Os tardígrados (ursos-d'água) sobreviverão ao fim do mundo que nós conhecemos

sexta-feira, julho 21, 2017

The Resilience of Life to Astrophysical Events

David Sloan, Rafael Alves Batista & Abraham Loeb

Scientific Reports 7, Article number: 5419 (2017)


Download Citation

Astrobiology Exoplanets

Received: 18 January 2017 Accepted: 05 June 2017 

Published online: 14 July 2017

Source/Fonte: Science News

Abstract

Much attention has been given in the literature to the effects of astrophysical events on human and land-based life. However, little has been discussed on the resilience of life itself. Here we instead explore the statistics of events that completely sterilise an Earth-like planet with planet radii in the range 0.5–1.5R⊕ and temperatures of ∼300 K, eradicating all forms of life. We consider the relative likelihood of complete global sterilisation events from three astrophysical sources – supernovae, gamma-ray bursts, large asteroid impacts, and passing-by stars. To assess such probabilities we consider what cataclysmic event could lead to the annihilation of not just human life, but also extremophiles, through the boiling of all water in Earth’s oceans. Surprisingly we find that although human life is somewhat fragile to nearby events, the resilience of Ecdysozoa such as Milnesium tardigradum renders global sterilisation an unlikely event.

Acknowledgements

D.S. and R.A.B. acknowledge the financial support from the John Templeton Foundation.

Author information

Affiliations

Department of Physics - Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, OX1 3RH, Oxford, UK

David Sloan & Rafael Alves Batista

Astronomy Department, Harvard University, 60 Garden Street, Cambridge, MA, 02138, USA

Abraham Loeb

Contributions

The idea of this work was conceived by A.L., D.S. and R.A.B. contributed equally to the analysis of results, with some input from A.L. D.S. did most of the writing, with aid of R.A.B. Figures were produced by R.A.B., A.L. was responsible for the scope and accuracy checking of the analysis.

Competing Interests

The authors declare that they have no competing interests.

Corresponding author

Correspondence to Rafael Alves Batista.

FREE PDF GRATIS: Science Reports

Sacudindo o paradigma da matéria escura

quinta-feira, julho 20, 2017

Shaking the dark matter paradigm

07/18/17 By Ali Sundermier

A theory about gravity challenges our understanding of the universe.

Illustration by Ana Kova

For millennia, humans held a beautiful belief. Our planet, Earth, was at the center of a vast universe, and all of the planets and stars and celestial bodies revolved around us. This geocentric model, though it had floated around since 6th century BCE, was written in its most elegant form by Claudius Ptolemy in 140 AD.

When this model encountered problems, such as the retrograde motions of planets, scientists reworked the data to fit the model by coming up with phenomena such as epicycles, mini orbits.

It wasn’t until 1543, 1400 years later, that Nicolaus Copernicus set in motion a paradigm shift that would give way to centuries of new discoveries. According to Copernicus’ radical theory, Earth was not the center of the universe but simply one of a long line of planets orbiting around the sun.

But even as evidence that we lived in a heliocentric system piled up and scientists such as Galileo Galilei perfected the model, society held onto the belief that the entire universe orbited around Earth until the early 19th century.

To Erik Verlinde, a theoretical physicist at the University of Amsterdam, the idea of dark matter is the geocentric model of the 21st century. 

“What people are doing now is allowing themselves free parameters to sort of fit the data,” Verlinde says. “You end up with a theory that has so many free parameters it's hard to disprove.”

Dark matter, an as-yet-undetected form of matter that scientists believe makes up more than a quarter of the mass and energy of the universe, was first theorized when scientists noticed that stars at the outer edges of galaxies and galaxy clusters were moving much faster than Newton’s theory of gravity said they should. Up until this point, scientists have assumed that the best explanation for this is that there must be missing mass in the universe holding those fast-moving stars in place in the form of dark matter. 

But Verlinde has come up with a set of equations that explains these galactic rotation curves by viewing gravity as an emergent force — a result of the quantum structure of space.

The idea is related to dark energy, which scientists think is the cause for the accelerating expansion of our universe. Verlinde thinks that what we see as dark matter is actually just interactions between galaxies and the sea of dark energy in which they’re embedded.

“Before I started working on this I never had any doubts about dark matter,” Verlinde says. “But then I started thinking about this link with quantum information and I had the idea that dark energy is carrying more of the dynamics of reality than we realize.”

Verlinde is not the first theorist to come up with an alternative to dark matter. Many feel that his theory echoes the sentiment of physicist Mordehai Milgrom’s equations of “modified Newtonian dynamics,” or MOND. Just as Einstein modified Newton’s laws of gravity to fit to the scale of planets and solar systems, MOND modifies Einstein’s laws of gravity to fit to the scale of galaxies and galaxy clusters.

Verlinde, however, makes the distinction that he’s not deriving the equations of MOND, rather he’s deriving what he calls a “scaling relation,” or a volume effect of space-time that only becomes important at large distances. 

Stacy McGaugh, an astrophysicist at Case Western Reserve University, says that while MOND is primarily the notion that the effective force of gravity changes with acceleration, Verlinde’s ideas are more of a ground-up theoretical work.

“He's trying to look at the structure of space-time and see if what we call gravity is a property that emerges from that quantum structure, hence the name emergent gravity,” McGaugh says. “In principle, it's a very different approach that doesn't necessarily know about MOND or have anything to do with it.”

One of the appealing things about Verlinde’s theory, McGaugh says, is that it naturally produces evidence of MOND in a way that “just happens.” 

“That's the sort of thing that one looks for,” McGaugh says. “There needs to be some basis of why MOND happens, and this theory might provide it.”

Verlinde’s ideas have been greeted with a fair amount of skepticism in the scientific community, in part because, according to Kathryn Zurek, a theoretical physicist at the US Department of Energy’s Lawrence Berkeley National Laboratory, his theory leaves a lot unexplained. 

“Theories of modified gravity only attempt to explain galactic rotation curves [those fast-moving planets],” Zurek says. “As evidence for dark matter, that's only one very small part of the puzzle. Dark matter explains a whole host of observations from the time of the cosmic microwave background when the universe was just a few hundred thousand years old through structure formation all the way until today.”
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Read more here/Leia mais aqui: Symmetry

Alô ETs, disquem 0800-NASA e digam alô: a prevalência de espécies tecnológicas no universo

quarta-feira, julho 19, 2017

A New Empirical Constraint on the Prevalence of Technological Species in the Universe

To cite this article:

Frank A. and Sullivan W.T. III. Astrobiology. May 2016, 16(5): 359-362. https://doi.org/10.1089/ast.2015.1418

Source/Fonte: Revista Exame

Published in Volume: 16 Issue 5: May 13, 2016

Online Ahead of Print: April 22, 2016

A. Frank1 and W.T. Sullivan III2

1Department of Physics and Astronomy, University of Rochester, Rochester, New York.

2Department of Astronomy and Astrobiology Program, University of Washington, Seattle, Washington.

Address correspondence to:

A. Frank

Department of Physics and Astronomy

University of Rochester

Rochester, NY 14620

E-mail: afrank@pas.rochester.edu

Submitted 5 October 2015

Accepted 16 February 2016

Abstract

In this article, we address the cosmic frequency of technological species. Recent advances in exoplanet studies provide strong constraints on all astrophysical terms in the Drake equation. Using these and modifying the form and intent of the Drake equation, we set a firm lower bound on the probability that one or more technological species have evolved anywhere and at any time in the history of the observable Universe. We find that as long as the probability that a habitable zone planet develops a technological species is larger than ∼10−24, humanity is not the only time technological intelligence has evolved. This constraint has important scientific and philosophical consequences. 

Key Words: Life—Intelligence—Extraterrestrial life. 

Astrobiology 2016, 359–362.

FREE PDF GRATIS: Astrobiology

Engenheiros eliminaram uma lei científica centenária descrevendo como o fluido flui através das rochas

Dynamic fluid connectivity during steady-state multiphase flow in a sandstone

Catriona A. Reynolds a,b,1, Hannah Menke a,b, Matthew Andrew c, Martin J. Blunt a,b, and Samuel Krevor a,b

Author Affiliations

aDepartment of Earth Science and Engineering, Imperial College London, London SW7 2AZ, United Kingdom;
bQatar Carbonates and Carbon Storage Research Centre, Imperial College London, London SW7 2AZ, United Kingdom;
cCarl Zeiss X-ray Microscopy Ltd., Pleasanton, CA 94588
Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved June 21, 2017 (received for review February 18, 2017)

Significance

The movement of immiscible fluids through permeable media occurs in many settings, including oil and water flow through rock. Here we present observations of a previously unidentified type of steady-state flow behavior that we term “dynamic connectivity.” We demonstrate that flow of the nonwetting phase occurs through a network of connections that continuously rearrange between filled pores. This observation suggests that we need to modify our models of two-phase flow that are fundamental to describing subsurface flow processes such as geologic CO2 storage and hydrocarbon recovery.

Abstract

The current conceptual picture of steady-state multiphase Darcy flow in porous media is that the fluid phases organize into separate flow pathways with stable interfaces. Here we demonstrate a previously unobserved type of steady-state flow behavior, which we term “dynamic connectivity,” using fast pore-scale X-ray imaging. We image the flow of N2 and brine through a permeable sandstone at subsurface reservoir conditions, and low capillary numbers, and at constant fluid saturation. At any instant, the network of pores filled with the nonwetting phase is not necessarily connected. Flow occurs along pathways that periodically reconnect, like cars controlled by traffic lights. This behavior is consistent with an energy balance, where some of the energy of the injected fluids is sporadically converted to create new interfaces.


steady state pore-scale imaging immiscible two-phase flow dynamic connectivity geologic CO2 storage

Footnotes
1To whom correspondence should be addressed. Email: catriona.reynolds11@imperial.ac.uk.

Author contributions: C.A.R. designed research; C.A.R., H.M., and M.A. performed research; C.A.R. and H.M. analyzed data; and C.A.R., H.M., M.A., M.J.B., and S.K. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1702834114/-/DCSupplemental.

Freely available online through the PNAS open access option.

FREE PDF GRATIS: PNAS 48.6 MBs

Universidade laica afasta o dogma e respeita a diferença: será???

Universidade laica afasta o dogma e respeita a diferença
18 de julho de 2017

Imagem meramente ilustrativa

A premissa de que os profissionais envolvidos no sistema público de ensino devem ser preparados para apartar os dogmas religiosos do cotidiano das salas de aula norteou a discussão da mesa-redonda Formação de professores na universidade laica, realizada na tarde de segunda-feira, 17, durante a 69ª Reunião Anual da SBPC.

“A universidade não é o lugar do dogma. A circulação do saber crítico deve prevalecer sobre toda crença que se pretenda impor como uma verdade absoluta”, defendeu o professor Carlos Roberto Jamil Cury, da pós-graduação em Educação da PUC Minas.

Em seu pronunciamento, o educador defendeu que a educação no âmbito do estado deve ser “expressão de cidadania aberta”, evocando noções presentes no texto da Constituição Federal, alinhadas com o combate a todos os tipos de preconceito. “Compatíveis com a Lei brasileira, que nos protege de diferencialismos segregadores, as diretrizes curriculares têm como princípio formar docentes compromissados com o projeto social, político e ético de nação, valorizando, dessa forma, a diversidade e a emancipação dos indivíduos”.
...

LEIA MAIS AQUI: SBPC NA UFMG

Teoria de informação lógica: novas fundações lógicas para a teoria da informação

Logical Information Theory: New Logical Foundations for Information Theory

Ellerman, David (2017) 

Logical Information Theory: New Logical Foundations for Information Theory. [Preprint]




Abstract

Here is a new theory of information based on logic. The definition of Shannon entropy as well as the notions on joint, conditional, and mutual entropy as defined by Shannon can all be derived by a uniform transformation from the corresponding formulas of logical information theory. Information is first defined in terms of sets of distinctions without using any probability measure. When a probability measure is introduced, the logical entropies are simply the values of the (product) probability measure on the sets of distinctions. The compound notions of joint, conditional, and mutual entropies are obtained as the values of the measure, respectively, on the union, difference, and intersection of the sets of distinctions. These compound notions of logical entropy satisfy the usual Venn diagram relationships (e.g., inclusion-exclusion formulas) since they are values of a measure (in the sense of measure theory). The uniform transformation into the formulas for Shannon entropy is linear so it explains the long-noted fact that the Shannon formulas satisfy the Venn diagram relations--as an analogy or mnemonic--since Shannon entropy is not a measure (in the sense of measure theory) on a given set.

What is the logic that gives rise to logical information theory? Partitions are dual (in a category-theoretic sense) to subsets, and the logic of partitions was recently developed in a dual/parallel relationship to the Boolean logic of subsets (the latter being usually mis-specified as the special case of "propositional logic"). Boole developed logical probability theory as the normalized counting measure on subsets. Similarly the normalized counting measure on partitions is logical entropy--when the partitions are represented as the set of distinctions that is the complement to the equivalence relation for the partition.

In this manner, logical information theory provides the set-theoretic and measure-theoretic foundations for information theory. The Shannon theory is then derived by the transformation that replaces the counting of distinctions with the counting of the number of binary partitions (bits) it takes, on average, to make the same distinctions by uniquely encoding the distinct elements--which is why the Shannon theory perfectly dovetails into coding and communications theory.

FREE PDF GRATIS: PhilSci

A controvérsia sobre o DNA lixo continua: 75% é lixo, segundo Dan Graur.

terça-feira, julho 18, 2017

An upper limit on the functional fraction of the human genome 

Dan Graur

Genome Biol Evol evx121. DOI: https://doi.org/10.1093/gbe/evx121

Published: 11 July 2017 Article history

Received: 25 March 2017 Revision Received: 20 June 2017

Accepted: 28 June 2017


Abstract:

For the human population to maintain a constant size from generation to generation, an increase in fertility must compensate for the reduction in the mean fitness of the population caused, among others, by deleterious mutations. The required increase in fertility due to this mutational load depends on the number of sites in the genome that are functional, the mutation rate, and the fraction of deleterious mutations among all mutations in functional regions. These dependencies and the fact that there exists a maximum tolerable replacement level fertility can be used to put an upper limit on the fraction of the human genome that can be functional. Mutational load considerations lead to the conclusion that the functional fraction within the human genome cannot exceed 25%, and is probably considerably lower.

Issue Section: Research article

© The Author(s) 2017. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

A bifurcação na estrada para o conserto do DNA

Inhibition of RIF1 by SCAI Allows BRCA1-Mediated Repair

Shin-Ya Isobe, Koji Nagao, Naohito Nozaki, Hiroshi Kimura, Chikashi Obuse5,

5Lead Contact

Open Access


Article Info

Publication History

Published: July 11, 2017 Accepted: June 21, 2017

Received in revised form: April 24, 2017 Received: October 7, 2016

User License

Creative Commons Attribution – NonCommercial – NoDerivs (CC BY-NC-ND 4.0)


Highlights

• SCAI slowly accumulates at damaged sites depending on 53BP1

• 53BP1 S/TP phosphorylation sites are critical for SCAI binding

• SCAI can inhibit RIF1 function

• SCAI facilitates BRCA1-mediated DNA repair

Summary

DNA double-strand breaks (DSBs) are repaired by either the homology-directed repair (HDR) or the non-homologous end-joining (NHEJ) pathway. RIF1 (RAP1-interacting factor homolog) was recently shown to stimulate NHEJ through an interaction with 53BP1 (p53-binding protein 1) phosphorylated at S/TQ sites, but the molecular mechanism underlying pathway choice remains unclear. Here, we show that SCAI (suppressor of cancer cell invasion) binds to 53BP1 phosphorylated at S/TP sites and facilitates HDR. Upon DNA damage, RIF1 immediately accumulates at damage sites and then gradually dissociates from 53BP1 and is subsequently replaced with SCAI. Depletion of SCAI reduces both the accumulation of HDR factors, including BRCA1 (breast cancer susceptibility gene 1), at damage sites and the efficiency of HDR, as detected by a reporter assay system. These data suggest that SCAI inhibits RIF1 function to allow BRCA1-mediated repair, which possibly includes alt-NHEJ and resection-dependent NHEJ in G1, as well as HDR in S/G2.

Keywords:

DNA double-strand breaks, BRCA1, RIF1, 53BP1, SCAI, NHEJ, HDR, alternative NHEJ, resection-dependent NHEJ, genomic instability

FREE PDF GRATIS: Cell Reports

Uma alternativa legal às publicações acadêmicas pagas

domingo, julho 16, 2017

A legal alternative to academic publishing paywalls

April 12, 2017 1:40 AM   Subscribe


Unpaywall is a web browser extension which finds free versions of paywalled or fee-to-view articles. Launched in early April, it provides an interface to a database of 86+ million digital object identifiers (DOIs). When an Unpaywall user lands on the page of a research article, the software scours thousands of institutional repositories, preprint servers, and websites like PubMed Central to see if an open-access copy of the article is available. If it is, users can click a small green tab on the side of the screen to view a PDF. The developers say Unpaywall doesn't ask for, track or store any personal information. Developed by Impactstory and funded by the National Science Foundation and the Alfred P. Sloan Foundation. Alternatives are available...
...

Read more/Leia mais aqui: MetaFilter

Micro ondas revelam estrutura detalhada de motor molecular artificial: mero acaso, fortuita necessidade ou design inteligente?

sexta-feira, julho 14, 2017

Cold Snapshot of a Molecular Rotary Motor Captured by High-Resolution Rotational Spectroscopy

Authors

Dr. Sérgio R. Domingos, Dr. Arjen Cnossen, Prof. Dr. Wybren J. Buma, Prof. Dr. Wesley R. Browne, Prof. Dr. Ben L. Feringa, Prof. Dr. Melanie Schnell

First published: 20 June 2017 Full publication history

DOI: 10.1002/anie.201704221 View/save citation



Abstract

We present the first high-resolution rotational spectrum of an artificial molecular rotary motor. By combining chirped-pulse Fourier transform microwave spectroscopy and supersonic expansions, we captured the vibronic ground-state conformation of a second-generation motor based on chiral, overcrowded alkenes. The rotational constants were accurately determined by fitting more than 200 rotational transitions in the 2–4 GHz frequency range. Evidence for dissociation products allowed for the unambiguous identification and characterization of the isolated motor components. Experiment and complementary quantum-chemical calculations provide accurate geometrical parameters for the C27H20 molecular motor, the largest molecule investigated by high-resolution microwave spectroscopy to date.

FREE PDF GRATIS: Angewandte Chemie

Cientistas descobrem que é mais bem aventurado dar do que receber...

A neural link between generosity and happiness

Soyoung Q. Park, Thorsten Kahnt, Azade Dogan, Sabrina Strang, Ernst Fehr & Philippe N. Tobler

Nature Communications 8, Article number: 15964 (2017)


Download Citation

Cooperation Human behaviour

Received: 21 October 2016 Accepted: 12 May 2017

Published online: 11 July 2017


Abstract

Generous behaviour is known to increase happiness, which could thereby motivate generosity. In this study, we use functional magnetic resonance imaging and a public pledge for future generosity to investigate the brain mechanisms that link generous behaviour with increases in happiness. Participants promised to spend money over the next 4 weeks either on others (experimental group) or on themselves (control group). Here, we report that, compared to controls, participants in the experimental group make more generous choices in an independent decision-making task and show stronger increases in self-reported happiness. Generous decisions engage the temporo-parietal junction (TPJ) in the experimental more than in the control group and differentially modulate the connectivity between TPJ and ventral striatum. Importantly, striatal activity during generous decisions is directly related to changes in happiness. These results demonstrate that top–down control of striatal activity plays a fundamental role in linking commitment-induced generosity with happiness.

Acknowledgements

This work was supported by grant 0036/AB16 from the Templeton World Charity Foundation, grants PP00P1_128574, PP00P1_150739, 00014_165884 and CRSII3_141965 from the Swiss National Science Foundation and grants PA-2682/1-1 and INST 392/125-1 (Project C07 from SFB/TRR 134) from the German Research Foundation. We thank Christine Schneider and Michel Wälti for their help with data acquisition, Gabriele Bellucci for methodological support and Tamara Jean Herz for language editing. We also gratefully acknowledge the support of the Neuroscience Center Zurich.

Author information

Affiliations

Department of Psychology I, University of Lübeck, Lübeck 23562, Germany
Soyoung Q. Park & Sabrina Strang

Department of Neurology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA
Thorsten Kahnt

Laboratory for Social and Neural Systems Research, Department of Economics, University of Zurich, Zurich 8006, Switzerland
Azade Dogan, Ernst Fehr & Philippe N. Tobler

Contributions

S.Q.P., T.K. and P.N.T. conceived and designed the study. S.Q.P., T.K. and A.D. conducted the experiments and analysed the data. S.Q.P., T.K., S.S., E.F. and P.N.T. wrote the manuscript and S.Q.P., T.K., S.S., E.F. and P.N.T. edited the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Soyoung Q. Park.

As cinco grandes extinções em massa

The big five mass extinctions

Biologists suspect we’re living through the sixth major mass extinction. Earth has witnessed five, when more than 75% of species disappeared. Palaeontologists spot them when species go missing from the global fossil record, including the iconic specimens shown here. “We don’t always know what caused them but most had something to do with rapid climate change”, says Melbourne Museum palaeontologist Rolf Schmidt.


End Ordovician, 444 million years ago, 86% of species lost

— Graptolite 2-3 cm length

Graptolites, like most Ordovician life, were sea creatures. They were filter-feeding animals and colony builders. Their demise over about a million years was probably caused by a short, severe ice age that lowered sea levels, possibly triggered by the uplift of the Appalachians. The newly exposed silicate rock sucked CO2 out of the atmosphere, chilling the planet.

CREDIT: JAIME MURCIA / MUSEUM VICTORIA



Late Devonian, 375 million years ago, 75% of species lost
— Trilobite, 5 cm length

Trilobites were the most diverse and abundant of the animals that appeared in the Cambrian explosion 550 million years ago. Their great success was helped by their spiky armour and multifaceted eyes. They survived the first great extinction but were nearly wiped out in the second. The likely culprit was the newly evolved land plants that emerged, covering the planet during the Devonian period. Their deep roots stirred up the earth, releasing nutrients into the ocean. This might have triggered algal blooms which sucked oxygen out of the water, suffocating bottom dwellers like the trilobites.

CREDIT: CHIP CLARK / SMITHSONIAN INSTITUTION
...

Read more here/Leia mais aqui: Cosmos Magazine

Tamanho corporal de peixes ósseos não foi um fator seletivo na maior de todas as extinções em massa de todos os tempos

quinta-feira, julho 13, 2017

Body length of bony fishes was not a selective factor during the biggest mass extinction of all time

Authors

Mark N. Puttick, Jürgen Kriwet, Wen Wen, Shixue Hu, Gavin H. Thomas, Michael J. Benton

First published: 30 June 2017 Full publication history

DOI: 10.1111/pala.12309  View/save citation

Data archiving statement All the trees, R code, and data used in this study are available on the Dryad Digital Repository: https://doi.org/10.5061/dryad.394hm

Source/Fonte: PhysOrg

Abstract

The Permo-Triassic mass extinction devastated life on land and in the sea, but it is not clear why some species survived and others went extinct. One explanation is that lineage loss during mass extinctions is a random process in which luck determines which species survive. Alternatively, a phylogenetic signal in extinction may indicate a selection process operating on phenotypic traits. Large body size has often emerged as an extinction risk factor in studies of modern extinction risk, but this is not so commonly the case for mass extinctions in deep time. Here, we explore the evolution of non-teleostean Actinopterygii (bony fishes) from the Devonian to the present day, and we concentrate on the Permo-Triassic mass extinction. We apply a variety of time-scaling metrics to date the phylogeny, and show that diversity peaked in the latest Permian and declined severely during the Early Triassic. In line with previous evidence, we find the phylogenetic signal of extinction increases across the mass extinction boundary: extinction of species in the earliest Triassic is more clustered across phylogeny compared to the more randomly distributed extinction signal in the late Permian. However, body length plays no role in differential survival or extinction of taxa across the boundary. In the case of fishes, size did not determine which species survived and which went extinct, but phylogenetic signal indicates that the mass extinction was not a random field of bullets.

FREE PDF GRATIS: Palaeontology

A Terra já está enfrentando a Sexta Onda de Extinção em Massa das espécies de animais?

quarta-feira, julho 12, 2017

Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines

Gerardo Ceballosa,1, Paul R. Ehrlichb,1, and Rodolfo Dirzob 

Author Affiliations

aInstituto de Ecología, Universidad Nacional Autónoma de México, Mexico City 04510, Mexico;

bDepartment of Biology, Stanford University, Stanford, CA 94305

Contributed by Paul R. Ehrlich, May 23, 2017 (sent for review March 28, 2017; reviewed by Thomas E. Lovejoy and Peter H. Raven)

Source/Fonte: AFP

Significance

The strong focus on species extinctions, a critical aspect of the contemporary pulse of biological extinction, leads to a common misimpression that Earth’s biota is not immediately threatened, just slowly entering an episode of major biodiversity loss. This view overlooks the current trends of population declines and extinctions. Using a sample of 27,600 terrestrial vertebrate species, and a more detailed analysis of 177 mammal species, we show the extremely high degree of population decay in vertebrates, even in common “species of low concern.” Dwindling population sizes and range shrinkages amount to a massive anthropogenic erosion of biodiversity and of the ecosystem services essential to civilization. This “biological annihilation” underlines the seriousness for humanity of Earth’s ongoing sixth mass extinction event.

Abstract

The population extinction pulse we describe here shows, from a quantitative viewpoint, that Earth’s sixth mass extinction is more severe than perceived when looking exclusively at species extinctions. Therefore, humanity needs to address anthropogenic population extirpation and decimation immediately. That conclusion is based on analyses of the numbers and degrees of range contraction (indicative of population shrinkage and/or population extinctions according to the International Union for Conservation of Nature) using a sample of 27,600 vertebrate species, and on a more detailed analysis documenting the population extinctions between 1900 and 2015 in 177 mammal species. We find that the rate of population loss in terrestrial vertebrates is extremely high—even in “species of low concern.” In our sample, comprising nearly half of known vertebrate species, 32% (8,851/27,600) are decreasing; that is, they have decreased in population size and range. In the 177 mammals for which we have detailed data, all have lost 30% or more of their geographic ranges and more than 40% of the species have experienced severe population declines (>80% range shrinkage). Our data indicate that beyond global species extinctions Earth is experiencing a huge episode of population declines and extirpations, which will have negative cascading consequences on ecosystem functioning and services vital to sustaining civilization. We describe this as a “biological annihilation” to highlight the current magnitude of Earth’s ongoing sixth major extinction event.

sixth mass extinction population declines population extinctions conservation ecosystem service

Footnotes

1To whom correspondence may be addressed. Email: gceballo@ecologia.unam.mx or pre@stanford.edu.

Author contributions: G.C., P.R.E., and R.D. designed research; G.C. and P.R.E. performed research; G.C., P.R.E., and R.D. contributed new reagents/analytic tools; G.C. analyzed data; and G.C., P.R.E., and R.D. wrote the paper.

Reviewers: T.E.L., George Mason University; and P.H.R., Missouri Botanical Garden.

The authors declare no conflict of interest.

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1704949114/-/DCSupplemental.

Freely available online through the PNAS open access option.

FREE PDF GRATIS: PNAS

Mais outro indivíduo de Denisova

terça-feira, julho 11, 2017

A fourth Denisovan individual

Viviane Slon1,*, Bence Viola2,3,4, Gabriel Renaud1, Marie-Theres Gansauge1, Stefano Benazzi3,5, Susanna Sawyer1, Jean-Jacques Hublin3, Michael V. Shunkov4,6, Anatoly P. Derevianko4,7, Janet Kelso1, Kay Prüfer1, Matthias Meyer1 and Svante Pääbo1

1Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, D-04103 Leipzig, Germany.

2Department of Anthropology, University of Toronto, M5S 2S2 Toronto, Ontario, Canada.

3Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, D-04103 Leipzig, Germany.

4Institute of Archaeology and Ethnography, Russian Academy of Sciences, Siberian Branch, Novosibirsk RU-630090, Russia.

5Department of Cultural Heritage, University of Bologna, 48121 Ravenna, Italy.

6Novosibirsk National Research State University, Novosibirsk RU-630090, Russia.

7Altai State University, Barnaul RU-656049, Russia.

↵*Corresponding author. Email: viviane_slon@eva.mpg.de

Science Advances 07 Jul 2017:

Vol. 3, no. 7, e1700186

DOI: 10.1126/sciadv.1700186 


Abstract

The presence of Neandertals in Europe and Western Eurasia before the arrival of anatomically modern humans is well supported by archaeological and paleontological data. In contrast, fossil evidence for Denisovans, a sister group of Neandertals recently identified on the basis of DNA sequences, is limited to three specimens, all of which originate from Denisova Cave in the Altai Mountains (Siberia, Russia). We report the retrieval of DNA from a deciduous lower second molar (Denisova 2), discovered in a deep stratigraphic layer in Denisova Cave, and show that this tooth comes from a female Denisovan individual. On the basis of the number of “missing substitutions” in the mitochondrial DNA determined from the specimen, we find that Denisova 2 is substantially older than two of the other Denisovans, reinforcing the view that Denisovans were likely to have been present in the vicinity of Denisova Cave over an extended time period. We show that the level of nuclear DNA sequence diversity found among Denisovans is within the lower range of that of present-day human populations.

Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).

This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited.

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A comparative analysis of human and mouse islet G-protein coupled receptor expression

Stefan Amisten, Patricio Atanes, Ross Hawkes, Inmaculada Ruz-Maldonado, Bo Liu, Fariborz Parandeh, Min Zhao, Guo Cai Huang, Albert Salehi & Shanta J. Persaud

Scientific Reports 7, Article number: 46600 (2017)
 
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Type 2 diabetes

Received: 26 August 2016 Accepted: 22 March 2017
Published online: 19 April 2017


Abstract

G-protein coupled receptors (GPCRs) are essential for islet function, but most studies use rodent islets due to limited human islet availability. We have systematically compared the GPCR mRNA expression in human and mouse islets to determine to what extent mouse islets can be used as surrogates for human islets to study islet GPCR function, and we have identified species-specific expression of several GPCRs. The A3 receptor (ADORA3) was expressed only in mouse islets and the A3 agonist MRS 5698 inhibited glucose-induced insulin secretion from mouse islets, with no effect on human islets. Similarly, mRNAs encoding the galanin receptors GAL1 (GALR1), GAL2 (GALR2) and GAL3 GALR3) were abundantly expressed in mouse islets but present only at low levels in human islets, so that it reads (GALR3) and galanin inhibited insulin secretion only from mouse islets. Conversely, the sst1 receptor (SSTR1) was abundant only in human islets and its selective activation by CH 275 inhibited insulin secretion from human islets, with no effect on mouse islets. Our comprehensive human and mouse islet GPCR atlas has demonstrated that species differences do exist in islet GPCR expression and function, which are likely to impact on the translatability of mouse studies to the human context.

Acknowledgements

We are grateful to the relatives of organ donors for human pancreases for research. This study was supported by grants from the EFSD/Boehringer-Ingelheim Research Programme and a Diabetes UK RD Lawrence Fellowship to Stefan Amisten (11/0004172).

Author information

Affiliations

Diabetes Research Group, Division of Diabetes & Nutritional Sciences, Faculty of Life Sciences & Medicine, King’s College London, London, UK
Stefan Amisten, Patricio Atanes, Ross Hawkes, Inmaculada Ruz-Maldonado, Bo Liu, Min Zhao, Guo Cai Huang & Shanta J. Persaud
Department of Clinical Science, Division of Islet Cell Physiology, SUS, University of Lund, Malmö, Sweden
Fariborz Parandeh & Albert Salehi

Contributions

The study was designed by S.A., P.A., R.H., A.S. and S.J.P. Data were collected and analysed by S.A., R.H., P.A., I.R.M., F.P. and B.L. G.C.H. and M.Z. provided the isolated human islets of Langerhans. The article was drafted by S.A. and S.J.P. All authors revised the article critically for important intellectual content. All authors gave their final approval of the current version to be published. S.A. and S.J.P. take responsibility for the contents of the article.

Competing interests
The authors declare no competing financial interests.

Corresponding authors
Correspondence to Stefan Amisten or Shanta J. Persaud.

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