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发表于 2014-6-30 23:31:49
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Part II: Speed Earliest skeletal animals were reef builders
Ecological reef-building adaptation in skeletal animals
appeared much earlier than previously thought.
Time2
Animal reef-building evolved millions of years earlier than previously thought, researchers report today in Science1. Scientists have discovered fossils indicating that animal, or metazoan, reefs date to as far back as about 548 million years ago, some seven million years earlier than previously estimated. This suggests they appeared prior to the Cambrian explosion, a wellspring of diverse life that is generally thought to have driven the proliferation of reef-building.
“This succession of rocks that we’ve been looking at in Namibia encompasses a period of time important in animal life,” says Amelia Penny, a geologist at the University of Edinburgh, UK, and first author of the study. “As far as we know, these are the earliest animal building reefs.” The scientists found the fossils in Nama Group rocks, a series of layered carbonates and silicates deposited in an ancient ocean that covered what is now Namibia, hundreds of millions of years ago.
Palaeontologists estimate that microbial reefs date back at least three billion years, followed by animal reef-makers around the time of the Cambrian explosion. Animals' so-called skeletal reef building entails the deposition of shells made of calcium carbonate, while microbial reefs typically consist of cyanobacteria and other microorganisms.
What Penny and her colleagues show is the ecological evolution from one to the other, says Guy Narbonne, a palaeobiologist at Queen’s University in Kingston, Ontario. Narbonne says the discovery shows for the first time that both microbes and skeletal animals contributed to reef-building in the Ediacaran, the geologic time period immediately preceding the Cambrian. “The question we have now is how big those relative roles were and how that changed,” he says.[365]
Time3
Strong foundations
The reefs were made of tiny, filter-feeding animals known as Cloudina, a widely studied animal that lived prior to the Cambrian explosion. The authors identified key characteristics in clusters of the reef-makers: To build a reef, the animals must have a base to start from (such as the ocean floor), a way of attaching to one another and the ability to form a rigid structure.
“Modern-day reefs are a result of ecological pressures,” says geologist and study co-author Rachel Wood, also at the University of Edinburgh. Reefs typically help to protect the animals that create them from predators and they provide a means to harvest nutrients from the water. The study suggests that these natural selection pressures were in operation earlier than researchers previously thought, she says.
The discovery will drive researchers who study ancient reef-builders to look back beyond 540 million years ago for other signs of skeletal reef ecology, says Mary Droser, a palaeobiologist at the University of California, Riverside.
Meanwhile, Penny and her colleagues are constructing a three-dimensional model of the reef from slices of rock brought back from their field site to further scrutinize the Cloudina reef. With the help of international collaborators, the authors plan to study the geochemistry of the rocks to understand how the oxygen content of ancient oceans changed over time — and how this affected animal evolution. “We don’t fully understand how one affects the other,” Wood says, noting the possibility that the changing of availability of oxygen could have driven the evolution of complex life. [254]
Source:
http://www.nature.com/news/earliest-skeletal-animals-were-reef-builders-1.15470
A new view of dinosaurs, a clearer view of lunar origins
Time4
Dinosaurs have undergone any number of scientific makeovers in the last few decades. When I was young, they were depicted as lumbering, over-sized lizards, “cold-blooded” and drab. That simplistic image was eventually replaced with a more vibrant one. The velociraptor à la Jurassic Park was agile, quick, birdlike — and quite possibly festooned in feathers. Bright colors (though maybe not Barney purple) and rich social lives have also been proposed.
Scientists’ latest look at dinosaurs offers up another revision. As Meghan Rosen describes in "Dinosaurs had middling metabolisms," the new work compares dinosaur growth rates, estimated from fossils, with growth rates from modern animals for insights into dino metabolism. Energetically, dinosaurs were neither fowl nor lizard, but something in between, the researchers conclude. Like today’s sea-faring tuna and great white sharks, dinos share some traits with both ectotherms (what people mean when they say “cold-blooded”) and endotherms (“warm-blooded”).
In science, revisionism can be a good thing. Finding ways to test assumptions and accepted truths can lead to insight and discovery. As Tina Hesman Saey reports in "Human-ape split gets an earlier date," for example, the latest DNA studies of chimpanzees are forcing a rethink of just how long ago chimps and humans shared a common ancestor. And despite popular thinking that the Internet can be harnessed to power good causes, one of the first long-term scientific studies of giving in a major online movement reveals far more “slacktivism” than activism, Bruce Bower writes in our feature story "Token Gestures." At the same time, other new experiments suggest ways to motivate the public to action.
Of course, science also confirms what we think we know. Take the origin of the moon. The best theory holds it formed after a planet-sized object collided with a young Earth. The resulting explosion created the moon, which would have been chemically distinct from Earth. But chemical analyses of lunar and terrestrial rocks revealed no differences. Now, a more precise comparison of the rocks has found distinctions that support the leading theory, Rosen reports in "Rocks' chemistry reveals details of moon's origins."
Testing, revising, substantiating: That’s just what science is supposed to do.[356]
Source:
https://www.sciencenews.org/article/new-view-dinosaurs-clearer-view-lunar-origins
Biosafety in the balance
An accident with anthrax demonstrates that pathogen research always carries a risk of release — and highlights the need for rigorous scrutiny of gain-of-function flu studies.
Time5
The news last week of an accident involving live anthrax bacteria at the US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, is troubling. Some 84 workers were potentially exposed to the deadly Ames strain at three CDC labs. But the incident will cause much wider ripples: it highlights the risks of the current proliferation of biocontainment labs and work on dangerous pathogens. If an accident can happen at the CDC, then it can happen anywhere.
Details are sparse, but it seems that the anthrax was being inactivated in a biosafety-level-3 (BSL-3) high-containment lab so that it could be studied at the three BSL-2 labs. But live bacteria survived the inactivation step, and were not detected before samples were sent out. The CDC considers the risk that the exposed workers have been infected to be low, and all have been offered protective antibiotics.
Such lab accidents are fortunately not commonplace. A CDC analysis in 2012 reported, for example, that there were 727 incidents of theft, loss or release of Select Agents and Toxins in the United States between 2004 and 2010, resulting in 11 laboratory-acquired infections and no secondary transmission (R. D. Henkel et al. Appl. Biosafety 17, 171–180; 2012). Anthrax is contracted by direct exposure to spores, and does not spread between people. Much more potentially dangerous are lab accidents involving agents that do. It is impossible to read about the CDC incident and not breathe a large sigh of relief that it did not involve a novel engineered pandemic influenza strain.
Groups led by Ron Fouchier of the Erasmus Medical Center in Rotterdam, the Netherlands, and Yoshihiro Kawaoka of the University of Wisconsin–Madison created a storm in late 2011 when they artificially engineered potentially pandemic forms of the H5N1 avian flu virus. In January last year, researchers ended a voluntary 12-month moratorium on such gain-of-function flu research, which can increase the host range, transmissibility or virulence of viruses (see Nature 493, 460; 2013), and work resumed.[332]
Time6
This month, Kawaoka’s group reported that it had engineered a de novo flu virus from wild-avian-flu-strain genes that coded for proteins similar to those in the 1918 pandemic virus (T. Watanabe Cell Host Microbe 15, 692–705; 2014). The researchers were able to make a virulent version that could transmit between ferrets, and they concluded that a 1918-like virus could therefore emerge from wild avian flu viruses.
In the century since the 1918 flu hit, no similar pandemic variant has emerged despite wild animal flu viruses mutating and reassorting incessantly. The 1918 H1N1 virus was reconstructed in 2005, but human immunity to it became widespread following the 2009 H1N1 pandemic. There are no mammalian-transmissible 1918-like avian flus in the wild; the only ones that exist are Kawaoka’s team’s engineered strains.
Researchers such as Kawaoka and Fouchier argue that by engineering mutant viruses in the lab, they can identify mutations and traits that allow the pathogens to spread between mammals. This in turn, they argue, allows assessment of the pandemic potential of animal-flu viruses. In the long term, such experiments could help to elucidate the mechanisms of virus transmissibility and pathogenicity. But their shorter-term public-health benefits have been overstated. The risks and benefits must therefore be carefully weighed, and rigorous oversight is needed to ensure that such work is done only at facilities with the highest standards of biosafety.
Other scientists argue that the concept of predicting the pandemic potential of flu viruses from mutations, although appealing, is simplistic. They say that the identified mutations are but a handful out of millions of possible combinations, many of which might also allow mammalian transmission. They argue that mutations in specific proteins cannot reliably predict traits, and that outcomes depend on interactions between various other background genetic changes throughout the virus. [298]
Source:
http://www.nature.com/news/biosafety-in-the-balance-1.15447
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