the KTeV collaboration. The values found are g1/f1 = 1.16+/-0.03+/-0.01 and Gamma = (0.80+/-0.03+/-0.01) x 10^6 s^-1.Comment: Presented at the III Int. Conf. on Hyperons, Charm and Beauty Hadrons (Genova, June-July 1998). 3 pages, LaTeX2e, uses fleqn, espcrc2, acromake and axodraw packages (incl.

Tectonic blocks and molecular clocks

Evolutionary timescales have mainly used fossils for calibrating molecular clocks, though fossils only really provide minimum clade age constraints. In their place, phylogenetic trees can be calibrated by precisely dated geological events that have shaped biogeography. However, tectonic episodes are protracted, their role in vicariance is rarely justified, the biogeography of living clades and their antecedents may differ, and the impact of such events is contingent on ecology. Biogeographic calibrations are no panacea for the shortcomings of fossil calibrations, but their associated uncertainties can be accommodated. We provide examples of how biogeographic calibrations based on geological data can be established for the fragmentation of the Pangaean supercontinent: (i) for the uplift of the Isthmus of Panama, (ii) the separation of New Zealand from Gondwana, and (iii) for the opening of the Atlantic Ocean. Biogeographic and fossil calibrations are complementary, not competing, approaches to constraining molecular clock analyses, providing alternative constraints on the age of clades that are vital to avoiding circularity in investigating the role of biogeographic mechanisms in shaping modern biodiversity. This article is part of the themed issue ‘Dating species divergences using rocks and clocks’