ORLANDO, Fla. — Interbreeding with Neandertals restored some genetic heirlooms that modern humans left behind in the ancient exodus from Africa, new research suggests.

Those heirlooms are versions of genes, or alleles, that were present in humans’ and Neandertals’ shared ancestors. Neandertals carried many of those old alleles, passing them along generation after generation, while developing their own versions of other genes. A small number of humans left Africa around 100,000 years ago and settled in Asia and Europe. These migrants “lost” the ancestral alleles.
But when the migrants or their descendants interbred with Neandertals, Eurasians reinherited the ancestral heirlooms along with Neandertal DNA, John “Tony” Capra reported October 20 at the annual meeting of the American Society of Human Genetics.

Present-day Europeans have more than 47,000 of these reintroduced ancestral alleles, and East Asians — who have more Neandertal ancestry than Europeans (SN Online: 2/12/15) — carry more than 56,000, said Capra, an evolutionary geneticist at Vanderbilt University in Nashville.

Capra and others have evidence that Neandertal versions of genes make humans more prone to some diseases (SN: 3/5/16, p. 18). Of the thousands of ancestral variants reintroduced into modern humans, only 41 have been linked in genetic studies to diseases, such as skin conditions and neurological and psychiatric disorders, he said. The researchers can’t tell for sure whether the effect is from the ancestral variant or neighboring Neandertal DNA. Capra and Vanderbilt colleague Corinne Simonti’s analyses indicate that the Neandertal DNA is more likely to blame. Many of the ancestral alleles are still present in modern-day Africans, Capra said, “so they’re unlikely to be very, very bad.”

Earth may not provide the best blueprint for how rocky planets are born.

An analysis of planets outside the solar system suggests that most hot, rocky exoplanets started out more like gassy Neptunes. Such planets are rocky now because their stars blew their thick atmospheres away, leaving nothing but an inhospitable core, researchers report in a paper posted online October 15 at arXiv.org. That could mean these planets are not as representative of Earth as scientists thought, and using them to estimate the frequency of potentially life-hosting worlds is misleading.
“One of the big discoveries is that Earth-sized, likely rocky planets are incredibly common, at least on hotter orbits,” says planetary scientist Eric Lopez of NASA’s Goddard Space Flight Center in Greenbelt, Md., who wasn’t involved in the study. “The big question is, are those hot exoplanets telling us anything about the frequency of Earthlike planets? This suggests that they might not be.”

Observations so far suggest that worlds about Earth’s size probably cluster into two categories: rocky super-Earths and gaseous mini-Neptunes (SN Online: 6/19/17). Super-Earths are between one and 1.5 times as wide as Earth; mini-Neptunes are between 2.5 and four times Earth’s size. Earlier work showed that there’s a clear gap between these planet sizes.

Because planets that are close to their stars are easier for telescopes to see, most of the rocky super-Earths discovered so far have close-in orbits — with years lasting between about two to 100 Earth days — making the worlds way too hot to host life as we know it. But because they are rocky like Earth, scientists include these worlds with their cooler brethren when estimating how many habitable planets might be out there.

If hot super-Earths start out rocky, perhaps it is because the worlds form later than their puffy mini-Neptune companions, when there’s less gas left in the growing planetary system to build an atmosphere. Or, conversely, such planets, along with mini-Neptunes, may start with thick atmospheres. These rocky worlds may have had their atmospheres stripped away by stellar winds.
Now, exoplanet astronomer Vincent Van Eylen of Leiden University in the Netherlands and his colleagues have shown that the fault is in the stars. “You really have these two populations, and the influence of the star is what creates this separation,” Van Eylen says. That result could warn astronomers not to rely too heavily on these hot, rocky worlds when calculating how many habitable planets are likely to exist.

To measure the planets’ sizes, astronomers need to know the sizes of their stars. Van Eylen and colleagues analyzed 117 planets whose host stars’ sizes had been measured using astroseismology. This technique tracks how often the star’s brightness changes as interior oscillations ripple through it, and uses the frequency to determine its size.

“Think of the stars as musical instruments,” Van Eylen says. A double bass and a violin produce sound the same way, but the pitch is different because of the instrument’s size. “It’s exactly the same thing with stars.”

The researchers then calculated the planets’ sizes — between one and four times the Earth — with about four times greater precision than in previous studies. As expected, the planets clustered in groups of around 1.5 and 2.5 times Earth’s radius, leaving a gap in the middle.

Next the team looked at how the planets’ sizes changed with distance from the host star. Planets that were rocky from the start should be smaller close to the stars, where studies of other young star systems suggest there should have been less material available when these planets were forming. But if proximity to a star’s winds is key, there should be some larger rocky worlds closer in, with smaller gaseous worlds farther out.

Van Eylen’s planets matched the second picture: The largest of the rocky planets nestled close to the stars were bigger than the distant ones. That suggests the rocky planets once had atmospheres, and lost them.

“It’s not fair to take the close-in planets and assume that the more distant planets are just like them,” says exoplanet astronomer Courtney Dressing of the University of California, Berkeley. “You might be fooling yourself.”

Kleptopredation
klep-toe-preh-day-shun n.
A food-gathering strategy of eating an organism and the meal it just ate.

A wily sea slug has a way to get two meals in one: It gobbles up smaller predators that have recently gulped in their own prey.

“Kleptopredation” is the term Trevor Willis of the University of Portsmouth in England and his colleagues propose for this kind of food theft by well-timed predation.

Researchers knew that the small Mediterranean nudibranch Cratena peregrina, with a colorful mane of streamers rippling off its body, climbs and preys on pipe cleaner‒skinny, branched colonies of Eudendrium racemosum hydroids, which are distant relatives of corals. The nudibranchs devour the individual hydroid polyps and, new tests show, prefer them well fed.
In experimental buffets with fed or hungry polyps, the nudibranchs ate faster when polyps were fat with just-caught plankton. In this way, at least half of a nudibranch’s diet is plankton. This quirk explains why some biochemical signatures that distinguish predators from prey don’t work out clearly for nudibranchs and hydroids, the researchers report November 1 in Biology Letters.

A weird echo of this meal-stealing strategy shows up in certain jumping spiders. The arachnids don’t have the biology to drink vertebrate blood themselves. Instead, they catch a lot of female mosquitoes that have just tanked up (SN: 10/15/05, p. 246).

When you lock eyes with a baby, it’s hard to look away. For one thing, babies are fun to look at. They’re so tiny and cute and interesting. For another, babies love to stare back. I remember my babies staring at me so hard, with their eyebrows raised and unblinking eyes wide open. They would have killed in a staring contest.

This mutual adoration of staring may be for a good reason. When a baby and an adult make eye contact, their brain waves fall in sync, too, a new study finds. And those shared patterns of brain activity may actually pave the way for better communication between baby and adult: Babies make more sweet, little sounds when their eyes are locked onto an adult who is looking back. The scientists report the results online November 28 in the Proceedings of the National Academy of Sciences.

Psychologist Victoria Leong of the University of Cambridge and Nanyang Technological University in Singapore and colleagues invited infants into the lab for two experiments. In the first, the team outfitted 17 8-month-old babies with EEG caps, headwear covered with electrodes that measure the collective behavior of nerve cells across the brain. The infants watched a video in which an experimenter, also outfitted in an EEG cap, sung a nursery rhyme while looking either straight ahead at the baby, at the baby but with her head turned at a 20-degree angle, or away from the baby and with her head turned at a 20-degree angle.
When the researcher looked at the baby (either facing the baby or with her head slightly turned), the babies’ brains responded, showing activity patterns that started to closely resemble those of the researcher.

The second experiment moved the test into real life. The same researcher from the video sat near 19 different babies. Again, both the babies and the researcher wore EEG caps to record their brain activity. The real-life eye contact prompted brain patterns similar to those seen in the video experiment: When eyes met, brain activity fell in sync; when eyes wandered, brain activity didn’t match as closely.

The baby’s and the adult’s brain activity appeared to get in sync by meeting in the middle. When gazes were shared, a baby’s brain waves became more like the researcher’s, and the researcher’s more like the baby’s. That finding is “giving new insights into infants’ amazing abilities to connect to, and tune in with, their adult caregivers,” Leong says.

What are simpatico brain waves actually good for, you might ask? Well, researchers don’t know exactly, but they have some ideas. When high school students’ brain waves were in sync with one another, the kids reported being more engaged in the classroom, a recent study found. And when two adults reach a mutual understanding, their brains synchronize, too, says another study. These findings hint that such synchronization lets signals flow easily between two brains, though Leong says that much more research needs to be done before scientists understand synchronization’s relevance to babies’ communication and learning.
That easy signal sending is something that happened between the babies and the adult, too. When the experimenter was looking at the babies, the babies made more vocalizations. And in turn, these sweet sounds seemed to have made the experimenter’s brain waves even more similar to those of the babies.

It’s a beautiful cycle, it seems, when eyes and brains meet. And that meeting spot is probably where some interesting learning happens, for both adult and baby.

NEW ORLEANS — Jupiter’s Great Red Spot has deep roots. Data from the first pass of NASA’s Juno spacecraft over the incessant storm show that its clouds stretch at least 350 kilometers down into the planet’s atmosphere. That means the storm is about as deep as the International Space Station is high above the Earth.

Juno has been orbiting Jupiter since July 4, 2016, and it made its first close flyby of the red spot about a year later (SN Online: 7/7/17). As the spacecraft swooped 9,000 kilometers above the giant storm, Juno’s microwave radiometer peered through the deep layers of cloud, measuring the atmosphere’s temperature down hundreds of kilometers.
“Juno is probing beneath these clouds, and finding the roots of the red spot,” Juno co-investigator Andrew Ingersoll of Caltech said December 11 at a news conference at the American Geophysical Union’s fall meeting. Cheng Li of Caltech presented the research at AGU on December 12.
The radiometer probes different layers of the atmosphere by measuring the gas in six different microwave wavelengths. Ingersoll and his colleagues found that the gas beneath the red spot’s surface gets warmer with depth, and a warm zone at the same location as the spot was visible down to 350 kilometers
The fact that the 16,000-kilometer-wide spot is warmer at the bottom than at the top could help explain the storm’s screaming wind speeds of about 120 meters per second. Warm air rises, so the internal heat could provide energy to churn the storm.

Juno principal investigator Scott Bolton of the Southwest Research Institute in San Antonio notes that the spot “goes as deep as we can see,” but it could go deeper. “I’m not sure we’ve established the true foot,” he says. On a future flyby, Juno will try to use gravity data to detect the storm at depths of thousands of kilometers. If the spot does go down that deep, theorists will struggle to explain why, Bolton says.

The only previous data on Jupiter’s interior came from the Galileo spacecraft, which ended its mission by entering Jupiter’s atmosphere at a single point in 1995. “I like to say that if aliens sent a probe to Earth and it landed in the Sahara, they would conclude the Earth is all desert,” says planetary scientist Michael Wong of Caltech, who was not involved in the new study. “Juno getting this global view gives us a new understanding of the inner workings … We have never really seen the interior of a giant planet in this way before.”

NEW ORLEANS — For the first time, scientists have definitively linked human-caused climate change to extreme weather events.

A handful of extreme events that occurred in 2016 — including a deadly heat wave that swept across Asia — simply could not have happened due to natural climate variability alone, three new studies find. The studies were part of a special issue of the Bulletin of the American Meteorological Society, also known as BAMS, released December 13.
These findings are a game changer — or should at least be a conversation changer, Jeff Rosenfeld, editor in chief of BAMS, said at a news conference that coincided with the studies’ release at the American Geophysical Union’s annual meeting. “We can no longer be shy about talking about the connection between human causes of climate change and weather,” he said.

For the last six years, BAMS has published a December issue containing research on extreme weather events from the previous year that seeks to disentangle the role of anthropogenic climate change from natural variability. The goal from the start has been to find ways to improve the science of such attribution, said Stephanie Herring of the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information in Boulder, Colo., who was lead editor of the latest issue.

To date, BAMS has published 137 attribution studies. But this is the first time that any study has found that a weather event was so extreme that it was outside the bounds of natural variability — let alone three such events, Herring said.

Story continues below map
In addition to the Asia heat wave, those events were the record global heat in 2016 and the growth and persistence of a large swath of high ocean temperatures, nicknamed “the Blob,” in the Bering Sea off the coast of Alaska. The unusually warm waters, which lingered for about a year and a half, have been linked to mass die-offs of birds, collapsed codfish populations in the Gulf of Alaska and altered weather patterns that brought drought to California.

Many of the other 24 studies in the new issue found a strong likelihood of human influence on extreme weather events, but stopped short of saying they were completely out of the realm of natural variability. One study found that an already strong El Niño in 2016 was probably enhanced by human influence, contributing to drought and famine conditions in southern Africa. Another reported that greenhouse gas–driven warming of sea surface temperatures in the Coral Sea was the main factor driving an increase in coral bleaching risk along the Great Barrier Reef. But not all of the studies linked 2016’s extreme events to human activity. Record-breaking rainfall in southeastern Australia between July and September, for example, was due to natural variability, one study found.

With hurricanes, wildfires and drought, 2017 is chock-full of extreme event candidates for next year’s crop of BAMS attribution studies. Already, the likelihood of human influence on the extreme rainfall from Hurricane Harvey is the subject of three independent studies, two of which were also presented at the American Geophysical Union meeting. The storm dropped about 1.3 meters of water on Houston and its surrounding areas in August. The three studies, discussed in a separate news conference December 13, found that human influence probably increased the hurricane’s total rainfall, by anywhere from at least 15 percent to at least 19 percent.

Story continues below image
“I think [the BAMS studies] speak to the profound nature of the impacts we’re now seeing,” says Michael Mann, a climate scientist at Penn State who was not involved in any of the studies. But Mann says he’s concerned that many researchers are too focused on quantifying how much human influence was responsible for a particular event, rather than how human influence affects various processes on the planet. One example, he notes, is the established link between rising temperatures and increased moisture in the atmosphere that is also implicated in Hurricane Harvey’s extreme rainfall.

Another possible issue with attribution science, he says, is that the current generation of simulations simply may not be capable of capturing some of the subtle changes in the climate and oceans — a particular danger when it comes to studies that find no link to human activities. It’s a point that climate scientist Andrew King of the University of Melbourne in Australia, who authored the paper on Australia’s rainfall, also noted at the news conference.

“When we find no clear signal for climate change, there might not have been a human influence on the event, or [it might be that] the particular factors of the event that were investigated were not influenced by climate change,” he said. “It’s also possible that the given tools we have today can’t find this climate change signal.”

Rosenfeld noted that people tend to talk about the long odds of an extreme weather event happening. But with studies now saying that climate change was a necessary condition for some extreme events, discussions about long odds no longer apply, he said. “These are new weather extremes made possible by a new climate.”

The neutron star collision heard and seen around the world has failed to fade. That lingering glow could mean that a jet of bright matter created in the crash has diffused into a glowing, billowy cocoon that surrounds the merged star, researchers report online December 20 in Nature.

Gravitational waves from the collision between two ultradense stellar corpses was picked up in August by the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, and its sister experiment in Italy, Advanced Virgo (SN: 11/11/17, p. 6). Using telescopes on the ground and in space, physicists raced to conduct follow-up observations, and found that the collision released light across the electromagnetic spectrum.
Right away, the event looked unusual, says astrophysicist Kunal Mooley, who conducted the research while at the University of Oxford. Physicists think that a jet of fast-moving, bright material blasts out of the center of neutron star collisions. If that jet is aimed directly at Earth, telescopes can see it as an ephemeral flash of light called a short gamma-ray burst, or GRB.
But the gamma-ray signals produced by the August collision were 10,000 times less bright than those seen in other detected short gamma-ray bursts. Even stranger, X-rays and radio waves from the event didn’t appear until about 16 days after the collision. Most short gamma-ray bursts are visible in X-rays and radio waves right away and fade over time.
Astronomers thought those oddities meant the jet was facing slightly away from Earth and expected the light to fade quickly. But Mooley and colleagues continued tracking the glow with three radio telescope arrays on three continents for more than 100 days after the collision. Radio wave emissions continued to brighten for at least 93 days, and are still visible now, the team found. (X-rays were temporarily blocked when the neutron star moved behind the sun from Earth’s perspective.)

“This thing continues to rise, instead of fading into oblivion as we expected,” says astrophysicist Wen-fai Fong of Northwestern University in Evanston, Ill., who was not involved in the new study.

The finding may mean that astronomers are seeing a new kind of gamma-ray burst. Mooley and colleagues suggest that the rise in radio wave emissions could be explained if the jet slammed into a shell of neutron-rich material kicked out in the neutron star crash, transferring most of its energy to that debris and smothering the jet. That extra energy could create a glowing cocoon that keeps radiating far longer than the original blast.

The new result is “really challenging our understanding of what physics is happening from this merger,” Fong says. But, she adds, “the jury is still out on whether this is the same as the short GRBs we’ve seen over the past decade, or whether it’s something completely different,” such as a luminescent cocoon. She and her colleagues also took radio wave observations of the merged stars in the first 100 days after the collision. The team is preparing a paper with a different interpretation that includes a jet emerging from the wreckage later, she says.

Other explanations for the lingering light are possible, Mooley acknowledges. Future detections “will give us an opportunity to really study … what fraction of neutron star mergers give rise to [short] GRBs and what fraction give rise to other phenomena and explosions that we haven’t seen so far in our universe,” he says.

2017 revealed some surprising biology of organisms large and small, from quick-dozing elephants to sex-changing lizards and carbon-dumping sea creatures.

Switch it up
Toasty temperatures trump genetics when it comes to the sex of a bearded dragon lizard. Now researchers have found how RNA editing helps turn overheated male embryos into females (SN Online: 6/14/17).

Homegrown
Giant larvaceans don’t have noses, but they sure know how to blow snot bubbles. The sea invertebrates live in disposable “mucus houses” that, based on recent observations, collect food fast. When these larvaceans ditch a dirty house and “sneeze” themselves a new one, they might send a lot of carbon to the deep sea (SN: 6/10/17, p. 13).

Blood and guts
Antarctic-dwelling sea spiders use their long legs for more than creepy-crawling below the ice. Stretches of digestive tract in the creatures’ legs do double duty — not only digesting meals, but also pumping an arthropod version of blood and oxygen through the rest of the body (SN: 2/4/17, p. 13).

Fluorescent fashion
South American polka dot tree frogs are the first amphibians known to naturally fluoresce. The frogs’ intense blue-green glow might play a role in complex courtship and fighting behaviors, biologists propose (SN: 4/15/17, p. 4).

Brainless beauty sleep
Upside-down jellyfish are the first brainless animals known to catch some z’s, lab experiments suggest (SN: 10/28/17, p. 10). The finding raises new questions about when and why sleep evolved.

Pachyderm power nap
For some wild elephants, a good night’s sleep ends soon after it starts. Electronic monitoring of two African elephants found that the animals snooze about two hours per day — the shortest sleep requirement recorded for mammals (SN: 4/1/17, p. 10).

Heads up
Chop off a hydra’s head, and two more grow in its place — or so the ancient Greek myth goes. By fiddling with the cytoskeletons of real-life hydras, researchers found that the pond polyps rely on mechanical forces as well as molecular cues to regenerate head and tentacles in the right places (SN: 3/4/17, p. 19).

Balancing act
Flamingos may be more stable standing on one leg than two, especially when asleep, researchers reported (SN: 6/24/17, p. 15). The blushing bird’s center of gravity is located near its tucked-in knee, which helps with stability. A one-legged stance requires little muscular effort, the scientists say, but others caution that it may not be an energy saver.

Ultimate survivor
Tardigrades are known for withstanding extreme temperatures, intense radiation and even the vacuum of space. Those adaptations could help this hardy lineage survive until Earth is engulfed by the sun in several billion years, researchers estimate (SN Online: 7/14/17). An analysis of the microscopic water bears’ genetic blueprints offers clues to their survival strategies, and challenges claims that tardigrades are extreme gene swappers (SN: 8/19/17, p. 13).

Paint it blue
Scientists borrowed a gene each from Canterbury bells and butterfly peas to breed the world’s first true blue chrysanthemums. The method could be used to give other flower species the blues (SN: 8/19/17, p. 12).

Corals are in hot water.

Severe bleaching events are hitting coral reefs five times as often as in 1980, researchers report in the Jan. 5 Science.

Scientists surveyed 100 coral reef locations in tropical zones around the world, tracking each spot’s fate from 1980 to 2016. At first, only a few of the locations had experienced bleaching. But by 2016, all had been hit by at least one bleaching event, and all but six had suffered a severe event — defined as affecting more than 30 percent of corals in an area.
The median time between pairs of severe bleaching events has also decreased, the researchers found — it’s now just under six years, versus 25 to 30 years in the early 1980s. That’s not enough time for corals to fully bounce back before getting hit again.

Consistently higher tropical water temperatures, the result of climate change, are in part to blame for the increase in bleaching, researchers say. Warm water stresses corals and strips away their symbiotic algae — their main source of food and the reason they’re colorful. Bleaching episodes can be fatal, especially if corals can’t recover between events.

In the past, major bleaching events were most likely to happen when El Niño brought bands of warmer water to the tropics. But sea surface temperatures in tropical areas are now warmer during today’s La Niña years (when the water is typically cooler) than during El Niño events 40 years ago, says study coauthor Terry Hughes, a coral researcher at James Cook University in Townsville, Australia. Because those temperatures continue to rise, “we have a narrowing window of opportunity to save reefs,” he says.

It was one of the flashiest mysteries in the news about a decade ago — honeybee workers were vanishing fast for no clear reason. To this day, that puzzle has never been entirely solved, researchers acknowledge.

And maybe it never will be. Colony collapse disorder, or CCD, as the sudden mass honeybee losses were called, has faded in recent years as mysteriously as it began. It’s possible the disappearances could start up again, but meanwhile bees are facing other problems.
CCD probably peaked around 2007 and faded since, says Jeff Pettis, who during the heights of national curiosity was running the Beltsville, Md., honeybee lab for the U.S. Department of Agriculture’s research wing. And five years have passed since Dennis vanEngelsdorp, who studies bee health at the University of Maryland in College Park, has seen a “credible case” of colony collapse.

Beekeepers still report some cases, but Pettis and vanEngelsdorp aren’t convinced such cases really are colony collapse disorder, a term that now gets used for a slew of things that are bad for bees. To specialists, colony collapse is a specific phenomenon. An apparently healthy colony over the course of days or a few weeks loses much of its workforce, while eggs and larvae, and often the queen herself, remain alive. Also food stores in collapsing colonies don’t get raided by other bees as a failing colony’s treasures usually do.

“I think I know what happened,” says Pettis, now in Salisbury, Md., consulting on pollinator health. His proposed scenario for CCD, like those of some other veterans of the furor, is complex and doesn’t rest on a single exotic killer. But so far, no experiment has nailed the proof.
Looking back, Pettis realizes he had heard about what might have been early cases of CCD, described as colonies “just falling apart,” for several years before the phenomenon made headlines. Then in November 2006, Pennsylvania beekeeper David Hackenberg, as usual, sent his colonies to Florida for the winter. They arrived in fine shape. Soon after, however, many buzzing colonies had shrunk to stragglers. Yet there were no dire parasite infestations and no dead bee bodies in sight.

“It was, ‘OK, something weird just happened,’ ” remembers Jay Evans of the USDA’s honeybee lab in Beltsville. “It looked like a ‘flu,’ something that kind of swept through miraculously fast.”

No single menace, however, could be tightly linked to every sick colony, or only to sick colonies. Varroa mites, small hive beetles, Nosema fungi, deformed wing virus, unusual signs of pesticide exposure, for instance —screening techniques at the time just weren’t picking up a clear pattern in any of these bee bedevilments.

“People were following this story like crazy,” Pettis says. The bees’ unexplained plight prompted a national outbreak of amateur entomology. “There were people saying, ‘Why aren’t you doing more with jet contrails?’ There were ‘alien abductions.’ And the rapture — the bees were being called home.”

Entomologists were hounded by the press, not to mention leaned on by politicians and pursued by would-be entrepreneurs. “For me, what made it rewarding,” Pettis says, “was that people were learning about the value of pollination.”
A Columbia University researcher who had identified pathogens in mysterious human disease outbreaks took a crack at the problem. Ian Lipkin had never worked with bees, but he and his lab collaborated with entomologists and other bee specialists to search for any genetic signature of a pathogen appearing only in collapsing colonies. The approach of searching through mass samples, with their messy traces of gut microbes and random parasites, is now familiar as metagenomics. At the time, this way of searching for pathogens was groundbreaking, says collaborator Diana Cox-Foster, then at Penn State. The resulting paper, in Science , pointed to several viruses, especially the previously obscure Israeli Acute Paralysis Virus , or IAPV ( SN: 9/8/07, p. 147 ).
That emphasis on IAPV, which got a lot of attention at the time, hasn’t held up well. “It’s not 100 percent ruled out,” Evans says. But the explanation’s main problem is shared by other threats proposed as a single cause of CCD. After finding IAPV or another presumed single menace in sick bees in one place, he says, “you could go to other apiaries that were collapsing and not find it, or you could find it in healthier colonies.”

As an apiary inspector for Pennsylvania at the time, vanEngelsdorp monitored for signs of collapse in over 200 hives. “We tried to watch it happen but we couldn’t,” he says. None collapsed. Even finding the sickest bees in collapsing colonies was a challenge. Doomed bees presumably flew off in multiple directions, and birds or other scavengers usually found the bees before scientists could.

A gang of killers
Pettis now sees the disaster as a two-step process. Various stressors such as poor nutrition and pesticide exposure weakened bees so much that a virus, maybe IAPV, could quickly kill them in droves. Evans, too, sees various stressors mixing and matching. When pressed for his best guess, he says “all of the above.”

Cox-Foster has managed to re-create part of the process, the vanishing effect that marked the end for stressed bees. When she infected honeybee colonies in a greenhouse with a virus, the sick bees left the hive but were trapped by the greenhouse walls before dispersing too far to be found. (Of course, this experiment doesn’t demonstrate how colonies with no sign of a virus died.)

That tendency for sick bees to leave hives, vanEngelsdorp proposes, could have developed as a hygiene benefit. “Altruistic suicide,” as social-insect biologists call it. Flying away from the colony could minimize a sick bee’s tendency to pass disease to the rest of the family.
Today, hive losses remain high even with CCD waning or gone, according to national surveys by the Bee Informed Partnership, a nonprofit bee health collaboration. Beekeepers typically note that they either expect or can tolerate annual losses between 15 and 20 percent of their total number of colonies. Yet from April 2016 until March 2017, losses across the United States ran at about a third of hives. And that was a so-called good year, the second-lowest loss in the seven years with data on annual losses.

Classic CCD may not be much threat these days, but the “four p’s” — poor nutrition, pesticides, pathogens and parasites — are, says Cox-Foster, now at a USDA lab for pollinating insects in Logan, Utah. While honeybees aren’t likely to go extinct, these threats to the beekeeping industry boost pollination costs, which could affect food prices.

Coping with the four p’s may not fire the imaginations of armchair entomologists. But it’s more than enough of a challenge for the bees.