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Sierra NC, Gold DA. The evolution of cnidarian stinging cells supports a Precambrian radiation of animal predators. Evol Dev 2024; 26:e12469. [PMID: 38236185 DOI: 10.1111/ede.12469] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Revised: 11/22/2023] [Accepted: 12/31/2023] [Indexed: 01/19/2024]
Abstract
Cnidarians-the phylum including sea anemones, corals, jellyfish, and hydroids-are one of the oldest groups of predatory animals. Nearly all cnidarians are carnivores that use stinging cells called cnidocytes to ensnare and/or envenom their prey. However, there is considerable diversity in cnidocyte form and function. Tracing the evolutionary history of cnidocytes may therefore provide a proxy for early animal feeding strategies. In this study, we generated a time-calibrated molecular clock of cnidarians and performed ancestral state reconstruction on 12 cnidocyte types to test the hypothesis that the original cnidocyte was involved in prey capture. We conclude that the first cnidarians had only the simplest and least specialized cnidocyte type (the isorhiza) which was just as likely to be used for adhesion and/or defense as the capture of prey. A rapid diversification of specialized cnidocytes occurred through the Ediacaran (~654-574 million years ago), with major subgroups developing unique sets of cnidocytes to match their distinct feeding styles. These results are robust to changes in the molecular clock model, and are consistent with growing evidence for an Ediacaran diversification of animals. Our work also provides insight into the evolution of this complex cell type, suggesting that convergence of forms is rare, with the mastigophore being an interesting counterexample.
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Affiliation(s)
- Noémie C Sierra
- Department of Earth and Planetary Sciences, University of California, Davis, Davis, California, USA
- Integrative Genetics and Genomics, University of California, Davis, Davis, California, USA
| | - David A Gold
- Department of Earth and Planetary Sciences, University of California, Davis, Davis, California, USA
- Integrative Genetics and Genomics, University of California, Davis, Davis, California, USA
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Abstract
The Ediacaran period (635–541 Ma) was a time of major environmental change, accompanied by a transition from a microbial world to the animal world we know today. Multicellular, macroscopic organisms preserved as casts and molds in Ediacaran siliciclastic rocks are preserved worldwide and provide snapshots of early organismal, including animal, evolution. Remarkable evolutionary advances are also witnessed by diverse cellular and subcellular phosphatized microfossils described from the Doushantuo Formation in China, the only source showing a diversified assemblage of microfossils. Here, we greatly extend the known distribution of this Doushantuo-type biota in reporting an Ediacaran Lagerstätte from Laurentia (Portfjeld Formation, North Greenland), with phosphatized animal-like eggs, embryos, acritarchs, and cyanobacteria, the age of which is constrained by the Shuram–Wonoka anomaly (c. 570–560 Ma). The discovery of these Ediacaran phosphatized microfossils from outside East Asia extends the distribution of the remarkable biota to a second palaeocontinent in the other hemisphere of the Ediacaran world, considerably expanding our understanding of the temporal and environmental distribution of organisms immediately prior to the Cambrian explosion. The Doushantuo biota of China is incredibly important for understanding the evolution of complex animals. Willman et al. report on evidence of Doushantuo-like biota from the Ediacaran of North Greenland, indicating that these important organisms were distributed across multiple palaeocontinents.
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Yin Z, Vargas K, Cunningham J, Bengtson S, Zhu M, Marone F, Donoghue P. The Early Ediacaran Caveasphaera Foreshadows the Evolutionary Origin of Animal-like Embryology. Curr Biol 2019; 29:4307-4314.e2. [DOI: 10.1016/j.cub.2019.10.057] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Revised: 08/21/2019] [Accepted: 10/29/2019] [Indexed: 01/01/2023]
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Erwin DH. Eric Davidson and deep time. HISTORY AND PHILOSOPHY OF THE LIFE SCIENCES 2017; 39:29. [PMID: 29030723 DOI: 10.1007/s40656-017-0156-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Eric Davidson had a deep and abiding interest in the role developmental mechanisms played in generating evolutionary patterns documented in deep time, from the origin of the euechinoids to the processes responsible for the morphological architectures of major animal clades. Although not an evolutionary biologist, Davidson's interests long preceded the current excitement over comparative evolutionary developmental biology. Here I discuss three aspects at the intersection between his research and evolutionary patterns in deep time: First, understanding the mechanisms of body plan formation, particularly those associated with the early diversification of major metazoan clades. Second, a critique of early claims about ancestral metazoans based on the discoveries of highly conserved genes across bilaterian animals. Third, Davidson's own involvement in paleontology through a collaborative study of the fossil embryos from the Ediacaran Doushantuo Formation in south China.
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Affiliation(s)
- Douglas H Erwin
- Department of Paleobiology, MRC-121, National Museum of Natural History, Washington, DC, 20013-7012, USA.
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Wray GA. Molecular clocks and the early evolution of metazoan nervous systems. Philos Trans R Soc Lond B Biol Sci 2016; 370:rstb.2015.0046. [PMID: 26554040 DOI: 10.1098/rstb.2015.0046] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The timing of early animal evolution remains poorly resolved, yet remains critical for understanding nervous system evolution. Methods for estimating divergence times from sequence data have improved considerably, providing a more refined understanding of key divergences. The best molecular estimates point to the origin of metazoans and bilaterians tens to hundreds of millions of years earlier than their first appearances in the fossil record. Both the molecular and fossil records are compatible, however, with the possibility of tiny, unskeletonized, low energy budget animals during the Proterozoic that had planktonic, benthic, or meiofaunal lifestyles. Such animals would likely have had relatively simple nervous systems equipped primarily to detect food, avoid inhospitable environments and locate mates. The appearance of the first macropredators during the Cambrian would have changed the selective landscape dramatically, likely driving the evolution of complex sense organs, sophisticated sensory processing systems, and diverse effector systems involved in capturing prey and avoiding predation.
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Affiliation(s)
- Gregory A Wray
- Department of Biology and Center for Genomic and Computational Biology, Duke University, Durham, NC 27708, USA
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Cunningham JA, Vargas K, Pengju L, Belivanova V, Marone F, Martínez-Pérez C, Guizar-Sicairos M, Holler M, Bengtson S, Donoghue PCJ. Critical appraisal of tubular putative eumetazoans from the Ediacaran Weng'an Doushantuo biota. Proc Biol Sci 2016; 282:20151169. [PMID: 26180072 PMCID: PMC4528530 DOI: 10.1098/rspb.2015.1169] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Molecular clock analyses estimate that crown-group animals began diversifying hundreds of millions of years before the start of the Cambrian period. However, the fossil record has not yielded unequivocal evidence for animals during this interval. Some of the most promising candidates for Precambrian animals occur in the Weng'an biota of South China, including a suite of tubular fossils assigned to Sinocyclocyclicus, Ramitubus, Crassitubus and Quadratitubus, that have been interpreted as soft-bodied eumetazoans comparable to tabulate corals. Here, we present new insights into the anatomy, original composition and phylogenetic affinities of these taxa based on data from synchrotron radiation X-ray tomographic microscopy, ptychographic nanotomography, scanning electron microscopy and electron probe microanalysis. The patterns of deformation observed suggest that the cross walls of Sinocyclocyclicus and Quadratitubus were more rigid than those of Ramitubus and Crassitubus. Ramitubus and Crassitubus specimens preserve enigmatic cellular clusters at terminal positions in the tubes. Specimens of Sinocyclocyclicus and Ramitubus have biological features that might be cellular tissue or subcellular structures filling the spaces between the cross walls. These observations are incompatible with a cnidarian interpretation, in which the spaces between cross walls are abandoned parts of the former living positions of the polyp. The affinity of the Weng'an tubular fossils may lie within the algae.
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Affiliation(s)
- John A Cunningham
- School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK Department of Palaeobiology and Nordic Center for Earth Evolution, Swedish Museum of Natural History, Stockholm 10405, Sweden
| | - Kelly Vargas
- School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Liu Pengju
- Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing 100037, People's Republic of China
| | - Veneta Belivanova
- Department of Palaeobiology and Nordic Center for Earth Evolution, Swedish Museum of Natural History, Stockholm 10405, Sweden
| | - Federica Marone
- Swiss Light Source, Paul Scherrer Institute, Villigen 5232, Switzerland
| | - Carlos Martínez-Pérez
- School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK Department of Geology, University of Valencia, C/Dr. Moliner 50, Burjassot, Valencia 46100, Spain
| | | | - Mirko Holler
- Swiss Light Source, Paul Scherrer Institute, Villigen 5232, Switzerland
| | - Stefan Bengtson
- Department of Palaeobiology and Nordic Center for Earth Evolution, Swedish Museum of Natural History, Stockholm 10405, Sweden
| | - Philip C J Donoghue
- School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK
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Affiliation(s)
- David J Bottjer
- Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089-0740, United States
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Abstract
Eric Harris Davidson was a unique and creative intellectual force who grappled with the diversity of developmental processes used by animal embryos and wrestled them into an intelligible set of principles, then spent his life translating these process elements into molecularly definable terms through the architecture of gene regulatory networks. He took speculative risks in his theoretical writing but ran a highly organized, rigorous experimental program that yielded an unprecedentedly full characterization of a developing organism. His writings created logical order and a framework for mechanism from the complex phenomena at the heart of advanced multicellular organism development. This is a reminiscence of intellectual currents in his work as observed by the author through the last 30-35 years of Davidson's life.
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Affiliation(s)
- Ellen V Rothenberg
- Division of Biology & Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
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Kaye TG, Falk AR, Pittman M, Sereno PC, Martin LD, Burnham DA, Gong E, Xu X, Wang Y. Laser-stimulated fluorescence in paleontology. PLoS One 2015; 10:e0125923. [PMID: 26016843 PMCID: PMC4446324 DOI: 10.1371/journal.pone.0125923] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2015] [Accepted: 03/26/2015] [Indexed: 11/19/2022] Open
Abstract
Fluorescence using ultraviolet (UV) light has seen increased use as a tool in paleontology over the last decade. Laser-stimulated fluorescence (LSF) is a next generation technique that is emerging as a way to fluoresce paleontological specimens that remain dark under typical UV. A laser's ability to concentrate very high flux rates both at the macroscopic and microscopic levels results in specimens fluorescing in ways a standard UV bulb cannot induce. Presented here are five paleontological case histories that illustrate the technique across a broad range of specimens and scales. Novel uses such as back-lighting opaque specimens to reveal detail and detection of specimens completely obscured by matrix are highlighted in these examples. The recent cost reductions in medium-power short wavelength lasers and use of standard photographic filters has now made this technique widely accessible to researchers. This technology has the potential to automate multiple aspects of paleontology, including preparation and sorting of microfossils. This represents a highly cost-effective way to address paleontology's preparatory bottleneck.
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Affiliation(s)
- Thomas G. Kaye
- Burke Museum of Natural History and Culture, Seattle, Washington, United States of America
- * E-mail:
| | - Amanda R. Falk
- Southwestern Oklahoma State University, Department of Biology, Weatherford, Oklahoma, United States of America
| | - Michael Pittman
- Vertebrate Palaeontology Laboratory, Department of Earth Sciences, University of Hong Kong, Pokfulam, Hong Kong, China
| | - Paul C. Sereno
- Department of Organismal Biology and Anatomy, University of Chicago, Chicago, Illinois, United States of America
| | - Larry D. Martin
- Division of Vertebrate Paleontology, Biodiversity Institute, Natural History Museum, University of Kansas, Lawrence, Kansas, United States of America
| | - David A. Burnham
- Division of Vertebrate Paleontology, Biodiversity Institute, Natural History Museum, University of Kansas, Lawrence, Kansas, United States of America
| | - Enpu Gong
- Department of Geology, Northeastern University, Shenyang, Liaoning, China
| | - Xing Xu
- Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China
| | - Yinan Wang
- 1111 Army Navy Drive, Arlington, Virginia, United States of America
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Xiao S, Muscente AD, Chen L, Zhou C, Schiffbauer JD, Wood AD, Polys NF, Yuan X. The Weng'an biota and the Ediacaran radiation of multicellular eukaryotes. Natl Sci Rev 2014. [DOI: 10.1093/nsr/nwu061] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Abstract
The rise of multicellularity represents a major evolutionary transition and it occurred independently in multiple eukaryote clades. Although simple multicellular organisms may have evolved in the Mesoproterozoic Era or even earlier, complex multicellular eukaryotes began to diversify only in the Ediacaran Period, just before the Cambrian explosion. Thus, the Ediacaran fossil record can provide key paleontological evidence about the early radiation of multicellular eukaryotes that ultimately culminated in the Cambrian explosion. The Ediacaran Weng'an biota in South China hosts exceptionally preserved eukaryote fossils, including various acanthomorphic acritarchs, pseudoparenchymatous thalli, tubular microfossils, and spheroidal fossils such as Megasphaera, Helicoforamina, Spiralicellula, and Caveasphaera. Many of these fossils have been interpreted as multicellular eukaryotes, although alternative interpretations have also been proposed. In this review, we critically examine these various interpretations, focusing particularly on Megasphaera, which has been variously interpreted as a sulfur-oxidizing bacterium, a unicellular protist, a mesomycetozoean-like holozoan, a volvocine green alga, a stem-group animal, or a crown-group animal. We conclude that Megasphaera is a multicellular eukaryote with evidence for cell-to-cell adhesion, a flexible membrane unconstrained by a rigid cell wall, spatial cellular differentiation, germ–soma separation, and programmed cell death. These features are inconsistent with the bacterium, unicellular protist, and mesomycetozoean-like holozoan interpretations. Thus, the surviving hypotheses, particularly the stem-group animal and algal interpretations, should be further tested with additional evidence. The Weng'an biota also hosts cellularly differentiated pseudoparenchymatous thalli with specialized reproductive structures indicative of an affinity with florideophyte red algae. The other Weng'an fossils reviewed here may also be multicellular eukaryotes, although direct cellular evidence is lacking in some and phylogenetic affinities are poorly constrained in others. The Weng'an biota offers many research opportunities to resolve the life histories and phylogenetic diversity of early multicellular eukaryotes and to illuminate the evolutionary prelude to the Cambrian explosion.
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Affiliation(s)
- Shuhai Xiao
- Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | - A. D. Muscente
- Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | - Lei Chen
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China
- College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Chuanming Zhou
- Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China
| | - James D. Schiffbauer
- Department of Geological Sciences, University of Missouri, Columbia, MO 65211, USA
| | - Andrew D. Wood
- Advanced Research Computing, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | - Nicholas F. Polys
- Advanced Research Computing, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | - Xunlai Yuan
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China
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Nielsen C. Life cycle evolution: was the eumetazoan ancestor a holopelagic, planktotrophic gastraea? BMC Evol Biol 2013; 13:171. [PMID: 23957497 PMCID: PMC3751718 DOI: 10.1186/1471-2148-13-171] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2013] [Accepted: 08/06/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Two theories for the origin of animal life cycles with planktotrophic larvae are now discussed seriously: The terminal addition theory proposes a holopelagic, planktotrophic gastraea as the ancestor of the eumetazoans with addition of benthic adult stages and retention of the planktotrophic stages as larvae, i.e. the ancestral life cycles were indirect. The intercalation theory now proposes a benthic, deposit-feeding gastraea as the bilaterian ancestor with a direct development, and with planktotrophic larvae evolving independently in numerous lineages through specializations of juveniles. RESULTS Information from the fossil record, from mapping of developmental types onto known phylogenies, from occurrence of apical organs, and from genetics gives no direct information about the ancestral eumetazoan life cycle; however, there are plenty of examples of evolution from an indirect development to direct development, and no unequivocal example of evolution in the opposite direction. Analyses of scenarios for the two types of evolution are highly informative. The evolution of the indirect spiralian life cycle with a trochophora larva from a planktotrophic gastraea is explained by the trochophora theory as a continuous series of ancestors, where each evolutionary step had an adaptational advantage. The loss of ciliated larvae in the ecdysozoans is associated with the loss of outer ciliated epithelia. A scenario for the intercalation theory shows the origin of the planktotrophic larvae of the spiralians through a series of specializations of the general ciliation of the juvenile. The early steps associated with the enhancement of swimming seem probable, but the following steps which should lead to the complicated downstream-collecting ciliary system are without any advantage, or even seem disadvantageous, until the whole structure is functional. None of the theories account for the origin of the ancestral deuterostome (ambulacrarian) life cycle. CONCLUSIONS All the available information is strongly in favor of multiple evolution of non-planktotrophic development, and only the terminal addition theory is in accordance with the Darwinian theory by explaining the evolution through continuous series of adaptational changes. This implies that the ancestor of the eumetazoans was a holopelagic, planktotrophic gastraea, and that the adult stages of cnidarians (sessile) and bilaterians (creeping) were later additions to the life cycle. It further implies that the various larval types are of considerable phylogenetic value.
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Affiliation(s)
- Claus Nielsen
- Zoological Museum, The Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, DK-2100, Copenhagen, Denmark.
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Xiao S. Neoproterozoic Glaciations and the Fossil Record. THE EXTREME PROTEROZOIC: GEOLOGY, GEOCHEMISTRY, AND CLIMATE 2013. [DOI: 10.1029/146gm16] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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Evolution of centralized nervous systems: two schools of evolutionary thought. Proc Natl Acad Sci U S A 2012; 109 Suppl 1:10626-33. [PMID: 22723354 DOI: 10.1073/pnas.1201889109] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Understanding the evolution of centralized nervous systems requires an understanding of metazoan phylogenetic interrelationships, their fossil record, the variation in their cephalic neural characters, and the development of these characters. Each of these topics involves comparative approaches, and both cladistic and phenetic methodologies have been applied. Our understanding of metazoan phylogeny has increased greatly with the cladistic analysis of molecular data, and relaxed molecular clocks generally date the origin of bilaterians at 600-700 Mya (during the Ediacaran). Although the taxonomic affinities of the Ediacaran biota remain uncertain, a conservative interpretation suggests that a number of these taxa form clades that are closely related, if not stem clades of bilaterian crown clades. Analysis of brain-body complexity among extant bilaterians indicates that diffuse nerve nets and possibly, ganglionated cephalic neural systems existed in Ediacaran organisms. An outgroup analysis of cephalic neural characters among extant metazoans also indicates that the last common bilaterian ancestor possessed a diffuse nerve plexus and that brains evolved independently at least four times. In contrast, the hypothesis of a tripartite brain, based primarily on phenetic analysis of developmental genetic data, indicates that the brain arose in the last common bilaterian ancestor. Hopefully, this debate will be resolved by cladistic analysis of the genomes of additional taxa and an increased understanding of character identity genetic networks.
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Cunningham JA, Thomas CW, Bengtson S, Kearns SL, Xiao S, Marone F, Stampanoni M, Donoghue PCJ. Distinguishing geology from biology in the Ediacaran Doushantuo biota relaxes constraints on the timing of the origin of bilaterians. Proc Biol Sci 2012; 279:2369-76. [PMID: 22319125 DOI: 10.1098/rspb.2011.2280] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The Ediacaran Doushantuo biota has yielded fossils that include the oldest widely accepted record of the animal evolutionary lineage, as well as specimens with alleged bilaterian affinity. However, these systematic interpretations are contingent on the presence of key biological structures that have been reinterpreted by some workers as artefacts of diagenetic mineralization. On the basis of chemistry and crystallographic fabric, we characterize and discriminate phases of mineralization that reflect: (i) replication of original biological structure, and (ii) void-filling diagenetic mineralization. The results indicate that all fossils from the Doushantuo assemblage preserve a complex mélange of mineral phases, even where subcellular anatomy appears to be preserved. The findings allow these phases to be distinguished in more controversial fossils, facilitating a critical re-evaluation of the Doushantuo fossil assemblage and its implications as an archive of Ediacaran animal diversity. We find that putative subcellular structures exhibit fabrics consistent with preservation of original morphology. Cells in later developmental stages are not in original configuration and are therefore uninformative concerning gastrulation. Key structures used to identify Doushantuo bilaterians can be dismissed as late diagenetic artefacts. Therefore, when diagenetic mineralization is considered, there is no convincing evidence for bilaterians in the Doushantuo assemblage.
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Affiliation(s)
- John A Cunningham
- School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK.
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Baron C. A web of controversies: complexity in the burgess shale debate. JOURNAL OF THE HISTORY OF BIOLOGY 2011; 44:745-780. [PMID: 20706775 DOI: 10.1007/s10739-010-9248-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Using the Burgess Shale controversies as a case-study, this paper argues that controversies within different domains may interact as to create a situation of "com- plicated intricacies," where the practicing scientist has to navigate through a context of multiple thought collectives. To some extent each of these collectives has its own dynamic complete with fairly negotiated standards for investigation and explanation, theoretical background assumptions and certain peculiarities of practice. But the intellectual development in one of these collectives may "spill over" having far reaching consequences for the treatment of apparently independent epistemic problems that are subject of investigation in other thought collectives. For the practicing scientist it is necessary to take this complex web of interactions into account in order to be able to navigate in such a situation. So far most studies of academic science have had a tendency to treat the practicing scientist as members of a single (enclosed) thought collective that stands intellectually isolated from other similar entities unless the discipline was in a state of crisis of paradigmatic proportions. The richness and complexity of Burgess Shale debate shows that this encapsulated kind of analysis is not enough.
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Affiliation(s)
- Christian Baron
- Center for the Philosophy of Nature and Science Studies, University of Copenhagen, Blegdamsvej 17, 2100 , Copenhagen, Denmark,
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Complex embryos displaying bilaterian characters from Precambrian Doushantuo phosphate deposits, Weng'an, Guizhou, China. Proc Natl Acad Sci U S A 2009; 106:19056-60. [PMID: 19858483 DOI: 10.1073/pnas.0904805106] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Three-dimensionally preserved embryos from the Precambrian Ediacaran Doushantuo Formation, Weng'an, Guizhou, southern China, have attracted great attention as the oldest fossil evidence yet found for multicellular animal life on Earth. Many embryos are early cleavage embryos and most of them yield a limited phylogenetic signal. Here we report the discovery of two Doushantuo embryos that are three-dimensionally preserved and complex. Imaging techniques using propagation phase-contrast based synchrotron radiation microtomography (PPC-SR-microCT) reveal that the organization of cells demonstrates several bilaterian features, including the formation of anterior-posterior, dorso-ventral, and right-left polarities, and cell differentiation. Unexpectedly, our observations show a noticeable difference in organization patterns between the embryos, suggesting that they represent two distinct taxa. These embryos provide further evidence for the presence of bilaterian animals in the Doushantuo biota. Furthermore, these bilaterians had already diverged into distantly related groups at least 40 million years before the Cambrian radiation, indicating that the last common ancestor of the bilaterians lived much earlier than is usually thought.
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Nielsen C. How did indirect development with planktotrophic larvae evolve? THE BIOLOGICAL BULLETIN 2009; 216:203-215. [PMID: 19556589 DOI: 10.1086/bblv216n3p203] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The two main types of theories for the evolution of the biphasic life cycles in marine invertebrates are discussed. The "intercalation" theories propose that the larval stages (planktotrophic or lecithotrophic) have evolved as specializations from the ancestral, direct life cycle. The opposing "terminal addition" theories propose that the ancestor was holopelagic and that the adult stage was added to the life cycle with the pelagic stage retained as a planktotrophic larva. It is emphasized that theories based on hypothetical ancestors that were unable to feed must be rejected. This applies to planula theories based on a compact planula. Various arguments against the theories that consider the feeding larvae as ancestral in the major eumetazoan lineages and in particular against the trochaea theory are discussed and found untenable. It is suggested that the "Cambrian explosion" was actually a rapid Ediacaran radiation of the eubilaterians that was made possible by the evolution of a tubular gut with all the resulting possibilities for new body plans.
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Affiliation(s)
- Claus Nielsen
- Zoological Museum, The Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark.
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20
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Matz MV, Frank TM, Marshall NJ, Widder EA, Johnsen S. Giant deep-sea protist produces bilaterian-like traces. Curr Biol 2008; 18:1849-54. [PMID: 19026540 DOI: 10.1016/j.cub.2008.10.028] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2008] [Revised: 10/06/2008] [Accepted: 10/07/2008] [Indexed: 10/21/2022]
Abstract
One of the strongest paleontological arguments in favor of the origin of bilaterally symmetrical animals (Bilateria) prior to their obvious and explosive appearance in the fossil record in the early Cambrian, 542 million years ago, is the occurrence of trace fossils shaped like elongated sinuous grooves or furrows in the Precambrian. Being restricted to the seafloor surface, these traces are relatively rare and of limited diversity, and they do not show any evidence of the use of hard appendages. They are commonly attributed to the activity of the early nonskeletonized bilaterians or, alternatively, large cnidarians such as sea anemones or sea pens. Here we describe macroscopic groove-like traces produced by a living giant protist and show that these traces bear a remarkable resemblance to the Precambrian trace fossils, including those as old as 1.8 billion years. This is the first evidence that organisms other than multicellular animals can produce such traces, and it prompts re-evaluation of the significance of Precambrian trace fossils as evidence of the early diversification of Bilateria. Our observations also render indirect support to the highly controversial interpretation of the enigmatic Ediacaran biota of the late Precambrian as giant protists.
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Affiliation(s)
- Mikhail V Matz
- Section of Integrative Biology, University of Texas at Austin, Austin, TX 78712, USA.
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21
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Budd GE. The earliest fossil record of the animals and its significance. Philos Trans R Soc Lond B Biol Sci 2008; 363:1425-34. [PMID: 18192192 DOI: 10.1098/rstb.2007.2232] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The fossil record of the earliest animals has been enlivened in recent years by a series of spectacular discoveries, including embryos, from the Ediacaran to the Cambrian, but many issues, not least of dating and interpretation, remain controversial. In particular, aspects of taphonomy of the earliest fossils require careful consideration before pronouncements about their affinities. Nevertheless, a reasonable case can now be made for the extension of the fossil record of at least basal animals (sponges and perhaps cnidarians) to a period of time significantly before the beginning of the Cambrian. The Cambrian explosion itself still seems to represent the arrival of the bilaterians, and many new fossils in recent years have added significant data on the origin of the three major bilaterian clades. Why animals appear so late in the fossil record is still unclear, but the recent trend to embrace rising oxygen levels as being the proximate cause remains unproven and may even involve a degree of circularity.
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Affiliation(s)
- Graham E Budd
- Department of Earth Sciences, Palaeobiology, Uppsala University, Villavägen 16, Uppsala 752 36, Sweden.
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22
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Chi H, Feng M, Xiao Z, Lu Z. Preservation and fluorescence of the microfossils from Neoproterozoic Doushantuo formation. Microsc Res Tech 2007; 71:260-6. [PMID: 18072284 DOI: 10.1002/jemt.20547] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The phosphatized microfossils from Doushantuo Formation, Southeast China show us the biodiversity about 600 million years ago, which is a unique window for the evolution of the early life on earth. However, the process of phosphatic fossilization in detail still remains unknown. Here we report our study on the preservation state of the fossils by using confocal laser scanning microscopy. We found that fluorescent signal of the fossil could reflect the preservation state when compared with the transmission light microscopy. First, we found the fluorescent signal of the decayed cells of the fossil was weaker than that of the nondecayed part. Second, we found that the three-dimensional reconstruction of the fluorescent signals could help to judge the degree of mineralization of the fossil cells, compared with the observation by transmission light microscope. Third, we found that almost all of the fossil specimens we observed could fluoresce more or less when excited by laser light. Therefore, the fluorescent microscopy provides a useful method for the study of the preservation state of the phosphatic fossil cells.
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Affiliation(s)
- Huimei Chi
- State Key Laboratory of Bioelectronics, Southeast University, Nanjing 210096, China.
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23
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Fontanillas E, Welch JJ, Thomas JA, Bromham L. The influence of body size and net diversification rate on molecular evolution during the radiation of animal phyla. BMC Evol Biol 2007; 7:95. [PMID: 17592650 PMCID: PMC1929056 DOI: 10.1186/1471-2148-7-95] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2007] [Accepted: 06/26/2007] [Indexed: 11/23/2022] Open
Abstract
Background Molecular clock dates, which place the origin of animal phyla deep in the Precambrian, have been used to reject the hypothesis of a rapid evolutionary radiation of animal phyla supported by the fossil record. One possible explanation of the discrepancy is the potential for fast substitution rates early in the metazoan radiation. However, concerted rate variation, occurring simultaneously in multiple lineages, cannot be detected by "clock tests", and so another way to explore such variation is to look for correlated changes between rates and other biological factors. Here we investigate two possible causes of fast early rates: change in average body size or diversification rate of deep metazoan lineages. Results For nine genes for phylogenetically independent comparisons between 50 metazoan phyla, orders, and classes, we find a significant correlation between average body size and rate of molecular evolution of mitochondrial genes. The data also indicate that diversification rate may have a positive effect on rates of mitochondrial molecular evolution. Conclusion If average body sizes were significantly smaller in the early history of the Metazoa, and if rates of diversification were much higher, then it is possible that mitochondrial genes have undergone a slow-down in evolutionary rate, which could affect date estimates made from these genes.
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Affiliation(s)
- Eric Fontanillas
- Centre for the Study of Evolution, School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9QG, UK
- Centre for Macroevolution and Macroecology, School of Botany and Zoology, Australian National University, Canberra, A.C.T. 0200 Australia
| | - John J Welch
- Centre for the Study of Evolution, School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9QG, UK
- Institute of Evolutionary Biology; School of Biological Sciences; University of Edinburgh, West Mains Rd., Edinburgh, EH9 3JT, UK
| | - Jessica A Thomas
- Centre for the Study of Evolution, School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9QG, UK
- Centre for Macroevolution and Macroecology, School of Botany and Zoology, Australian National University, Canberra, A.C.T. 0200 Australia
| | - Lindell Bromham
- Centre for the Study of Evolution, School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9QG, UK
- Centre for Macroevolution and Macroecology, School of Botany and Zoology, Australian National University, Canberra, A.C.T. 0200 Australia
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24
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Chi H, Xiao Z, Chen J, Lu Z. Application of atomic force microscopy on observing the ultra-fine structure of the neoproterozoic microfossils from China. SCANNING 2007; 29:102-8. [PMID: 17455261 DOI: 10.1002/sca.20008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Phosphatic microfossils from the Doushantuo Formation, Guizhou, China, have been reported with preserved cellular structure or even sub-cellular structure in micron scale. However, more details in sub-micro scale have not been reported as having been found. The Fossil embryos from the acid residue of the phosphorite rocks of the Neoproterozoic Doushantuo Formation in south China have been studied with a scanning electron microscope (SEM) and an atomic force microscope (AFM). Some ultra-structures in sub-micro scale have been found by AFM on the surface of the fossil embryos. There are four types of structures found on the surface of the selected fossil embryos, the sizes of which vary from 30 to 645 nm in diameter under our AFM. One of the structures is composed of several big sub-units integrated with each other, and the size of the big sub-units is from 250 to 645 nm. Meanwhile, we also found an ultra-layer structure on the surface of the big sub-units, the thickness of which was about 10 nm. Thus we speculate that it could most probably be of biological origin. Therefore, AFM provides a new method for direct observation of the ultra-structure of the Doushantuo fossils in the sub-micro scale.
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Affiliation(s)
- Huimei Chi
- State Key Laboratory of Bioelectronics, Southeast University, Nanjing, China
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25
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Li CW, Chen JY, Lipps JH, Gao F, Chi HM, Wu HJ. Ciliated protozoans from the Precambrian Doushantuo Formation, Wengan, South China. ACTA ACUST UNITED AC 2007. [DOI: 10.1144/sp286.11] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractCiliates, a major eukaryotic crown-group lineage with thousands of living species, are poorly represented in the fossil record. Ciliate biomarkers are known from the Precambrian, but only one group, the tintinnids, have an extensive fossil record dating back to the Ordovician. Thus, the occurrence of probable ciliate body fossils in Neoproterozoic rocks confirms their earlier appearance, so far inferred only from molecular sequence data and biomarkers. In this paper, we describe those fossils from the 580 million year old Precambrian Doushantuo phosphates, Guizhou, South China. Three new monospecific genera (100 µm to 200 µm in size) are represented by three-dimensional specimens with exceptionally well-preserved cell bodies including cilia, cytostome and tentacles. Two possess loricas and are referred to the tintinnids. The third has numerous tentacles, an apical cytostome and somatic cilia; it is interpreted as an ancestral early suctorian ciliate. These fossils indicate that the origin and evolutionary differentiation and specialization of ciliates took place before or along with the radiation of other crown-group eukaryotes, including metazoans.
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Affiliation(s)
- C.-W. Li
- Department of Life Sciences, National Tsing Hua University, Hsinchu, Taiwan, China (e-mail: )
| | - J.-Y. Chen
- Nanjing Institute of Geology and Paleontology, Nanjing 210008, China
| | - J. H. Lipps
- Divisions of Biology, California Institute of Technology, Pasadena, CA 91125, USA
| | - F. Gao
- Nanjing Institute of Geology and Paleontology, Nanjing 210008, China
- Department of Integrative Biology, Museum of Paleontology, University of California, Berkeley, CA 94720, USA
| | - H.-M. Chi
- Nanjing Institute of Geology and Paleontology, Nanjing 210008, China
| | - H.-J. Wu
- Department of Life Sciences, National Tsing Hua University, Hsinchu, Taiwan, China (e-mail: )
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Bailey JV, Joye SB, Kalanetra KM, Flood BE, Corsetti FA. Evidence of giant sulphur bacteria in Neoproterozoic phosphorites. Nature 2006; 445:198-201. [PMID: 17183268 DOI: 10.1038/nature05457] [Citation(s) in RCA: 167] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2006] [Accepted: 11/20/2006] [Indexed: 11/09/2022]
Abstract
In situ phosphatization and reductive cell division have recently been discovered within the vacuolate sulphur-oxidizing bacteria. Here we show that certain Neoproterozoic Doushantuo Formation (about 600 million years bp) microfossils, including structures previously interpreted as the oldest known metazoan eggs and embryos, can be interpreted as giant vacuolate sulphur bacteria. Sulphur bacteria of the genus Thiomargarita have sizes and morphologies similar to those of many Doushantuo microfossils, including symmetrical cell clusters that result from multiple stages of reductive division in three planes. We also propose that Doushantuo phosphorite precipitation was mediated by these bacteria, as shown in modern Thiomargarita-associated phosphogenic sites, thus providing the taphonomic conditions that preserved other fossils known from the Doushantuo Formation.
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Affiliation(s)
- Jake V Bailey
- Department of Earth Sciences, University of Southern California, Los Angeles, California 90089, USA.
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Guder C, Philipp I, Lengfeld T, Watanabe H, Hobmayer B, Holstein TW. The Wnt code: cnidarians signal the way. Oncogene 2006; 25:7450-60. [PMID: 17143289 DOI: 10.1038/sj.onc.1210052] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Cnidarians are the simplest metazoans with a nervous system. They are well known for their regeneration capacity, which is based on the restoration of a signalling centre (organizer). Recent work has identified the canonical Wnt pathway in the freshwater polyp Hydra, where it acts in organizer formation and regeneration. Wnt signalling is also essential for cnidarian embryogenesis. In the sea anemone Nematostella vectensis 11 of the 12 known wnt gene subfamilies were identified. Different wnt genes exhibit serial and overlapping expression domains along the oral-aboral axis of the embryo (the 'wnt code'). This is reminiscent of the hox code (cluster) in bilaterian embryogenesis that is, however, absent in cnidarians. It is proposed that the common ancestor of cnidarians and bilaterians invented a set of wnt genes that patterned the ancient main body axis. Major antagonists of Wnt ligands (e.g. Dkk 1/2/4) that were previously known only from chordates, are also present in cnidarians and exhibit a similar conserved function. The unexpectedly high level of genetic complexity of wnt genes evolved in early multi-cellular animals about 650 Myr ago and suggests a radical expansion of the genetic repertoire, concurrent with the evolution of multi-cellularity and the diversification of eumetazoan body plans.
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Affiliation(s)
- C Guder
- Department of Molecular Evolution and Genomics, University of Heidelberg, Heidelberg, Germany
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29
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Howard-Ashby M, Materna SC, Brown CT, Tu Q, Oliveri P, Cameron RA, Davidson EH. High regulatory gene use in sea urchin embryogenesis: Implications for bilaterian development and evolution. Dev Biol 2006; 300:27-34. [PMID: 17101125 PMCID: PMC1790870 DOI: 10.1016/j.ydbio.2006.10.016] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2006] [Revised: 10/13/2006] [Accepted: 10/13/2006] [Indexed: 01/13/2023]
Abstract
A global scan of transcription factor usage in the sea urchin embryo was carried out in the context of the Strongylocentrotus purpuratus genome sequencing project, and results from six individual studies are here considered. Transcript prevalence data were obtained for over 280 regulatory genes encoding sequence-specific transcription factors of every known family, but excluding genes encoding zinc finger proteins. This is a statistically inclusive proxy for the total "regulome" of the sea urchin genome. Close to 80% of the regulome is expressed at significant levels by the late gastrula stage. Most regulatory genes must be used repeatedly for different functions as development progresses. An evolutionary implication is that animal complexity at the stage when the regulome first evolved was far simpler than even the last common bilaterian ancestor, and is thus of deep antiquity.
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30
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Hagadorn JW, Xiao S, Donoghue PCJ, Bengtson S, Gostling NJ, Pawlowska M, Raff EC, Raff RA, Turner FR, Chongyu Y, Zhou C, Yuan X, McFeely MB, Stampanoni M, Nealson KH. Cellular and Subcellular Structure of Neoproterozoic Animal Embryos. Science 2006; 314:291-4. [PMID: 17038620 DOI: 10.1126/science.1133129] [Citation(s) in RCA: 160] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Stereoblastic embryos from the Doushantuo Formation of China exhibit occasional asynchronous cell division, with diminishing blastomere volume as cleavage proceeded. Asynchronous cell division is common in modern embryos, implying that sophisticated mechanisms for differential cell division timing and embryonic cell lineage differentiation evolved before 551 million years ago. Subcellular structures akin to organelles, coated yolk granules, or lipid vesicles occur in these embryos. Paired reniform structures within embryo cells may represent fossil evidence of cells about to undergo division. Embryos exhibit no evidence of epithelial organization, even in embryos composed of approximately 1000 cells. Many of these features are compatible with metazoans, but the absence of epithelialization is consistent only with a stem-metazoan affinity for Doushantuo embryos.
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31
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Donoghue PCJ, Bengtson S, Dong XP, Gostling NJ, Huldtgren T, Cunningham JA, Yin C, Yue Z, Peng F, Stampanoni M. Synchrotron X-ray tomographic microscopy of fossil embryos. Nature 2006; 442:680-3. [PMID: 16900198 DOI: 10.1038/nature04890] [Citation(s) in RCA: 241] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2006] [Accepted: 05/10/2006] [Indexed: 11/08/2022]
Abstract
Fossilized embryos from the late Neoproterozoic and earliest Phanerozoic have caused much excitement because they preserve the earliest stages of embryology of animals that represent the initial diversification of metazoans. However, the potential of this material has not been fully realized because of reliance on traditional, non-destructive methods that allow analysis of exposed surfaces only, and destructive methods that preserve only a single two-dimensional view of the interior of the specimen. Here, we have applied synchrotron-radiation X-ray tomographic microscopy (SRXTM), obtaining complete three-dimensional recordings at submicrometre resolution. The embryos are preserved by early diagenetic impregnation and encrustation with calcium phosphate, and differences in X-ray attenuation provide information about the distribution of these two diagenetic phases. Three-dimensional visualization of blastomere arrangement and diagenetic cement in cleavage embryos resolves outstanding questions about their nature, including the identity of the columnar blastomeres. The anterior and posterior anatomy of embryos of the bilaterian worm-like Markuelia confirms its position as a scalidophoran, providing new insights into body-plan assembly among constituent phyla. The structure of the developing germ band in another bilaterian, Pseudooides, indicates a unique mode of germ-band development. SRXTM provides a method of non-invasive analysis that rivals the resolution achieved even by destructive methods, probing the very limits of fossilization and providing insight into embryology during the emergence of metazoan phyla.
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32
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Chen JY, Bottjer DJ, Davidson EH, Dornbos SQ, Gao X, Yang YH, Li CW, Li G, Wang XQ, Xian DC, Wu HJ, Hwu YK, Tafforeau P. Phosphatized polar lobe-forming embryos from the Precambrian of southwest China. Science 2006; 312:1644-6. [PMID: 16778054 DOI: 10.1126/science.1125964] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
In developing embryos of some extant spiralian animals, polar lobe formation is one of the symmetry-breaking mechanisms for segregation of maternal cytoplasmic substances to certain blastomeres and not others. Polar lobe formation leads to unique early cleavage morphologies that include trilobed, J-shaped, and five-lobed structures. Fossil embryos similar to modern lobeforming embryos are recognized from the Precambrian Doushantuo Formation phosphates, Weng'an, Guizhou Province, China. These embryos are abundant and form a developmental sequence comparable to different developing stages observed in lobe-forming embryos of extant spiralians. These data imply that lobe formation is an evolutionarily ancient process of embryonic specification.
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Affiliation(s)
- Jun-Yuan Chen
- Nanjing Institute of Geology and Paleontology, Institute of Evo/Developmental Biology, and State Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing 210093, China.
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Raff EC, Villinski JT, Turner FR, Donoghue PCJ, Raff RA. Experimental taphonomy shows the feasibility of fossil embryos. Proc Natl Acad Sci U S A 2006; 103:5846-51. [PMID: 16571655 PMCID: PMC1416897 DOI: 10.1073/pnas.0601536103] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The recent discovery of apparent fossils of embryos contemporaneous with the earliest animal remains may provide vital insights into the metazoan radiation. However, although the putative fossil remains are similar to modern marine animal embryos or larvae, their simple geometric forms also resemble other organic and inorganic structures. The potential for fossilization of animals at such developmental stages and the taphonomic processes that might affect preservation before mineralization have not been examined. Here, we report experimental taphonomy of marine embryos and larvae similar in size and inferred cleavage mode to presumptive fossil embryos. Under conditions that prevent autolysis, embryos within the fertilization envelope can be preserved with good morphology for sufficiently long periods for mineralization to occur. The reported fossil record exhibits size bias, but we show that embryo size is unlikely to be a major factor in preservation. Under some conditions of death, fossilized remains will not accurately reflect the cell structure of the living organism. Although embryos within the fertilization envelope have high preservation potential, primary larvae have negligible preservation potential. Thus the paleo-embryological record may have strong biases on developmental stages preserved. Our data provide a predictive basis for interpreting the fossil record to unravel the evolution of ontogeny in the origin of metazoans.
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Affiliation(s)
- Elizabeth C Raff
- Department of Biology and Indiana Molecular Biology Institute, Indiana University, Myers Hall 150, 915 East Third Street, Bloomington, IN 47405, USA.
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Chi H, Xiao Z, Fu D, Lu Z. Analysis of fluorescence from algae fossils of the Neoproterozoic Doushantuo formation of China by confocal laser scanning microscope. Microsc Res Tech 2006; 69:253-9. [PMID: 16586481 DOI: 10.1002/jemt.20295] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Chinese algae fossils can provide unique information about the evolution of the early life. Thin sections of Neoproterozoic algae fossils, from Guizhou, China, were studied by confocal laser scanning microscopy, and algae fossils were fluorescenced at different wavelengths when excited by laser light of 488 nm, 476 nm, and 568 nm wavelength. When illuminated by 488 nm laser light, images of the algae fossils were sharper and better defined than when illuminated by 476 nm and 568 nm laser light. The algae fossils fluoresce at a wide range of emission wavelengths. The three-dimensional images of the fluorescent algae fossils were compared with the transmission images taken by light microscope. We found that the fluorescence image of the confocal laser scanning microscope in a single optical section could pass for the transmission image taken by a light microscope. We collected images at different sample depths and made a three-dimensional reconstruction of the algae fossils. And on the basis of the reconstruction of the three-dimensional fluorescent images, we conclude that the two algae fossils in our present study are red algae.
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Affiliation(s)
- Huimei Chi
- State Key Laboratory of Bioelectronics, Southeast University, Nanjing 210096, China.
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Dong XP, Donoghue PCJ, Cunningham JA, Liu JB, Cheng H. The anatomy, affinity, and phylogenetic significance of Markuelia. Evol Dev 2005; 7:468-82. [PMID: 16174039 DOI: 10.1111/j.1525-142x.2005.05050.x] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The fossil record provides a paucity of data on the development of extinct organisms, particularly for their embryology. The recovery of fossilized embryos heralds new insight into the evolution of development but advances are limited by an almost complete absence of phylogenetic constraint. Markuelia is an exception to this, known from cleavage and pre-hatchling stages as a vermiform and profusely annulated direct-developing bilaterian with terminal circumoral and posterior radial arrays of spines. Phylogenetic analyses have hitherto suggested assignment to stem-Scalidophora (phyla Kinorhyncha, Loricifera, Priapulida). We test this assumption with additional data and through the inclusion of additional taxa. The available evidence supports stem-Scalidophora affinity, leading to the conclusion that scalidophorans, cyclonerualians, and ecdysozoans are primitive direct developers, and the likelihood that scalidophorans are primitively metameric.
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Affiliation(s)
- Xi-Ping Dong
- Department of Earth and Space Sciences, Peking University, Beijing 100871, China
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Abstract
The phylogenetic relationships among deuterostome animals have been debated for many years, and a diversity of hypotheses have been proposed based on both morphological and molecular data. Here we have assembled sequences of 217 nuclear-encoded proteins to address specific questions concerning their relationships and times of origin. We recovered significant support for urochordates as the closest relative of vertebrates with an analysis of 59 proteins (17,400 amino acids) and suggest that the basal position of urochordates found in previous molecular studies may have been the result of long-branch attraction biases. Our results also support Ambulacraria, the pairing of hemichordates with echinoderms (nine proteins; 2,382 amino acids), and Cyclostomata, the pairing of lampreys with hagfish (25 proteins; 6,895 amino acids). In addition, 325 shared proteins (102,110 amino acids) were obtained from the complete genomes of six vertebrates and a urochordate for phylogenetic analysis and divergence time estimation. An evolutionary timescale was estimated using a local (Bayesian) molecular clock method. We found that most major lineages of deuterostomes arose prior to the Cambrian Explosion of fossils (approximately 520 MYA) and that several lineages had originated before periods of global glaciation in the Precambrian.
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Affiliation(s)
- Jaime E Blair
- NASA Astrobiology Institute and Department of Biology, The Pennsylvania State University, University Park, USA.
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Hubert B, Álvaro JJ, Chen JY. Microbially mediated phosphatization in the Neoproterozoic Doushantuo Lagerstätte, South China. ACTA ACUST UNITED AC 2005. [DOI: 10.2113/176.4.355] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Abstract
Detailed petrographic and geochemical studies of pore-filling cements and replaced (epigenic) membranes of some organic-walled microorganisms preserved in the Neoproterozoic Doushantuo Lagerstätte (China) are based on an energy dispersive system (EDS) of elemental mapping attached to backscattered MEB. Their microcrystalline apatite (collophane) occurs predominantly as phosphatized microbial pseudomorphs: phosphatic crusts of chasmolithic bio-films (or microstromatolites) and globular clusters occur lining intraparticular porosities. Three major pre-compactional cement types are identified on algal thalli, embryos and vase-shaped microfossils: epigenic collophane (by replacement of membranes), polyphasic filling of collophane and crystalline apatite and fluorapatite within intraparticular porosities (some of them microbially mediated), and latest carbonate precipitation filling the remaining intraparticular porosities (preserved at present as dedolomitized calcite). P2O5 concentration has a clear peak in the microbial pseudomorphs and uniformly low concentrations elsewhere, whereas MgO, Na2O, K2O and SiO2 show a slight increase in concentration through successive cements. These geochemical trends evidence a slight change of pore fluids accompanied by a final rise in pH, presumably following the main interval of decay, which favoured precipitation of CaCO3 postdating that of apatite.
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Affiliation(s)
- Benoìt Hubert
- Laboratoire de Paléontologie et Paléogéographie du Paléozoïque, UMR 8014 CNRS, FUPL/ISA, 13 rue de Toul, 59046 Lille, France.
| | - J. Javier Álvaro
- Dpto. Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain
- LP3, UMR 8014 CNRS, Université des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq, France.
| | - Jun-Yuan Chen
- Nanjing Institute of Geology and Paleontology, Academia Sinica, Nanjing 210008 China, and Early Life Research Center, 18 Wenmiao Street, Cheng-jiang, Yunnan, 652500 China.
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Seipel K, Schmid V. Evolution of striated muscle: Jellyfish and the origin of triploblasty. Dev Biol 2005; 282:14-26. [PMID: 15936326 DOI: 10.1016/j.ydbio.2005.03.032] [Citation(s) in RCA: 128] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2004] [Revised: 03/09/2005] [Accepted: 03/27/2005] [Indexed: 12/20/2022]
Abstract
The larval and polyp stages of extant Cnidaria are bi-layered with an absence of mesoderm and its differentiation products. This anatomy originally prompted the diploblast classification of the cnidarian phylum. The medusa stage, or jellyfish, however, has a more complex anatomy characterized by a swimming bell with a well-developed striated muscle layer. Based on developmental histology of the hydrozoan medusa this muscle derives from the entocodon, a mesoderm-like third cell layer established at the onset of medusa formation. According to recent molecular studies cnidarian homologs to bilaterian mesoderm and myogenic regulators are expressed in the larval and polyp stages as well as in the entocodon and derived striated muscle. Moreover striated and smooth muscle cells may have evolved directly and independently from non-muscle cells as indicated by phylogenetic analysis of myosin heavy chain genes (MHC class II). To accommodate all evidences we propose that striated muscle-based locomotion coevolved with the nervous and digestive systems in a basic metazoan Bauplan from which the ancestors of the Ctenophora (comb jellyfish), Cnidaria (jellyfish and polyps), as well as the Bilateria are derived. We argue for a motile tri-layered cnidarian ancestor and a monophyletic descent of striated muscle in Cnidaria and Bilateria. As a consequence, diploblasty evolved secondarily in cnidarian larvae and polyps.
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Affiliation(s)
- Katja Seipel
- Institute of Zoology, Biocenter/Pharmacenter, Klingelbergstrasse 50, CH-4056 Basel, Switzerland
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Zhao Y, Chen M, Peng J, Yu M, He M, Wang Y, Yang R, Wang P, Zhang Z. Discovery of a Miaohe-type Biota from the Neoproterozoic Doushantuo Formation in Jiangkou County, Guizhou Province, China. ACTA ACUST UNITED AC 2004. [DOI: 10.1007/bf03185792] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Chen JY, Bottjer DJ, Oliveri P, Dornbos SQ, Gao F, Ruffins S, Chi H, Li CW, Davidson EH. Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian. Science 2004; 305:218-22. [PMID: 15178752 DOI: 10.1126/science.1099213] [Citation(s) in RCA: 220] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Ten phosphatized specimens of a small (<180 micrometers) animal displaying clear bilaterian features have been recovered from the Doushantuo Formation, China, dating from 40 to 55 million years before the Cambrian. Seen in sections, this animal (Vernanimalcula guizhouena gen. et sp. nov.) had paired coeloms extending the length of the gut; paired external pits that could be sense organs; bilateral, anterior-posterior organization; a ventrally directed anterior mouth with thick walled pharynx; and a triploblastic structure. The structural complexity is that of an adult rather than a larval form. These fossils provide the first evidence confirming the phylogenetic inference that Bilateria arose well before the Cambrian.
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Affiliation(s)
- Jun-Yuan Chen
- Nanjing Institute of Geology and Paleontology, Nanjing 210008, China.
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41
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Early Cambrian phosphatized blastula- and gastrula-stage animal fossils from southern Shaanxi. ACTA ACUST UNITED AC 2004. [DOI: 10.1007/bf02900970] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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42
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Abstract
There has been limited corroboration to date for McClintock's vision of gene regulation by transposable elements (TEs), although her proposition on the origin of species by TE-induced complex chromosome reorganizations in combination with gene mutations, i.e., the involvement of both factors in relatively sudden formations of species in many plant and animal genera, has been more promising. Moreover, resolution is in sight for several seemingly contradictory phenomena such as the endless reshuffling of chromosome structures and gene sequences versus synteny and the constancy of living fossils (or stasis in general). Recent wide-ranging investigations have confirmed and enlarged the number of earlier cases of TE target site selection (hot spots for TE integration), implying preestablished rather than accidental chromosome rearrangements for nonhomologous recombination of host DNA. The possibility of a partly predetermined generation of biodiversity and new species is discussed. The views of several leading transposon experts on the rather abrupt origin of new species have not been synthesized into the macroevolutionary theory of the punctuated equilibrium school of paleontology inferred from thoroughly consistent features of the fossil record.
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Affiliation(s)
- Wolf-Ekkehard Lonnig
- Max-Planck-Institut für Züchtungsforschung, Carl-von-Linné-Weg 10, D-50829 Köln, Germany.
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Chen JY, Huang DY, Peng QQ, Chi HM, Wang XQ, Feng M. The first tunicate from the Early Cambrian of South China. Proc Natl Acad Sci U S A 2003; 100:8314-8. [PMID: 12835415 PMCID: PMC166226 DOI: 10.1073/pnas.1431177100] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Here we report the discovery of eight specimens of an Early Cambrian fossil tunicate Shankouclava near Kunming (South China). The tunicate identity of this organism is supported by the presence of a large and perforated branchial basket, a sac-like peri-pharyngeal atrium, an oral siphon with apparent oral tentacles at the basal end of the siphonal chamber, perhaps a dorsal atrial pore, and an elongated endostyle on the mid-ventral floor of the pharynx. As in most modern tunicates, the gut is simple and U-shaped, and is connected with posterior end of the pharynx at one end and with an atrial siphon at the other, anal end. Shankouclava differs from Cheungkongella, which was previously called a tunicate. Based on new, more complete "Cheungkongella" specimens that show branching tentacles, this form may be a lophophorate, and in any case is not a tunicate.
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Affiliation(s)
- Jun-Yuan Chen
- Nanjing Institute of Geology and Palaeontology, Nanjing 210008, China.
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Abstract
None of the supraspecific taxonomic categories can be defined objectively. Each taxon should of course be monophyletic, but there is no morphological or molecular character that identifies, for example, the phylum level. This has led some authors to abandon the Linnaean categories, but they appear to be practical "handles" in daily communication. It has been proposed that each phylum exhibits a characteristic Bauplan, but the identification of such "types" have in practice proved difficult or impossible for several phyla. Monophyly of some of the approximately 30 morphology-based phyla has been put in question by molecular studies, but recent reports clearly show that the 18S rRNA molecule, which has been used extensively in phylogenetic analyses, cannot be used alone in identifying phyla (or other higher taxonomic groups). Some higher taxa, for example Chordata, Vertebrata, and Echinodermata, consistently show up as monophyletic in the analyses, whereas molluscan and annelidan subgroups just as consistently are mixed with each other and with a number of other protostomian phyla in varying patterns.
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Affiliation(s)
- Claus Nielsen
- Zoological Museum, Universitetsparken 15, DK-2100 Copenhagen, Denmark.
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Chen JY, Oliveri P, Gao F, Dornbos SQ, Li CW, Bottjer DJ, Davidson EH. Precambrian animal life: probable developmental and adult cnidarian forms from Southwest China. Dev Biol 2002; 248:182-96. [PMID: 12142030 DOI: 10.1006/dbio.2002.0714] [Citation(s) in RCA: 134] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The evolutionary divergence of cnidarian and bilaterian lineages from their remote metazoan ancestor occurred at an unknown depth in time before the Cambrian, since crown group representatives of each are found in Lower Cambrian fossil assemblages. We report here a variety of putative embryonic, larval, and adult microfossils deriving from Precambrian phosphorite deposits of Southwest China, which may predate the Cambrian radiation by 25-45 million years. These are most probably of cnidarian affinity. Large numbers of fossilized early planula-like larvae were observed under the microscope in sections. Though several forms are represented, the majority display remarkable conformity, which is inconsistent with the alternative that they are artifactual mineral inclusions. Some of these fossils are preserved in such high resolution that individual cells can be discerned. We confirm in detail an earlier report of the presence in the same deposits of tabulates, an extinct crown group anthozoan form. Other sections reveal structures that most closely resemble sections of basal modern corals. A large number of fossils similar to modern hydrozoan gastrulae were also observed. These again displayed great morphological consistency. Though only a single example is available, a microscopic animal remarkably similar to a modern adult hydrozoan is also presented. Taken together, the new observations reported in this paper indicate the existence of a diverse and already differentiated cnidarian fauna, long before the Cambrian evolutionary event. It follows that at least stem group bilaterians must also have been present at this time.
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Affiliation(s)
- Jun-Yuan Chen
- Nanjing Institute of Geology and Paleontology, Nanjing 210008, China
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Abstract
Many regulatory genes appear to be utilized in at least superficially similar ways in the development of particular body parts in Drosophila and in chordates. These similarities have been widely interpreted as functional homologies, producing the conventional view of the last common protostome-deuterostome ancestor (PDA) as a complex organism that possessed some of the same body parts as modern bilaterians. Here we discuss an alternative view, in which the last common PDA had a less complex body plan than is frequently conceived. This reconstruction alters expectations for Neoproterozoic fossil remains that could illustrate the pathways of bilaterian evolution.
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Affiliation(s)
- Douglas H Erwin
- Department of Paleobiology, National Museum of Natural History, Washington, D.C. 20560, USA.
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Abstract
Energy is the motor of life. Energy ensures the organism's survival and competitive advantage for reproductive success. For almost 3 billion years, unicellular organisms were the only life form on earth. Competition for limited energy resources and raw materials exerted an incessant selective pressure on organisms. In the adverse environment and due to their 'feast and famine' life style, hardiness to a variety of stressors, particularly to nutrient deprivation, was the selection principle. Both resistance and mutagenic adaptation to stressors were established as survival strategies by means of context-specific processes creating stability or variability of DNA sequence. The conservation of transduction pathways and functional homology of effector molecules clearly bear witness that the principles of life established during prokaryotic and eukaryotic unicellular evolution, although later diversified, have been unshakably cast to persist during metazoan phylogenesis. A wealth of evidence suggests that unicellular organisms evolved the phenomena of differentiation and apoptosis, sexual reproduction, and even aging, as responses to environmental challenges. These evolutionary accomplishments were elaborated from the dichotomous resistance/mutagenesis response and sophisticated the capacity of cells to tune their genetic information to changing environmental conditions. Notably, the social deprivation responses, differentiation and apoptosis, evolved as intercellularly coordinated events: a multitude of differentiation processes were elaborated from sporulation, the prototypic stress resistance response, while apoptosis, contrary to current concepts, is no altruistic cell suicide but was programmed as a mutagenic survival response; this response, however, is socially thwarted leading into mutagenic error catastrophe. In the hybrid differentiation-apoptosis process, cytocide and cannibalism of apoptotic cells thus serve the purpose of fueling the survival of the selfish genes in the differentiating cells. However, successful mutagenesis, although repressed, persisted in the asocial stress response of carcinogenesis as a regression to primitive unicellular behavior following failure of intercellular communication. While somatic mutagenesis was largely prevented, Metazoa elaborated germ cell mutagenesis as an evolutionary vehicle. Genetic competence, a primitive, stress-induced mating behavior, evolved into sexual reproduction which harnessed mutagenesis by subjecting highly mutable germ cells to a rigid viability selection. These processes were programmatically fixed as life- and cell-cycle events but retained their deprivation response phenotypes. Thus, the differentiation-apoptosis tandem evolved as the 'clay' to mold the specialized structures and functions of a multicellular organism while sexual reproduction elaborated the principle of quality-checked mutagenesis to create the immense diversity of Metazoa following the Cambrian explosion. Throughout these events, reactive oxygen and nitrogen species, which are regulated by energy homeostasis, shape the genetic information in a regulated but random, uncoded process providing the fitness-related feedback of phenotype to genotype. The interplay of genes and environment establishes a dynamic stimulus-response feedback cycle which, in animate nature, may be the organizing principle to contrive the reciprocal duality of energy and matter.
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Affiliation(s)
- K Heininger
- Department of Neurology, Heinrich Heine Universität, Düsseldorf, Germany.
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New observations on spiculelike structures from Doushantuo phosphorites at Weng’an, Guizhou Province. ACTA ACUST UNITED AC 2001. [DOI: 10.1007/bf02900561] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Discovery of phosphatized gastrula fossils from the Doushantuo Formation, Weng’an, Guizhou Province, China. ACTA ACUST UNITED AC 2001. [DOI: 10.1007/bf02900658] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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50
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Abstract
The role of Brachyury and other T-box genes in the differentiation of mesoderm and endoderm of vertebrates is well established. Recently, homologues of Brachyury have been isolated from an increasing number of diverse organisms ranging from Cnidaria to vertebrates and insects. Comparative expression and function analysis allows the origin of the mesoderm and the evolution of the developmental role of Brachyury gene family in metazoans to be traced. The data suggest that an ancestral function of Brachyury was to designate a blastoporal region that had distinct properties in induction and axis elongation. A subset of blastoporal cells expressing Brachyury and other genes that convey specific mesodermal functions may have segregated as a distinct cell population from this region in the course of mesoderm evolution.
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Affiliation(s)
- U Technau
- Molecular Cell Biology, Institute for Zoology, Darmstadt University of Technology, Schnittspahnstr. 10, 64287 Darmstadt, Germany.
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