Dollo’s Law, a theory proposed by the scientist Louis Dollo in the 1800s, says that when a particular property is lost in a species, it never comes back. It explains why humans have no tails, birds and turtles have no teeth and snakes have not regained legs.
But a new analysis about frogs, done by a scientist at Stony Brook University, found that they lost teeth in the lower jaw at least 200 million years ago, but a particular type of marsupial tree frog regained those lower teeth about 20 million years ago.
“It’s a very clear-cut case of re-evolution because of the large time span,” said John Wiens, the Stony Brook biologist who wrote the paper in the journal Evolution.
Dr. Wiens analyzed DNA samples of 170 modern and fossilized frogs to approximate the dates of loss and re-evolution of the teeth. Most frogs have teeth on their upper jaws, which may have made the re-evolution in the tree frog, known as Gastrotheca guentheri, easier, Dr. Wiens said. “They already had teeth in the upper jaw, so they had the enamel, dentine and other necessities,” he said. “There was a way to facilitate new teeth after 200 million years.”
The species is the only known modern frog species with lower teeth, though certain other species with upper teeth have structures similar to teeth on the lower jaw. “That’s a big question now: What’s preventing the other frogs from developing real teeth on the lower jaw?” Dr. Wiens said.
By Sindya N. Bhanoo at www.nytimes.com. Picture by Chris Gash.
Now, scientists report in the journal Nature that genes in certain plants keep infections at a distance with the help of the clock as well. Twenty-two genes in the plant Arabidopsis, all connected to the plant’s ability to resist infection, were expressed only from the evening onward, reaching their highest point at the beginning of day.
The timing corresponds with the formation of spores in a funguslike pathogen that attacks the plant and results in a condition known as mildew disease. The disease weakens the plant and forms a repugnant layer of mildew.
“From what we know, the pathogen forms spores at night and disseminates them at the beginning of day, so that’s when the danger of infection is highest,” said Xinnian Dong, a biologist at Duke University and one of the study’s authors. During the day, when the pathogen does not attack, the genes were not expressed.
This is the first time scientists have made a connection between the circadian clock and pathogen resistance, Dr. Dong said. She believes that if we analyze the complexity of the relationship between pathogens and hosts, and their circadian rhythms, there may be practical applications. Pesticide treatments could be timed to have maximum impact, for instance. Or it may even be possible to determine ideal times for administering medications in humans, she said.
By Sindya N. Bhanoo, www.nytimes.com. Picture by Wei Wang and Xinnian Dong.
Reduced levels of omega-3 in mice had consequences on emotional behaviors, French investigators say. The Institut National de la Santé et de la Recherche Medicale and the French National Institute for Agricultural Research say the imbalanced ratio between omega-6 and omega-3 increased continuously over the course of the 20th century.
The team studied mice fed a permanent diet unstable in omega-3 and omega-6 fatty acids. They found omega-3 deficiency disturbed neuronal communication and the neuronal dysfunction was accompanied by depressive behaviors among the malnourished mice.
"Our results can now corroborate clinical and epidemiological studies which have revealed associations between an omega-3/omega-6 imbalance and mood disorders. To determine if the omega-3 deficiency is responsible for these neuropsychiatric disorders additional studies are, of course, required."
The results give the first biological components of an explanation for the observed correlation between omega-3 poor diets -common in the industrialized world- and mood disorders such as depression.
By UPI.com. No credits for picture.
Conservationists in Egypt have discovered a new species of wolf, which shares DNA with Indian and Himalayan cousins. The "Egyptian jackal", as it's known, is not jackal at all, despite the visual similarities with the golden jackal. The discovery throws light on how wolf species migrated through Africa and Europe - proving that grey wolves emerged in Africa about three million years before they spread to the northern hemisphere.
As long ago as 1880 it had been noticed that the Egyptian jackal looked suspiciously like the grey wolf, and some biologists in the 20th century, studying skulls, made the same observation. However, the creature retained its name. Now, the difference has been formalised.
The investigation is published in the journal PLOS One, with author David Macdonald telling Wired.co.uk in an email: "A wolf in Africa is not only important conservation news, but raises fascinating biological questions about how the new African wolf evolved and lived alongside the real golden jackals."
Eli Rueness of the University of Oslo, who also contributed to the study, added: "We could hardly believe our own eyes when we found wolf DNA that did not match anything." However, the new species' DNA is quite similar to wolves found 2,500 kilometres away in the highlands of Ethiopia.
Professor Claudio Sillero, who has worked in Ethiopia for more than two decades, told Wired.co.uk: "This discovery contributes to our understanding of the biogeography of Afroalpine fauna, a group of species with African and Eurasian ancestry which evolved in the relative isolation of the highlands of the Horn of Africa. Rare Ethiopian wolves are themselves a recent immigrant to Africa, and separated from the grey wolf even earlier than the newly discovered African wolf."
By Duncan Geere in Wired.co.uk. Picture by www.muyinteresante.es.
Homo sapiens are an terribly vain species. We love to exhibit our big brains and our opposable thumbs — and we wouldn't be good for much without them. But there's one human attribute that doesn't get enough attention: the ability to throw things really, really far. According to a new study published in the journal Evolution and Human Behavior, not only was a good arm essential for our early survival, it is also an innate talent, deep into us from the moment of birth.
Humanity's rapid rise to the top on a planet with lots of competing species was never a sure thing. We're slow, we're soft and we have good teeth but they're nothing compared with those of the big cats or the great apes. We needed to kill the predators from a safe distance — first with rocks and later with spears.
"The ability to throw great distances was not a small thing," says Geoffrey P. Bingham, an experimental psychologist at Indiana University. "We are the only animals with that talent." Before we pick something up, we begin tensing muscles in the arm and hand to accommodate the anticipated weight. If that weight is finally less than we guessed, we bring more muscle power to the job than is necessary, making the object feel light.
Projectile selection is a talent that some people have in greater abundance than others. Everyone, however, is born with the basic skill set, and all of us get better with practice. "You acquire the ability at the same time you're learning to throw," says Bingham. That was very good news for your most distant ancestors — and very bad news for a long-ago mastodon.
By Jeffrey Kluger, TIME Magazine. Picture by The Bridgeman Art Library / Getty Images.
