scholarly journals Shape-preserving erosion controlled by the graded microarchitecture of shark tooth enameloid

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Shahrouz Amini ◽  
Hajar Razi ◽  
Ronald Seidel ◽  
Daniel Werner ◽  
William T. White ◽  
...  
Keyword(s):  
Functional Morphology ◽  
Tooth Erosion ◽  
Shape Preserving ◽  
Evolutionary Diversification ◽  
Experimental Support ◽  
Shark Teeth ◽  
Damage Response ◽  
The Face ◽  
Port Jackson ◽  
Dominant Theory

AbstractThe teeth of all vertebrates predominantly comprise the same materials, but their lifespans vary widely: in stark contrast to mammals, shark teeth are functional only for weeks, rather than decades, making lifelong durability largely irrelevant. However, their diets are diverse and often mechanically demanding, and as such, their teeth should maintain a functional morphology, even in the face of extremely high and potentially damaging contact stresses. Here, we reconcile the dilemma between the need for an operative tooth geometry and the unavoidable damage inherent to feeding on hard foods, demonstrating that the tooth cusps of Port Jackson sharks, hard-shelled prey specialists, possess unusual microarchitecture that controls tooth erosion in a way that maintains functional cusp shape. The graded architecture in the enameloid provokes a location-specific damage response, combining chipping of outer enameloid and smooth wear of inner enameloid to preserve an efficient shape for grasping hard prey. Our discovery provides experimental support for the dominant theory that multi-layered tooth enameloid facilitated evolutionary diversification of shark ecologies.

scholarly journals Archaeal Genome Guardians Give Insights into Eukaryotic DNA Replication and Damage Response Proteins

Archaea ◽  
2014 ◽  
Vol 2014 ◽  
pp. 1-24 ◽  
Author(s):  
David S. Shin ◽  
Ashley J. Pratt ◽  
John A. Tainer
Keyword(s):  
Dna Replication ◽  
Environmental Stress ◽  
Stress Responses ◽  
Protein Structures ◽  
Genome Integrity ◽  
Damage Response ◽  
Dna Replication And Repair ◽  
The Face ◽  
Domains Of Life ◽  
Fundamental Systems

As the third domain of life, archaea, like the eukarya and bacteria, must have robust DNA replication and repair complexes to ensure genome fidelity. Archaea moreover display a breadth of unique habitats and characteristics, and structural biologists increasingly appreciate these features. As archaea include extremophiles that can withstand diverse environmental stresses, they provide fundamental systems for understanding enzymes and pathways critical to genome integrity and stress responses. Such archaeal extremophiles provide critical data on the periodic table for life as well as on the biochemical, geochemical, and physical limitations to adaptive strategies allowing organisms to thrive under environmental stress relevant to determining the boundaries for life as we know it. Specifically, archaeal enzyme structures have informed the architecture and mechanisms of key DNA repair proteins and complexes. With added abilities to temperature-trap flexible complexes and reveal core domains of transient and dynamic complexes, these structures provide insights into mechanisms of maintaining genome integrity despite extreme environmental stress. The DNA damage response protein structures noted in this review therefore inform the basis for genome integrity in the face of environmental stress, with implications for all domains of life as well as for biomanufacturing, astrobiology, and medicine.

scholarly journals Male-Male Competition as a Force in Evolutionary Diversification: Evidence in Haplochromine Cichlid Fish

2011 ◽  
Vol 2011 ◽  
pp. 1-9 ◽  
Author(s):  
Peter D. Dijkstra ◽  
Ton G. G. Groothuis
Keyword(s):  
Sibling Species ◽  
Cichlid Fish ◽  
Character Displacement ◽  
Intrasexual Competition ◽  
Female Competition ◽  
Evolutionary Diversification ◽  
The Face ◽  
Negative Frequency Dependent Selection ◽  
Colour Morphs ◽  
Asymmetric Dominance

It has been suggested that intrasexual competition can be a source of negative frequency-dependent selection, causing agonistic character displacement and facilitating speciation and coexistence of (sibling) species. In this paper we synthesise the evidence that male-male and female-female competition contributes to cichlid diversification, showing that competition is stronger among same-coloured individuals than those with different colours. We argue that intrasexual selection is more complex because there are several examples where males do not bias aggression towards their own type. In addition, sibling species or colour morphs often show asymmetric dominance relationships. We briefly discuss potential mechanisms that might promote the maintenance of covariance between colour and aggression-related traits even in the face of gene-flow. We close by proposing several avenues for future studies that might shed more light on the role of intrasexual competition in cichlid diversification.

scholarly journals Review of the Danian vertebrate fauna of southern Scandinavia.

2017 ◽  
Vol 65 ◽  
pp. 1-23
Author(s):  
Jan S. Adolfssen ◽  
Jesper Milàn ◽  
Matt Friedman
Keyword(s):  
Cervical Vertebra ◽  
World Heritage Site ◽  
Unesco World Heritage ◽  
Vertebrate Fauna ◽  
Shark Teeth ◽  
Heritage Site ◽  
Unesco World Heritage Site ◽  
Bony Fishes ◽  
Southern Scandinavia ◽  
The Face

The vertebrate fauna in the Danian deposits of Denmark and southern Sweden is reviewed. Remains of sharks and bony fishes are widely distributed but not common in the Danian limestones, with the exception of the K/Pg-boundary clay, the Fiskeler Member, at the UNESCO World Heritage Site Stevns Klint, which can include substantial quantities of shark teeth and fragments of bony fishes. Articulated remains of bony fishes are known from the Fiskeler Member at Stevns Klint and the København Limestone Formation in the Limhamn quarry. Sharks are only found as isolated teeth and rare isolated vertebrae. The gavialoid crocodylian Thoracosaurus is represented by a complete skull and associated postcranial material and an additional jaw fragment from the Limhamn quarry. Remains of a crocodylian skull, a cervical vertebra, a limb bone and isolated teeth have been found in the Faxe quarry, and a single possibly alligatorid tooth is known from the basal conglomerate of the Lellinge Greensand Formation from now closed exposures below Copenhagen. Fragmentary turtle material has been found in the face and Limhamn quarries and in the København Limestone in Copenhagen, and bird remains are exclusively known from the Limhamn quarry. Despite the fragmentary nature of many of the finds, the total picture of the vertebrate fauna of southern Scandinavia is quite diverse comprising four classes, 23 orders, 41 families and 54 identifiable genera of which most can be identified to species level.

scholarly journals Evolutionary dynamics of a quantitative trait in a finite asexual population.

2015 ◽  
Author(s):  
Florence Debarre ◽  
Sarah Otto
Keyword(s):  
Genetic Drift ◽  
Quantitative Trait ◽  
Social Evolution ◽  
Evolutionary Dynamics ◽  
Evolutionary Branching ◽  
Asexual Population ◽  
Evolutionary Diversification ◽  
Trait Variance ◽  
The Face ◽  
Evolutionary Lineages

In finite populations, mutation limitation and genetic drift can hinder evolutionary diversification. We consider the evolution of a quantitative trait in an asexual population whose size can vary and depends explicitly on the trait. Previous work showed that evolutionary branching is certain (``deterministic branching'') above a threshold population size, but uncertain (``stochastic branching'') below it. Using the stationary distribution of the population's trait variance, we identify three qualitatively different sub-domains of ``stochastic branching'' and illustrate our results using a model of social evolution. We find that in very small populations, branching will almost never be observed; in intermediate populations, branching is intermittent, arising and disappearing over time; in larger populations, finally, branching is expected to occur and persist for substantial periods of time. Our study provides a clearer picture of the ecological conditions that facilitate the appearance and persistence of novel evolutionary lineages in the face of genetic drift.

Functional significance of preserved color patterns of mollusks from the Gosport Sand (Eocene) of Alabama

1988 ◽  
Vol 62 (01) ◽  
pp. 83-87 ◽  
Author(s):  
Patricia H. Kelley ◽  
Charles T. Swann
Keyword(s):  
Functional Morphology ◽  
Functional Significance ◽  
Intraspecific Variability ◽  
Color Pattern ◽  
Color Patterns ◽  
Historical Factors ◽  
Life Mode ◽  
Molluscan Fauna ◽  
Excellent Preservation ◽  
Architectural Constraints

The excellent preservation of the molluscan fauna from the Gosport Sand (Eocene) at Little Stave Creek, Alabama, has made it possible to describe the preserved color patterns of 15 species. In this study the functional significance of these color patterns is tested in the context of the current adaptationist controversy. The pigment of the color pattern is thought to be a result of metabolic waste disposal. Therefore, the presence of the pigment is functional, although the patterns formed by the pigment may or may not have been adaptive. In this investigation the criteria proposed by Seilacher (1972) for testing the functionality of color patterns were applied to the Gosport fauna and the results compared with life mode as interpreted from knowledge of extant relatives and functional morphology. Using Seilacher's criteria of little ontogenetic and intraspecific variability, the color patterns appear to have been functional. However, the functional morphology studies indicate an infaunal life mode which would preclude functional color patterns. Particular color patterns are instead interpreted to be the result of historical factors, such as multiple adaptive peaks or random fixation of alleles, or of architectural constraints including possibly pleiotropy or allometry. The low variability of color patterns, which was noted within species and genera, suggests that color patterns may also serve a useful taxonomic purpose.

Why do people believe in a zero-sum economy?

2018 ◽  
Vol 41 ◽  
Author(s):  
Samuel G. B. Johnson
Keyword(s):  
Perspective Taking ◽  
Evolutionary Model ◽  
Everyday Experience ◽  
Coalitional Psychology ◽  
The Face ◽  
Zero Sum

AbstractZero-sum thinking and aversion to trade pervade our society, yet fly in the face of everyday experience and the consensus of economists. Boyer & Petersen's (B&P's) evolutionary model invokes coalitional psychology to explain these puzzling intuitions. I raise several empirical challenges to this explanation, proposing two alternative mechanisms – intuitive mercantilism (assigning value to money rather than goods) and errors in perspective-taking.

Mars: was There an Ancient Eden?

1997 ◽  
Vol 161 ◽  
pp. 203-218 ◽  
Author(s):  
Tobias C. Owen
Keyword(s):  
Positive Answer ◽  
Biogenic Elements ◽  
Habitable Zones ◽  
The Face ◽  
The Origin Of Life ◽  
Early Mars ◽  
Favorable Conditions ◽  
Open Question ◽  
Rocky Planets ◽  
Impact Erosion

AbstractThe clear evidence of water erosion on the surface of Mars suggests an early climate much more clement than the present one. Using a model for the origin of inner planet atmospheres by icy planetesimal impact, it is possible to reconstruct the original volatile inventory on Mars, starting from the thin atmosphere we observe today. Evidence for cometary impact can be found in the present abundances and isotope ratios of gases in the atmosphere and in SNC meteorites. If we invoke impact erosion to account for the present excess of129Xe, we predict an early inventory equivalent to at least 7.5 bars of CO2. This reservoir of volatiles is adequate to produce a substantial greenhouse effect, provided there is some small addition of SO2(volcanoes) or reduced gases (cometary impact). Thus it seems likely that conditions on early Mars were suitable for the origin of life – biogenic elements and liquid water were present at favorable conditions of pressure and temperature. Whether life began on Mars remains an open question, receiving hints of a positive answer from recent work on one of the Martian meteorites. The implications for habitable zones around other stars include the need to have rocky planets with sufficient mass to preserve atmospheres in the face of intensive early bombardment.

Evidence for a shear mechanism for the precipitation of γ-zirconium hydride in zirconium

1978 ◽  
Vol 36 (1) ◽  
pp. 658-659
Author(s):  
G.J.C. Carpenter
Keyword(s):  
Elevated Temperature ◽  
Strain Field ◽  
Zirconium Hydride ◽  
Zirconium Atom ◽  
Atom Diffusion ◽  
Solvus Temperature ◽  
Hexagonal Close Packed ◽  
Partial Dislocations ◽  
The Face

In zirconium-hydrogen alloys, rapid cooling from an elevated temperature causes precipitation of the face-centred tetragonal (fct) phase, γZrH, in the form of needles, parallel to the close-packed <1120>zr directions (1). With low hydrogen concentrations, the hydride solvus is sufficiently low that zirconium atom diffusion cannot occur. For example, with 6 μg/g hydrogen, the solvus temperature is approximately 370 K (2), at which only the hydrogen diffuses readily. Shears are therefore necessary to produce the crystallographic transformation from hexagonal close-packed (hep) zirconium to fct hydride.The simplest mechanism for the transformation is the passage of Shockley partial dislocations having Burgers vectors (b) of the type 1/3<0110> on every second (0001)Zr plane. If the partial dislocations are in the form of loops with the same b, the crosssection of a hydride precipitate will be as shown in fig.1. A consequence of this type of transformation is that a cumulative shear, S, is produced that leads to a strain field in the surrounding zirconium matrix, as illustrated in fig.2a.

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