Early Metazoan Research Articles

Cytoskeletal and synaptic polarity of LWamide-like+ ganglion neurons in the sea anemone Nematostella vectensis.

The centralized nervous systems of bilaterian animals rely on directional signaling facilitated by polarized neurons with specialized axons and dendrites. It is not known whether axo-dendritic polarity is exclusive to bilaterians or was already present in early metazoans. We therefore examined neurite polarity in the starlet sea anemone Nematostella vectensis (Cnidaria). Cnidarians form a sister clade to bilaterians and share many neuronal building blocks characteristic of bilaterians, including channels, receptors and synaptic proteins, but their nervous systems comprise a comparatively simple net distributed throughout the body. We developed a tool kit of fluorescent polarity markers for live imaging analysis of polarity in an identified neuron type, large ganglion cells of the body column nerve net that express the LWamide-like neuropeptide. Microtubule polarity differs in bilaterian axons and dendrites, and this in part underlies polarized distribution of cargo to the two types of processes. However, in LWamide-like+ neurons, all neurites had axon-like microtubule polarity suggesting that they may have similar contents. Indeed, presynaptic and postsynaptic markers trafficked to all neurites and accumulated at varicosities where neurites from different neurons often crossed, suggesting the presence of bidirectional synaptic contacts. Furthermore, we could not identify a diffusion barrier in the plasma membrane of any of the neurites like the axon initial segment barrier that separates the axonal and somatodendritic compartments in bilaterian neurons. We conclude that at least one type of neuron in Nematostella vectensis lacks the axo-dendritic polarity characteristic of bilaterian neurons.

Evolutionary origins of chemical synapses.

Synaptic transmission is a fundamental neurobiological process by which neurons interact with each other and non-neuronal cells. It involves release of active substances from the presynaptic neuron onto receptive elements of postsynaptic cells, inducing waves of spreading electrochemical response. While much has been learned about the cellular and molecular mechanisms driving and governing transmitter release and sensing, the evolutionary origin of synaptic connections remains obscure. Herein, we review emerging evidence and concepts suggesting that key components of chemical synapse arose independently from neurons, in different functional and biological contexts, before the rise of multicellular living forms. We argue that throughout evolution, distinct synaptic constituents have been co-opted from ancestral forms for a new role in early metazoan, leading to the rise of chemical synapses and neurotransmission. Such a mosaic model of the origin of chemical synapses agrees with and supports the pluralistic hypothesis of evolutionary change.

Conserved Immunoglobulin Domain Similarities of Higher Plant Proteins

The traces of immunoglobulin domain similarities were searched in sequences of higher plants using bioinformatic tools to look for possible early phylogenic structural relationships. 280 thousand sequence IDs, obtained by sixteen types of primary BLAST searches, were differently processed by seventeen selection procedures and an anti-redundant sequence-related approach using JavaScript, PHP, Windows programs and conserved domain searches by means CDD. The resulting seventeen sets of records describing conserved domain similarities of 1323 different sequence IDs yielded a set of next generation (final set) comprising forty-nine records containing superior (“non-refutable”) conserved immunoglobulin domain similarities. The selected sets and their subsets were mapped and subsequently statistically compared with respect to immunoglobulin-related as well as other reciprocal domain linkages. The list of frequently occurring conserved domain similarities concerned first of all domains important for plant and metazoan immunity, e.g. tyrosine kinases accompanying variable immunoglobulin domains in early Metazoa, toll-like receptors, lectin and leucine-rich repeat domains. Detailed description of immunoglobulin domain similarities occurring in the final set was completed by fold analysis of the restricted segments. The data were then discussed with respect to i) immunoglobulin fold evolution, ii) possible structural importance of domains cd14066 (IRAK) and PLN00113 (LRR-associated kinase) for deep evolution of catalytic serine/threonine/tyrosine kinase domains, iii) interatomic, structural and specificity standpoints and iv) traces of antibody-like phosphorylation sites described in our previous paper.

Transdifferentiation and mesenchymal-to-epithelial transition during regeneration in Demospongiae (Porifera).

Origin and early evolution of regeneration mechanisms remain among the most pressing questions in animal regeneration biology. Porifera have exceptional regenerative capacities and, as early Metazoan lineage, are a promising model for studying evolutionary aspects of regeneration. Here, we focus on reparative regeneration of the body wall in the Mediterranean demosponge Aplysina cavernicola. The epithelialization of the wound surface is completed within 2 days, and the wound is completely healed within 2 weeks. The regeneration is accompanied with the formation of a mass of undifferentiated cells (blastema), which consists of archaeocytes, dedifferentiated choanocytes, anucleated amoebocytes, and differentiated spherulous cells. The main mechanisms of A. cavernicola regeneration are cell dedifferentiation with active migration and subsequent redifferentiation or transdifferentiation of polypotent cells through the mesenchymal-to-epithelial transformation. The main cell sources of the regeneration are archaeocytes and choanocytes. At early stages of the regeneration, the blastema almost devoid of cell proliferation, but after 24 hr postoperation (hpo) and up to 72 hpo numerous DNA-synthesizing cells appear there. In contrast to intact tissues, where vast majority of DNA-synthesizing cells are choanocytes, all 5-ethynyl-2'-deoxyuridine-labeled cells in the blastema are mesohyl cells. Intact tissues, distant from the wound, retains intact level of cell proliferation during whole regeneration process. For the first time, the apoptosis was studied during the regeneration of sponges. Two waves of apoptosis were detected during A. cavernicola regeneration: The first wave at 6-12 hpo and the second wave at 48-72 hpo.

Characterisation of early metazoan secretion through associated signal peptidase complex subunits, prohormone convertases and carboxypeptidases of the marine sponge (Amphimedon queenslandica).

Efficient communication between cells requires the ability to process precursor proteins into their mature and biologically active forms, prior to secretion into the extracellular space. Eukaryotic cells achieve this via a suite of enzymes that involve a signal peptidase complex, prohormone convertases and carboxypeptidases. Using genome and transcriptome data of the demosponge Amphimedon queenslandica, a universal ancestor to metazoan multicellularity, we endeavour to bridge the evolution of precursor processing machinery from single-celled eukaryotic ancestors through to the complex multicellular organisms that compromise Metazoa. The precursor processing repertoire as defined in this study of A. queenslandica consists of 3 defined signal peptidase subunits, 6 prohormone convertases and 1 carboxypeptidase, with 2 putative duplicates identified for signal peptidase complex subunits. Analysis of their gene expression levels throughout the sponge development enabled us to predict levels of activity. Some A. queenslandica precursor processing components belong to established functional clades while others were identified as having novel, yet to be discovered roles. These findings have clarified the presence of precursor processing machinery in the poriferans, showing the necessary machinery for the removal of precursor sequences, a critical post-translational modification required by multicellular organisms, and further sets a foundation towards understanding the molecular mechanism for ancient protein processing.

Spatial and temporal evolution of Ediacaran carbon and sulfur cycles in the Lower Yangtze Block, South China

Major radiations of microscopic and macroscopic eukaryotes occurred respectively in the early and middle Ediacaran Period. Various hypotheses have been proposed to attribute these evolutionary events to changes in ocean redox conditions. To date, published models of the Ediacaran ocean in South China have largely been focused on the Upper and Middle Yangtze blocks, as opposed to the slope and basin sections of the Lower Yangtze Block, where the oldest complex macrofossils of the Ediacaran (i.e. the ~600 Ma Lantian Biota) are preserved. To achieve a holistic understanding of the record of ocean chemistry in the entire Yangtze Block, we carried out carbon (δ13Ccarb and δ13Corg) and sulfur (δ34SCAS and δ34Spyr) isotopic investigations of four new sections (i.e., Wujialing, Meishuxia, Wangfu and Zhushuwu) in the Lower Yangtze Block, in addition to one previously reported drill core at Lantian. The Doushantuo and Lantian formations at these sections represent shelf margin, upper slope, lower slope, and deep basin environments. In conjunction with previous work on sections of the Upper and Middle Yangtze blocks, our study reconstructs the redox structure of the entire Ediacaran ocean in South China. The new results show profound δ13Ccarb negative excursions in the slope and deep basinal sections, which can be correlated to the EN3 and Shuram excursions at a global scale. Notably, the δ13Ccarb and δ34Spyr profiles from shelf to basinal sections show distinct spatial and temporal patterns, which can be explained by model of a redox stratified ocean during the early and middle Ediacaran Period. The finding of isotopically light (34S-depleted) pyrite from this time suggests that the oceanic chemocline extended to intermediate depth. Integrating this study with existing ecological and taphonomic data, it is likely that marine redox stratification in the early Ediacaran limited the spatial distribution of early metazoans in the Lower Yangtze Block.

Neoproterozoic microbially-induced sedimentary structures (MISS) from Ediacaran Podillya Basin, Ukraine: mineralogical particularity and paleoenvironmental application

The Neoproterozoic Podillya sedimentary Basin is well known to the imprints of the Ediacaran soft-bodied fauna which were previously described by many ukrainian and foreign authors. At this period, fossil-rich siliciclastic sediments recognized as traces of early metazoans also contain evidence of significant microbiological activity. In these ediacaran sediments, many structures can be interpreted as microbially induced sedimentary structures (MISS). Their morphologies have a great similarity with modern structures observed in relation with micro-organism activity. These specific structure and surfaces and their mineral composition are the criteria used to study the bacterial structures from the ukrainian Neoproterozoic sedimentary basin. Our results demonstrate microorganisms were organized in bacterial mats whose activity was recorded in the difference of mineralogy between biological films and host rocks. On outcrop, the different type of MISS are often associated with lenticular beddings, ripples and hummocky cross structures indicative of coastal-marine conditions close to the littoral zone of the basin at this epoch. If MISS are important in the issue of paleogeographic reconstructions, they also give precious informations about early diagenetic processes, syn- and post-sedimentation. By mineralogical approach we show that during the time of development of MISS structures and the burial that followed the diagenetic processes have remained moderate. Finally, the close coexistence with ediacarian fossils suggest that such bacterial mats could be at the origin of the fossilization process of soft-bodies of enigmatic Ediacaran biota of Mohyliv-Podylska Group and their preservation until today.

1001 - PRIMITIVE SENSING AND COMMUNICATION MECHANISMS REGULATING BONE MARROW

Studying bone marrow hematopoiesis has provided insights into how heterologous cells interrelate to dynamically regulate production of mature effector cells. The interactions that have been defined have largely been at the level of receptor proteins and signaling pathways that are common among mammalian tissues but are likely to be late in evolutionary time. We hypothesized that organized complex tissues like bone marrow also retain primitive means of communicating from early metazoan ancestors. Multicellular life must have developed simple sensing and communication methods to coordinate responses to alterations in their microenvironment. These are likely to be rapid and non-redundant with subsequent, more complex processes. We considered it likely that these primitive mechanisms remain and may participant in stress and disease states. Evaluating bone marrow hematopoiesis with attention to possible evolutionarily primitive processes, we defined two scenarios. First, a small non-coding RNA based method of rapidly altering adjacent cell protein translation and proliferation that is based on vesicular exchange of cytoplasmic contents. This occurs between select stromal and hematopoietic cells and appears to be responsive to stress. Second, we found that proton partitioning across the cell membrane affects anabolic metabolism to enhance cell proliferation. This is accomplished in normal hematopoietic cells largely secondary to lactate production and mass action in settings of nutrient abundance. However, epigenetic alterations at specific sites affects intracellular shifts of pH in malignant myeloid cells that enforces a metabolic alteration sufficient to provide cells a competitive growth advantage. The bone marrow therefore includes a broad repertoire of strategies to modulate hematopoiesis that extend well beyond defined cytokine and chemokine pathways. These may be responsive to stress conditions or be coopted in settings of disease and may offer new targets for therapeutics.

Cd isotopes trace periodic (bio)geochemical metal cycling at the verge of the Cambrian animal evolution

Abstract Cadmium (Cd) isotopes are an emerging proxy for biological controlled metal and nutrient cycling in the modern oceans, but its potential as a geochemical proxy in ancient environments is still uncertain yet. Sequential leaching experiments of organic matter (OM)-rich shales from the early Cambrian Niutitang Formation (Fm.) were performed in order to understand the cycling of bioessential metals short after the Cambrian animal evolution. Carbonate, OM, sulphide and silicate leachates of OM-rich shales show an overall Cd isotope variation of 6 e112Cd/110Cd (e112Cd) units, indicating preferential incorporation of light Cd isotopes in the order sulphide > OM > carbonate > silicate. Carbonate leachates not only show negative correlations of e112Cd with bulk-rock total organic carbon (TOC) and δ13Corg but also show co-variations with redox-sensitive elements and bioessential metal concentrations, indicating a combined redox and primary productivity evolution of the early Cambrian Nanhua Basin on the Yangtze. Together with increased Cd/Zn ratios and decreasing total organic carbon (TOC) and redox-sensitive elements (RSE) concentrations in the upper Niutitang, this argues for an increase in essential metal availability for primary producers. Coinciding with the transition from a highly unstable ecosystem shortly after the Precambrian/Cambrian boundary to a more habitable environment increased nutrient uptake, oxygen availability and enhanced dissolved organic carbon (DOC) recycling match with the diversification of early metazoan fossil findings at the studied local. Our findings demonstrate that Cd isotopes in combination with trace metals can be used to infer changes in biogeochemical metal cycling in paleoenvironments and further allow establishing Cd isotope systematics as a reliable paleoproductivity proxy in the search for Earth’s earliest phototrophic life.

Development of an apatite oxygen paleobarometer: Experimental characterization of Sm3+-substituted apatite fluorescence as a function of oxygen availability

Global, apatite-bearing phosphorites represent unique biogeochemical periods coincident with major transitions in biological evolution and, particularly, marine oxygenation. However, current understanding of such oxygenation is limited by qualitative and not uncommonly contrasting interpretations of the marine redox conditions evidenced by sedimentary isotope and trace element abundances. A potentially novel measure of ancient marine oxygenation has previously been indicated by fluorescence signatures detected in Sm3+-substituted microfossil-preserving apatite from Early Cambrian phosphorites, consistent with experimental studies demonstrating an oxygen-dependent mechanism for Sm3+ incorporation. Quantitative calibration of these signatures would enable the interpretation of oxygen concentrations during sedimentary apatite formation. In the experiments described, heat-promoted substitution of Sm3+ in apatite powder pellets has been conducted under gaseous oxygen concentrations ranging from 0 to 20.9%. The resulting fluorescence signals provide a comparison to those observed in naturally occurring phosphorites that should reflect the levels of oxygen in the immediate precipitating environment. These analyses suggest that a metric describing the relative spectral characteristics derived from end-member oxic and anoxic experiments, here described as an apatite oxygen paleobarometer (AOP), robustly correlates with gaseous oxygen concentrations. The application of this quantifiable metric to phosphorite apatite is expected to provide a fundamentally new dataset by which to probe ancient marine redox conditions, particularly during the Neoproterozoic-Cambrian phosphogenic event and diversification of early metazoans.

Three-dimensionally preserved soft tissues and calcareous hexactins in a Silurian sponge: implications for early sponge evolution.

Sponges (Porifera), as one of the earliest-branching animal phyla, are crucial for understanding early metazoan phylogeny. Recent studies of Lower Palaeozoic sponges have revealed a variety of character states and combinations unknown in extant taxa, challenging our views of early sponge morphology. The Herefordshire Konservat–Lagerstätte yields an abundant, diverse sponge fauna with three-dimensional preservation of spicules and soft tissue. Carduispongia pedicula gen. et sp. nov. possesses a single layer of hexactine spicules arranged in a regular orthogonal network. This spicule type and arrangement is characteristic of the reticulosans, which have traditionally been interpreted as early members of the extant siliceous Class Hexactinellida. However, the unusual preservation of the spicules of C. pedicula reveals an originally calcareous composition, which would be diagnostic of the living Class Calcarea. The soft tissue architecture closely resembles the complex sylleibid or leuconid structure seen in some modern calcareans and homoscleromorphs. This combination of features strongly supports a skeletal continuum between primitive calcareans and hexactinellid siliceans, indicating that the last common ancestor of Porifera was a spiculate, solitary, vasiform animal with a thin skeletal wall.

The Challenge of the Sponge Suberites domuncula (Olivi, 1792) in the Presence of a Symbiotic Bacterium and a Pathogen Bacterium.

Sponges, which are in close contact with numerous bacteria in prey/predator, symbiotic and pathogenic relationships, must provide an appropriate response in such situations. This starts with a discriminating recognition of the partner either by a physical contact or through secreted molecules or both. We investigated the expression of the Toll-like receptor, Caspase 3/7, Tumor Necrosis Factor receptor-associated factor 6, Bcl-2 homology protein-2 and macrophage expressed genes of axenic sponge cells in the presence of a symbiotic bacterium (Endozoicomonas sp. Hex311), a pathogen bacterium (Pseudoalteromonas sp. 1A1), their exoproducts and lipopolysaccharides. The vast majority of answers are in line with what could be observed with the symbiotic bacterium. The pathogenic bacterium seems to profit from the eukaryotic cell: suppression of the production of the antibacterial compound, inhibition of the apoptosis caspase-dependent pathway, deregulation of bacterial recognition. This work contributes new scientific knowledge in the field of immunology and apoptosis in early branching metazoan harboring within its tissue and cells a large number of symbiotic bacteria.

Sedimentology and chemostratigraphy of the terminal Ediacaran Dengying Formation at the Gaojiashan section, South China.

The late Ediacaran Dengying Formation (ca. 551.1-538.8 Ma) in South China is one of two successions where Ediacara-type macrofossils are preserved in carbonate facies along with skeletal fossils and bilaterian animal traces. Given the remarkable thickness of carbonate-bearing strata deposited in less than 12.3 million years, the Dengying Formation holds the potential for a relatively continuous chemostratigraphic profile for the terminal Ediacaran stage. In this study, a detailed sedimentological and chemostratigraphic (δ13Ccarb, δ18Ocarb, δ13Corg, δ34Spyrite, and 87Sr/86Sr) investigation was conducted on the Dengying Formation at the Gaojiashan section, Ningqiang County of the southern Shaanxi Province, South China. Sedimentological results reveal an overall shallow marine depositional environment. Carbonate breccia, void-filling botryoidal precipitates, and aragonite crystal fans are common in the Algal Dolomite Member of the Dengying Formation, suggesting that peritidal facies were repeatedly karstified. The timing of karstification was likely early, probably soon after the deposition of the dolomite sediments. The presence of authigenic aragonite cements suggests high alkalinity in the terminal Ediacaran ocean. Geochemical analysis of micro-drilled samples shows that distinct compositions are registered in different carbonate phases, which should be considered when constructing chemostratigraphic profiles representative of true temporal variations in seawater chemistry. Integrated chemostratigraphic data suggest enhanced burial of organic carbon and pyrite, and the occurrence of extensive marine anoxia (at least in the Gaojiashan Member). Rapid basinal subsidence and carbonate accumulation during a time of elevated seawater alkalinity and increased rates of pyrite burial may have facilitated the evolutionary innovation of early biomineralizing metazoans.

Initial function of microRNAs as a defence mechanism against invading organisms

BackgroundAlthough microRNA (miRNA) regulation is widely considered as a mechanism to regulate gene expression in metazoans, plants and viruses, there are recent reports that show the interaction between viruses and their mammal hosts via miRNAs produced from both sides. MiRNAs are highly conserved among mammals, whereas the early miRNAs seem to be more diverse, implying a dynamic functional evolution of miRNAs in the early species. To obtain an evolution landscape of miRNA function and elucidate the initial function of miRNAs, we investigated the targets of miRNAs in the viral system and among metazoan species.MethodsThe targets in a set of 5361 viral genomes for all the miRNAs encoded by 17 metazoan species that occur at the key evolutionary nodes on metazoan phylogeny were calculated according to base matching of miRNAs to their target sites and the free energy of miRNA-mRNA duplex.ResultsThe results showed that sponge miRNAs had the high targeting potential against viral systems, whereas those in other early metazoans showed lower targeting potential. The miRNAs of ancient species tended to have more targets in double-stranded DNA viruses and bacteriophages than in other viruses. The metazoan miRNA targets on self-genomes showed an increased tendency along with evolution.ConclusionsThe results of miRNA target analysis for 17 metazoan and virus genomes suggest that the initial function of miRNAs was predominantly antiviral, as evolution proceeded, miRNAs acted more specifically on self-genomes. This may imply the origin of microRNAs as a defensive rather than a regulatory strategy.

The kinetics of cellular and humoral immune responses of common carp to presporogonic development of the myxozoan Sphaerospora molnari

BackgroundSphaerospora molnari is a myxozoan parasite causing skin and gill sphaerosporosis in common carp (Cyprinus carpio) in central Europe. For most myxozoans, little is known about the early development and the expansion of the infection in the fish host, prior to spore formation. A major reason for this lack of information is the absence of laboratory model organisms, whose life-cycle stages are available throughout the year.ResultsWe have established a laboratory infection model for early proliferative stages of myxozoans, based on separation and intraperitoneal injection of motile and dividing S. molnari stages isolated from the blood of carp. In the present study we characterize the kinetics of the presporogonic development of S. molnari, while analyzing cellular host responses, cytokine and systemic immunoglobulin expression, over a 63-day period. Our study shows activation of innate immune responses followed by B cell-mediated immune responses. We observed rapid parasite efflux from the peritoneal cavity (< 40 hours), an initial covert infection period with a moderate proinflammatory response for about 1–2 weeks, followed by a period of parasite multiplication in the blood which peaked at 28 days post-infection (dpi) and was associated with a massive lymphocyte response. Our data further revealed a switch to a massive anti-inflammatory response (up to 1456-fold expression of il-10), a strong increase in the expression of IgM transcripts and increased number of IgM+ B lymphocytes, which produce specific antibodies for the elimination of most of the parasites from the fish at 35 dpi. However, despite the presence of these antibodies, S. molnari invades the liver 42 dpi, where an increase in parasite cell number and indistinguishable outer cell membranes are indicative of effective exploitation and disguise mechanisms. From 49 dpi onwards, the acute infection changes to a chronic one, with low parasite numbers remaining in the fish.ConclusionsTo our knowledge, this is the first time myxozoan early development and immune modulation mechanisms have been analyzed along with innate and adaptive immune responses of its fish host, in a controlled laboratory system. Our study adds important information on host–parasite interaction and co-evolutionary adaptation of early metazoans (Cnidaria) with basic vertebrate (fish) immune systems and the evolution of host adaptation and parasite immune evasion strategies.

Differential regulation of myc homologs by Wnt/β-Catenin signaling in the early metazoan Hydra.

The c‐Myc protein is a transcription factor with oncogenic potential controlling fundamental cellular processes. Homologs of the human c‐myc protooncogene have been identified in the early diploblastic cnidarian Hydra (myc1, myc2). The ancestral Myc1 and Myc2 proteins display the principal design and biochemical properties of their vertebrate derivatives, suggesting that important Myc functions arose very early in metazoan evolution. c‐Myc is part of a transcription factor network regulated by several upstream pathways implicated in oncogenesis and development. One of these signaling cascades is the Wnt/β‐Catenin pathway driving cell differentiation and developmental patterning, but also tumorigenic processes including aberrant transcriptional activation of c‐myc in several human cancers. Here, we show that genetic or pharmacological stimulation of Wnt/β‐Catenin signaling in Hydra is accompanied by specific downregulation of myc1 at mRNA and protein levels. The myc1 and myc2 promoter regions contain consensus binding sites for the transcription factor Tcf, and Hydra Tcf binds to the regulatory regions of both promoters. The myc1 promoter is also specifically repressed in the presence of ectopic Hydra β‐Catenin/Tcf in avian cell culture. We propose that Hydra myc1 is a negative Wnt signaling target, in contrast to vertebrate c‐myc, which is one of the best studied genes activated by this pathway. On the contrary, myc2 is not suppressed by ectopic β‐Catenin in Hydra and presumably represents the structural and functional c‐myc ortholog. Our data implicate that the connection between β‐Catenin‐mediated signaling and myc1 and myc2 gene regulation is an ancestral metazoan feature. Its impact on decision making in Hydra interstitial stem cells is discussed.

Does resource availability help determine the evolutionary route to multicellularity?

Genetic heterogeneity and homogeneity are associated with distinct sets of adaptive advantages and bottlenecks, both in developmental biology and population genetics. Whereas populations of individuals are usually genetically heterogeneous, most multicellular metazoans are genetically homogeneous. Observing that resource scarcity fuels genetic heterogeneity in populations, we propose that monoclonal development is compatible with the resource‐rich and stable internal environments that complex multicellular bodies offer. In turn, polyclonal development persists in tumors and in certain metazoans, both exhibiting a closer dependence on external resources. This eco‐evo‐devo approach also suggests that multicellularity may originally have emerged through polyclonal development in early metazoans, because of their reduced shielding from environmental fluctuations.

Unusually variable paleocommunity composition in the oldest metazoan fossil assemblages

AbstractRecent excavations of Ediacaran assemblages have revealed striking bed-to-bed variation in diversity–abundance structure, offering potential insight into the ecology and taphonomy of these poorly understood early Metazoan ecosystems. Here we compare faunal variability in Ediacaran assemblages to that of younger benthic assemblages, both fossil and modern. We decompose the diversity of local assemblages into within-collection (α) and among-collection (β) components and show that β diversity in Ediacaran assemblages is unusually high relative to younger assemblages. Average between-bed ecological dissimilarities in the Phanerozoic fossil record are comparable to within-habitat dissimilarities typically observed over meter to kilometer scales in modern benthic marine habitats, but dissimilarities in Ediacaran assemblages are comparable to those typically observed over 10–100 km scales in modern habitats. We suggest that the unusually variable diversity–abundance structure of Ediacaran assemblages is due both to their preservation as near snapshots of benthic communities and to original ecological differences, in particular the paucity of motile taxa and the near lack of predation and infaunalization.

Integrated records of environmental change and evolution challenge the Cambrian Explosion

The 'Cambrian Explosion' describes the rapid increase in animal diversity and abundance, as manifest in the fossil record, between ~540 and 520 million years ago (Ma). This event, however, is nested within a far more ancient record of macrofossils extending at least into the late Ediacaran at ~571 Ma. The evolutionary events documented during the Ediacaran-Cambrian interval coincide with geochemical evidence for the modernisation of Earth's biogeochemical cycles. Holistic integration of fossil and geochemical records leads us to challenge the notion that the Ediacaran and Cambrian worlds were markedly distinct, and places biotic and environmental change within a longer-term narrative. We propose that the evolution of metazoans may have been facilitated by a series of dynamic and global changes in redox conditions and nutrient supply, which, potentially together with biotic feedbacks, enabled turnover events that sustained multiple phases of radiation. We argue that early metazoan diversification should be recast as a series of successive, transitional radiations that extended from the late Ediacaran and continued through the early Palaeozoic. We conclude that while the Cambrian Explosion represents a radiation of crown-group bilaterians, it was simply one phase amongst several metazoan radiations, some older and some younger.

De novo transcriptome assembly of the cubomedusa Tripedalia cystophora, including the analysis of a set of genes involved in peptidergic neurotransmission

BackgroundThe phyla Cnidaria, Placozoa, Ctenophora, and Porifera emerged before the split of proto- and deuterostome animals, about 600 million years ago. These early metazoans are interesting, because they can give us important information on the evolution of various tissues and organs, such as eyes and the nervous system. Generally, cnidarians have simple nervous systems, which use neuropeptides for their neurotransmission, but some cnidarian medusae belonging to the class Cubozoa (box jellyfishes) have advanced image-forming eyes, probably associated with a complex innervation. Here, we describe a new transcriptome database from the cubomedusa Tripedalia cystophora.ResultsBased on the combined use of the Illumina and PacBio sequencing technologies, we produced a highly contiguous transcriptome database from T. cystophora. We then developed a software program to discover neuropeptide preprohormones in this database. This script enabled us to annotate seven novel T. cystophora neuropeptide preprohormone cDNAs: One coding for 19 copies of a peptide with the structure pQWLRGRFamide; one coding for six copies of a different RFamide peptide; one coding for six copies of pQPPGVWamide; one coding for eight different neuropeptide copies with the C-terminal LWamide sequence; one coding for thirteen copies of a peptide with the RPRAamide C-terminus; one coding for four copies of a peptide with the C-terminal GRYamide sequence; and one coding for seven copies of a cyclic peptide, of which the most frequent one has the sequence CTGQMCWFRamide. We could also identify orthologs of these seven preprohormones in the cubozoans Alatina alata, Carybdea xaymacana, Chironex fleckeri, and Chiropsalmus quadrumanus. Furthermore, using TBLASTN screening, we could annotate four bursicon-like glycoprotein hormone subunits, five opsins, and 52 other family-A G protein-coupled receptors (GPCRs), which also included two leucine-rich repeats containing G protein-coupled receptors (LGRs) in T. cystophora. The two LGRs are potential receptors for the glycoprotein hormones, while the other GPCRs are candidate receptors for the above-mentioned neuropeptides.ConclusionsBy combining Illumina and PacBio sequencing technologies, we have produced a new high-quality de novo transcriptome assembly from T. cystophora that should be a valuable resource for identifying the neuronal components that are involved in vision and other behaviors in cubomedusae.