Blogs / 80beats

Researchers have determined the mechanism by which the world’s simplest vision system works. A team of biologists spent a decade studying the larvae of the marine rag-worm Platynereis, a tiny creature with just two cells that respond to light and direct the worm to swim towards it. The rag-worm and other zooplankton like krill drift in the ocean’s water columns, swimming up from the depths towards the light in order to graze on marine plants called phytoplankton near the surface. This movement, called phototaxis, is the biggest biomass displacement in the world [AFP].

The rag-worm has two cells that work together as “proto-eyes”: one pigment cell and one light-sensitive cell. First, the pigment cell absorbs light and casts a shadow over the photoreceptor cell. The shape of the shadow varies according to the position of the light source. The photoreceptor cell then converts this light signal into electricity, sending it in a signal along a nerve that connects to a band of cells endowed with thin hairs, called cilia, that beat to displace water [AFP]. So although the worm sees no images, it can sense the difference between light and dark and swim in the right direction.

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The evolution of minerals on our planet has been propelled by the evolution of life on earth, a sweeping new study demonstrates. While the underlying assumption isn’t new, the study is the first to chart how the emergence of algae and then complex microorganisms gave rise to the 4,300 or so minerals that are now present on earth.

In the early days of the universe, clouds of gas and dust contained all the naturally occurring elements found in the periodic table, but most were too widely dispersed to form minerals; scientists believe there were only about a dozen minerals in the interstellar medium. According to the study, around a further 60 different minerals formed 4.5 billion years ago, as clumps of matter collided and coalesced to begin forming the Solar System. The smaller fragments congealed into larger, planet-sized bodies, where volcanism and the effects of water took the mineral count into the hundreds. The planets Mars and Venus have got this far [Nature News], and have minerals created by hot magma like quartz and zircon.

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The roots of mammalian hair go far back into evolutionary history, according to a new study. Hair, which provides insulation and protection, is seen as one of the main evolutionary innovations that led to the rise of mammals. But the origins of hair date back to an unknown reptile ancestor that lived more than 300 million years ago, in the Paleozoic era, the new study says [National Geographic News].

Previously, biologists had considered the possibility that hair evolved from scales or feathers, but the paucity of fossils showing the evolution from reptiles to mammals has made the question a hard one to examine. So in this new study, published in the Proceedings of the National Academy of Sciences [subscription required], researchers ignored the fossil record and looked instead to the genetic record of living animals: namely, a chicken and an anole lizard.

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The tiny skull of a juvenile dinosaur with a strange set of chompers has delighted paleontologists, who believe it proves that the species was a transitional phase between carnivorous dinosaurs and herbivores. The Heterodontosaurus has both sharp canine teeth for biting and molars for grinding, suggesting that the species dined on both small reptiles and insects as well as leafy greens.

Says study coauthor Laura Porro: “It’s likely that all dinosaurs evolved from carnivorous ancestors. Since Heterodontosaurs are among the earliest dinosaurs adapted to eating plants, they may represent a transition phase between meat-eating ancestors and more sophisticated, fully herbivorous descendants” [Telegraph]. The omnivorous dino lived 190 million years ago in the Early Jurassic period, Porro says.

Only two other Heterodontosaurus fossils have been found previously, and those both belonged to adults. This newly discovered fossilized skull measures less than 2 inches in length and belonged to a juvenile weighing less than two sticks of butter… [The researchers] studied the juvenile’s skull and determined the individual was probably buried alive in a sandstorm, a mode of death that left its remains in “relatively good condition” [Discovery News].

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Researchers have found a “bizarre” feathered dinosaur with a hodgepodge of characteristics, including four long tail feathers that researchers say may have evolved for display purposes–perhaps to attract a mate or scare off a rival. The well-preserved fossil of the new species, named Epidexipteryx hui, shows that the beast was covered in short, fluffy feathers but lacked the “contour feathers” that help modern birds fly; researchers say Epidexipteryx must have been flightless.

Paleontologist expert Angela Milner commented that the find “shows that feathers were likely being used for ornamentation for many millions of years before they were modified for flight. It provides fascinating evidence of evolutionary experiments with feathers that were going on before small dinosaurs finally took to the air and became birds” [BBC News].

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Several rare varieties of staghorn coral have begun mating across species lines and are creating surprisingly robust hybrids, according to a new study; researchers believe the unusual step is an effort to adapt to changing ocean conditions and avoid extinction. The findings are an unexpected piece of promising news about coral reefs, which usually make the headlines for their potential fate as one of the first victims of global warming.

Coral reefs around the world are under pressure from pollution and gradually warming oceans, and researchers have worried that rare species are particularly vulnerable to extinction. But in the case of these staghorns, the new study shows that when faced with a shortage of mates of their own kind, these rare corals have cast a wider net and started cross-breeding with other coral species, producing hybrids. “It pushes the boundaries of our traditional understanding of species,” said a researcher, Zoe Richards. “They are being a little promiscuous” [Sydney Morning-Herald].

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A new study of a the fossilized remains of the Tiktaalik, the “walking fish” that illuminates how swimming fish evolved into land-dwelling amphibians, shows that there was more to the transition than the switch from fins to limbs. The study shows that the head and braincase were changing, a mobile neck was emerging and a bone associated with underwater feeding and gill respiration was diminishing in size, a beginning of the bone’s adaptation for an eventual role in hearing for land animals [The New York Times].

The creature, dubbed Tiktaalik roseae — or, to be less formal, Fishapod — lived 375 million years ago 600 miles north of the Arctic Circle in a subtropical floodplain that eventually became Ellesmere Island, where it was discovered in 2004 [Wired News]. The fishapod has already earned its reputation as a “missing link” in evolutionary history due to its sturdy, jointed fins and its dual breathing system, with both gills and lungs. But the new study suggests that changes to the animal’s head and the development of the first neck also played a critical role in its evolution.

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Elephants, bacteria, and trees may not have much in common besides their status as living organisms that consume energy to power their basic life functions, but a new study has found a remarkable similarity within that commonality. A team of researchers examined over 3,000 organisms from different branches of the tree of life and found that while creatures may vary enormously in size and complexity, their metabolisms use energy at roughly the same rate.

The researchers examined the at-rest metabolisms of all the species and compared their energy usage, pound for pound. While there were some outliers, most species fell within a narrow range, using between 1 and 10 watts per kilogram of biomass. Study coauthor Anastassia Makarieva says that since such a large number of species falls within this narrow range, she hypothesises there may be an optimum metabolic rate for all organisms. “Organisms that lie close to this value may be the fittest to survive,” she says [New Scientist].

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Researchers believe they have found the earliest known animal footprints, left by a centipede-like creature 570 million years ago; if they’re right, the discovery means that animals were walking on the earth 30 million years earlier than previously thought. Researchers say the fossil shows a track of parallel dots, each about two millimeters in diameter, which may have been pressed into the muddy sand by the tiny feet of one of the earliest complex organisms.

But some experts are not convinced by what they’ve seen. Precambrian paleontologist Nick Butterfield said he was “deeply skeptical,” about the conclusions drawn. “From the description—paired rows of dots—it just doesn’t sound like a trackway…. Centipedes and their ilk shuffle along and leave continuous traces in soft (sub-aerially exposed) sediments—they don’t carefully step ahead, lifting each foot out of the mud to place it exactly in a previously made footprint,” he said [National Geographic News].

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In Africa’s Lake Victoria, researchers believe they’ve caught a fish population in the act of splitting into two distinct species. Researchers say this example of evolution-in-action is remarkable because the two sub-populations of fish aren’t geographically isolated and could theoretically interbreed, but adaptations to their vision are causing them to diverge.

Lead researcher Norihiro Okada and his colleagues had previously shown that cichlid fish in Lake Victoria’s shallow waters are bathed in bluer light, while the turbid water of the lake predominantly lets redder light filter down to fish living in deeper water. The researchers showed that the fish’s eyes have adapted to this difference so that fish that live in deeper water have a pigment in their eyes that is more sensitive to red light, while shallow-water fish have a pigment that’s sensitive to blue [Science News]. Okada’s new study, published in Nature [subscription required], shows that those eye adaptations have also affected mating patterns.

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A 33-foot long, carnivorous dinosaur that lived 85 million years ago had a breathing system similar to that used by modern birds, and researchers say the finding is further evidence of the evolutionary link between dinosaurs and birds. A fossil found in a riverbank in Argentina shows evidence of efficient air sacs that pumped air into the dinosaur’s lungs.

Lead researcher Paul Sereno named the new dinosaur Aerosteon riocoloradensis, which means “air bones from the Rio Colorado.” Instead of lungs that expand and contract, Sereno thinks this beast had air sacs that worked like a bellows, blowing air into the beast’s stiff lungs, much like modern birds…. Most paleontologists believe birds evolved from small, feathered meat-eating dinosaurs, and the earliest known birds were strikingly similar to these dinosaurs [Reuters].

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In a striking example of the evolutionary benefits of altruism, researchers have found a species of ants that sends a few workers out each evening on a suicide mission to ensure the continued survival of the colony. The tiny ant Forelius pusillus, which makes its home in sugar cane fields in Brazil, makes a nightly ritual of covering the entrance to its nest with sand. To be sure that the entrance is sealed shut tightly, a few ants remain outside each evening to finish kicking sand over the hole. Those ants, stuck outside in the cold and the wind, die during the night.

“In a colony with many thousands of workers, losing a few workers each evening to improve nest defense would be favored by natural selection,” said co-author Francis Ratnieks…. The ants stuck outside might be old or sick, [co-author Adam] Tofilski conjectured. Thus, they may have essentially sacrificed themselves for the greater good, being more expendable members of the colony [ScienceNOW Daily News].

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In the middle of the Australian outback along a mountain chain called the Flinders Ranges, researchers have discovered a 650 million year old reef that was once underwater. Researchers say the tiny fossils they’ve already found in the ancient reef may be the earliest examples of multicellular organisms ever found, and may answer questions about how animal life evolved.

Researcher Malcolm Wallace explains that the oldest-known animal fossils are 570 million years old. The reef in the Flinders Ranges is 80 million years older than that and was, he said, “the right age to capture the precursors to animals” [The Times]. The first fossils discovered in the reef appear to be sponge-like multicellular organisms that resemble tiny cauliflowers, measuring less than an inch in diameter, but Wallace cautions that the creatures haven’t been thoroughly studied yet. The reef’s discovery was announced at a meeting of the Geological Society of Australia this week.

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Researchers have found the first small finger-like bones in the fins of a fish that lived 380 million years ago, about 15 million years before the first four-footed creatures, called tetrapods, clambered onto the land.

The finding upends the most recent theory of the evolution of digits: The need to adapt to swampy marshlands and terra firma, the theory went, is what drove the gradual shift through natural selection from fish fins suitable only for swimming to weight-bearing limbs with articulated joints. The study, however, reveals that rudimentary fingers were already present inside the fins of the shallow-water Panderichthys, a transitional species that was nonetheless more fish than tetrapod [The Daily Telegraph].

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A newly discovered ant from the Amazon rainforest is so strange that researchers have named it “the ant from Mars.” Found in Brazil, the ant has a pale body and no eyes, says [lead researcher] Christian Rabeling…. Its mouthparts stick out like sharp forceps and are longer than the rest of its head. Its DNA may be even more interesting. Genetic analysis puts the new ant so far from other species that it deserves its own subfamily [Science News].

Researchers named the subterranean ant Martialis heureka, which translates to “eureka ant from Mars,” because of the new species‘ odd morphology and because of their own excitement over finding it. Researchers say that a DNA analysis suggests that the M. heureka evolved earlier than any other living ant, and that it has changed little over 50 million years. “This discovery lends support to the idea that blind, subterranean predator ants arose at the dawn of ant evolution,” Rabeling said [LiveScience].

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