Location: The galaxy NGC1052–DF2, about 65 million light-years from Earth.
An unusual galaxy is surprisingly lacking in dark matter, scientists report March 28 in Nature.
In typical galaxies, normal matter is swamped by dark matter, an unidentified invisible substance that makes up most of the matter in the universe. The existence of dark matter explains the unexpectedly fast speeds at which stars swirl around galaxies, and how galaxies move within clusters. But one galaxy, NGC1052–DF2, appears to have less dark matter than normal matter, or potentially none at all. Given its mass — it holds stars with about 200 million times the mass of the sun — it would be expected to have about 300 times as much dark matter as normal matter. That adds up to about 60 billion times the sun’s mass in missing dark matter.
Using observations from several telescopes, Yale University astronomer Pieter van Dokkum and colleagues studied 10 bright clumps of stars within the galaxy, known as globular clusters, and measured their velocities. The more mass there is in the galaxy, the faster the clusters should move around it. So if dark matter were present, the clusters should cruise at a relatively rapid clip. Instead, the clusters were moving slowly, indicating a dark matter–free zone. In most galaxies, stars move faster than naïvely expected, which suggests dark matter lurks within them, providing an extra source of mass. Most physicists believe dark matter is an undetected type of particle. But some think that the hint of extra matter might be a mirage, caused by an incomplete understanding of the workings of gravity. These researchers favor a theory known as modified Newtonian dynamics, or MOND (SN: 3/31/07, p. 206), which adjusts the rules of gravity to make sense of stars’ motions, without requiring any new, elusive particles.
The new study, says van Dokkum, bolsters the idea that dark matter is real, instead of an illusion. “Until now, whenever we saw a galaxy, we also saw dark matter,” says van Dokkum. “We didn’t know for sure whether dark matter and galaxies were two separable things.”
Because MOND proposes tweaking the laws of physics, then — if correct — its effects should be felt in every galaxy across the cosmos. That makes it hard for MOND to explain the unusually slow speeds of the star clusters in NGC1052–DF2.
“It’s intriguing, but it’s not something I’m going to lose sleep over,” says Stacy McGaugh, an astrophysicist at Case Western Reserve University in Cleveland. He studies MOND and thinks the theory might still be able to explain this galaxy. That’s because NGC1052–DF2 is nestled close to another galaxy. That other galaxy could alter MOND’s predictions, perhaps explaining why the star clusters move slowly. The effect of that proximity needs to be taken into account to determine if MOND can explain the observations, he says.
Still, McGaugh acknowledges that NGC1052–DF2 is problematic for MOND. But it is also problematic for the standard dark matter picture, he says, as it’s not clear how such a galaxy could form in the first place. Most galaxies are thought to form around clumps of dark matter, so a galaxy devoid of the stuff is hard to explain.
NGC1052–DF2 is unusual in other ways. It’s a faint, ghostly blob known as an ultradiffuse galaxy. Although about the same volume as the Milky Way, NGC1052–DF2 contains many fewer stars. Scientists are struggling to understand why such galaxies look so different from most others (SN: 12/10/16, p. 18). Finding an ultradiffuse galaxy without dark matter further complicates the puzzle.
If scientists can explain how the galaxy formed, it might improve understanding of the properties of dark matter. “In physics we always want to find really extreme laboratories to test theories and ideas,” says astrophysicist James Bullock of the University of California, Irvine. This galaxy is extreme indeed.
Some victims were found at home. An 84-year-old woman who’d spent over half her life in the same Sacramento, Calif., apartment died near her front door, gripping her keys. A World War II veteran succumbed in his bedroom. Many died outside, including a hiker who perished on the Pacific Crest Trail, his water bottles empty.
The killer? Heat. Hundreds of others lost their lives when a stifling air mass settled on California in July 2006. And this repeat offender’s rap sheet stretches on. In Chicago, a multiday scorcher in July 1995 killed nearly 700. Elderly, black residents and people in homes without air conditioning were hardest hit. Europe’s 2003 heat wave left more than 70,000 dead, almost 20,000 of them in France. Many elderly Parisians baked to death in upper-floor apartments while younger residents who might have checked in on their neighbors were on August vacation. In 2010, Russia lost at least 10,000 residents to heat. India, in 2015, reported more than 2,500 heat-related deaths.
Year in and year out, heat claims lives. Since 1986, the first year the National Weather Service reported data on heat-related deaths, more people in the United States have died from heat (3,979) than from any other weather-related disaster — more than floods (2,599), tornadoes (2,116) or hurricanes (1,391). Heat’s victim counts would be even higher, but unless the deceased are found with a fatal body temperature or in a hot room, the fact that heat might have been the cause is often left off of the death certificate, says Jonathan Patz, director of the Global Health Institute at the University of Wisconsin–Madison.
As greenhouse gases accumulate in the atmosphere, heat’s toll is expected to rise. Temperatures will probably keep smashing records as carbon dioxide, methane and other gases continue warming the planet. Heat waves (unusually hot weather lasting two or more days) will probably be longer, hotter and more frequent in the future. Beyond deaths, researchers are beginning to document other losses: Heat appears to rob us of sleep, of smarts and of healthy births. “Heat has the ability to affect so many people,” says Rupa Basu, an epidemiologist with the California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment in Oakland. “Everybody’s vulnerable.”
Many people see heat as more of an annoyance than a threat, but climate change, extreme heat and human health are entwined. “There might not be a huge burden of disease from heat-related illness right now in your community,” says Jeremy Hess, an emergency medicine physician and public health researcher at the University of Washington in Seattle. “But give it another 20 years, and it might be a more significant issue.” Adaptation has limits The human body can’t tolerate excessive heat. The biological and chemical processes that keep us alive are best carried out at a core temperature of 36° to 37° Celsius (96.8° to 98.6° Fahrenheit), with slight variation from person to person. Beyond that, “the body’s primary response to heat is to try and get rid of it,” says Jonathan Samet, dean of the Colorado School of Public Health in Aurora. Blood vessels in the skin dilate and heart rate goes up to push blood flow to the skin, where the blood can release heat to cool down. Meanwhile, sweating kicks in to cool the skin.
With repeated exposure to high temperatures, the body can become more efficient at shedding excess heat. That’s why a person can move from cold Minneapolis to steamy Miami and get used to the higher heat and humidity. But there is a limit to how much a person can adjust, which depends on the person’s underlying health and the ambient temperature and humidity. If the outside is hotter than the body, blood at the skin surface won’t release heat. If humidity is high, sweating won’t cool the skin. Two scientists proposed in 2008 that humans cannot effectively dissipate heat with extended exposure to a wet-bulb temperature, which combines heat and humidity, that is greater than 35° C. Forced to regulate heat without a break, the body gets worn out. Heat exhaustion leads to weakness, dizziness and nausea. If a person doesn’t cool off, heat stroke is likely — and likely fatal. The ability to regulate heat breaks down and core body temperature reaches or exceeds 40° C. A person suffering heat stroke may have seizures, convulsions or go into a coma.
No one is immune to heat, but it hits some groups harder than others. The elderly, considered the most vulnerable, have fewer sweat glands and their bodies respond more slowly to rising temperatures. Children haven’t fully developed the ability to regulate heat, and pregnant women can struggle due to the demands of the fetus. People with chronic diseases like diabetes, cardiovascular disease and obesity can have trouble dissipating heat. And, of course, people living in poverty often lack air conditioning and other resources to withstand sweltering conditions. Collateral damage Researchers are discovering more ways that heat can hurt. Take sleep: The onset and duration of sleep is sensitive to temperature. The body cools down as it prepares to sleep; this decrease in core temperature is a signal to bring on the z’s. Body temperature stays low throughout the night, then rises just before awakening. A good night’s rest is a cornerstone of health.
Hot nights make for bad sleep, according to a study combining responses to a U.S. Centers for Disease Control and Prevention sleep survey of 765,000 U.S. residents from 2002 to 2011 with data on nighttime temperatures during that period. The higher the nighttime temperatures, the more nights respondents reported getting too little shut-eye. The effect hit low-income respondents and the elderly hardest, the researchers reported in May 2017 in Science Advances.
The ability to think and calculate may take a beating in the heat, according to a small study presented in January in Austin, Texas, at the American Meteorological Society’s annual meeting. Researchers from Harvard University tested undergraduate students for 12 days — the time before, during and after a heat wave. Twenty-four lived in buildings with air conditioning and 20 in buildings without. The researchers assessed how quickly and accurately students performed an addition and subtraction test and a test that asked for the color of a written word, rather than the word itself. During the heat wave, the students without air conditioning got about 6 percent fewer correct answers on the math problems and 10 percent fewer on the color problems than the students with air conditioning.
Heat may even increase the risk of stillbirth. Researchers with the National Institute of Child Health and Human Development in Bethesda, Md., analyzed weather data and more than 223,000 U.S. births from 2002 to 2008. During the warm months of the year, a 1 degree C increase in temperature during the week before birth was associated with about four additional stillbirths per 10,000 births, the researchers reported in June 2017 in Environmental Health Perspectives. As heat gets vicious, it threatens to disrupt the fabric of society. Extreme heat — beyond a wet-bulb temperature of 35° C — could become more regular in South Asia and the Persian Gulf, rendering parts of those areas uninhabitable, according to studies in the August 2017 Science Advances (SN: 9/2/17, p. 10) and the February 2016 Nature Climate Change. It’s not hard to imagine that there will be profound societal and political instability “in a world where tens of millions of people have to move and are looking for cooler places to live,” says Howard Frumkin, a physician epidemiologist specializing in environmental health at the University of Washington.
Emerald cities Fifty-four percent of the world’s population — and around 80 percent of U.S. residents — live in urban areas. Cities are where some action to combat heat can be taken now, says Brian Stone Jr., an environmental planner and member of the Urban Climate Lab at Georgia Tech in Atlanta. “If we’re waiting for the national government to signal it’s time to do this, we’re going to wait too long,” he says. “We are well into a world that’s been altered by climate change.”
Heat thrives in cities. All of the nonreflective roofs, walls, roads and other surfaces absorb and retain heat during the day. Waste heat, emitted from air conditioners and vehicles, concentrates in cities too. Together, these factors contribute to what’s called an urban heat island, an amplification of heat that occurs within cities. On average, a city with at least a million residents can be 1 to 3 degrees C hotter than surrounding areas. At night, the temperature differences widen. Cities may be as much as 12 degrees C hotter than surrounding areas in the evening hours, because cities release built-up heat back out among buildings and avenues.
Hotlanta These Landsat satellite images show urban Atlanta on September 28, 2000. The core urban area is at the center of the images. The left side shows areas of vegetation (green), bare ground (brown) and roads and dense development (gray). The heat map on the right shows the areas of densest development also have the hottest land surface temperatures (red), near 30 degrees Celsius. The areas of heaviest vegetation are the coolest (yellow) due to evaporation of water and shade. City planners can rid their locales of some of this heat with several strategies. One is to plant more trees to create shade for residents and structures. Trees also lower the air temperature by transferring water from the soil through the tree to the air. The surrounding air is cooled as the water changes from a liquid to a vapor. The process is “much like the way sweating works for our bodies,” says George Ban-Weiss, an environmental engineer at the University of Southern California in Los Angeles.
Another strategy is to reduce the amount of sunlight that city surfaces absorb by using “cool” materials on exposed surfaces. The best known are cool roofs, which “reflect more sunlight than usual,” says Ronnen Levinson of Lawrence Berkeley National Laboratory in Berkeley, Calif., who studies cool surfaces and urban heat islands. In general, to make a surface cool, you make it lighter, with coatings or other light-colored materials. For example, a white roof that reflects 80 percent of the sun’s light on a typical summer afternoon will stay about 31 degrees C cooler than a gray roof that reflects only 20 percent. Giving buildings cool-surface makeovers counters the urban heat island effect and reduces the temperature inside a building. “In disadvantaged communities, people simply may not have air conditioning to help them ride out hot summers,” Levinson says. Cooling off the insides of buildings is “where I think the greatest potential benefits are for improving human comfort and health,” he says.
Stone has estimated how many heat-related deaths could be avoided by reducing urban heat island effects. In 2016, he and colleagues produced a report for the city of Louisville, Ky., that analyzed the impact of adding 450,000 trees, converting 168 square kilometers of surfaces to cool materials and more. The researchers estimated that areas of the city could reduce average summertime temperatures by as much as 1.7 degrees C or more. And based on the 53 deaths Stone attributed to the city’s unusually warm summer of 2012, there could be 11 fewer deaths from heat, a reduction of 21 percent. “When we get a big heat wave,” Stone says, “that could really translate into hundreds of lives.”
Many cities in the United States and abroad are working on tempering their urban heat islands with a variety of strategies, including programs to install cool roofs or plant more trees. The city of Los Angeles now requires that new or replaced roofs for homes and other residential buildings meet a solar reflectance index value — a measure of a materials’ ability to stay cool in the sun between zero (black surface) and 100 (white) — of at least 75 for flatter roofs and 16 for steeper ones. Through a provision in California’s building energy efficiency code, cities throughout the state have been converting flat, commercial roofs, like those on big-box stores, to light-colored cool roofs when a new topper is needed. New York City has planted a million new trees since 2007 and committed additional funds to adding even more to streets and parks. The city also has coated 0.62 square kilometers of roof surfaces white since 2009. The city of Ahmedabad, India, where about 25 percent of the residents live in slum communities, announced a heat action plan in 2017 that includes a cool roofs initiative to paint or otherwise convert at least 500 slum household roofs and to improve the reflectivity of roofs on government buildings and schools.
Measures that tackle the urban heat island effect also make cities more energy efficient (by reducing the cooling needs inside buildings) and more comfortable (by shading city residents). Individual cities need to implement strategies that make sense for their landscapes, their water resources, their usual climate and their populations, Ban-Weiss says.
But ameliorating urban heat can only do so much. There will still need to be a worldwide push to reduce emissions of greenhouse gases. Ban-Weiss and colleagues estimated how much cool roofs could counter warming from climate change in Southern California. Assuming that greenhouse gas emissions continue to increase, the widespread adoption of cool roofs in the Los Angeles metropolitan area would offset some of the warming expected by midcentury, the team reported in 2016 in Environmental Research Letters. But by the end of the century, Ban-Weiss says, the cool roof benefits “become mostly dwarfed by climate change.”
The world’s longest system of levees and floodways, meant to rein in the mighty Mississippi River, may actually make flooding worse.
Using tree rings and lake sediments, researchers re-created a history of flooding along the lower Mississippi River extending back to the 1500s. This paleoflood record suggests that the past century of river engineering — intended to minimize flood damage to people living along the river’s banks — has instead increased the magnitude of the largest floods by 20 percent, the researchers report April 5 in Nature. Climate patterns that bring extra rainfall to the region don’t account for the dramatic increase in flood size, the team found. “The obvious culprit is that we have really modified the river itself,” says Samuel Munoz, a geoscientist at Northeastern University in Boston.
Settlers built the first levees on the Mississippi in the early 1800s. After a massive flood displaced hundreds of thousands of people in 1927, the U.S. government built the current system of spillways and levees. The engineering projects profoundly altered the river’s shape and sediment content. But how these changes affected the size of the river’s largest floods has been unclear, in part because water gauges have tracked the river’s flow for just 150 years. “One of the difficult things about studying extreme floods is that you don’t get many,” says paleohydrologist Scott St. George of the University of Minnesota in Minneapolis, who wrote an accompanying commentary in Nature . “Floods like the one in 1927 don’t come around very often.” Munoz and his colleagues studied tree rings and sediments from oxbow lakes to create their 500-year record of Mississippi River floods. Oxbow lakes form as a river meanders and twists across its floodplain; sometimes, a large loop becomes cut off from the main channel, forming an isolated lake. When a river’s waters rise high enough, they can spill over into the lake, dropping loads of sand and silt.
“You get deposits of river material in which the coarse stuff settles out fastest and the finer stuff is on top,” Munoz says. As evidence of past floods, the team looked for this sediment pattern in cores from three oxbow lakes. Comparing recent flood sediment sequences with those floods’ actual size, the researchers created a template for assessing the magnitude of older floods.
Identifying “flood rings” in tree-ring samples from 35 oak trees along the lower river’s floodplain helped researchers pin down the timing of the floods. When a tree is inundated, tree ring vessels — cells that transport water and nutrients — may shrink or be distributed differently within that ring, compared with in rings not affected by floods.
The researchers next considered the influence of two large weather patterns known to bring wetter conditions to the central United States — the El Niño-Southern Oscillation and the Atlantic Multidecadal Oscillation. The team analyzed historical data for these patterns back to the late 19th century, and reconstructed the patterns back to 1500. Those weather patterns are linked to warmer surface temperatures in the Pacific and Atlantic oceans, respectively, and correlated with the timing of observed floods on the lower Mississippi. But they weren’t the whole story. “The early 20th century got a lot of flooding,” but only 25 percent of the increase in flood magnitude over the past century can be explained by those climate patterns, Munoz says. The other 75 percent was probably due to the river modifications, the researchers found.
River modification is a plausible explanation for the increase in Mississippi flood extremes, St. George says. But there are other possible climate impacts, he notes, such as the fact that the area is warmer now than 150 years ago. These could also have affected rainfall and river flow in the Mississippi River basin.
Still, he says, the 500-year flood record is an important part of solving that puzzle. “It gives a long-term perspective on the Mississippi, which you really need to understand a river of its size and majesty.”
Munoz says this method of establishing a flood record that predates river gauges can be applied to other rivers, whether heavily managed or not. It could also help scientists understand how flood risks might change with increasing greenhouse gases in the atmosphere (SN: 9/2/19, p. 14). “This approach can help take the pulse of a river and determine how unprecedented such changes might be.”
Every autumn, a quiet mountain pass in the Swiss Alps turns into an insect superhighway. For a couple of months, the air thickens as millions of migrating flies, moths and butterflies make their way through a narrow opening in the mountains. For Myles Menz, it’s a front-row seat to one of the greatest movements in the animal kingdom.
Menz, an ecologist at the University of Bern in Switzerland, leads an international team of scientists who descend on the pass for a few months each year. By day, they switch on radar instruments and raise webbed nets to track and capture some of the insects buzzing south. At sunset, they break out drinks and snacks and wait for nocturnal life to arrive. That’s when they lure enormous furry moths from the sky into sampling nets, snagging them like salmon from a stream. “I love it up there,” Menz says. He loves the scenery and the science. This pass, known as the Col de Bretolet, is an iconic field site among European ecologists. For decades, ornithologists have tracked birds migrating through. Menz is doing the same kind of tracking, but this time, he’s after the insects on which the birds feast.
Migrating insects, like those that zip through the Swiss mountain pass, provide crucial ecosystem services. They pollinate crops and wild plants and gobble agricultural pests.
“Trillions of insects around the world migrate every year, and we’re just beginning to understand their connections to ecosystems and human life,” says Dara Satterfield, an ecologist at the Smithsonian Institution in Washington, D.C.
Scientists like Menz are fanning out across the globe to track butterflies, moths, hoverflies and other insects on their great journeys. Among the new discoveries: Painted lady butterflies time their round trips between Africa and Europe to coincide within days of their favorite flowers’ first blossoms. Hoverflies navigate unerringly across Europe for more than 100 kilometers per day, chowing down on aphids that suck the juice out of greening shoots. What’s more, some agricultural pests that ravage crops in Texas and other U.S. farmlands are now visible using ordinary weather radar, giving farmers a better chance of fighting off the pests. Until now, most studies of animal migration have focused on large, easy-to-study birds and mammals. But entomologists say that insects can also illuminate the phenomenon of mass movement. “How are these animals finding their way across such large scales? Why do they do it?” asks Menz. “It’s really quite fantastic.” To warmer worlds Animals migrate for many reasons, but the aim is usually to eat, breed or otherwise survive year-round. One of the most famous insect migrations, of North America’s monarch butterflies (Danaus plexippus), happens when the animals fly south from eastern North America to overwinter in Mexico’s warmer setting. (A second population from western North America overwinters in California.) In Taiwan, the purple crow butterfly (Euploea tulliolus) migrates south from northern and central parts of the island to the warmer Maolin scenic area every winter, where the butterfly masses draw crowds of lepidopteran-loving tourists. In Australia, the bogong moth (Agrotis infusa) escapes the hot and dry summer of the country’s eastern parts by traveling in the billions to cool mountain caves in the southeast.
The migrations can be arduous. Each spring, the painted lady butterfly (Vanessa cardui) moves out of northern Africa into Europe, crossing the harsh Sahara and then the Mediterranean Sea before retracing the route in the autumn (SN Online: 10/12/16). Because adult life spans are only about a month, the journey is a family affair: Up to six generations are needed to make the round trip. It’s like running a relay race, with successive generations of butterflies passing the baton across thousands of kilometers. Constantí Stefanescu, a butterfly expert at the Museum of Natural Sciences in Granollers, Spain, has been tracking the painted lady migrations. He relies on citizen scientists who alert him when the orange-and-black-winged painted ladies arrive in people’s backyards each year, as well as field studies by groups of scientists. In 2014, 2015 and 2016, Stefanescu led autumn expeditions to Morocco and Algeria to try to catch the return of the painted ladies to their wintering grounds.
By surveying swaths of North Africa, Stefanescu’s team confirmed that the painted ladies virtually disappeared from the area during the hot summer months and returned in huge numbers in October. The fliers arrived back in Africa just in time to feed on the daisylike false yellowhead (Dittrichia viscosa) and other flowers. The findings make clear how well the butterflies are able to time their migrations to take advantage of resources, Stefanescu reported in December in Ecological Entomology. Other insect species are less visibly stunning than the painted lady, but just as important to the study of migrations. One emerging model species is the marmalade hoverfly (Episyrphus balteatus), which migrates from northern to southern Europe and back each year.
Marmalade hoverflies have translucent wings and an orange-and-black striped body. As larvae, they eat aphids that would otherwise damage crops. As adults, the traveling hoverflies help pollinate plants. “They’re useful for so many things,” says Karl Wotton, a geneticist at the University of Exeter in England.
Wotton started thinking about the importance of insect migration after 2011, when windblown midges carried an exotic virus into the southern United Kingdom that caused birth defects in cattle on his family’s farm. Intrigued, Wotton set up camp at a spot in the Pyrenees at the border of Spain and France to study migrating hoverflies. Then he heard that Menz was doing almost exactly the same kind of research at the Col de Bretolet and a neighboring pass. The two connected, hit it off and now collaborate in both the Pyrenees and the Alps. Funneled by the high mountain topography, hoverflies whiz through the passes like rush hour commuters through a railway station. “We’re talking about an immense number of insects,” Menz says. Millions of flies traverse the Swiss passes each year. Extrapolating to all of Europe, Wootton estimates that many billions of hoverflies are probably migrating. The insects consume billions of aphids that otherwise would have feasted on agricultural crops.
As astonishing as this migration is, most people never notice it. Only at the passes do the hoverflies become noticeable, a never-ending stream of tiny bodies glinting in the mountain light. They ride high on tailwinds and scoot low when the wind is against them. “They fly fast and low and they don’t stop,” Wotton says. “The butterflies are getting turned around like in a tumble dryer, but the hoverflies just shoot straight over.”
Wotton, Menz and colleagues use specialized upward-looking radar to track signals reflecting off of insects passing overhead. The researchers also use traps to catch individual flies to identify the species passing through. And they study navigation in a sort of hoverfly flight simulator. The researchers glue the backs of flies to the heads of pins and watch how the flies navigate when held between two magnets. The aim is to see if the insects are using cues from Earth’s magnetic field to find their way. Suspended between the magnets, the insects can move freely left or right, choosing their direction of travel. The whole contraption is enclosed in an opaque plastic barrel so the flies cannot see the visual cues of the surrounding mountains. Preliminary findings suggest the flies do indeed find their way using some kind of compass, Wotton reported in Denver in November 2017 at a meeting of the Entomological Society of America. Season after season, the researchers are building up a hoverfly census. By comparing that information with a 1960s survey done at the Col de Bretolet, the team hopes to determine whether species’ numbers have changed over time. Menz says: “I wouldn’t be surprised if they’ve declined.”
Other entomologists have documented sharp drops in the numbers of insects across Europe. In October 2017, a Dutch-German-British research team reported in PLOS ONE that the total insect biomass collected at 63 nature-protection areas in Germany over 27 years had dropped by more than 76 percent.
The paper garnered media headlines around the world as heralding an “insect Armageddon.” That may be overly dramatic. The work covered just one small part of Europe, and the authors could not explain what might be causing the drop, whether climate change, habitat destruction or something else. But if hoverfly numbers are dropping, that would mean fewer are around to eat destructive aphids and to spread beneficial pollen. Hoverflies, which pollinate a wide range of plants, are the second most important group of pollinators in Europe after bees, Wotton says. Hoverflies also migrate in North America, in ways that are far less understood than in Europe. This month, Menz and Wotton are visiting Montaña de Oro State Park on California’s Central Coast, where last year an entomologist reported spotting a rare hoverfly migration. The researchers hope to see whether the American hoverflies, probably a different species, are moving in the same ways their European cousins do.
Swoop in the destroyers Not all migrating insects are beneficial. Some are troublemakers that chase ripening crops with the season. Farmers can spray pesticides once insects arrive in the fields, but knowing more about when and where to expect the critters can help growers better prepare for the onslaught.
Weather radar — Doppler data that meteorologists use to follow rain, hail and snow in near real time — is beginning to help. The radar signals reflect off of birds and other animals flying through the air. And although many insect species are too small to be detected in Doppler radar data, researchers are finding new ways to extract the signals of insects and track their migrations as they happen.
John Westbrook, a research meteorologist at the U.S. Department of Agriculture’s Agricultural Research Service in College Station, Texas, has been using weather radar to follow insect flyways in the south-central United States. A 1995 outbreak of two migratory moth species — beet armyworm (Spodoptera exigua) and cabbage looper (Trichoplusia ni) — devastated cotton crops in Texas’ Lower Rio Grande Valley. Westbrook recently dug through the Doppler data from 1995 and was able to pick out the signals of these two species moving during the outbreak, Westbrook and USDA colleague Ritchie Eyster wrote in November 2017 in Remote Sensing Applications: Society and Environment. “Outbreaks are unpredictable,” Westbrook says. “But the weather radar can show where they are occurring.” Modern weather radar contains even more information than 1995 systems did, he notes — and farmers can use that data to their advantage. They may decide to spray heavily where most of the insects are gathering before they spread. Or farmers might stock up on pesticides if a particularly dangerous outbreak is headed in their direction.
Another way to track destructive insects is to grind them up and test the chemistry of their tissues. As caterpillars grow, they take on a characteristic chemical signature of the environment, with hydrogen, oxygen and other elements fixed in tissues in varying amounts. Analyzing those ratios can reveal the geographic region of a caterpillar’s origin.
Keith Hobson of Western University in London, Canada, and colleagues have been studying the insect pest known as the true armyworm moth (Mythimna unipuncta). It travels between Canada and the southern United States every year, damaging crops along the way. But scientists weren’t sure exactly where the insects originated each year, making it harder to figure out how to manage the problem with pesticides.
In new experiments, Hobson’s team captured true armyworm moths in Ontario throughout the year and analyzed the hydrogen retained within the moths’ wings. Moths captured early in the season had values similar to those seen in Texas waters, while those captured in the summer showed values closer to Canadian waters. The reverse was also true: Adult moths captured in autumn in Texas had Canadian-type values.
It is the first direct evidence that individual moths are making these long-distance round trips, the scientists wrote in January in Ecological Entomology. Further studies could reveal how to better control the pests throughout the growing season, by showing precisely where the insects are coming from and how far they will travel. The migrating masses For Menz, Wotton, Satterfield and the rest, the ultimate goal is to go from studying individual species to investigating broader questions of how and why animals move around. That includes exploring how insects alter food webs during migrations across the landscape.
For instance, Mexican free-tailed bats (Tadarida brasiliensis) in Texas and Mexico forage for nocturnal moths, which migrate in very narrow layers in the atmosphere based on how the wind is blowing. “These are like food webs in the sky,” says Jason Chapman, an ecologist at the University of Exeter. “Can bats read the weather patterns and predict where the insects are going to be?”
Similarly, many dragonflies attempt to migrate 3,500 kilometers or more across the Indian Ocean from India to east Africa and back each year, breeding in temporary ponds created by monsoon rains. The dragonfly-eating Amur falcon (Falco amurensis) makes a similar journey, in one of the longest-known migrations for any raptor. If the dragonflies are the reason for the falcon migration, then tiny insects are a major player in this important bird movement.
Insects rule the migratory world by virtue of their sheer numbers. Compared with birds, mammals and other migratory animals, insects are by far the most numerous. Roughly 3.5 trillion migrate each year over just the southern United Kingdom, a 2016 radar study suggested (SN: 2/4/17, p. 12). That means that the majority of land migrations are made by insects.
To Aislinn Pearson, an entomologist at Rothamsted Research in Harpenden, England, studying insects will boost scientific understanding of how animals flow around the planet. “In the next 10 years,” she says, “a lot of the key findings of migration are going to come from these tiny little animals.”
Moody red lighting in a lab is helping researchers figure out what fruit flies like best about sex.
The question has arisen as scientists try to tease out the neurobiological steps in how the brain’s natural reward system can get hijacked in alcoholism, says neuroscientist Galit Shohat-Ophir of Bar-Ilan University in Ramat Gan, Israel.
Male fruit flies (Drosophila melanogaster) were genetically engineered to ejaculate when exposed to a red light. Ejaculation increased signs in the insects’ brains of a rewarding experience and decreased the lure of alcohol, researchers found. After several days in this red-light district, the flies tended to prefer a plain sugary beverage over one spiked with ethanol. Males not exposed to the red light went for the boozier drink, Shohat-Ophir and colleagues report April 19 in Current Biology. Earlier lab research has shown that male flies repeatedly rejected by females are more likely to get drunk. Those with happy fly sex lives don’t show much interest in alcohol. Shohat-Ophir wondered what aspect of sex, or lack thereof, had such a profound effect on the brain’s reward system.
The answer wasn’t that obvious. In rats, for instance, the brains of first-timer males light up with intense biochemical signs of reward just from rodent intercourse, regardless of whether ejaculation occurs. In female rats, copulation needs the right circumstances to evoke reward chemistry.
The red-light system let researchers remove the possibly confounding factor of female presence and see that male flies find ejaculation itself rewarding. (Among the evidence: pairing the red light with an odor cue, which males eagerly sought out afterward.) The red light triggers what are called Crz nerve cells in the abdomen, which cause sperm release and a surge of neuropeptide F, a cousin of a human brain reward compound called neuropeptide Y. Male flies’ bedazzlement with the right light or drinking binges after rejection may be easy for humans to understand. Shohat-Ophir says that’s because brain reward chemistry is so ancient that parts of it have been inherited by creatures with six legs as well as two.
Two major groups of plants have shown a surprising reversal of fortunes in the face of rising levels of carbon dioxide in the atmosphere.
During a 20-year field experiment in Minnesota, a widespread group of plants that initially grew faster when fed more CO2 stopped doing so after 12 years, researchers report in the April 20 Science. Meanwhile, the extra CO2 began to stimulate the growth of a less common group of plants that includes many grasses. This switcheroo, if it holds true elsewhere, suggests that in the future the majority of Earth’s plants might not soak up as much of the greenhouse gas as previously expected, while some grasslands might take up more. “We need to be less sure about what land ecosystems will do and what we expect in the future,” says ecosystem ecologist Peter Reich of the University of Minnesota in St. Paul, who led the study. Today, land plants scrub about a third of the CO2 that humans emit into the air. “We need to be more worried,” he says, about whether that trend continues.
The two kinds of plants in the study respond differently to CO2 because they use different types of photosynthesis. About 97 percent of plant species, including all trees, use a method called C3, which gets its name from the three-carbon molecules it produces. Most plants using the other method, called C4, are grasses. Both processes ultimately feed plants by pulling carbon dioxide from the air. But C4 plants use CO2 more efficiently, so they’re less hungry for it. As a result, it has long been dogma that when CO2 increases in the air, C3 plants gobble up more of it — and thus grow faster — while C4 plants ignore it. And that’s what experiments on plants grown in elevated CO2 have always shown — until now. For 20 years, scientists at the Cedar Creek Ecosystem Science Reserve in Minnesota have grown both C3 and C4 grasses in 88 plots, pumping extra CO2 into half of them to increase concentrations by 180 parts per million. That amounts to about 50 percent more CO2 than was in ambient air at the experiment’s beginning, and double preindustrial levels.
For the first 12 years, the plants hummed along as expected, with C3 plants responding more strongly to extra CO2 — a 20 percent boost in growth compared with plants grown in ambient air — and C4 plants largely ignoring the difference. But then something unexpected happened: The pattern reversed. Over the next eight years, C3 plants grew on average 2 percent less plant material if they received extra CO2, while C4 plants grew 24 percent more.
“I’m not at all surprised that an experiment like this would produce the unexpected,” says forest ecologist Rich Norby of Oak Ridge National Laboratory in Tennessee. Norby led a different project that tested a forest’s response to elevated CO2 for 12 years, and says the new results highlight the importance of such long-term experiments.
In particular, Norby says, soil fertility can affect how plants respond to CO2 in the long run.
In fact, soil nutrients may have been key to the flip-flop in Minnesota. Without the nitrogen they need, plants can’t take advantage of extra CO2 no matter how much there is. Over the course of the experiment, nitrogen grew to be in shorter supply for C3 plants, but in greater supply for C4 plants. The team suspects that differences in decomposing plant material might have led to changes over time in the community of microbes that process nitrogen in the soil and make it available to plants.
Since grasslands cover 30 to 40 percent of Earth’s land area, Reich says it’s important to learn how they could store carbon in the future. If grasslands worldwide behave as in the experiment, C4 grasslands — found in warm, dry regions — may absorb more CO2 than thought, while more abundant C3 plants could soak up less. As for crops, which can be either C3 like wheat or C4 like corn, the future is even less clear since farmlands are highly managed and often fertilized with nitrogen.
More studies are needed to figure out whether, and how, the world’s plants could shift in their response to increasing CO2. In the meantime, says Reich, “this means we shouldn’t be as confident we’re right about the ability of … ecosystems to save our hides.”
Uranus’ upper clouds are made of hydrogen sulfide — the same molecule that gives rotten eggs their noxious odor.
“At the risk of schoolboy sniggers, if you were there, flying through the clouds of Uranus, yes, you’d get this pungent, rather disastrous smell,” says planetary scientist Leigh Fletcher of the University of Leicester in England.
Using a spectrograph on the Gemini North telescope in Hawaii, Fletcher and his colleagues detected the chemical fingerprint of hydrogen sulfide at the top of the planet’s clouds, the team reports April 23 in Nature Astronomy.
That wasn’t a complete surprise: Observations from the 1990s showed hints of hydrogen sulfide lurking deeper in Uranus’ atmosphere. But the gas hadn’t been conclusively detected before. The clouds aren’t just smelly — they can help nail down details of the early solar system. Uranus’ hydrogen sulfide clouds set it apart from the gas giant planets, Jupiter and Saturn, whose cloud tops are mostly ammonia.
Hydrogen sulfide freezes at colder temperatures than ammonia. So it’s more likely that frozen hydrogen sulfide ice crystals would have been abundant in the further reaches of the early solar system, where the crystals could have glommed onto newly forming planets. That suggests that ice giants Uranus and Neptune were born farther from the sun than Jupiter and Saturn.
“This tells you the gas giants and the ice giants formed in a slightly different way,” Fletcher says. “They had access to different reservoirs of material back in the forming days of the solar system.”
Fletcher is far from repelled by the malodorous clouds. He and other planetary scientists want to send a spacecraft to the ice giants — the first since the Voyager spacecraft visited in the 1980s — to find out more (SN: 2/20/16, p. 24).
I am not the first person who has considered composing poetry to the placenta. One writer begins: “Oh Lady Placenta! What a life you lived in magenta.” Another almost coos to the “constant companion, womb pillow friend.” It might sound like odd inspiration for verse, but it’s entirely justified.
This vital organ, which is fully formed by about 12 weeks, nurtures a growing fetus throughout pregnancy, offering oxygen, nutrients and antibodies and eliminating waste. The placental cells forge a deep connection between mom and baby, a symbolic early step in a lifelong bond. Recent research suggests a placenta that works properly might be even more important than previously thought. Myriam Hemberger of the Babraham Institute and the University of Cambridge, along with colleagues in England and Austria, looked at more than 100 genes in mice that are known to be necessary for an embryo to survive. More than two-thirds of those mouse genes were linked to problems with the placenta. And death of the embryo around days 10 to 15 —when, in mice, the placenta takes over from the yolk sac to supply nutrients — was almost always tied to these placental problems.
The study makes you wonder: How many birth defects in humans might have their roots in the placenta? “You cannot just look at the embryo,” says Susan Fisher of the University of California, San Francisco, who studies how placental cells invade the uterus early in pregnancy. “You should work backward from the placenta.”
Both Hemberger and Fisher believe the placenta is underappreciated. I certainly thought much more about my little embryo turned fetus, growing from sesame seed to grape-sized, grapefruit and beyond, than I did about the disk of tissue supporting my baby-to-be. Fisher calls the placenta “the forgotten organ.”
In 2013, Tina Hesman Saey wrote a feature in Science News about new and growing efforts to understand the placenta. The New York Times published a story the following year, headlined “The Mysterious Tree of a Newborn’s Life.” Then came the launch of the Human Placenta Project, an initiative of the Eunice Kennedy Shriver National Institute of Child Health and Human Development. Since 2015, the project has invested more than $65 million in the development of technologies that can study the placenta in its natural environment, while a woman is pregnant.
“There is a long history of research involving the placenta, for many, many years,” says neonatal geneticist Diana Bianchi, director of the NICHD, who calls the placenta the Rodney Dangerfield of organs. Like the comedian, it gets no respect. “But the research had pretty much exclusively been after delivery.”
Shortly after a baby is born and his umbilical cord is cut, the placenta is expelled from the mother. At that point, it’s straightforward to inspect its size and blood vessels, and to see if scarring or calcium deposits provide clues to poor function. But it’s much too late to predict a fetus in trouble or to intervene in any way that might ultimately protect mom or baby.
Through the Human Placenta Project, researchers are, for example, using ultrasound to investigate placental blood vessels and blood flow in 3-D during the middle trimester and using magnetic resonance imaging to study oxygen distribution in twins who share a placenta but have separate amniotic sacs. How and when such work might make it to the clinic to affect current and future mommies isn’t yet clear.
Bianchi predicts that a deeper appreciation of the role of the placenta, encouraged through Hemberger’s work and similar studies, could change how pregnant women are monitored in the United States. There’s currently very little monitoring for women in the earliest weeks of pregnancy, the window when the placenta is becoming established. Doctor visits then ramp up as the pregnancy progresses. More attention in the first trimester, including attention to the placenta, could identify women who might be at a high risk for stillbirth or premature delivery, even if they are young and healthy by other standards. “That is a very conceivable, no pun intended, but very likely outcome of this research,” Bianchi says.
After identifying so many genes that affect the placenta, Hemberger’s team went on to show that many of those genes are associated in mice with blood vessel, heart and brain problems in a developing fetus. In other words, problems in the heart may have begun elsewhere, in the placenta. Among three of the mouse genes studied in much more detail, the researchers identified one for which the placenta problem was solely responsible for the death of the embryo at around 10 days. Even if the gene was absent from the embryo, restoring it to the placenta could prolong the embryo’s survival.
If the work holds for humans, it might mean that a fix to the placenta could change the course for a dramatic number of babies who would otherwise be born too small or with birth defects. That’s powerful stuff for would-be moms.
And there’s much more work to be done. “You need to understand normal development before you can address anything that goes wrong,” Hemberger says. A lot of pregnancy complications, including those related to the placenta, originate in the first two to eight weeks, which is still “the black box,” she says.
Recent research out of Japan may help. In January, a team there announced deriving and growing human trophoblast stem cells, the cells that form a large part of the placenta. Though such cells have been studied from mice, this could mark the beginning of more fruitful, detailed efforts to understand placenta formation in people. “Approaches like this,” Hemberger says, “can open up what happens in these early stages.”
Once more is known about how it all begins, it may feel perfectly natural for every person born to sing the praises of the placenta, “The tree of life, the mother-child link, Nourishing baby before it can drink.”
Stephen Nicol is here to change your mind about krill: They’re not microscopic and they’re far from boring. The biologist is so sick of people misunderstanding his study subjects that he’s even gotten a (slightly botched) krill tattooed on his arm to help enlighten strangers.
In The Curious Life of Krill, Nicol is taking his mission to an even bigger audience. The book is an ode to Antarctic krill (Euphausia superba), which are among the most abundant animals in the world by mass. Each several centimeters long, krill cloud the ocean in swarms that can span 20 kilometers. They’re a linchpin of ocean ecosystems — a key food source for whales, penguins and other marine life. And yet, Nicol points out, few people would be able to identify these translucent, red-and-green-speckled creatures with feathery appendages. Anyone who has ever nurtured an affection for a species that others find odd or distasteful or unremarkable will understand Nicol’s devotion. His wry and earnest way of describing krill and their ecology will probably draw in those interested in biology or environmental science. As one of the world’s leading experts on krill, Nicol offers an insider’s view of the political negotiations over krill fishing in the Southern Ocean. And yet the book’s conversational (sometimes slightly rambling) style makes you feel as if you’re part of an engaging dinnertime conversation. Nicol chronicles the challenges of estimating krill populations and of studying the complex behavior of an animal too small to tag or track. And he shares plenty of delightful anecdotes. At one point, for instance, his lab amassed the world’s largest collection of whale poop to study whether the cetaceans could fertilize the surface ocean by recycling the nutrient iron picked up through the krill they ate. The answer: probably yes. The book tackles tougher subjects, too. Nicol delves into the threats that Antarctic krill face from fishing — the animals are gathered up for aquaculture feed and also ground into extracts and powders for dietary supplements and medical research — and describes efforts to regulate the industry. He ponders how krill may fare in warming oceans. The critters are resilient, he says, but it’s not clear how quickly these animals, which are known to live as long as about a decade, will adapt to rapidly changing sea temperatures.
Like millions of parents, I post pictures of my kid on Instagram. When she was born, her father and I had a brief conversation about whether it was “dangerous” in a very nebulous sense. Comforted by the fact that I use a fake name on my account, we agreed to not post nudie pics and then didn’t give it much more thought. Until recently.
As she gets older, and privacy on social media dominates the news, I’m revisiting this conversation. Am I invading my daughter’s privacy by sharing her kooky dance moves or epic Nick Nolte hair? Will she feel violated when she’s older? My generation had to contend with mom showing an embarrassing baby photo to our prom date. Is an awkward Instagram picture just today’s equivalent, or does the fact that that the photo can be revisited again and again, by potentially hundreds or even millions of eyes, change things? There’s a growing amount of scholarship on this issue and the results are somewhat comforting: Most kids aren’t opposed to parents sharing pictures of them, but like most human beings, they would like their feelings to be considered. “Ask your kids’ permission, at least sometimes,” says Sarita Schoenebeck, an expert on how families use technology at the University of Michigan in Ann Arbor. “Pay attention to what they do and don’t like and respect that.”
Schoenebeck and her colleagues recently surveyed 331 parent-child pairs to examine both parents’ and children’s preferences about what’s fair game to share on social media. Overall, the kids, who ranged in age from 10 to 17, didn’t mind when parents posted “positive” content, Schoenebeck’s team reported. Kid-approved posts included pictures showing them engaged in hobbies like sports, or depicting a happy family moment. Embarrassing pictures, on the other hand, were not appreciated. (No “naked butt baby pictures,” said one kid). The team reported its findings in 2017 at the Association for Computing Machinery’s Conference on Human Factors in Computing Systems in Denver.
Kids also expressed being aware of their own privacy in ways adults often don’t give them credit for. Photos with potential boyfriends or girlfriends were not acceptable. Content deemed too candid (such as “what they are really like at home” and “private stuff”) was also off-limits.
This self-awareness was reassuring to me. Much of being a kid is playing literal and figurative dress-up; it’s figuring out what’s OK and not OK, personally, as a family member and as a citizen of the world. I’ve worried that today’s online ecosystem might quash the freedom to do this important experimentation. Kids seem to be tuned into this dilemma too. Most parents thought they should probably ask their kid’s permission before posting more often. Indeed, they were right: The kids thought parents should ask for permission more often than they do. Previous work by Schoenebeck is in line with that sentiment: Children were twice as likely as parents to report that adults shouldn’t “overshare” by posting about children online without permission.
The issue of kid privacy extends beyond posting pictures, notes computer security and privacy expert Franziska Roesner. “Until what age do you track location on their phone, or even use the camera function on a baby monitor?” says Roesner, of the University of Washington in Seattle. “It’s an evolving space without clear answers.”
It’s too early to say how kids growing up in the current technology climate will feel about their parents’ sharing in hindsight. But a small study by Schoenebeck offers some insight. The researchers asked college students to reflect on their own potentially embarrassing teenage Facebook posts. The students valued the authenticity of their own historical content even if it was potentially embarrassing, Schoenebeck says. As one study participant put it: “When I look at [my old content], it’s kind of like ugh, like ‘yikes!’ [But] if someone finds it I’ll just be like, ‘yeah, I had a thing with song lyrics as my status when I was 15 years old. Get over it.’”
But just because kids didn’t mind their teenage posts surviving online, that doesn’t mean they won’t mind what you post about them. My daughter isn’t old enough yet to say, “You’re not the boss of me.” But I know that time is coming. Before that happens, I plan to start asking her permission about what I post about her and give her the option of deleting old posts.
Given the myriad other concerns parents have about kids and social media — from bullying to body image issues to what potential employers or colleges might see — asking our kids’ permission about what we share seems like an easy, thoughtful step to take.
Laura Sanders is away on maternity leave. Rachel Ehrenberg is a Boston-based science journalist and former reporter at Science News, with degrees in botany and evolutionary biology. She has raised many plants and is now trying to raise a human being.
