COLUMBIA, Mo. — If you find a daddy longlegs in your house, don’t be scared. “Daddy longlegs are actually pretty docile animals when it comes to interacting with humans,” says evolutionary biologist Kasey Fowler-Finn, who studies the arachnids at St. Louis University. Specifically, she studies daddy longlegs sex. She is using this common group of arachnids (they’re not spiders) to explore how mating behaviors can be shaped by evolutionary forces.
Daddy longlegs — which can be found in forests, in leaf litter, on tree trunks and, of course, in your garage in eastern North America — are a group of harvestmen with elongated legs. And like all harvestmen, their second pair of legs, which is used in sensory exploration instead of walking, is particularly long.
But what makes daddy longlegs especially interesting is what happens when they mate. “Most of us just think ‘ew’ when we see them, but they have this really fascinating suite of [mating] behaviors,” Fowler-Finn said July 31 at the 53rd Annual Conference of the Animal Behavior Society. “The same basic stuff happens with all species in the clade, but the details vary quite a bit.”
The mating ritual starts with individuals bumping into each other (scientists don’t yet know how males and females find one another). “Then shortly thereafter, males will attempt to engage the females in what’s called a ‘mating embrace,’” Fowler-Finn said. “They hook their pedipalps [a type of appendage on the front of the arachnid] behind the female’s sensory legs … and then there’s a bunch of back and forth between males and females that varies in duration across species.” Mating can last for 15 seconds in some species, and three to four hours in others. The male then delivers a nuptial gift and his ejaculate, and the pair separates.
There can be a lot of aggression during all of this, with males and females biting each other and even losing legs during mating. And this, too, can vary from species to species. Leiobunum vittatum encounters, for instance, are almost always violent, while L. aldrichi matings are aggressive only about half of the time.
L. aldrichiis one of Fowler-Finn’s favorites. “The male actually grabs the female’s second leg … and then they shake them by one leg,” she said. “And, in fact, this is so particular to the second leg that males who initially grab other legs on the female will continue to search until they find that second leg. So there’s something really cool going on here.” What that might be, though, is a mystery.
Fowler-Finn is still working out whether characteristics of the various daddy longlegs species can predict their mating styles. But she noted that she and her colleagues are finding a lot of variation in behavior not just across species but also by geographic area. She suspects that as she and her team describe these differences, they are going to find evidence for plenty of new species to scare the arachnophobes out there.
Over the last several years, spacecraft have beamed back images from all across the solar system, revealing a complex tapestry of landscapes. Dust shapes the scenery on comet 67P, whereas ice rules on Pluto and the moons of Saturn.
At first glance, many of these terrains seem the same — mountains, craters and canyons show up everywhere. But each world adds its own geologic signature that marks the land as utterly alien.
While several of the spacecraft’s missions will end in the coming year, a fleet of new explorers ensures that our interplanetary adventures are far from over.
Bonobos — chimpanzees’ sister species — don’t get the credit they deserve as tool users.
Bonobos in a sanctuary’s protected forests in the Democratic Republic of Congo crack nuts with stones nearly as well as wild chimps in other parts of Africa do, researchers report online August 26 in the American Journal of Primatology. Wild bonobos have rarely been observed using tools and have never been reported to pound open nuts with stones (SN: 9/19/15, p. 22).
All 18 adult and adolescent bonobos tracked during April and May 2015 cracked oil palm nuts with stones of various sizes that researchers had placed near oil palm trees, says a team led by Johanna Neufuss of the University of Kent in England. Bonobos chose pounding stones well-suited to busting palm oil nutshells. These animals employed 15 grips to hold nut-cracking stones, including 10 grips not previously observed in nonhuman primates.
Genetic surgery is far away for humans — Optimism concerning application of genetic experiments to improve mankind is unwarranted now, a Canadian pediatrician told the Third International Congress of Human Genetics meeting in Chicago…. Although striking and sometimes controversial experiments in genetic surgery have in fact been performed in multicellular systems, he explained, public demand seems likely to outstrip scientific resources for the treatment of many forms of genetic disease. — Science News, September 24, 1966
UPDATE Things are looking up for “genetic surgery.” Gene therapy has been around since the 1980s, but researchers have recently developed more precise gene-editing tools, including one that sent a child’s leukemia into remission in 2015. Scientists are most excited about a molecular scalpel known as CRISPR/Cas9 that cuts and manipulates DNA (SN: 9/3/16, p. 22). Researchers are optimistic about the tool’s potential to treat several diseases, but it may be a while before CRISPR is widely used.
Inside a large cave in northwestern Australia’s remote Kimberley region, someone painted an elongated, yamlike shape on a ceiling at least 16,000 years ago, new research suggests. That long-ago creation in the unnamed cavern adds fuel to the argument that rock art in Australia goes back even earlier to the continent’s first inhabitants, researchers contend.
This discovery joins a small number of drawings and paintings from Down Under that have been dated to around the same time or earlier, say archaeologist June Ross of the University of New England in Armidale, Australia, and colleagues. Some scientists have questioned the accuracy of these dates. But the new work, Ross’ team asserts, gives a critical boost to a previous, contested report that a piece of Kimberley rock art depicting a humanlike figure painted over a hand stencil dates to a minimum of about 16,400 years ago. Ross’ group also obtained minimum age estimates, ranging from around 5,100 to 530 years, for nine other pieces of Kimberley rock art, the researchers report August 31 in PLOS ONE. People first reached Australia around 50,000 years ago ( SN: 3/15/03, p. 173 ). Researchers generally assume the continent’s colonizers brought rock art traditions with them from Asia. In southeastern Australia’s Yaranda Cave, for instance, claw marks of a type of marsupial that died out around 50,000 years ago appear on top of pigmented human finger marks, says Robert Bednarik, an independent scholar and self-taught rock art authority based in Caulfield South, Australia. But it is difficult to accurately date such art. Ross’ team — like the researchers who dated the humanlike figure — focused on dating sand grains found inside mud wasps’ nests that the insects built on cave walls and ceilings, covering parts of artistic depictions. Eventually, surviving nests fossilized. Light-induced release of radiation from sand grains in the lab enabled calculations of the time since each grain was last exposed to sunlight, providing a minimum age for the painting beneath the nest. Four pieces of Kimberley rock art — but not the proposed 16,000-year-old painting — also yielded radiocarbon dates from bits of surviving nests and beeswax stuck to drawings.
Without a confirming radiocarbon date, the new minimum age estimate of 16,000 years for the yamlike Kimberley painting is provisional, Bednarik says. But the timeframe isn’t out-of-bounds. Mineral deposits partly covering hand stencils in an Indonesian cave date to nearly 40,000 years old (SN: 11/15/14, p. 6), although, similarly, no radiocarbon dates exist to confirm that. And researchers have known for decades that meandering impressions on the walls of Koonalda Cave in southern Australian, made by pigment-coated human fingers, must be older than 15,000 years, Bednarik says. The marked walls in Koonalda Cave became inaccessible after that time.
Cosmic mismatch Researchers used supernovas, cosmic microwave background radiation and patterns of galaxy clusters to measure the Hubble constant — the rate at which the universe expands — but their results were mismatched, Emily Conover reported in “Debate persists on cosmic expansion” (SN: 8/6/16, p. 10).
Reader J.R. Kennedy thought that light-dimming space dust and debris might explain the discrepancy.
Gas and dust in space can have an impact on the brightness of standard candles — objects with known brightness such as type 1a supernovas and some variable stars, Conover says. But astronomers correct for those discrepancies in their measurements. In the absence of gas and dust, a candle’s apparent brightness should decrease in relation to its distance from Earth. “But if there’s dust in the way, it can make the candle dim more than that,” Conover says. “However, this intervening material doesn’t dim the candle quite in the same way as distance does. It will dim the shorter, bluer wavelengths of light more than the redder ones. Astronomers can look for this effect to identify the impact of dust and correct for it.” So the mismatch stands. Great escape High-speed video captured how the offspring of red-eyed tree frogs prematurely break free from their eggs when in danger, Helen Thompson reported in “Under threat, tadpoles make early escape” (SN: 8/6/16, p. 32). Online reader myndflyte wondered if early hatching had any long-term de-velopmental effects on the tadpoles.
There’s definitely a trade-off involved in hatching early to escape a predator or some other threat, Thompson says. Past work by tree frog researcher Karen Warkentin, now at Boston University, shows that red-eyed tree frog embryos grow tails and mouthparts in the last few days of their roughly weeklong incubation. Those that hatch earlier, up to four days if threatened, tend to be underdeveloped with smaller bodies and shorter tails. “In the short term, this developmental deficit puts early hatchlings at greater risk of getting eaten by pond shrimp and fish than their older brethren,” Thompson says. “But there’s also evidence to suggest that early hatchers compensate down the line and grow at higher rates as tadpoles.”
More to the story Although the death rate from motor vehicle crashes in the United States has declined since 2000, the country still tops 19 other high-income nations in motor vehicle deaths, Alex Maddon wrote in “U.S. still leads in fatal motor vehicle crashes” (SN: 8/6/16, p. 5).
Some readers took issue with the conclusions presented and thought the researchers should have measured fatalities per miles driven instead of per population. “Using a per capita metric makes the U.S. look unsafe when the opposite is true,” John Underwood wrote. “Since A-mericans drive more miles per year than the other countries in the chart, we will have the highest fatality rate per 100,000 population.”
It’s true that fatalities per miles driven changes the ranking. Using the measure “per 100 million vehicle miles traveled,” the United States drops to fifth place, says Deputy M-anaging Editor, Features Cori Vanchieri. When the researchers looked at deaths per 10,000 registered vehicles, however, the United States still topped the list. The researchers’ overall message is that the United States could further reduce crash deaths if seat belt use goes up and alcohol-impaired driving and speeding go down.
Clarification “Under threat, tadpoles make early escape” (SN: 8/6/16, p. 32) states that the tree frog embryos gape their mouths to stretch out their egg membranes. Not all embryos gape their mouths, and ultimately, an enzyme secreted from the embryo’s snout breaks open the membrane.
Humankind’s bombs, plastics, chickens and more have altered the planet enough to usher in a new chapter in Earth’s geologic history. That’s the majority opinion of a group of 35 experts tasked with evaluating whether the current human-dominated time span, unofficially dubbed the Anthropocene, deserves a formal place in Earth’s geologic timeline alongside the Eocene and the Pliocene.
In a controversial move, the Anthropocene Working Group has declared that the Anthropocene warrants being a full-blown epoch (not a lesser age), with its start pegged to the post–World War II economic boom and nuclear weapons tests of the late 1940s and early 1950s. The group made these provisional recommendations August 29 at the International Geological Congress in Cape Town, South Africa. If eventually approved by the International Commission on Stratigraphy (ICS) — the gatekeepers of geologic time — and the Executive Committee of the International Union of Geological Sciences, the Anthropocene would usurp the current Holocene Epoch, which has reigned since the end of the last glacial period around 11,700 years ago. The Holocene would become the shortest completed epoch in history, just thousandths the length of the next shortest epoch.
“We’ve left an indelible mark on the Earth,” says Jan Zalasiewicz, a geologist at the University of Leicester in England and convener of the working group. “We now cannot go back to anything that’s ostensibly the same as the Holocene.”
Not all scientists are onboard with the plan. Critics say it’s grounded in politics and pop culture, not science, and that not enough time has passed to put just decades-old changes in context. Any proposal advocating for the Anthropocene will face strong skepticism, says Whitney Autin, a sedimentary geologist at the State University of New York at Brockport. “The idea of amending geologic time carries the same weight as eliminating an amendment to the U.S. Constitution,” he says. To build its case for the new epoch, the working group will spend the next two to three years scouring natural records, such as rocks, mud and tree rings, for evidence that humankind’s impacts have brought about a distinct new phase in the stratigraphic record. The group will then submit a formal proposal for approval.
“We’re leaving physical signals in sediments, in corals, in trees that are going to be long lasting if not permanent,” says Colin Waters, a geologist at the British Geological Survey in Keyworth and a member of the working group. “It’s not just history, it’s geology as well.” And those geologic changes merit official recognition as a new epoch, Waters says.
The goal of the geologic time scale is to label and formalize discrete phases in Earth’s stratigraphic record as a tool for geologists and other scientists. This time scale allows scientists to easily identify, describe and discuss rocks of similar age across the planet.
The term “Anthropocene” has risen in popularity among scientists and the general public in recent years, driven in part by its use in a 2002 article by atmospheric chemist and Nobel laureate Paul Crutzen. The article argued that humans’ exploitation of natural resources has reshaped the planet enough to bring about a new epoch.
While “Anthropocene” now appears in the titles of papers, conference talks and books about everything from climate change to philosophy, those who embrace the term nonetheless disagree on its definition. Some researchers pin the start of the epoch to when humans first started converting forests to farmland thousands of years ago, while others, such as Crutzen, use the start of the Industrial Revolution or the recent acceleration in fossil fuel burning.
The Anthropocene Working Group was convened by the ICS in 2009 to sort out the definition of the Anthropocene and assess whether the time interval should be formally added to the geologic time scale. Among its 35 members, the working group contains an international mix of geologists, climate scientists, archaeologists and other experts.
In January, members of the working group published a review of evidence for the Anthropocene in Science. Pro-Anthropocene arguments come from multiple areas of science, from biology to climate to chemistry, the researchers reported. For instance, humans have introduced species such as the domestic chicken worldwide and driven many others to extinction (SN Online: 8/26/15). Emissions from human activities such as fossil fuel burning have altered Earth’s climate (SN: 4/16/16, p. 22). Manufactured materials such as plastics, aluminum and concrete will remain embedded in the ground as “technofossils.” Fallout from nuclear weapons tests has left a radioactive mark in soil, marine sediments and even ice. These human impacts make the Anthropocene distinct in the stratigraphic record from the Holocene, the researchers concluded.
For the Anthropocene to become official, the working group will have to establish a starting point for the proposed epoch. That can be accomplished by picking a nice round number — the Hadean-Archean switchover is an even 4 billion years ago, for instance — or by linking the starting point to a physical marker in the global sedimentary record, an approach now favored by ICS.
The marker for the start of the Holocene, for instance, is linked to chemical and physical changes in the Greenland ice sheet caused by the warming that brought Earth out of its last bout of glacial growth. Such markers — also called “golden spikes,” similar to the ceremonial spike that marked the union of the first U.S. transcontinental railroad — are chosen for being ubiquitous and consistent throughout the world. Golden spikes are not necessarily important or even relevant to the differences that distinguish geologic time frames, says Stan Finney, a geologist at California State University, Long Beach, and former chair of the ICS. For instance, the Thanetian Age — a 3.2-million-year stretch during the Paleocene Epoch — is marked by just one of many reversals in Earth’s magnetic field.
While a golden spike’s geologic signal may be global, the official physical spike itself is literally a single point in the stratigraphic record somewhere on Earth. (A single point avoids the problem of using multiple points that could end up having different ages, muddling the time boundary.) The golden spike for the Holocene is inside an ice core collected from Greenland and kept chilled in a freezer at the University of Copenhagen.
The need for a golden spike shaped the working group’s Anthropocene proposal, Zalasiewicz says. While phases in human history such as early agriculture and the Industrial Revolution have had profound impacts on the planet, they didn’t have a simultaneous worldwide effect that could be used to mark the start of the new epoch. Had a major volcanic eruption spewed a distinctive layer of ash across the globe near the start of the Industrial Revolution, “it would have been a pretty good candidate,” Zalasiewicz says. Even though the eruption would have had nothing to do with human activity, the ash would have been a ubiquitous and easily identifiable marker for geologists.
Radioactive carbon and plutonium blasted from the ramp up in atmospheric nuclear tests during the 1950s is another story. And the timing is so recent that it opens up many new places to hunt for the proposed epoch’s golden spike, including in living organisms such as trees and corals. “We’re a bit like confused kids wandering around an enormous sweetshop wondering how we’re going to choose,” Zalasiewicz says.
Even if the group finds a golden spike, its proposal will face criticism from scientists who contend that the Anthropocene doesn’t warrant its own epoch. Radioactive fallout “is a widespread marker that qualifies for the rules that they need to follow to make a recommendation,” says William Ruddiman, a professor emeritus at the University of Virginia in Charlottesville, “but that doesn’t mean that it’s right, or that it makes sense.”
Not enough time has passed since the proposed start date of the Anthropocene to have enough perspective to put the observed changes in the sedimentary record in proper context, Autin says. “A lot of stratigraphers would say that maybe in thousands or millions of years there will be a distinctive demarcation in the rock record at this point in time, but right now it’s a proposal that’s premature.”
Placing the boundary so recently is “dubious, to say the least,” agrees Mike Walker, a professor emeritus at the University of Wales Trinity Saint David who helped establish the golden spike that represents the start of the Holocene. Divisions of geologic time “should have a utility for geoscientists, archaeologists, anthropologists, et cetera,” he says. “I see little of value to the wider science community in an epoch boundary at A.D. 1950.”
The formalization of the Anthropocene is not just scientifically motivated, but also driven by a desire to highlight humankind’s impact on the environment, suggests Lucy Edwards, a geologist with the U.S. Geological Survey in Reston, Va. “It’s a meme,” she says. “The thinking is that if you have a concept and you give it a new word, it carries more weight.”
The motivation behind the newly announced proposal isn’t overly focused on humankind being to blame for recent changes, Zalasiewicz responds. “If we had all the same changes, but caused by something else, like volcanoes or a meteorite or my cat, then it would be just as significant.”
More time isn’t needed to recognize that modern sediments are unique, he adds. After all, he says, if humans had been around 50 years after the environmental catastrophe that wiped out the dinosaurs about 66 million years ago, they would have clearly seen that Earth’s environment and ecology had permanently changed.
ORLANDO, Fla. — When sex chromosomes among common pill bugs go bad from disuse, borrowed bacterial DNA comes to the rescue. Certain pill bugs grow up female because of sex chromosomes cobbled together with genes that jumped from the bacteria.
Genetic analysis traces this female-maker DNA to Wolbachia bacteria, Richard Cordaux, based at the University of Poitiers with France’s scientific research center CNRS, announced September 29 at the International Congress of Entomology.
Various kinds of Wolbachia infect many arthropods, spreading from mother to offspring and often biasing their hosts’ sex ratios toward females (and thus creating even more female offspring). In the common pill bug (Armadillidium vulgare), Wolbachia can favor female development in two ways. Just by bacterial infection without any gene transfer, bacteria passed down to eggs can make genetic males develop into functional females. Generations of Wolbachia infections determining sex let these pill bugs’ now-obsolete female-making genes degenerate. Which makes it very strange that certain populations of pill bugs with no current Wolbachia infection still produce abundant females. That’s where Cordaux and Poitier colleague Clément Gilbert have demonstrated a second way that Wolbachia makes lady pill bugs — by donating DNA directly to the pill bug genes. The researchers, who share an interest in sex determination, have built a case that Wolbachia inserted feminizing genes into pill bug chromosomes. The bacterial genes thus created a new sex chromosome.
“Incredible,” said Steve Perlman after hearing the talk, not in disbelief but in wonder at the biology. Perlman, of the University of Victoria in Canada, studies symbiosis and parasitism and says this new example of far-flung gene transfer is part of “a big thing in the field now.” Such transfers provide exotic genetic variation that fuels evolutionary processes. Audience members Ellen Martinson and Vincent Martinson, both of the University of Rochester in New York, were themselves coauthors of a 2016 paper describing microsporidian fungus DNA that has become a venom gene in some wasps.
The world’s most minuscule machines operate on the molecular level and have won their creators the 2016 Nobel Prize in chemistry. The prize is shared between Jean-Pierre Sauvage of the University of Strasbourg in France, J. Fraser Stoddart of Northwestern University in Evanston, Ill., and Bernard Feringa of the University of Groningen in the Netherlands.
Sauvage and colleagues first linked two ring-shaped molecules together in 1983 to form a necklacelike chain. In 1991, Stoddart’s team created an atom-scale axle, paving the way to build molecular “muscles” and “elevators.” Through electrochemistry, Feringa and colleagues powered up the first light-powered molecular motor in 1999 and even designed a four-wheel drive, nano-sized car.
These fantastic machines have opened up the molecular world to manipulating and moving objects at the smallest levels imaginable. There are “endless opportunities,” Feringa said in a phone interview during the announcement ceremony.
Scaling up from one cell to many may have been a small step rather than a giant leap for early life on Earth. A single-celled organism closely related to animals controls its life cycle using a molecular toolkit much like the one animals use to give their cells different roles, scientists report October 13 in Developmental Cell.
“Animals are regarded as this very special branch, as in, there had to be so many innovations to be an animal,” says David Booth, a biologist at the University of California, Berkeley who wasn’t part of the study. But this research shows “a lot of the machinery was there millions of years before animals evolved.” Multicellular organisms need to be able to send messages between their cells and direct them to particular roles within the body. That requires a great deal of cell-to-cell coordination — something that unicellular organisms don’t have to deal with. But an amoeba (Capsaspora owczarzaki) employs many of those same tricks to switch its single-celled body between different life stages. That means that the earliest animals were probably “recycling mechanisms that were already present before,” says study coauthor Iñaki Ruiz-Trillo, a biologist at the Institute for Evolutionary Biology in Barcelona.
C. owczarzaki goes through three different life stages, acting independently in some stages and aggregating with other amoebas in others. Ruiz-Trillo and colleagues analyzed C. owczarzaki’s proteome — its complete set of proteins — during each life stage.
The amoeba made different amounts of its proteins in each life stage, the team found, suggesting that it was responding to new demands. But it went a step further, too, also shifting the way its proteins behaved during each stage.
Proteins can change their behavior by grabbing on to a molecular fragment called a phosphate ion. The phosphate ion’s effect depends on where it sticks to the protein and whether there are other phosphate ions stuck on nearby. C. owczarzaki showed distinct differences in the pattern of these phosphate add-ons between its three life stages. That parallels what’s seen in animals: Proteins in different organs within the same animal show similar modification differences.
The researchers also found changes in the molecules that control the protein modification process. Certain enzymes within a cell act like molecular concierges, helping phosphate ions latch on to proteins. The type of enzyme often determines where the ion sticks — and thus the effect it has. For instance, enzymes called tyrosine kinases often guide modifications that help multicellular organisms send messages between cells. Those enzymes aren’t thought to be widely used by single-celled species, says study coauthor Eduard Sabidó, a biologist at the Centre for Genomic Regulation in Barcelona. But C. owczarzaki uses these enzymes across all of its life stages, generating them in different quantities depending on the stage. Previous research showed that other single-celled organisms had the genes for tyrosine signaling, but this study shows how widely it’s actually used and how closely it’s linked to specific life changes, says Booth.
The shared molecular mechanisms suggest that the unicellular common ancestor of today’s animals and C. owczarzaki probably used these same tricks, too, paving the way for multicellular life. That’s not to say animals don’t get any credit, says Sabidó — they’ve expanded this toolkit further over time. But the perceived chasm between a simple single-celled existence and a complex multicellular one might not have required a flying leap to cross. “This gap,” Sabidó says, “maybe isn’t such a gap.”
