New high precision U-Pb CA-ID-TIMS zircon ages from the Ediacaran in Namibia

2021 ◽  
Author(s):  
Fabio Messori ◽  
Ulf Linnemann ◽  
Mandy Hofmann ◽  
Johannes Zieger ◽  
Gerd Geyer ◽  
...  
Keyword(s):  
High Precision ◽  
Causal Link ◽  
Environmental Perturbations ◽  
Complete Section ◽  
Evolutionary Changes ◽  
Younger Age ◽  
Organizational Levels ◽  
Terra Nova ◽  
Multicellular Organisms ◽  
Stratigraphic Range

<p>The Ediacaran records a transition from a planet largely dominated by microscopic organisms to macroscopic multicellular organisms during the Phanerozoic. Temporal calibration of the record of changing climates and coevally diversifying biota is crucial to understand how metazoan life gained an early foothold on Earth.</p><p>A causal link between climate-driven environmental perturbations and biotic changes is generally accepted. However, a chronological relationship is needed to prove which event acted as a trigger for the biological turnover, i.e. extinction or the development of new organizational levels. A connection between environmental perturbations associated with the appearance and disappearance of the Ediacaran biota is profoundly complicated because of the scarcity of available geochronological and chemostratigraphical records. Therefore, it is crucial to expand existing datasets for this period, particularly through additional chronology.</p><p>The Nama Group in southern Namibia serves as a unique archive for major geobiological changes across the Ediacaran–Cambrian transition exemplified by a near complete section through the terminal Ediacaran. The region exposes the full stratigraphic range of the Nama assemblage and records several environmental perturbations. Establishing a precise timeframe of the terminal Ediacaran environmental and biological changes in Nama group enables a much-enhanced understanding of the nature and rates of the evolutionary changes.</p><p>Following pioneering research by Grotzinger et al. (1995), the Ediacaran–Cambrian boundary in Namibia has recently been dated ca. 2 Ma younger than previously assumed [1]. Additional high-precision U-Pb CA-ID-TIMS zircon ages from silicified tuffs of the Nama Group allow additional insights for the timeframe of the entire terminal Nama. Our results indicate that (i) the oldest ash bed in the Zaris subbasin is 547.3 Ma old, which makes it more than 0.5 Ma younger than the previously dated tuff in the same subbasin; (ii) a newly explored section at the base of the terminal Ediacaran Spitskop Member near the MTC tower (Witpütz Nord farm) revealed a slightly younger age of 539 Ma, which permits a precise correlation of this section with the Swartpunt section and indicates the position of the Ediacaran-Cambrian boundary.</p><p>[1] Linnemann, U. et al., (2019) Terra Nova 31(1) 49-58.</p>

scholarly journals Evolution of weak cooperative interactions for biological specificity

2018 ◽  
Vol 115 (47) ◽  
pp. E11053-E11060 ◽  
Author(s):  
Ang Gao ◽  
Krishna Shrinivas ◽  
Paul Lepeudry ◽  
Hiroshi I. Suzuki ◽  
Phillip A. Sharp ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Liquid Phase ◽  
Evolutionary Model ◽  
Cross Reactivity ◽  
Cellular Functions ◽  
Cooperative Interactions ◽  
Lethal Mutations ◽  
Evolutionary Changes ◽  
Biological Specificity ◽  
Multicellular Organisms

A hallmark of biological systems is that particular functions and outcomes are realized in specific contexts, such as when particular signals are received. One mechanism for mediating specificity is described by Fisher’s “lock and key” metaphor, exemplified by enzymes that bind selectively to a particular substrate via specific finely tuned interactions. Another mechanism, more prevalent in multicellular organisms, relies on multivalent weak cooperative interactions. Its importance has recently been illustrated by the recognition that liquid-liquid phase transitions underlie the formation of membraneless condensates that perform specific cellular functions. Based on computer simulations of an evolutionary model, we report that the latter mechanism likely became evolutionarily prominent when a large number of tasks had to be performed specifically for organisms to function properly. We find that the emergence of weak cooperative interactions for mediating specificity results in organisms that can evolve to accomplish new tasks with fewer, and likely less lethal, mutations. We argue that this makes the system more capable of undergoing evolutionary changes robustly, and thus this mechanism has been repeatedly positively selected in increasingly complex organisms. Specificity mediated by weak cooperative interactions results in some useful cross-reactivity for related tasks, but at the same time increases susceptibility to misregulation that might lead to pathologies.

Transgenerational Epigenetic Inheritance

2018 ◽  
Vol 52 (1) ◽  
pp. 21-41 ◽  
Author(s):  
Ana Bošković ◽  
Oliver J. Rando
Keyword(s):  
Genomic Dna ◽  
Epigenetic Inheritance ◽  
Model Systems ◽  
Future Generations ◽  
Molecular Pathways ◽  
Epigenetic Changes ◽  
Transgenerational Epigenetic Inheritance ◽  
Epigenetic Information ◽  
Environmental Perturbations ◽  
Multicellular Organisms

Inheritance of genomic DNA underlies the vast majority of biological inheritance, yet it has been clear for decades that additional epigenetic information can be passed on to future generations. Here, we review major model systems for transgenerational epigenetic inheritance via the germline in multicellular organisms. In addition to surveying examples of epivariation that may arise stochastically or in response to unknown stimuli, we also discuss the induction of heritable epigenetic changes by genetic or environmental perturbations. Mechanistically, we discuss the increasingly well-understood molecular pathways responsible for epigenetic inheritance, with a focus on the unusual features of the germline epigenome.

COROT-high-precision stellar photometry on a low Earth orbit: solutions to minimize environmental perturbations

2003 ◽  
Author(s):  
Michel Auvergne ◽  
Laurent Boisnard ◽  
Jean-Tristan M. Buey ◽  
Gerard Epstein ◽  
Herve Hustaix ◽  
...  
Keyword(s):  
High Precision ◽  
Low Earth Orbit ◽  
Earth Orbit ◽  
Stellar Photometry ◽  
Environmental Perturbations

Developmental Mechanisms for Evolutionary Novelties

2014 ◽  
Author(s):  
Günter P. Wagner
Keyword(s):  
Hind Limb ◽  
Positional Information ◽  
Morphological Characters ◽  
Mechanical Stimuli ◽  
Body Parts ◽  
Environmental Perturbations ◽  
Developmental Mechanisms ◽  
Evolutionary Changes ◽  
Evolutionary Novelties

This chapter examines the developmental mechanisms underlying evolutionary novelties. It first considers the role of the environment in evolutionary innovations, with particular emphasis on how environmental perturbations result in the release of cryptic genetic variation. It then explores where the positional information for novel characters comes from before explaining derived mechanical stimuli and the origin of novelties in the avian hind limb skeleton. It also discusses the origin of character identity networks and the evolution of novel signaling centers, focusing on two novel morphological characters: the butterfly eyespot and the turtle carapace. Finally, it reflects on the developmental biology of novelties, emphasizing the complex and multifaceted nature of the evolutionary changes in the developmental mechanisms that contribute to the origin of novel body parts.

Cannibalism of nestling American kestrels by their parents and siblings

1991 ◽  
Vol 69 (6) ◽  
pp. 1447-1453 ◽  
Author(s):  
Gary R. Bortolotti ◽  
Karen L. Wiebe ◽  
William M. Iko
Keyword(s):  
Strong Evidence ◽  
Disease Transmission ◽  
Human Disturbance ◽  
Causal Link ◽  
Laying Date ◽  
North Central ◽  
American Kestrels ◽  
Younger Age ◽  
Food Shortages ◽  
Nestling Mortality

We examined the frequency of cannibalism of nestling American kestrels (Falco sparverius) in north-central Saskatchewan. We investigated human disturbance and food shortages as possible causes of it. Cannibalism of nestlings by their parents and siblings was confirmed by observation and by the presence of partially eaten carcasses, or inferred from the sudden disappearance of a nestling between frequent nest checks. Cannibalism occurred at 8% of 48 nests in 1988, and 18% of 92 nests in 1989. Not all nestlings that died were cannibalized. Where nestling mortality occurred, carcasses were eaten in at least 20% of nests in 1988, and 63% of nests in 1989. The chicks that were cannibalized died at a significantly younger age than those that died but were not cannibalized. The mass and age of the parent and the laying date were not associated with the occurrence of cannibalism. We found no strong evidence of a causal link between human disturbance and nestling mortality or cannibalism; however, the abundance of small mammal prey was inversely related to the frequency of cannibalism between years, and there were fewer prey and lower prey delivery rates in territories where cannibalism occurred than in territories where nestling mortality did not occur. The fact that some nestlings died but were not eaten suggests that such mortality was unrelated to food shortages. The food advantage of cannibalism may not outweigh potential disadvantages such as disease transmission.

scholarly journals Maturation of Newfoundland American plaice (Hippoglossoides platessoides): long-term trends in maturation reaction norms despite low fishing mortality?

2005 ◽  
Vol 62 (1) ◽  
pp. 56-64 ◽  
Author(s):  
S. Barot ◽  
M. Heino ◽  
M.J. Morgan ◽  
U. Dieckmann
Keyword(s):  
Life Histories ◽  
Gulf Of Maine ◽  
Life History Evolution ◽  
Reaction Norms ◽  
Fishing Mortality ◽  
Evolutionary Changes ◽  
Younger Age ◽  
Evolution Of Life ◽  
Long Term Trends

Abstract To interpret long-term trends in age and size at maturation, new statistical methods have recently been devised for estimating probabilistic maturation reaction norms based on data collected for the management of fisheries. Here we apply these methods to three Newfoundland stocks of American plaice (NAFO Divisions 2J3K, 3LNO, 3Ps) and report a clear long-term shift in the maturation reaction norms of these stocks towards maturation at younger age and smaller size. Theory predicts that such trends could result from fishing acting as a selective force, inducing evolutionary changes in the life histories of exploited populations. Matching long-term trends in maturation reactions norms have already been documented for several stocks that have experienced high fishing pressures (Gulf of Maine and Georges Bank cod, Northeast Arctic cod, North Sea plaice). Our results add a new dimension to these earlier findings: since fishing pressures for two stocks of Newfoundland plaice (2J3K and 3Ps) have been relatively low, our results imply that fishing is likely to result in the evolution of life histories even when fishing mortality is low, or that natural mortality has played an important role in determining selective pressures in these populations. Both options suggest that conditions for rapid life-history evolution in exploited stocks are less restrictive than previously appreciated.

Automatic measurement of SAED patterns from asbestos minerals

1988 ◽  
Vol 46 ◽  
pp. 846-847
Author(s):  
J. C. Russ ◽  
T. Taguchi ◽  
P. M. Peters ◽  
E. Chatfield ◽  
J. C. Russ ◽  
...  
Keyword(s):  
Diffraction Pattern ◽  
High Precision ◽  
Diffraction Data ◽  
Automatic Measurement ◽  
Automatic Method ◽  
Important Method ◽  
X Ray ◽  
Integrated Intensity ◽  
Asbestiform Minerals ◽  
True Center

Conventional SAD patterns as obtained in the TEM present difficulties for identification of materials such as asbestiform minerals, although diffraction data is considered to be an important method for making this purpose. The preferred orientation of the fibers and the spotty patterns that are obtained do not readily lend themselves to measurement of the integrated intensity values for each d-spacing, and even the d-spacings may be hard to determine precisely because the true center location for the broken rings requires estimation. We have implemented an automatic method for diffraction pattern measurement to overcome these problems. It automatically locates the center of patterns with high precision, measures the radius of each ring of spots in the pattern, and integrates the density of spots in that ring. The resulting spectrum of intensity vs. radius is then used just as a conventional X-ray diffractometer scan would be, to locate peaks and produce a list of d,I values suitable for search/match comparison to known or expected phases.

On effects of non-systematic reflections on weak-beam images of partial dislocations

1991 ◽  
Vol 49 ◽  
pp. 688-689
Author(s):  
K. Z. Botros ◽  
S. S. Sheinin
Keyword(s):  
High Precision ◽  
Stacking Fault ◽  
Important Application ◽  
Stacking Fault Energy ◽  
Sharp Peak ◽  
Weak Beam ◽  
Partial Dislocations ◽  
Deviation Parameter ◽  
Beam Diffraction

The main features of weak beam images of dislocations were first described by Cockayne et al. using calculations of intensity profiles based on the kinematical and two beam dynamical theories. The feature of weak beam images which is of particular interest in this investigation is that intensity profiles exhibit a sharp peak located at a position very close to the position of the dislocation in the crystal. This property of weak beam images of dislocations has an important application in the determination of stacking fault energy of crystals. This can easily be done since the separation of the partial dislocations bounding a stacking fault ribbon can be measured with high precision, assuming of course that the weak beam relationship between the positions of the image and the dislocation is valid. In order to carry out measurements such as these in practice the specimen must be tilted to "good" weak beam diffraction conditions, which implies utilizing high values of the deviation parameter Sg.

Cardiac myocytes cultured on a basement membrane extract of the ehs tumor

1986 ◽  
Vol 44 ◽  
pp. 270-271
Author(s):  
L. Terracio ◽  
A. Dewey ◽  
K. Rubin ◽  
T.K. Borg
Keyword(s):  
Extracellular Matrix ◽  
Basement Membrane ◽  
Cardiac Myocytes ◽  
Normal Tissue ◽  
Cell Spreading ◽  
Collagen Iv ◽  
Basement Membrane Extract ◽  
Membrane Extract ◽  
Growth Development ◽  
Multicellular Organisms

The recognition and interaction of cells with the extracellular matrix (ECM) effects the normal physiology as well as the pathology of all multicellular organisms. These interactions have been shown to influence the growth, development, and maintenance of normal tissue function. In previous studies, we have shown that neonatal cardiac myocytes specifically interacts with a variety of ECM components including fibronectin, laminin, and collagens I, III and IV. Culturing neonatal myocytes on laminin and collagen IV induces an increased rate of both cell spreading and sarcomerogenesis.

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