When asked the right way, a savvy bird species steers African hunter-gatherers to honey. All it takes is a loud trill followed by a grunt that sounds like “brrr-hm.”

Birds known as greater honeyguides (Indicator indicator) lead hunter-gatherers in Mozambique to honey-rich bees’ nests after hearing humans make this signature call, say evolutionary ecologist Claire Spottiswoode of the University of Cambridge and her colleagues. In exchange, the birds get human-aided access to perilous-to-reach food, the scientists report in the July 22 Science.

The new study provides the first solid evidence of two-way, collaborative communication between humans and a nonhuman animal in the wild. In some parts of the world, dolphins help fishermen herd fish into nets. But it’s unclear whether these dolphins respond to specific calls from fishermen.

Honeyguides associate Yao hunter-gatherers’ distinctive honey-hunting call with successful joint food hunts, Spottiswoode says. The birds respond to this call by making a loud chattering sound to alert humans to their presence. Honeyguides then fly from tree to tree until reaching one with a bees’ nest.
Although the wax-eating birds regularly scope out locations of bees’ nests in their home ranges, getting beeswax out of nests is dangerous. “Angry bees can and do sting honeyguides to death,” Spottiswoode says.

Yao honey hunters cut down trees containing bees’ nests nestled high up in crevices and smoke the insects out with flaming bundles of twigs and leaves. After removing honeycombs from nests, the Yao leave beeswax behind for their avian helpers and even put wax chunks on beds of leaves to reward honeyguides.

Written accounts of honeyguide-led expeditions to bees’ nests date to as early as 1588. But ax-like stone implements and human-made fires date to 1 million years ago or more (SN: 7/9/16, p. 10). So humans and honeyguides may have hunted together for at least that long, says Harvard University biological anthropologist Richard Wrangham.

In different parts of Africa, honeyguides respond to local honey-hunting calls of human groups, Spottiswoode suspects. A team led by Yale University biological anthropologist Brian Wood has found that Hadza honey hunters in Tanzania make a whistling sound to attract honeyguides. Other hunter-gatherers speak or shout words to call honeyguides, Wood says.
Unlike Yao honey hunters, the Hadza bury or burn much of the wax in bees’ nests. Hadza honey seekers believe this keeps honeyguides hungry and motivates them to lead further hunts. Wood’s team estimates that 8 to 10 percent of the Hadza’s diet comes from honeyguide-led hunts.

The new study “carefully documents one cultural tradition in how people and honeyguides interact,” Wood says.
Spottiswoode’s group conducted fieldwork in October 2013 and September and October 2015. The researchers tracked movements of six honeyguides fitted with radio transmitters. Overall, 73 of 97 bird-led honey hunts found at least one bees’ nest. During the study, nearly three-quarters of 149 bees’ nests found by the Yao involved honeyguide assistance.

In another experiment, Spottiswoode accompanied two Yao honey hunters on 72 searches for bees’ nests, each lasting 15 minutes. While they walked, a portable speaker played recordings every seven seconds either of a Yao honey hunter making the “brrr-hm” sound, a Yao individual saying words such as “honeyguide” or their own name, or a ring-necked dove’s song or excitement call.

Honeyguides joined 30 experimental searches. About two-thirds of searches that featured “brrr-hm” calls drew honeyguides’ assistance (although they did not always locate a bees’ nest). One-quarter of hunts that used recordings of words and one-third of those that played dove sounds received honeyguides’ help.

Spottiswoode’s team calculates that honey hunters who played the “brrr-hm” sound more than tripled their chances of actually finding a bees’ nest during 15-minute searches, compared with honey hunters who played Yao words or dove sounds.

Spottiswoode and Wood plan to investigate whether young honeyguides learn from adult birds to pay attention to humans’ honey-hunting calls and to lead humans to bees’ nests.

A large study of human genetic variation finds more than 7 million spots where one person’s DNA can differ from another’s. Analyses of such variants, compiled from cataloging the genes from more than 60,000 people, are already offering doctors helpful insights into diseases such as schizophrenia and some heart conditions.

Researchers from the Exome Aggregation Consortium first presented their analysis of the ExAC database online at bioRxiv.org last year (SN: 12/12/15, p. 8). Now, the project is getting its official debut in the Aug. 18 Nature.
An exome is just the protein-producing genes in a person’s genetic instruction book, or genome. Researchers from nearly two dozen studies around the world pooled exome data they had collected from 60,706 people, nearly 10 times more data than any previous study of human genetic variation. The people in the study were far more racially and ethnically diverse than any previous study as well, and included both people with various diseases and healthy people.

Any one person carries tens of thousands of DNA variants, said Daniel MacArthur, a geneticist at Massachusetts General Hospital in Boston, in a telephone press briefing. The ExAC team found that, on average, one in every eight DNA bases (the information-encoding chemical building blocks of DNA) differs among people. In total, the researchers recorded more than 7.4 million DNA variants, most of them changes in single DNA bases.

ExAC researchers released the data in 2014 for other scientists to use. Already these data have contributed to the day-to-day interpretation of genetic information in the clinic, says Eliezer Van Allen, a medical oncologist at Harvard Medical School. “It gives a new look into the drivers of human genetic diversity.”

A companion paper published August 17 in Nature Genetics, for instance, found that people are missing some genes or have extra copies of other genes. On average, people have 0.81 deleted genes and 1.75 duplicated genes. The analysis echoed previous studies in showing that people with schizophrenia are more likely to have such missing or duplicated genes, particularly genes important in the brain.
It’s a relief to researchers that the paper confirms the results of previous schizophrenia studies, says Jennifer Mulle, a psychiatric geneticist at Emory University in Atlanta who was not involved in the work. “We all breathe a collective sigh of relief that this thing we thought to be true continues to be true,” she says.
Now, the challenge is to figure out what all of the variations mean.

Two independent studies suggest that the ExAC data could give doctors and researchers a clearer picture of the gene changes that contribute to heart conditions known as cardiomyopathies.

As DNA sequencing studies, which decipher people’s genetic makeup, became more common in the last 10 years, researchers amassed a growing number of rare DNA variants implicated in causing the heart diseases. “There was always a lot of doubt cast about whether these [variants] were real or not,” says Roddy Walsh, a geneticist at Imperial College London.

Walsh and colleagues used the ExAC data and DNA data from 7,855 cardiomyopathy patients to reevaluate the likelihood that a particular variant would cause a heart problem. Finding a variant in heart patients that is rarely seen in people without the disease suggests the variant could be causing the disease. But if the variant appears just as often in the general population that don’t have cardiomyopathies as in patients, it is unlikely to cause disease.

Of the people in ExAC, 11.7 percent carry variants associated with hypertrophic cardiomyopathy, Walsh and colleagues report August 17 in Genetics in Medicine. That’s far more people than expected for a rare inherited heart condition, which strikes about one in 500 people. Those data and other evidence suggest that many of the variants implicated in the disease are actually benign, the researchers say.

ExAC data alone aren’t enough to rule out a potentially disease-causing variant, says Benjamin Meder, a cardiologist at Heidelberg University Hospital in Germany. Researchers don’t know the full medical history of the ExAC volunteers. Some may have undetected cases of cardiomyopathy, or others may have been misdiagnosed as having the disease, which could throw off the results, he says. It’s important to clearly define who has a disease and who doesn’t before conducting genetic studies, Meder says. “This paper does it the wrong way around.” Still, he says the study does offer some valuable insights into the genetics of heart problems.

Misdiagnosing a genetic disease can negatively affect entire families, says Isaac Kohane, a biomedical informaticist at Harvard Medical School. For instance, people related to a young person who collapses on the basketball court and is found to carry a rare variant associated with the heart condition may also be screened for the genetic variant. Family members carrying the disease-associated variant may be treated for a condition they don’t have.

Such misdiagnosis is much more likely for African-Americans, Kohane and colleagues report August 17 in the New England Journal of Medicine. Five variants previously associated with hypertrophic cardiomyopathy kept popping up again and again in the general population most of whom do not have the heart condition, Kohane’s team found. Those variants are far too common to cause a rare genetic disorder; 2.9 to 27.1 percent of black Americans were found to carry at least one copy of the variants, while 0.02 to 2.9 percent of white Americans had one of the variants.

Kohane and colleagues now say the variants are benign. The mistake could have been avoided if researchers had included even a few black Americans in their studies, most of which involved people of European descent who carry only a fraction of the genetic diversity found people with recent African ancestry. The researchers calculate that the ExAC data, with its great genetic diversity, could rule out many benign variants including ones carried by 0.1 percent of the population.

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.

SAN ANTONIO — The world’s earliest alphabet, inscribed on stone slabs at several Egyptian sites, was an early form of Hebrew, a controversial new analysis concludes.

Israelites living in Egypt transformed that civilization’s hieroglyphics into Hebrew 1.0 more than 3,800 years ago, at a time when the Old Testament describes Jews living in Egypt, says archaeologist and epigrapher Douglas Petrovich of Wilfrid Laurier University in Waterloo, Canada. Hebrew speakers seeking a way to communicate in writing with other Egyptian Jews simplified the pharaohs’ complex hieroglyphic writing system into 22 alphabetic letters, Petrovich proposed on November 17 at the annual meeting of the American Schools of Oriental Research.
“There is a connection between ancient Egyptian texts and preserved alphabets,” Petrovich said.

That’s a highly controversial contention among scholars of the Bible and ancient civilizations. Many argue, despite what’s recounted in the Old Testament, that Israelites did not live in Egypt as long ago as proposed by Petrovich. Biblical dates for the Israelites’ stay in Egypt are unreliable, they say.
Scholars have also generally assumed for more than 150 years that the oldest alphabetic script Petrovich studied could be based on any of a group of ancient Semitic languages. But not enough is known about those tongues to specify one language in particular.
Petrovich’s Hebrew identification for the ancient inscriptions is starved for evidence, said biblical scholar and Semitic language specialist Christopher Rollston of George Washington University in Washington, D.C. There is no way to tell which of many Semitic languages are represented by the early alphabetic system, Rollston contended.

The origins of writing in different parts of the world — including that of the alphabet carved into the Egyptian slabs — have long stimulated scholarly debates (SN: 3/6/93, p. 152). A German scholar identified the ancient Egyptian writing as Hebrew in the 1920s. But he failed to identify many letters in the alphabet, leading to implausible translations that were rejected by researchers.

Petrovich says his big break came in January 2012. While conducting research at the Egyptian Museum in Cairo, he came across the word “Hebrews” in a text from 1874 B.C. that includes the earliest known alphabetic letter. According to the Old Testament, Israelites spent 434 years in Egypt, from 1876 B.C. to 1442 B.C.
Petrovich then combined previous identifications of some letters in the ancient alphabet with his own identifications of disputed letters to peg the script as Hebrew. Armed with the entire fledgling alphabet, he translated 18 Hebrew inscriptions from three Egyptian sites.

Several biblical figures turn up in the translated inscriptions, including Joseph, who was sold into slavery by his half-brothers and then became a powerful political figure in Egypt, Joseph’s wife Asenath and Joseph’s son Manasseh, a leading figure in a turquoise-mining business that involved yearly trips to Egypt’s Sinai Peninsula. Moses, who led the Israelites out of Egypt, is also mentioned, Petrovich says.

One inscription, dated to 1834 B.C., translates as “Wine is more abundant than the daylight, than the baker, than a nobleman.” This statement probably meant that, at that time or shortly before, drink was plentiful, but food was scarce, Petrovich suspects. Israelites, including Joseph and his family, likely moved to Egypt during a time of famine, when Egyptians were building silos to store food, he suggests.

A book by Petrovich detailing his analyses of the ancient inscriptions will be published within the next few months. Petrovich says the book definitively shows that only an early version of Hebrew can make sense of the Egyptian inscriptions.

Our grasp of food allergy science is as jumbled as a can of mixed nuts. While there are tantalizing clues on how food allergies emerge and might be prevented, misconceptions are plentiful and broad conclusions are lacking, concludes a new report by the National Academies of Sciences, Engineering and Medicine.

As a result, both the general public and medical community are confused and ill-informed about food allergies and what to do about them. Most prevention strategies and many tests used to diagnose a food allergy aren’t supported by scientific evidence and should be abandoned, the 562-page report concludes.
“We are much more in the dark than we thought,” says Virginia Stallings, a coeditor of the new report, released November 30.

While solid data are hard to come by, the report notes, estimates suggest that 12 million to 15 million Americans suffer from food allergies. Common culprits include peanuts, milk, eggs, fish, shellfish, sesame, wheat and soy.

Food allergies should be distinguished from food intolerances; the two are often confused by the public and practitioners, says Stallings, a pediatrician and research director of the nutrition center at the Children’s Hospital of Philadelphia. Strictly defined food allergies, the primary focus of the report, arise from a specific immune response to even a small amount of the allergen; they produce effects such as hives, swelling, vomiting, diarrhea and, most crucially, anaphylaxis, a severe, potentially deadly allergic reaction. These effects reliably occur within two hours after every time a person ingests that food. Allergic reactions that fall outside this strict definition and food-related intolerances, such as a gastrointestinal distress after ingesting lactose, are a legitimate public health concern. But the mechanisms behind them are probably very different than the more strictly defined food allergies, as are the outcomes, says Stallings.

Anyone suspecting a food allergy should see a specialist. If medical history and preliminary results hint at problems, then the gold standard diagnostic test should be applied: the oral food challenge. This test exposes an individual to small amounts of the potentially offending food while under supervision. Doctors and others in health care should abandon many unproven tests, such as ones that analyze gastric juices or measure skin’s electrical resistance, the report concludes.

Regarding prevention, research has borne a little fruit: The authors recommend that parents should give infants foods that contain potential allergens. This recommendation is largely based on peanut allergy research suggesting early exposure is better than late (SN: 3/21/2015, p. 15). There’s little to no evidence supporting virtually all other behaviors thought to prevent food allergies, such as taking vitamin D supplements, or women avoiding allergens while pregnant or breastfeeding.
While additional rigorous long-term studies are needed to better understand why food allergies arise, the report addresses many issues that society can confront in the meantime. Industry needs to develop a low-dose (0.075 milligrams) epinephrine injector to treat infants who experience food allergy anaphylaxis; the U.S. Food and Drug Administration, Department of Agriculture and the food manufacturing industry need to revamp food labeling so it reflects allergy risks; and relevant agencies should establish consistent guidelines for schools and airplanes that include first-aid training and on-site epinephrine supplies.

“This report is mammoth and very impressive,” says Anita Kozyrskyj, whose research focuses on the infant gut microbiome. Kozyrskyj, of the University of Alberta in Canada, presented research to the reports’ authors while they were gathering evidence. She says the report identifies issues that can help guide the research community. But its real value is in the recommendations for parents, schools, caregivers and health care providers who are dealing with food allergies in the here and now.

A baby starfish scoops up snacks by spinning miniature whirlpools. These vortices catch tasty algae and draw them close so the larva can slurp them up, scientists from Stanford University report December 19 in Nature Physics.

Before starfish take on their familiar shape, they freely swim ocean waters as millimeter-sized larvae. To swim around on the hunt for food, the larvae paddle the water with hairlike appendages called cilia. But, the scientists found, starfish larvae also adjust the orientation of these cilia to fine-tune their food-grabbing vortices.

Scientists studied larvae of the bat star (Patiria miniata), a starfish found on the U.S. Pacific coast, by observing their activities in seawater suffused with tiny beads that traced the flow of liquid. (Watch a video of the experiment.) Too many swirls can slow a larva down, the scientists found, so the baby starfish adapts to the task at hand, creating fewer vortices while swimming and whipping up more of them when stopping to feed.

The part of the brain that governs emotions such as fear and anxiety also helps mice hunt. That structure, the amygdala, orchestrates a mouse’s ability to both stalk a cricket and deliver a fatal bite, scientists report January 12 in Cell.

Scientists made select nerve cells in mice’s brains sensitive to light, and then used lasers to activate specific groups of those cells. By turning different cells on and off, the researchers found two separate sets of nerve cells relaying hunting-related messages from the amygdala’s central nucleus. One set controlled the mice’s ability to chase their prey. The other affected their ability to deliver a solid chomp and kill a cricket.
“They’ve found these two behaviors — that are part of something we think of being very complex — are controlled by these two circuits,” says Cris Niell, a neuroscientist at the University of Oregon in Eugene who wasn’t part of the study. “You flip a switch to chase, you flip a switch to attack.”

Ramping both of those circuits up to high power at the same time even led mice to chase and capture a tiny bug-shaped robot that they would normally ignore or avoid.

“The central amygdala has been conceptualized as a center for emotion and fear and threat detection,” says study coauthor Ivan de Araujo, a neuroscientist at the John B. Pierce Laboratory in New Haven, Conn. Now, it seems that the structure also controls the relatively complex task of hunting.

Scientists don’t know how the new function relates to the amygdala’s better-known role as an emotional control center. But the amygdala does help control heart rate and blood pressure, which shift in emotionally charged situations but also need to be regulated when an animal is pursuing prey, de Araujo says.

The study also shows how even a complex task like hunting can be coordinated by different groups of very specialized nerve cells, or neurons, working together. In this case, one set of neurons made a signaling pathway that controlled chasing, while another controlled biting. Together, those neurons helped the mice grab dinner.
“I think over the years we’ve become progressively more surprised by the behavioral specificity of these particular pathways,” says Anthony Leonardo, a neuroscientist at the Howard Hughes Medical Institute’s Janelia Research Campus in Ashburn, Va. “Certainly the evidence is mounting for a very strongly specific role for neurons.” Leonardo has found similarly specialized neurons in the dragonfly brain, with groups of neurons that run in parallel to each other controlling different types of movements.

Next, de Araujo says, his lab hopes to figure out what flips the neural switches in a mouse’s brain — how seeing or smelling potential prey triggers the amygdala to send the critter after a meal.

The Arctic Ocean is a final resting place for plastic debris dumped into the North Atlantic Ocean, new research suggests.

A 2013 circumpolar expedition discovered hundreds of tons of plastic debris, from fishing lines to plastic films, ecologist Andrés Cózar of the University of Cádiz in Spain and colleagues report April 19 in Science Advances. While many areas remain relatively unpolluted, the density of plastic trash in the Arctic waters east of Greenland and north of Europe rivals plastic pileups in waters closer to the equator, despite few nearby human populations. Even more plastic probably lurks on the seafloor, the researchers suspect.

Ocean currents carried that plastic northward from the North Atlantic Ocean, the researchers propose. Based on the kind of plastic found, the researchers say the debris probably originated from the U.S. East Coast and Europe. While the study estimates that the Arctic contains less than 3 percent of all global floating plastic, that number will only rise as currents continue carrying pollution poleward, putting Arctic ecosystems at risk.

When we brought our first baby home from the hospital, our pediatrician advised us to have her sleep in our room. We put our tiny new roommate in a crib near our bed (though other containers that were flat, firm and free of blankets, pillows or stuffed animals would have worked, too).

The advice aims to reduce the risk of sleep-related deaths, including sudden infant death syndrome, or SIDS. Studies suggest that in their first year of life, babies who bunk with their parents (but not in the same bed) are less likely to die from SIDS than babies who sleep in their own room. The reasons aren’t clear, but scientists suspect it has to do with lighter sleep: Babies who sleep near parents might more readily wake themselves up and avoid the deep sleep that’s a risk factor for SIDS.

That’s an important reason to keep babies close. Room sharing also makes sense from a logistical standpoint. Middle of the night feedings and diaper changes are easier when there’s less distance between you and the babe.

But babies get older. They start snoring a little louder and eating less frequently, and it’s quite natural to wonder how long this room sharing should last. That’s a question without a great answer. In November 2016, the American Academy of Pediatrics task force on SIDS updated its sleep guidelines. The earlier recommendation was that babies ought to sleep in parents’ bedrooms for an entire year. The new suggestion softens that a bit to say infants should be there for “ideally for the first year of life, but at least for the first 6 months.”

Rachel Moon, a SIDS expert at the University of Virginia in Charlottesville who helped write the revised AAP guidelines, says that the update “gives parents a little more latitude after the first 6 months.” The vast majority of SIDS deaths happen in the first six months of life, but the studies that have found benefits for room sharing lumped together data from the entire first year. That makes it hard to say how protective room sharing is for babies between 6 and 12 months of age.

But a new study raises a reason why babies ought to get evicted before their first birthday: They may get more sleep at night in their own rooms. Babies who were sleeping in their own rooms at ages 4 or 9 months got more nighttime sleep than babies the same ages who roomed with parents, researchers reported online June 5 in Pediatrics.

The team asked hundreds of mothers to take sleep surveys when their children were 4, 9, 12 and 30 months old. Some of the 230 children slept in their own rooms when they were younger than 4 months, others moved to their own rooms between 4 and 9 months, and the rest were still sharing their parents’ rooms at 9 months.
At 9 months, babies who had been sleeping alone since 4 months of age slept an average of 40 minutes more than room sharers. The researchers found no differences in sleep duration between the groups of babies at age 12 months. By 30 months of age, though, children who had been sleeping in their own rooms by either 4 or 9 months of age slept on average 45 minutes longer at night than children who had been sharing their parents’ rooms at 9 months. (Important caveat: At 30 months, total daily sleep time didn’t differ between the groups. The former room sharers were making up for missed nighttime sleep with naps.)

Parents who want their babies age 6 months and older to sleep in their own room ought to be encouraged to make the move, says study coauthor Ian Paul, a pediatrician at Penn State. “The guidelines should reflect data, not opinion,” Paul says.

He suspects that sharing a bedroom with babies interferes with everyone’s sleep because normal nocturnal rustlings turn into full-blown wake-ups. Babies and adults alike experience brief arousals during sleep. But when parents are right next to babies, they’re more likely to respond to their children’s brief arousals, which then wakes the baby up more. “This then sets up the expectation from the baby that these arousals will be met with a parent reaction, causing a bad cycle to develop,” he says.

There was another difference that turned up between the two groups of babies. Babies who roomed with parents were four times more likely to be moved into their parents’ beds at some point during the night than babies who slept in their own rooms. Bed sharing is a big risk factor for sleep-related infant deaths.

But Moon cautions that the Pediatrics study is preliminary, and doesn’t warrant a change in the AAP guidelines. She and coauthors point out in an accompanying commentary that other factors might be behind the difference in sleep between the two groups of babies. For instance, babies who slept in their own room were more likely to have consistent bedtime routines, be put to bed drowsy but awake, and have bedtimes of 8 p.m. or earlier. Those are all signs of good “sleep hygiene” for babies, and might be contributing to the longer sleep times. “We know that consistent bedtime routine and consistent bedtime are very important in terms of sleep quality in children,” Moon says. “They could very well make a difference.”

So that’s where we are. Some things are clear, like putting your baby to sleep on her back on a flat, firm surface clear of objects and having your baby nearby during the first six months. But other decisions come with skimpier science, and whether to evict your 6-month-old is one of them. Because science can take you only so far, it may just come down to the snoring, stirring and sleep deprivation.

Maybe it’s more than reptile fashion. The high percentage of citified sea snakes wearing black might be a sign that pollution is an evolutionary force.

Off the coasts of Australia and New Caledonia, some turtle-headed sea snakes (Emydocephalus annulatus) sport pale bands on their dark skins. Others go all black. In 15 places surveyed, the all-black form was more likely to predominate in waters near cities, military sites or industrial zones than along reefs near less built-up coastlines, says evolutionary ecologist Rick Shine of the University of Sydney.
That trend plus some analysis of trace elements in snakes’ skin suggests that the abundant dark forms could turn out to be an example of industrial melanism, Shine and his colleagues propose August 10 in Current Biology.

The most famous example of this evolutionary phenomenon comes from a dark form of peppered moth that overtook pale populations in 19th century England (SN: 6/25/16, p. 6). Dark wings created better camouflage from hungry birds in the grimy industrializing landscape.
Shine doesn’t think the sea snakes are going for camouflage, though. Instead, the snakes could be more like the dark-feathered pigeons of Paris. The melanin that gives that city’s feral birds their urban chic also does a great job of binding traces of toxic metals such as zinc, explains evolutionary ecologist Marion Chatelain of the University of Warsaw. When birds molt, getting rid of darker feathers lets them unload more of the unhealthful urban pollutants, she and colleagues have reported.
This could explain why marine biologist and study coauthor Claire Goiran has so many dark turtle-headed sea snakes in a lagoon not far from her campus, the University of New Caledonia in Nouméa. Earlier studies had found only downsides to dark coloration: Seaweed spores preferentially settle on dark snakes and sprout fuzz that can cut swimming speed by 20 percent and cause a snake to shed its skin more often than normal.
To test a scenario of industrial melanism, or darkening due to pollution, the researchers collected data on skin colors for a total of about 1,450 snakes, both live and museum specimens, from 15 sites in New Caledonia and Australia. Higher percentages of all-dark snakes wriggled around the nine polluted sites surveyed. At one, a remote Australian reef that the military had long used as a bombing range, all 13 specimens were dark.

To test shed skins for trace metals, Goiran and Shine enlisted Paco Bustamante of the University of La Rochelle in France, who studies trace metal contamination in marine life.

Researchers managed to collect sloughed skins from 17 turtle-headed snakes, which inconveniently shed their skin underwater. To compare light and dark patches, the scientists turned to two local species of sea kraits, which have banded skin and visit land to shed it.
Overall, skins held concentrations of trace elements higher than those that can cause health problems in birds and mammals, the researchers report. In the krait skins, dark zones had slightly more of some contaminants, such as zinc and arsenic, than the pale bluish-white bands did.

The idea that polluted water favors melanized sea snakes “is a reasonable hypothesis based on what we know,” Chatelain says. Definitive tests will require more data and different approaches. Genetic testing, for example, would clarify whether dark populations arose instead from small groups of pioneers that happened to have a lot of black snakes.

That testing could be a long way off. Sea snakes are evolutionary cousins of cobras and mambas, and some of the species swimming around Australia and New Caledonia are “bowel-looseningly large,” Shine says. At least the little turtle-headed ones, which eat eggs of small reef fishes, have venom glands that have atrophied and “probably couldn’t fit a human finger in their mouths.” But until someone figures out how to keep them alive in captivity for more than a few days, Shine isn’t expecting definitive genetics.