September 20, 2012
Tabby may be a colloquial term for a female kitty, but it’s more properly the name for the common stripey pattern on a domestic cat’s coat. Those tabby markings come in two main varieties: proper vertical stripes of dark on a light background, known as the mackerel pattern, and a blotched variety consisting of less-organized, dark whorls. Now scientists from Stanford University and elsewhere have identified the gene that determines whether a tabby is mackerel or blotched and found that the same gene also can make a cheetah a king. The study appears in today’s issue of Science.
“We were motivated by a basic question: How do periodic patterns like stripes and spots in mammals arise?” study co-author Gregory Barsh, an investigator at HudsonAlpha and a Stanford geneticist, said in a press release. “Until now, there’s been no obvious biological explanation for cheetah spots or the stripes on tigers, zebras or even the ordinary house cat.”
Barsh and his colleagues examined DNA taken from feral kitties in Northern California that were captured, sterilized and released (a common practice employed to control the size of feral cat populations) and from tissue samples collected by the City of Huntsville Animal Services group. All the mackerel tabbies they studied had a normal version of a gene the researchers named Transmembrane Aminopeptidase Q (Taqpep) while all the blotched tabbies had a mutated form of the gene.
The Taqpep gene establishes the pattern of a cat’s coat while a kitty is still in the womb, likely by determining the level of expression of another gene–Endothelin3 (Edn3)–that drives the shade produced by a hair cell (lots of Edn3 results in darker hair). The form of the pattern is actually established out of a random interaction of chemicals that ends up producing something that looks non-random–British mathematician Alan Turing first proposed this theory in 1952, and it was later simulated in computer models and earlier this year scientists discovered the chemicals in question.
Still to be determined, though, is why some domestic cats don’t have any pattern at all despite the status of their Taqpep gene. (On a side note, blotched tabbies are sometimes called “classic” tabbies but not because they’re more common. The blotched pattern is a more recent mutation; the original wild ancestors of domestic kitties were mackerels similar to Old World wild cats of today.)
But domestic cats aren’t the only cats that can vary in coat pattern, of course. Most cheetahs, for example, are the common spotted variety, but a few rare cats are known as king cheetahs, and these sub-Saharan kitties have dark stripes running along their backs (see below). When the researchers examined skin and blood samples taken from captive and wild cheetahs from South Africa and Namibia, they found that not only did the cats have the same Taqpep gene as domestic kitties, but also the gene worked in a similar way on the wild cats’ coats. A normal Taqpep gene produced the regular spotted cats but a mutated Taqpep merged the spots into stripes, just as the gene had merged the tabby stripes into blotches.
Though scientists cannot yet explain how the zebra got its stripes, at least now they can explain how the king cheetah got his.
July 16, 2012
Last week, astronomers identified a fifth moon–named P5 for now–orbiting Pluto in images taken by the Hubble Space Telescope. The moon is a mere 6 to 15 miles in diameter and orbits in a 58,000-mile-diameter circular orbit around the dwarf planet. “The [five] moons form a series of neatly nested orbits, a bit like Russian dolls,” said team lead Mark Showalter of the SETI Institute.
The discovery provides some ammunition for those upset at Pluto’s demotion from the planetary ranks. “If you are important enough to have acquired five satellites, you are a planet!” says Kevin Baines, a planetary scientist at NASA’s Jet Propulsion Laboratory.
1. It orbits the Sun.
2. It has has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape.
3. It has cleared the neighborhood around its orbit.
The discovery of P5, however, does have important implications for the New Horizons spacecraft headed towards Pluto and scheduled to rendezvous in July 2015. “The inventory of the Pluto system we’re taking now with Hubble will help the New Horizons team design a safer trajectory for the spacecraft,” said New Horizons’ principal investigator Alan Stern of the Southwest Research Institute. There is real worry that New Horizons could be destroyed if it runs into even a small piece of debris as it zooms past Pluto at 30,000 miles per hour.
As for what P5 (and P4, discovered last year) will eventually be named, that’s still up in the air, although Showalter told New Scientist that after he had finished his search of the Hubble data and found all of Pluto’s moons he would suggest names in the Hades/underworld theme that gave us Charon, Hydra and Nix. I came up with a few options for moon names last year on this blog (Erberus, Styx and Hypnos–in our poll, our readers liked Styx best), but I think Showalter might be running out of options in his preferred theme and will have to do some real digging into classical history once he gets to P7 and beyond.
July 11, 2012
In 1961, a group of scientists set up a permanent camp on Possession Island, a bit of land located in the Crozet Archipelago, about halfway between Madagascar and Antarctica in the Indian Ocean. Their goal was a long-term study of king penguins (Aptenodytes patagonicus), and scientists have continued that study for more than 50 years, sometimes accompanied by a small number of tourists. The penguins appear to be habituated to the presence of humans, but a new study in BMC Ecology finds that even this limited human contact may be negatively affecting them.
A team of researchers from France and Switzerland compared 15 king penguins from the areas regularly disturbed by scientists and tourists with 18 birds that bred in an undisturbed area, recording the penguins’ heart rates (an indicator of stress) in response to three potential human stressors–loud noise, approaches by humans (similar to what would happen when a scientist or tourist would observe the birds) and capture (a rare but necessary technique used when studying the penguins).
With both loud noise and human approach, the penguins from the disturbed area were far less stressed than their counterparts from the undisturbed area. All the birds, however, found capture to be a stressful experience.
Is this evidence that the penguins from the regularly disturbed are habituated to humans? Maybe, say the researchers, but maybe not. While it’s possible that these penguins have grown used to the presence of humans in their breeding area–though not capture, since that is a rare occurrence–the regular disturbance may be contributing to the selection of specific phenotypes, those that are most suited to handle this kind of stress. Over time, the population would evolve to handle this disturbance better and better. That may seem like a good thing, but the resulting population, the scientists say, may be less able to cope with environmental change.
This is hardly the first time that researchers have found that their methods have had unintended consequences for the animals they study. A penguin study published last year, for example, found that the use of flipper bands resulted in lower survival rates for the birds; it was just the latest in four decades of research that had been hinting that banding penguins was bad for the birds. But this latest study is another reminder to the science community that they can easily become one of the anthropogenic disturbances that affect the animals they are studying.
“A central question for ecologists is the extent to which anthropogenic disturbances [such as tourism] might impact wildlife and affect the systems under study,” lead author Vincent Viblanc of the Université de Strasbourg said in a statement. “One of the major pitfalls of such research is in forgetting that, from the perspective of the wildlife studied, tourism and scientific research are not two worlds apart.”
July 9, 2012
While in Sydney earlier this year, I stopped in at Australia Museum, the city’s equivalent of the Smithsonian Museum of Natural History, and learned a bit about the continent’s extinct megafauna. Australia didn’t have mammoths or saber-toothed tigers, but there were giant marsupials, such as the bear-like wombat Diprotodon and the thylacine (a.k.a. the Tasmanian tiger). On a tour of the museum, I came across a display that said that most of these mega-mammals had gone extinct tens of thousands of years before, the victims of either changes to the climate that led to drier conditions or human impacts, including hunting and landscape burning. The thylacine was the one exception to the megafauna story–it hung on until British colonization and then it was hunted to extinction.
But this story was incomplete it seems, though the museum holds no blame. A couple weeks after I returned to Washington, Science published a study addressing this very issue (for all the megafauna but the thylacine, but we’ll get to the tigers in a moment). Susan Rule of Australian National University and her colleagues analyzed pollen and charcoal in two sediment cores taken from a lake in northeast Australia to create a record of vegetation, fire and climate changes over the past 130,000 years. They also looked at spores of the fungus Sporormiella, which is found in dung and is most prevalent when there are large herbivores in the area.
With this record, Rule and her colleagues determined that there were two great climate upsets 120,000 and 75,000 years ago, but the megafauna had no problems surviving those times. However, between about 38,000 and 43,000 years ago, Sporormiella spores decreased in the record, likely reflecting the disappearance of large herbivores during that time, which correlates with the arrival of humans on the Australian continent. Following the megafauna disappearance, the cores displayed an increase in charcoal, an indicator of a greater frequency of wildfires. “The fire increase that followed megafaunal decline could have been anthropogenic, but [the record suggests] instead that relaxation of herbivory directly caused increased fire, presumably by allowing the accumulation of fine fuel,” the authors write. The lack of herbivores in the Australian ecosystem led to changes in the types of plants growing there–rainforests were replaced by sclerophyll vegetation that burns more readily.
So, the likely story is that humans came to Australia around 40,000 years ago, hunted mega-mammals to extinction, which spurred changes to the vegetation growing in the area and resulted in an increase in wildfires.
But what about the thylacine? Only one species, Thylacinus cynocephalus, survived to more recent times, though it disappeared from much of New Guinea and mainland Australia by about 2,000 years ago, likely due to competition with humans and, maybe, dingoes. A few pockets of the species were reported in New South Wales and South Australia in the 1830s but they were soon extirpated. The thylacine’s last holdout was the island of Tasmania, but locals quickly hunted them to extinction, certain the thylacines were responsible for killing sheep. The last known thylacine in the wild was killed in 1930, and the last one in captivity died in 1936. They were declared extinct in 1986.
Recent research has helped to flesh out the thylacine’s story: A study published last year in the Journal of Zoology found that the thylacine’s jaw was too weak to take down an animal as large as a sheep–the animals had been hunted to extinction for crimes they were biologically unable to commit. Though is appears that the hunting may have simply hastened the inevitable. Another study, published in April in PLoS ONE, found that the thylacine had low genetic diversity, which would have made the species more susceptible to disease and further declines, possible leading to extinction.
But is the thylacine really gone? Tasmanians occasionally claim to have seen a thylacine or found evidence of one in the area–in January, for example, two brothers found a skull they claimed came from a thylacine–but none of these sightings has ever panned out with real evidence, such as a clear photo or video. Zoologist Jeremy Austin of the University of Adelaide tested DNA in alleged thylacine droppings collected between 1910 and 2010 but none were actually from a thylacine.
Australian Museum scientists had planned to attempt cloning a thylacine, but those efforts were abandoned years ago. So, for now at least, all of Australia’s mega-mammals will stay extinct.
July 2, 2012
The Washington, DC area has seen its fair share of destructive storms–we get hurricanes, tornadoes and even the rare snowpocalypse. But on Friday night we got hit with another type of storm–one that I’d never heard of–called a derecho (pronounced ”deh-REY-cho”).
The storm swept through the area late Friday evening, bringing an incredible amount of thunder and lightning, winds up to 80 mph and sheets of rain. By morning, hundreds of trees had been blown down, millions were left without power and several people were dead. Netflix, Pinterest and Instagram had all been taken down by Amazon server outages caused by the storm. The Smithsonian Folklife Festival had to shut down for a day to clean up the mess. We were all left wondering, “what in the world had happened?”
The stifling heat wave that we’d been suffering through, which had stretched from the Midwest through the mid-Atlantic to the Southeastern United States and brought temperatures in excess of 100 degrees Fahrenheit, was to blame for the fast-moving band of thunderstorms. The Capitol Weather Gang explains:
As this stifling air bubbled northward, clashing with the weather front draped from near Chicago to just north of D.C., thunderstorms erupted. They grew in coverage and intensity as they raced southeast, powered by the roaring upper level winds and fueled by the record-setting heat and oppressive humidity in their path.
The coverage and availability of this heat energy was vast, sustaining the storms on their 600 mile northwest to southeast traverse. The storms continually ingested the hot, humid air and expelled it in violent downdrafts – crashing into the ground at high speeds and spreading out, sometimes accelerating further.
Though unfamiliar to those of us here on the East Coast, derechos occur more commonly in the Corn Belt, which runs from Mississippi into the Ohio Valley, but even there they are relatively infrequent. They can wreak their havoc at any time of the year but are most likely to occur during May, June and July. Derechos get their starts in curved bands of thunderstorms called “bow echoes,” which are perhaps better known for their ability to spawn tornadoes. But instead of rotating cells of winds, derechos blow and travel in straight lines.
Derechos have a long history here in the United States. The term “derecho” was coined by University of Iowa physics professor Gustavus Hinrichs in an 1888 paper in the American Meteorological Journal in which he illustrated the path of such a storm that had crossed over Iowa on July 31, 1877. The storm’s straight path across the state gave Hinrichs the inspiration for the storm’s name–”derecho” means “straight” in Spanish. But path alone isn’t quite enough for a storm to qualify as a derecho; wind speeds must also reach a minimum of 57 mph.
Given that derechos are associated with warmer weather, could they become more common as the United States heats up due to climate change? Tom Kines, senior meteorologist at AccuWeather.com, told the Guardian: “If indeed we are seeing global warming, then it will certainly increase the risk of something like this happening again.”