Turtle shells didn’t get their start as natural armor, it seems. The reptiles’ ancestors might have evolved partial shells to help them burrow instead, new research suggests. Only later did the hard body covering become useful for protection.
The findings might also help explain how turtles’ ancestors survived a mass extinction 250 million years ago that wiped out most plants and animals on earth, scientists report online July 14 in Current Biology.
Most shelled animals, like armadillos, get their shells by adding bony scales all over their bodies. Turtles, though, form shells by gradually broadening their ribs until the bones fuse together. Fossils from ancient reptiles with partial shells made from thickened ribs suggest that turtles’ ancestors began to suit up in the same way. It’s an unusual mechanism, says Tyler Lyson, a paleontologist at the Denver Museum of Nature and Science who led the study. Thicker ribs don’t offer much in the way of protection until they’re fully fused, as they are in modern turtles. And the modification makes critical functions like moving and breathing much harder — a steep price for an animal to pay. So Lyson suspected there was some advantage other than protection to the partial shells.
He and his colleagues examined fossils from prototurtles, focusing on an ancient South African reptile called Eunotosaurus africanus.
Eunotosaurus shared many characteristics with animals that dig and burrow, the researchers found. The reptile had huge claws and large triceps in addition to thickened ribs. “We could tell that this animal was very powerful,” says Lyson. Broad ribs “provide a really, really strong and stable base from which to operate this powerful digging mechanism,” he adds. Like a backhoe, Eunotosaurus could brace itself to burrow into the dirt.
Thanks to a lucky recent find of a fossil preserving the bones around the eyes, the team was even able to tell that the prototurtles’ eyes were well adapted to low light. That’s another characteristic of animals that spend time underground.
Swimming and digging use similar motions, Lyson says, so you would expect to find similar skeletal adaptations in water-dwelling animals. But large claws good for moving dirt suggest a life on land.
Fossils from other prototurtle species also have wider ribs and big claws. So the researchers think these traits may have been important for early turtle evolution in general, not just for Eunotosaurus.
Not everyone is entirely convinced. “It’s a very plausible idea, although many other animals burrow but don’t have these specializations,” says Hans Sues, a paleontologist at the Smithsonian Institution’s National Museum of Natural History. Sues says that it will be important to find and study other turtle ancestors well-adapted to digging to bolster the explanation.
Lyson thinks the prototurtles’ burrowing tendencies might have helped them survive the end-Permian mass extinction around 250 million years ago (SN: 9/19/15, p. 10).
“Lots of animals at this time period burrowed underground to avoid the very, very arid environment that was present in South Africa,” Lyson says. “The burrow provides more climate control.”
A puzzling mismatch is plaguing two methods for measuring how fast the universe is expanding. When the discrepancy arose a few years ago, scientists suspected it would fade away, a symptom of measurement errors. But the latest, more precise measurements of the expansion rate — a number known as the Hubble constant — have only deepened the mystery.
“There’s nothing obvious in the measurements or analyses that have been done that can easily explain this away, which is why I think we are paying attention,” says theoretical physicist Marc Kamionkowski of Johns Hopkins University. If the mismatch persists, it could reveal the existence of stealthy new subatomic particles or illuminate details of the mysterious dark energy that pushes the universe to expand faster and faster.
Measurements based on observations of supernovas, massive stellar explosions, indicate that distantly separated galaxies are spreading apart at 73 kilometers per second for each megaparsec (about 3.3 million light-years) of distance between them. Scientists used data from NASA’s Hubble Space Telescope to make their estimate, presented in a paper to be published in the Astrophysical Journal and available online at arXiv.org. The analysis pegs the Hubble constant to within experimental errors of just 2.4 percent — more precise than previous estimates using the supernova method.
But another set of measurements, made by the European Space Agency’s Planck satellite, puts the figure about 9 percent lower than the supernova measurements, at 67 km/s per megaparsec with an experimental error of less than 1 percent. That puts the two measurements in conflict. Planck’s result, reported in a paper published online May 10 at arXiv.org, is based on measurements of the cosmic microwave background radiation, ancient light that originated just 380,000 years after the Big Bang.
And now, another team has weighed in with a measurement of the Hubble constant. The Baryon Oscillation Spectroscopic Survey also reported that the universe is expanding at 67 km/s per mega-parsec, with an error of 1.5 percent, in a paper posted online at arXiv.org on July 11. This puts BOSS in conflict with the supernova measurements as well. To make the measurement, BOSS scientists studied patterns in the clustering of 1.2 million galaxies. That clustering is the result of pressure waves in the early universe; analyzing the spacing of those imprints on the sky provides a measure of the universe’s expansion.
Although the conflict isn’t new (SN: 4/5/14, p. 18), the evidence that something is amiss has strengthened as scientists continue to refine their measurements. The latest results are now precise enough that the discrepancy is unlikely to be a fluke. “It’s gone from looking like maybe just bad luck, to — no, this can’t be bad luck,” says the leader of the supernova measurement team, Adam Riess of Johns Hopkins. But the cause is still unknown, Riess says. “It’s kind of a mystery at this point.” Since its birth from a cosmic speck in the Big Bang, the universe has been continually expanding. And that expansion is now accelerating, as galaxy clusters zip away from one another at an ever-increasing rate. The discovery of this acceleration in the 1990s led scientists to conclude that dark energy pervades the universe, pushing it to expand faster and faster.
As the universe expands, supernovas’ light is stretched, shifting its frequency. For objects of known distance, that frequency shift can be used to infer the Hubble constant. But measuring distances in the universe is complicated, requiring the construction of a “distance ladder,” which combines several methods that build on one another.
To create their distance ladder, Riess and colleagues combined geometrical distance measurements with “standard candles” — objects of known brightness. Since a candle that’s farther away is dimmer, if you know its absolute brightness, you can calculate its distance. For standard candles, the team used Cepheid variable stars, which pulsate at a rate that is correlated with their brightness, and type 1a supernovas, whose brightness properties are well-understood.
Scientists on the Planck team, on the other hand, analyzed the cosmic microwave background, using variations in its temperature and polarization to calculate how fast the universe was expanding shortly after the Big Bang. The scientists used that information to predict its current rate of expansion.
As for what might be causing the persistent discrepancy between the two methods, there are no easy answers, Kamionkowski says. “In terms of exotic physics explanations, we’ve been scratching our heads.”
A new type of particle could explain the mismatch. One possibility is an undiscovered variety of neutrino, which would affect the expansion rate in the early universe, says theoretical astrophysicist David Spergel of Princeton University. “But it’s hard to fit that to the other data we have.” Instead, Spergel favors another explanation: some currently unknown feature of dark energy. “We know so little about dark energy, that would be my guess on where the solution most likely is,” he says.
If dark energy is changing with time, pushing the universe to expand faster than predicted, that could explain the discrepancy. “We could be on our way to discovering something nontrivial about the dark energy — that it is an evolving energy field as opposed to just constant,” says cosmologist Kevork Abazajian of the University of California, Irvine.
A more likely explanation, some experts say, is that a subtle aspect of one of the measurements is not fully understood. “At this point, I wouldn’t say that you would point at either one and say that there are really obvious things wrong,” says astronomer Wendy Freedman of the University of Chicago. But, she says, if the Cepheid calibration doesn’t work as well as expected, that could slightly shift the measurement of the Hubble constant.
“In order to ascertain if there’s a problem, you need to do a completely independent test,” says Freedman. Her team is working on a measurement of the Hubble constant without Cepheids, instead using two other types of stars: RR Lyrae variable stars and red giant branch stars.
Another possibility, says Spergel, is that “there’s something missing in the Planck results.” Planck scientists measure the size of temperature fluctuations between points on the sky. Points separated by larger distances on the sky give a value of the Hubble constant in better agreement with the supernova results. And measurements from a previous cosmic microwave background experiment, WMAP, are also closer to the supernova measurements.
But, says George Efstathiou, an astrophysicist at the University of Cambridge and a Planck collaboration member, “I would say that the Planck results are rock solid.” If simple explanations in both analyses are excluded, astronomers may be forced to conclude that something important is missing in scientists’ understanding of the universe.
Compared with past disagreements over values of the Hubble constant, the new discrepancy is relatively minor. “Historically, people argued vehemently about whether the Hubble constant was 50 or 100, with the two camps not conceding an inch,” says theoretical physicist Katherine Freese of the University of Michigan in Ann Arbor. The current difference between the two measurements is “tiny by the standards of the old days.”
Cosmological measurements have only recently become precise enough for a few-percent discrepancy to be an issue. “That it’s so difficult to explain is actually an indication of how far we’ve come in cosmology,” Kamionkowski says. “Twenty-five years ago you would wave your hands and make something up.”
Cancer goes way, way back. A deadly form of this disease and a noncancerous but still serious tumor afflicted members of the human evolutionary family nearly 2 million years ago, two new investigations of fossils suggest.
If those conclusions hold up, cancers are not just products of modern societies, as some researchers have proposed. “Our studies show that cancers and tumors occurred in our ancient relatives millions of years before modern industrial societies existed,” says medical anthropologist Edward Odes of the University of the Witwatersrand in Johannesburg, a coauthor of both new studies. Today, however, pesticides, longer life spans and other features of the industrialized world may increase rates of cancers and tumors. A 1.6-million- to 1.8-million-year-old hominid, either from the Homo genus or a dead-end line called Paranthropus, suffered from a potentially fatal bone cancer, Odes and colleagues say in one of two papers published in the July/August South African Journal of Science. Advanced X-ray techniques enabled identification of a fast-growing bone cancer on a hominid toe fossil previously unearthed at South Africa’s Swartkrans Cave site, the researchers report. This malignant cancer consisted of a mass of bone growth on both the toe’s surface and inside the bone.
Until now, the oldest proposed cancer in hominids consisted of an unusual growth on an African Homo erectus jaw fragment dating to roughly 1.5 million years ago. Critics, though, regard that growth as the result of a fractured jaw, not cancer.
A second new study, led by biological anthropologist Patrick Randolph-Quinney, now at the University of Central Lancashire in England, identifies the oldest known benign tumor in a hominid in a bone from an Australopithecus sediba child. This tumor penetrated deep into a spinal bone, close to an opening for the spinal cord. Nearly 2-million-year-old partial skeletons of the child and an adult of the same species were found in an underground cave at South Africa’s Malapa site ( SN: 8/10/13, p. 26 ). Although not life-threatening, this tumor would have interfered with walking, running and climbing, the researchers say. People today, especially children, rarely develop such tumors in spinal bones.
“This is the first evidence of such a disease in a young individual in the fossil record,” Randolph-Quinney says.
X-ray technology allowed scientists to create and analyze 3-D copies of the inside and outside of the toe and spine fossils.
But studies of fossil bones alone, even with sophisticated imaging technology, provide “a very small window” for detecting cancers and tumors, cautions paleoanthropologist Janet Monge of the University of Pennsylvania Museum of Archaeology and Anthropology in Philadelphia. Microscopic analysis of soft-tissue cells, which are typically absent on fossils, confirms cancer diagnoses in people today, she says.
Without additional evidence of bone changes in and around the proposed cancer and tumor, Monge won’t draw any conclusions about what caused those growths.
Monge led a team that found a tumor on a 120,000- to 130,000-year-old Neandertal rib bone from Eastern Europe. Whether the tumor was cancerous or caused serious health problems can’t be determined, the scientists concluded in 2013 in PLOS ONE.
For the first time, scientists can see where molecular tags known as epigenetic marks are altered in the brain.
These chemical tags — which flag DNA or its protein associates, known as histones — don’t change the genes but can change gene activity. Abnormal epigenetic marks have been associated with brain disorders such as Alzheimer’s disease, schizophrenia, depression and addiction.
Researchers at Massachusetts General Hospital in Boston devised a tracer molecule that latches on to a protein that removes one type of epigenetic mark known as histone acetylation.
The scientists then used PET scans to detect where a radioactive version of the tracer appeared in the brains of eight healthy young adult men and women, the researchers report in the Aug. 10 Science Translational Medicine. Further studies could show that the marks change as people grow older or develop a disease. The team studied only healthy young volunteers so can’t yet say whether epigenetic marking changes with age or disease.
For some people, fentanyl can be a life-saver, easing profound pain. But outside of a doctor’s office, the powerful opioid drug is also a covert killer.
In the last several years, clandestine drugmakers have begun experimenting with this ingredient, baking it into drugs sold on the streets, most notably heroin. Fentanyl and closely related compounds have “literally invaded the entire heroin supply,” says medical toxicologist Lewis Nelson of New York University Langone Medical Center.
Fentanyl is showing up in other drugs, too. In San Francisco’s Bay Area in March, high doses of fentanyl were laced into counterfeit versions of the pain pill Norco. In January, fentanyl was found in illegal pills sold as oxycodone in New Jersey. And in late 2015, fentanyl turned up in fake Xanax pills in California. This ubiquitous recipe-tinkering makes it impossible for users to know whether they’re about to take drugs mixed with fentanyl. And that uncertainty has proved deadly. Fentanyl-related deaths are rising sharply in multiple areas. National numbers are hard to come by, but in many regions around the United States, fentanyl-related fatalities have soared in recent years.
Maryland is one of the hardest-hit states. From 2007 to 2012, the number of fentanyl-related deaths hovered around 30 per year. By 2015, that number had grown to 340. A similar rise is obvious in Connecticut, where in 2012, there were 14 fentanyl-related deaths. In 2015, that number was 188. In Massachusetts, two-thirds of people who died from opioid overdoses in the first half of 2016 showed signs of fentanyl. This wave of fentanyl-related overdoses is “horrendous,” says Daniel Ciccarone of the University of California, San Francisco. What’s worse, he says, “I think it’s here to stay.” Fentanyl is not a new drug. Available in the 1960s, it is still used in hospitals as an anesthetic and is available by prescription to fight powerful pain. What’s new, Ciccarone says, is that clandestine drug manufacturers have discovered that the euphoria-producing opioid can be made cheaply and easily — no poppy fields necessary.
Fentanyl is about 30 to 40 times stronger than heroin and up to 100 times more powerful than morphine, which means that a given effect on the body can be achieved with a much smaller amount of fentanyl. Inadvertently taking a bit of fentanyl can cause big trouble. “It’s a dosing problem,” Nelson says. “Because the drug is so potent, little changes in measurements can have very big implications for toxicity. That’s really the problem.”
That problem is made worse by the variability of illegal drugs — users often don’t know what they’re buying. Illegal labs aren’t pumping out products with carefully calibrated doses or uniform chemical makeup. The drugs change from day to day, making it nearly impossible for a user to know what he or she is about to take, Ciccarone says.
He has seen this struggle up close. Drug users have told him that the products they buy are unpredictable. Another thing people are telling him: “That they and their friends and compatriots are dropping like flies.” Tellingly, some of the most experienced drug users have recently begun doing “tester shots,” small doses to get a sense of the type and dose of drug they’re about to use, Ciccarone says.
Users are right to be wary. Typically, opioids can kill by gradually depressing a person’s ability to breathe. Illicit fentanyl, a recent study suggests, can kill within minutes by paralyzing muscles. Doctors have known that when injected quickly, fentanyl can paralyze chest wall muscles, prevent breathing and kill a person rapidly. That effect, called “wooden chest,” might help explain the rise in fentanyl-related deaths, scientists report in the June Clinical Toxicology.
A quick injection of fentanyl “literally freezes the muscles and you can’t move the chest,” says toxicologist Henry Spiller of the Central Ohio Poison Center in Columbus. That’s why doctors who dispense fentanyl in the hospital intentionally proceed very slowly and keep the opioid-counteracting drug naloxone (Narcan) on hand. “If you give it too fast, we know this occurs,” Spiller says. But it wasn’t known whether this same phenomenon might help explain the death rate of people using the drug illegally.
Spiller and colleagues tested post-mortem concentrations of fentanyl and its breakdown product norfentanyl in 48 fentanyl-related deaths. The body usually begins breaking down fentanyl into norfentanyl within two minutes, an earlier study found. Yet in 20 of the cases, the researchers found no signs of norfentanyl, indicating death came almost immediately after first receiving fentanyl.
Naloxone can counteract the effects of opioids if someone nearby can administer the antidote. But for people whose chests quickly freeze from fentanyl, resuscitation becomes more unlikely. Fentanyl “is just a bad drug,” Spiller says. Fentanyl’s danger is magnified for people not accustomed to taking opioids, such as those addicted to cocaine, a situation illustrated by a recent tragedy in New Haven, Conn.
New Haven authorities noticed a string of suspicious overdoses in late June, leaving three people dead. Drug users thought they were buying cocaine, but the drugs contained fentanyl, says analytical toxicologist Kara Lynch of the University of California, San Francisco. As one of the handful of labs capable of testing blood and urine for fentanyl, hers was called on to identify the culprit. Her lab spotted fentanyl in Norco tablets back in March.
Lynch’s group uses high-resolution mass spectrometry to detect many drugs’ chemical signatures. But this method reveals only the drugs scientists suspect. “We can look for what we know to look for,” she says. And success depends on getting the samples in the first place.
The logistical hurdles of figuring out exactly what a person took, and how much, and when, are large. Ciccarone contrasts the situation with cases of food poisoning. When people start getting sick, public health officials can figure out what lettuce people ate and test it for pathogens. The same kind of tracking system doesn’t exist for drugs. His efforts to develop a system for testing illegal drugs in Baltimore broke down in part because no one had time to do the work. “The coroner is so busy right now with dead bodies,” he says. “They don’t have the time to test the ‘lettuce.’ ”
In the quest to curb fentanyl-related deaths, scientists and public health officials are searching for new strategies. Spiller advocates a more targeted public health message to users, one that emphasizes that fentanyl is simply a deadly drug, not just a more potent high. Ciccarone says that facilities where drug users can take illegal drugs under the care of medical personnel might reduce the number of fatalities.
For now, the scope of the problem continues to grow, Nelson says. The situation is made worse by the ingenuity of illicit drugmakers, who readily experiment with new compounds. Fentanyl itself can be tweaked to create at least 16 related forms, one of which, acetyl fentanyl, has been linked to overdose deaths. New drugs and new tweaks to old drugs rapidly evolve (SN: 5/16/15, p. 22), Nelson says, creating a game of whack-a-mole in which designer drugs confound public health officials and law enforcement.
“There is no single easy solution to this problem,” he says.
Ice volcanoes, patches of water ice and a slew of hydrated minerals paint a picture of dwarf planet Ceres as a geologically active world — one where water has played a starring role. That’s the theme of six papers in the Sept. 2 Science that describe data collected by the Dawn spacecraft.
A 4-kilometer-high mountain dubbed Ahuna Mons, with its bowl-shaped summit and ridged flanks, has the appearance of a cryovolcano — one that erupts water instead of magma. The relatively young Oxo crater also appears to be home to splotches of frozen water. Given that ice should last only tens to hundreds of years on Ceres’ surface, the patches must be recent additions, possibly exposed by a landslide or impact with a meteorite. The surface is also slathered with a class of minerals known as phyllosilicates — silicon-bearing substances that form in the presence of water — which further support the idea that water has been present throughout Ceres’ history.
Ceres is the largest body between Mars and Jupiter. Dawn has been orbiting Ceres since March 6, 2015 (SN: 4/4/15, p. 9), studying its geology and composition to better understand the formation of rocky worlds.
Better bone scanning of fossils offers a glimpse of preteen life some 360 million years ago.
Improved radiation scanning techniques reveal accumulating growth zones in chunks of four fossil upper forelimb bones from salamander-shaped beasts called Acanthostega, scientists report online September 7 in Nature. Vertebrate bones typically show annual growth zones diminishing in size around the time of sexual maturity. But there’s no sign of that slowdown in these four individuals from East Greenland’s mass burial of Acanthostega, says study coauthor Sophie Sanchez of Uppsala University in Sweden. They were still juveniles. The bones came from tropical Greenland of the Devonian Period. Aquatic vertebrates were developing four limbs, which would serve tetrapods well when vertebrates eventually conquered land. This mass die-off doomed at least 20 individuals, presumably when a dry spell after a flood trapped them all in a big, vanishing puddle. This find makes the strongest case yet for identifying genuine youngsters among ancient tetrapods, Sanchez says. She suspects other individuals trapped could have been juveniles too.
Not many other species were found in the mass burial. So young tetrapods may have stuck together much as today’s young fish school, Sanchez speculates. The limb shape clearly indicates that the youngsters took a long time to start adding hard bone to the initial soft cartilage, she says. So these early tetrapods were at least 6-year-olds and probably 10 years old or more. For identifying stages of life, the improved technique “allows greater resolution and rigor, so in that regard it is a plus,” says Neil Shubin of the University of Chicago, who studies a fossil fish with some tetrapod-like features called Tiktaalik. There are Tiktaalik preteens, too, he notes.
What interests Nadia Fröbisch of Museum für Naturkunde in Berlin is that some of Acanthostega individuals were different sizes but had reached the same stage of bone development. She muses that they might even have been developing along different trajectories of growth, a flexibility that would be useful in a changeable environment.
New method to measure mass in space devised — A scale for measuring weight in space that does not depend upon the attraction of gravity has been devised…. In [William Thornton’s] method, the weight of the mass is determined [by] mechanically oscillating a weight in a tray. The heavier the mass, the slower the oscillation rate. The scale is tied to an electronic unit measuring the time required for five cycles of oscillation. A reference to a chart gives the mass’s weight. — Science News, October 1, 1966
UPDATE Not much has changed. The International Space Station has two spring-based contraptions for weighing in astronauts. An individual rides the Body Mass Measurement Device like a pogo stick — in four or five bounces, it calculates weight. The Space Linear Acceleration Mass Measurement Device uses springs to pull an astronaut; the acceleration reveals weight. In 2012, researchers in Europe experimented with compact computer imaging technology — developed for video games — using photos to estimate mass based on a person’s shape and size.
Dogs may look to humans for help in solving impossible tasks thanks to some genes previously linked to social disorders in people.
Beagles with particular variants in a gene associated with autism were more likely to sidle up to and make physical contact with a human stranger, researchers report September 29 in Scientific Reports.
That gene, SEZ6L, is one of five genes in a particular stretch of beagle DNA associated with sociability in the dogs, animal behaviorist Per Jensen and colleagues at Linköping University in Sweden say. Versions of four of those five genes have been linked to human social disorders such as autism, schizophrenia and aggression. “What we figure has been going on here is that there are genetic variants that tend to make dogs more sociable and these variants have been selected during domestication,” Jensen says.
But other researchers say the results are preliminary and need to be confirmed by looking at other dog breeds. Previous genetic studies of dog domestication have not implicated these genes. But, says evolutionary geneticist Bridgett vonHoldt of Princeton University, genes that influence sociability are “not an unlikely target for domestication — as humans, we would be most interested in a protodog that was interested in spending time with humans.”
Most dog studies take DNA samples from pets or village dogs and wild wolves. Jensen’s team instead studied beagles that had been raised in a lab. None of the dogs had been trained. To test sociability, the researchers gave the dogs an unsolvable problem in a room with a female human observer whom the beagles had never seen before. The puzzle was a device with three treats that the dogs could see and smell under sliding lids. One lid was sealed shut and could not be opened.
After opening two lids, the dogs “get very confident that this is not a difficult task, but then they encounter the third lid and that’s where the problem gets impossible,” Jensen says. Wolves would have kept trying to solve the problem on their own (SN: 10/17/15, p. 10). But after some futile attempts, many of the beagles looked to the human observer for help. Some dogs tried to catch her eye, glancing back and forth between the woman and the stuck lid. Other dogs made physical contact with or just tried to stay to close to the woman.
The researchers then looked for places in the dogs’ DNA where the most and least human-friendly dogs differed. A region on chromosome 26 kept popping up, indicating that genes in that region could be involved in social interactions with people. The finding is a statistical signal, but doesn’t establish what the genes might be doing to influence the dogs’ behavior, says Adam Freedman, an evolutionary geneticist at Harvard University. And since the researchers only examined the beagles, it’s not clear that the same genes would affect behavior in other dogs, he says.
Accidental chair squeaks in a lab have tipped off researchers to a new world of eavesdroppers.
Spiders don’t have eardrums, though their exquisitely sensitive leg hairs pick up vibrations humming through solids like web silk and leaves. Biologists thought that any airborne sounds more than a few centimeters away would be inaudible. But the first recordings of auditory nerve cells firing inside a spider brain suggest that the tiny Phidippus audax jumping spider can pick up airborne sounds from at least three meters away, says Ronald Hoy of Cornell University. During early sessions of brain recordings, Hoy’s colleagues saw bursts of nerve cell, or neuron, activity when a chair moved. Systematic experiments then showed that from several meters away, spiders were able to detect relatively quiet tones at levels comparable to human conversation. In a hearing test based on behavior, the spiders also clearly noticed when researchers broadcast a low droning like the wing sound of an approaching predatory wasp. In an instant, the spiders hunkered down motionless, the researchers report online October 13 in Current Biology.
Jumping spiders have brains about the size of a poppy seed, and Hoy credits the success of probing even tinier spots inside these (anesthetized) brains to Cornell coauthor Gil Menda and his rock-steady hands. “I close my eyes,” Menda says. He listens his way along, one slight nudge of the probe at a time toward the auditory regions, as the probe monitor’s faint popping sounds grow louder. When Menda first realized the spider brain reacted to a chair squeak, he and Paul Shamble, a study coauthor now at Harvard University, started clapping hands, backing away from the spider and clapping again. The claps didn’t seem earthshaking, but the spider’s brain registered clapping even when they had backed out into the hallway, laughing with surprise. Clapping or other test sounds in theory might confound the experiment by sending vibrations not just through the air but through equipment holding the spider. So the researchers did their Cornell neuron observations on a table protected from vibrations. They even took the setup for the scary wasp trials on a trip to the lab of coauthor Ronald Miles at State University of New York at Binghamton. There, they could conduct vibration testing in a highly controlled, echo-dampened chamber. Soundwise, Hoy says, “it’s really eerie.”
Neuron tests in the hushed chamber and at Cornell revealed a relatively narrow, low-pitched range of sensitivity for these spiders, Hoy says. That lets the spiders pick up rumbly tones pitched around 70 to 200 hertz; in comparison, he says, people hear best between 500 and 1,000 Hz and can detect tones from 50 Hz to 15 kilohertz. Spiders may hear low rumbles much as they do web vibes: with specialized leg hairs, Hoy and his colleagues propose. They found that making a hair twitch could cause a sound-responsive neuron to fire. “There seems to be no physical reason why a hair could not listen,” says Jérôme Casas of the University of Tours in France. When monitoring nerve response from hairs on cricket legs, he’s tracked airplanes flying overhead. Hoy’s team calculates that an 80 Hz tone the spiders responded to would cause air velocities of only 0.13 millimeters a second if broadcast at 65 decibels three meters away. That’s hardly a sigh of a breeze. Yet it’s above the threshold for leg hair response, says Friedrich Barth of the University of Vienna, who studies spider senses.
An evolutionary pressure favoring such sensitivity might have been eons of attacks from wasps, such as those that carry off jumping spiders and immobilize them with venom, Hoy says. A mother wasp then tucks an inert, still-alive spider into each cell of her nest where a wasp egg will eventually hatch to feed on fresh spider flesh. Wasps are major predators of many kinds of spiders, says Ximena Nelson of the University of Canterbury in Christchurch, New Zealand. If detecting their wing drone turns out to have been important in the evolution of hearing, other spiders might do long-distance eavesdropping, too.
