Caterpillars that masquerade as leaves or twigs, like this brimstone moth caterpillar ( Opisthograptis luteolata ), appear most effective at evading recognition by predators.
From crabs to caterpillars, a wide range of animals successfully use camouflage to hamper detection by hungry predators. But some concealment strategies are more effective than others, a new study suggests.
The analysis compiles and synthesizes data from scores of studies on animal camouflage. Comparisons between different camouflaging methods show that masquerading as specific objects in the environment is the best way to go unseen, scientists report September 14 in Proceedings B of the Royal Society .
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Behavioral and sensory ecologist João Vitor de Alcantara Viana had been studying animal camouflage for his doctoral research when he realized a comprehensive comparison of different camouflage strategies had never been done.
“There was a big gap in the literature on this topic,” says de Alcantara Viana, of the State University of Campinas in São Paulo, Brazil.
So, de Alcantara Viana and colleagues searched scientific publication databases for studies on animal camouflage dated from 1900 through July 2022. The team zeroed in on 84 studies that experimentally tested at least one camouflage strategy, and reported either how long predators took to find camouflaged prey or how often predators attacked. The team also limited their analysis to studies that compared camouflaged prey with noncamouflaged, often artificial, versions.
Next, the team grouped the data from these studies by the types of predators and prey analyzed and the variety of camouflage strategies examined. Camouflage tactics included “background matching,” where the animal matches the color and patterning of the environment , and “masquerading,” where prey mimics a particular object uninteresting to predators, like a twig, a leaf, a bird dropping or even a shed tarantula skin ( SN: 12/10/13; SN: 6/6/14 ).
Camouflage is generally effective at making the hunt difficult for predators, increasing their search time by more than 62 percent and dropping the rate they attack prey by more than 27 percent across the board, the team found.
But the type of prey mattered. Caterpillars got more benefit from camouflage than their winged adult forms, for example. This may be because moths and butterflies can fly and have other antipredator adaptations available to them, de Alcantara Viana says.
The masquerade strategy was especially effective at helping prey elude predators, increasing search time by nearly 300 percent. One of the most striking examples of this, says de Alcantara Viana, are caterpillars that disguise themselves as twigs. A study on brimstone moth caterpillars ( Opisthograptis luteolata ) and chickens showed that the birds take longer to attack masquerading caterpillars after being recently exposed to twigs.
Masquerading as the most effective camouflage strategy is intriguing, says Anna Hughes, a sensory ecologist at the University of Essex in England who was not involved with this research. “If this is indeed the case, it will be interesting to further investigate the constraints — size, movement requirements — that mean that not all animals evolve this strategy,” she says. The researchers note that masquerading is probably more likely to evolve if the animal is a similar size as the object it’s mimicking. This could limit what species can benefit from this super camo.
de Alcantara Viana and his colleagues think masquerading is so effective because it’s so specialized, with animals impersonating specific objects, compared with other strategies based on blending in against an irregular background. Prey that masquerade benefit from the predator misidentifying them as real objects in the environment, not just failing to detect the prey.
The quality of the new work is excellent, Hughes says. Still, it’s not quite clear if the noncamouflaged controls, which she says vary quite widely from one study to another, have inherently different effects on predator reactions. This could make the tested camouflage seem more or less effective than it is in nature.
Another notable finding from the new analysis is that most studies have been conducted in the Northern Hemisphere, Hughes says. “I think it is clear that our understanding of the evolution of camouflage strategies is going to be, by definition, incomplete unless more studies are carried out in the Southern Hemisphere.”
Much of recent camouflage research has also tried to understand precisely how specific defenses protect prey from attacks, says Tom Sherratt, an evolutionary ecologist at Carleton University in Ottawa, Canada, also not involved with this study.
“We are now at a point where we can begin to compare among these defenses,” Sherratt says, which can help researchers figure out why species use particular camouflage strategies.
de Alcantara Viana says he and his colleagues are working on another analysis to understand “the other side of the coin,” how camouflaged predators benefit from concealing themselves from prey.
Jake Buehler is a freelance science writer, covering natural history, wildlife conservation and Earth’s splendid biodiversity, from salamanders to sequoias. He has a master’s degree in zoology from the University of Hawaii at Manoa.
Science News was founded in 1921 as an independent, nonprofit source of accurate information on the latest news of science, medicine and technology. Today, our mission remains the same: to empower people to evaluate the news and the world around them. It is published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education (EIN 53-0196483).
Mwatime Hamadi, a tour guide at Gazi Ecotourism Ventures in Kenya, explains how dropping the propagule from her hand into the soil below will germinate a new mangrove plant.
On the fringe of Kenya’s Gazi village, 50 kilometers south of Mombasa, Mwatime Hamadi walks barefoot on a path of scorching-hot sand toward a thicket of trees that seem to float where the land meets the Indian Ocean. Behind her moves village life: Mothers carry babies on their backs while they hang laundry between palm trees, women sweep the floors of huts thatched with palm fronds and old men chat idly about bygone days under the shade of mango trees.
Hamadi is on her way to Gazi Forest, a dense patch of mangroves along Gazi Bay that coastal residents see as vital to their future. Mangroves “play a crucial role in safeguarding the marine ecosystem, which in turn is important for fisheries we depend on for our livelihood,” she says as she reaches a boardwalk that snakes through the coastal wetland.
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Hamadi is a tour guide with Gazi Ecotourism Ventures, a group dedicated to empowering women and their community through mangrove conservation. This group is part of a larger carbon offset project called Mikoko Pamoja that has taken root and is now being copied farther south on Kenya’s coastline and in Mozambique and Madagascar.
Through Mikoko Pamoja, residents of Gazi and nearby Makongeni are cultivating an economic ecosystem that relies on efforts to preserve and restore the mangrove forests. Revenue from carbon credits sold plus the money Hamadi and others earn from ecotourism are split between salaries, project costs and village improvements to health care, sanitation, schools and more.
“The mangrove vegetation was a thriving, healthy ecosystem in precolonial times,” says Ismail Barua, Mikoko Pamoja’s chairperson. During British rule, which stretched from the 1890s to 1963, the colonial government issued licenses to private companies to export mangrove wood. They did this without community involvement, which led to poaching of trees. Even after Kenya gained independence, mangroves were an important source of timber and fuel for industrial processes, main drivers of extensive destruction of the forests.
Today, mangrove restoration is helping the region enter a new chapter, one where labor and resources are well-managed by local communities instead of being exploited. “The community is now able to run its own affairs,” Barua notes. Through innovative solutions and hard work, he says, “we’re trying to bring back a semblance of that ecosystem.”
“The mangrove vegetation was a thriving, healthy ecosystem in precolonial times.…We’re trying to bring back a semblance of that ecosystem.”
The dominant mangrove species in Gazi Forest is Rhizophora murcronata . With oval, leathery leaves about the size of a child’s palm and spindly branches that reach to the sun, the trees can grow up to 27 meters tall. Their interlaced roots, which grow from the base of the trunk into the saltwater, make these evergreen trees unique.
Salt kills most plants, but mangrove roots separate freshwater from salt for the tree to use. At low tide, the looping roots act like stilts and buttresses, keeping trunks and branches above the waterline and dry. Speckling these roots are thousands of specialized pores, or lenticels. The lenticels open to absorb gases from the atmosphere when exposed, but seal tight at high tide, keeping the mangrove from drowning.
The thickets of roots also prevent soil erosion and buffer coastlines against tropical storms. Within these roots and branches, shorebirds and fish — and in some places, manatees and dolphins — thrive.
Mangrove roots support an ecosystem that stores four times as much carbon as inland forests. That’s because the saltwater slows decomposition of organic matter, says Kipkorir Lang’at, a principal scientist at the Kenya Marine and Fisheries Research Institute, or KMFRI. So when mangrove plants and animals die, their carbon gets trapped in thick soils. As long as mangroves stay standing, the carbon stays in the soil.
Robust estimates of mangrove forest area in Kenya before 1980 are not available, Lang’at says. However, with the clear-cutting of mangrove forests in Gazi Bay in the 1970s, he says, the area was left with vast expanses of bare, sandy coast.
Other parts of the country experienced similar losses: Kenya lost up to 20 percent of its mangrove forests between 1985 and 2009 because no mechanism existed for their protection. The losses had a steep price: Just as mangroves absorb more carbon than inland forests, when destroyed, they release more carbon than other forests. And since the mangroves provided habitat and shelter for fish, their destruction meant that fishers were catching less.
Amount of mangrove forest Kenya lost between 1985 and 2009
Recognizing this high cost, as well as the ecosystem’s other benefits, Kenya’s government ratified the Forest Conservation and Management Act of 2016, a law protecting mangroves and inland forests. Cutting down mangroves is now banned throughout the country, except in very specific areas under very specific circumstances.
Available data suggest that Kenya’s rate of mangrove loss has declined in the last two decades. The country is now losing about 0.65 percent of its mangrove forest annually, according to unpublished evaluations conducted in 2020 by KMFRI. Since the turn of the millennium, global mangrove deforestation has slowed as well, hovering between a loss of 0.2 and 0.7 percent per year, says a 2020 study in Scientific Reports .
Mikoko Pamoja offers hope for turning around those declines. The project, whose Swahili name means “mangroves together,” has its roots in a small mangrove restoration effort that started in 1991 in Gazi Bay, spearheaded by KMFRI. The effort evolved into a scientific experiment to see what it would take to restore a degraded ecosystem. It attracted collaborators from Edinburgh Napier University, Europe’s Earthwatch Institute and other organizations across Europe.
Now, Gazi Forest boasts 615 hectares of mangrove forest, including 56,000 individual seedlings planted by the community. Plans to plant more mangrove trees — at least 2,000 per year — are in the works.
Compared with other major forest types, mangrove forests capture and store more carbon dioxide, especially within tree roots and surrounding soil.
Gazi Forest siphons carbon from the atmosphere at a rate of 3,000 metric tons per year, says Rahma Kivugo, the outgoing project coordinator for Mikoko Pamoja. These aren’t merely ballpark numbers: To sell the carbon offsets collected by Mikoko Pamoja, forest managers must calculate the amount of carbon stored by mangroves.
Volunteers venture into the forest twice a year, checking on 10 selected 10-square-meter plots in the wild forest and five plots in planted forest. Workers measure the diameter of mature trees at an adult’s chest height. They then estimate the trees’ height. Finally, they classify young trees as knee-height, waist-height, chest-height and higher.
From these observations, researchers estimate the volume of mangrove material above ground in each plot and extrapolate for the whole forest area.
Once they have an idea of the volume of plant material above ground, team members can estimate root volume below ground using a standardized factor specific to mangrove forests, says Mbatha Anthony, a research assistant at KMFRI in charge of carbon accounting. Even though mangrove forests store a lot of soil carbon, the project calculates carbon stored only by the tree itself because “calculating soil carbon is a resource-intensive undertaking for a small project like Mikoko Pamoja,” Anthony says.
With an estimate of the total volume of biomass in the forest in hand, “we can then translate that into tons of carbon,” says environmental biologist Mark Huxham of Edinburgh Napier University, who helps Mikoko Pamoja with its calculations. In general, 50 percent of aboveground biomass is carbon. Below ground, 39 percent of biomass is carbon.
The amount of carbon stored by Gazi Forest is then relayed to the Plan Vivo Foundation , a group based in Scotland that certifies carbon calculations. Once its calculations are certified, Mikoko Pamoja receives Plan Vivo Certificates, or PVCs.
One PVC is equivalent to one metric ton of carbon dioxide emission reductions. These PVCs are submitted to the Association for Coastal Ecosystem Services — an organization that markets carbon credits for Mikoko Pamoja and similar projects. Through ACES, Mikoko Pamoja’s PVCs can then be purchased by anyone who wishes to offset their carbon emissions.
Roughly 117 hectares of Gazi Forest have been demarcated for the sale of carbon credits. “Mikoko Pamoja generates approximately $15,000 annually from the sale of carbon credits,” Anthony says. From 2014 to 2018, the project generated 9,880 credits — 9,880 tons of avoided carbon dioxide emissions.
Mikoko Pamoja sells carbon credits at more than $7 per ton. Revenues get split in a clearly defined manner, according to what residents decide are pressing needs of Makongeni and Gazi villages. Around 21 percent pays wages of residents involved with Mikoko Pamoja. And “more than half of what is earned goes toward community projects,” Kivugo says.
In total, about $117,000 has gone to community projects since Mikoko Pamoja was founded. These projects include donating medicine to health clinics and textbooks to schools and digging clean water wells. Plans are under way to revive a windmill in Gazi for pumping water and renovate Makongeni’s primary school.
“The need in the community is great. So carbon trading is unlikely to meet all the needs,” Huxham says. But the funds make a significant contribution to local livelihoods, which primes the community to support conservation, he says.
The approach seems to be working. On a winding path into the forest, visitors encounter a signboard, with large letters in Swahili declaring, “Take note! This is a Mikoko Pamoja area protected by the community. Littering is prohibited! Trimming trees is prohibited!”
Active community participation is central to Mikoko Pamoja’s success. Not only do community members plant mangrove seedlings and survey trees to gauge carbon storage, community scouts monitor the health of this ecosystem.
Scouts clean up litter within the forests and survey the forest’s biodiversity. From a wooden watchtower above the forest, scouts also track and report illegal logging.
“Should we spot suspicious activities in the forest, we will call the Kenya Forest Service rangers, who have the authority to detain and arrest any trespasser,” says local scout Shaban Jambia.
Back at the boardwalk, Hamadi leads a small knot of visitors through the mangroves, pausing occasionally to touch a tree’s waxy leaves. She plucks a propagule — a dark-brown pod longer than her hand — from a tree belonging to the mangrove species Bruguiera gymnorhiza .
She drops the propagule over the boardwalk’s handrail, into the soft marsh soil about 1.5 meters below. It lands, sticking almost perfectly perpendicular in the ground. “This will soon take root and germinate into a new plant,” she explains to the visitors. “That’s how this species propagates.”
Hamadi, the tour guide, is one of 27 members of the Gazi Women Mangrove Boardwalk group. Members offer interpretive services to visitors for a fee. The women also prepare Swahili cuisine for sale to groups visiting the area.
“A dish of coconut rice served with snapper fish is particularly popular, washed down with flavored black tea or tamarind juice,” says Mwanahamisi Bakari, the group’s treasurer.
These ecotourism efforts have attracted international support. The World Wide Fund for Nature Kenya, for instance, constructed a conference facility, which the women’s group rents to those who want to use the location as a backdrop to discuss sustainability efforts.
Mikoko Pamoja’s success is spurring conservation efforts throughout Kenya and beyond. For instance, on southern Kenya’s coast is the Vanga Blue Forest, a swath of mangroves five times as large as Gazi Forest. Of Vanga Blue’s more than 3,000 hectares of mangrove forest, a little more than 15 percent — 460 hectares — has been set aside for the sale of carbon credits following Mikoko Pamoja’s example.
In 2020, with help from KFMRI, a network of scientists from countries along the western Indian Ocean published a blueprint for mangrove restoration . These guidelines are now being customized to suit the restoration plans of individual countries, says Lang’at. The group is also using Mikoko Pamoja’s carbon credit example to set up projects of its own.
Madagascar’s first community-led mangrove carbon project, known as Tahiry Honko (which means “preserving mangroves” in the local Vezo dialect), was introduced in 2013 and then certified for carbon sale by Plan Vivo in 2019. With Mikoko Pamoja as a guide, Tahiry Honko “is helping tackle climate breakdown and build community resilience by preserving and restoring mangrove forests,” says Lalao Aigrette, an adviser at Blue Ventures, the conservation group coordinating the preservation effort.
Tahiry Honko is generating carbon credits through the conservation and restoration of over 1,200 hectares of mangroves surrounding the Bay of Assassins on Madagascar’s southwest coast.
In the meantime, the Limpopo estuary and other locations along the Mozambican coast are sites of mangrove restoration efforts. KMFRI is helping local organizers structure their efforts. “We also hope they will assist us when we start working with carbon credits,” Macamo adds.
Less than 1 percent of Earth’s surface is covered by mangroves , equivalent to 14.8 million hectares. “Because this area is minuscule compared to terrestrial forests, mangroves have been neglected throughout the world,” says James Kairo, chief scientist at KMFRI.
At Gazi Bay, a 2011 assessment by the United Nations Environment Programme estimated that the mangrove forests are worth about $1,092 per hectare per year , thanks in part to the potential of fisheries, aquaculture, carbon sequestration and damages averted by the coastal protection that mangroves provide. Assuming that numbers in Gazi Bay hold for the rest of the world, mangroves could provide more than $16 billion in economic benefits planetwide.
Toward the end of 2020, Kenya’s government included mangroves and seagrasses for the first time in its Nationally Determined Contributions, or NDCs — the greenhouse gas emission reduction commitments for countries that ratified the Paris Agreement. The agreement seeks to limit global warming to below 2 degrees Celsius above preindustrial levels.
This inclusion commits Kenya to conserving mangroves to balance its emissions. Kenya’s government now “recognizes the potential and importance of the mangrove and seagrass resources that Kenya has,” Huxham says.
“This is a great commitment on the part of the government. The next challenge is the implementation of these commitments,” says Kairo, who sits on the advisory board of the U.N. Decade of Ocean Science for Sustainable Development (2021–2030), which aims to support efforts to reverse the cycle of decline in ocean health.
Now, scientists and community managers for that effort need to determine how mangroves can adapt to rising sea levels. “How can communities next to the sea live in harmony with this system, without impacting on their resiliency and productivity?” Kairo asks.
Mikoko Pamoja is helping provide answers, Kairo adds. Thanks in large part to that small project that began in a secluded corner on the Kenya coast, those answers are now spreading to the rest of the world.
Science News was founded in 1921 as an independent, nonprofit source of accurate information on the latest news of science, medicine and technology. Today, our mission remains the same: to empower people to evaluate the news and the world around them. It is published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education (EIN 53-0196483).
The final results from the orbiting MICROSCOPE experiment (illustrated) provide the most precise confirmation yet that all things fall the same way under the influence of gravity.
Gravity doesn’t discriminate. An experiment in orbit has confirmed, with precision a hundred times greater than previous efforts, that everything falls the same way under the influence of gravity.
The finding is the most stringent test yet of the equivalence principle, a key tenet of Einstein’s theory of general relativity. The principle holds to about one part in a thousand trillion , researchers report September 14 in Physical Review Letters .
The idea that gravity affects all things equally might not seem surprising. But the slightest hint otherwise could help explain how general relativity, the foundational theory of gravity, meshes with the standard model of particle physics, the theoretical framework that describes all fundamental particles of matter. General relativity is a classical theory that sees the universe as smooth and continuous, whereas the standard model is a quantum theory involving grainy bits of matter and energy. Combining them into a single theory of everything has been an unfulfilled dream of scientists extending back to Einstein ( SN: 1/12/22 ).
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“The equivalence principle is the most important cornerstone of Einstein’s theory of general relativity,” says Sabine Hossenfelder, a physicist with the Frankfurt Institute for Advanced Studies in Germany who was not involved in the study. “We know [it] eventually has to be altered because it cannot in its present form take into account quantum effects.”
To help search for potential alterations, the MICROSCOPE experiment tracked the motion of nested metal cylinders — a 300-gram titanium outer cylinder and a 402-gram platinum inner one — as they orbited the Earth in near-perfect free fall. Any difference in the effect of gravity on the respective cylinders would cause them to move relative to each other. Small electrical forces applied to bring the cylinders back into alignment would have revealed a potential violation of the equivalence principle.
From April 2016 to October 2018, the cylinders were shielded inside a satellite that protected them from the buffeting of solar winds, the minuscule pressure that sunlight exerts and the residual atmosphere at an orbital altitude of a little over 700 kilometers high.
By performing the experiment in orbit, the researchers could compare the free fall of two different materials for extended periods without the confounding effects of vibrations or of objects nearby that could exert gravitational forces, says Manuel Rodrigues, a MICROSCOPE team member and physicist with the French aerospace lab ONERA in Palaiseau. “One of the lessons learned by MICROSCOPE is … that space is the best way to get an important improvement in the accuracy for this kind of test.”
Over its two-and-a-half-year mission, MICROSCOPE found no sign of cracks in the equivalence principle, the new study reports. The finding builds on a previous interim report from the experiment that found the same thing , but with less precision ( SN: 12/4/17 ).
Some physicists suspect that limits to the equivalence principle may never turn up in experiments, and that Einstein will perpetually be proven right.
Even 100 times greater precision from a follow-up MICROSCOPE 2 mission, tentatively planned for the 2030s, is unlikely to reveal an equivalence principle breakdown, says Clifford Will, a physicist at the University of Florida in Gainesville who is not affiliated with the experiment. “It really is still this basic idea that Einstein taught,” he says. What we see as the force of gravity is actually the curvature of spacetime. “Any body simply moves along the path in Earth’s spacetime,” whether it’s made of dense platinum, lighter titanium or any other material.
But even if physicists never prove Einstein wrong, Hossenfelder says, experiments like MICROSCOPE are still important. “These tests aren’t just about the equivalence principle,” she says. “They implicitly look for all other kinds of deviations, new forces and so on,” that aren’t part of general relativity. “So really it’s a multiple-purpose, high-precision measurement.”
Now that the mission is complete, the MICROSCOPE satellite will slowly spiral out of orbit. “It’s difficult to bet where in 25 years it will fall down,” Rodrigues says. Along with a reference set of platinum cylinders on board, “it’s [a] couple of millions of euros [in] platinum.” Where that precious platinum metal will land is anyone’s guess, but the gravity that pulls it down will tug on the titanium just as hard, to one part in a thousand trillion at least.
James Riordon is a freelance science writer who covers physics, math, astronomy and occasional lifestyle stories.
Science News was founded in 1921 as an independent, nonprofit source of accurate information on the latest news of science, medicine and technology. Today, our mission remains the same: to empower people to evaluate the news and the world around them. It is published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education (EIN 53-0196483).
Early humans at Abu Hureyra (illustrated), an ancient settlement in present-day Syria, burned dung as fuel and may have kept animals on-site nearly 13,000 years ago.
Hunter-gatherer groups living in southwest Asia may have started keeping and caring for animals nearly 13,000 years ago — roughly 2,000 years earlier than previously thought.
Ancient plant samples extracted from present-day Syria show hints of charred dung , indicating that people were burning animal droppings by the end of the Old Stone Age, researchers report September 14 in PLOS One . The findings suggest humans were using the dung as fuel and may have started animal tending during or even before the transition to agriculture. But what animals produced the dung and the exact nature of the animal-human relationship remain unclear.
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“We know today that dung fuel is a valuable resource , but it hasn’t really been documented prior to the Neolithic,” says Alexia Smith, an archaeobotanist at the University of Connecticut in Storrs ( SN: 8/5/03 ).
Smith and her colleagues reexamined 43 plant samples taken in the 1970s from a residential dwelling at Abu Hureyra, an archaeological site now lost under the Tabqa Dam reservoir. The samples date from roughly 13,300 to 7,800 years ago, spanning the transition from hunter-gatherer societies to farming and herding.
Throughout the samples, the researchers found varying amounts of spherulites, tiny crystals that form in the intestines of animals and are deposited in dung. There was a noticeable uptick between 12,800 and 12,300 years ago, when darkened spherulites also appeared in a fire pit — evidence they were heated to between 500⁰ and 700⁰ Celsius, and probably burned.
The team then cross-referenced these findings against previously published data from Abu Hureyra. It found that the dung burning coincided with a shift from circular to linear buildings, an indication of a more sedentary lifestyle, along with steadily rising numbers of wild sheep at the site and a decline in gazelle and other small game. Combined, the authors argue, these findings suggest humans may have started tending animals outside their homes and were burning the piles of dung at hand as a supplement to wood.
“The spherulite evidence reported here confirms that dung of some sort was used as fuel,” says Naomi Miller, an archaeobotanist at the University of Pennsylvania who was not involved with the study.
Figuring out what animal left the dung could reveal whether animals were tethered outside or not. While the authors propose wild sheep, which would have been more accommodating to capture, Miller suggests the source was probably roaming wild gazelle.
“Spherulites coming from off-site collection of gazelle dung, stored until burned as fuel, is to my mind a more plausible interpretation,” Miller says. Even if kept for a few days, she says, sheep wouldn’t produce large amounts of dung.
“The whole thing is a classic whodunit,” says anthropologist Melinda Zeder, something perhaps DNA analysis could solve ( SN: 7/6/17 ). Gazelle might be the source, she says, and if captured young, the animals may have even been tended for a while — even if they weren’t eventually domesticated.
“The interesting thing is that people [were] experimenting with their environment,” says Zeder, of the Smithsonian Institution in Washington, D.C. “Domestication is almost incidental to that.”
Science News was founded in 1921 as an independent, nonprofit source of accurate information on the latest news of science, medicine and technology. Today, our mission remains the same: to empower people to evaluate the news and the world around them. It is published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education (EIN 53-0196483).
Oral polio vaccines (shown) have been a key tool in global efforts to eradicate the virus. But the vaccines contain weakened viruses that can replicate and spread to others, and can, in rare cases, regain the ability to cause disease and spark outbreaks among communities with low vaccination rates.
A particular kind of poliovirus is spreading in the United States. The U.S. Centers for Disease Control and Prevention has confirmed that the country now joins a list of around 30 other countries where circulation of the virus has been identified. Those countries include the United Kingdom, Israel, Egypt, Yemen and around two dozen in Africa.
The news, announced September 13, comes after the identification in July of a case of paralytic polio in an unvaccinated adult in Rockland County in New York. Public health officials found the case was caused by what’s called a vaccine-derived poliovirus (find out more about this kind of poliovirus below). This spurred wastewater surveillance in Rockland and the surrounding counties, because people shed poliovirus in their stool. The wastewater samples showed that the virus was spreading in Rockland and neighboring areas .
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In response, New York Governor Kathy Hochul declared a state of emergency on September 9 to expand access to polio vaccination statewide. Three of the counties where poliovirus has been detected in wastewater — Rockland, Orange and Sullivan — have polio vaccination rates of only around 60 percent. The virus has also turned up in New York City and Nassau County.
While most people infected with polio don’t have symptoms, some might feel like they have the flu, with fever, fatigue or a sore throat. In rare cases, the virus can cause permanent paralysis, and the disease can turn deadly if that paralysis hits the muscles that control breathing or swallowing. Anyone unvaccinated is at risk of paralytic polio if they get infected.
Here are six things to know about polio right now.
Polio vaccines come as a shot, given in the arm or leg, or a liquid given orally. These vaccines provide protection against wild poliovirus and vaccine-derived poliovirus. Both polio vaccines used to be given in the United States, but since 2000, the shot has been the only polio vaccine available in the country ( SN: 10/27/21 ).
The shot is an inactivated vaccine given as part of routine childhood vaccinations in the United States. It is made using poliovirus that has been “killed,” stripped of its ability to cause disease. Kids receive a total of four shots. The inactivated vaccine protects against paralysis.
The oral vaccine, still used in many countries, is an attenuated vaccine, made with live but weakened poliovirus. This vaccine can help prevent wild poliovirus from being passed along further if a vaccinated person drinks water or eats food that has been contaminated with stool containing the pathogen. That means it can prevent the spread of poliovirus in a community while also protecting against paralysis ( SN: 1/8/21 ).
But because these attenuated versions can replicate, the virus can spread from cell to cell and possibly to other people. Which leads us to the next question.
These viruses are related to the oral vaccine. Since the viruses used in the vaccine can replicate, they can spread but they’re too weakened to cause serious disease. The problem comes when an attenuated virus from the oral vaccine spreads among too many people and regains its ability to cause paralysis, says Adam Lauring, a virologist and infectious diseases physician at the University of Michigan in Ann Arbor. “Because it can replicate, it will evolve.”
In a community with low or no vaccination against polio, such vaccine-derived polioviruses can cause disease.
The Global Polio Eradication Initiative , which includes the World Health Organization, CDC, United Nations Children’s Fund and other groups, has been working since 1988 to eradicate polio. The oral vaccine has been a key tool for global efforts to get rid of polio, Lauring says. That’s not only because that vaccine is inexpensive and easy to use in low- and middle-income countries, but also because studies suggest it better protects the gut, the part of the body where the virus grows. The more protected the gut, the better the chances of reducing transmission and stopping an outbreak.
It’s a sign that poliovirus is spreading among people in those regions.
Paralysis from poliovirus is rare — affecting around 1 out of 200 infected people. So the single paralytic case identified in July in New York was already a hint that there may have been hundreds of other infections. The virus has since been detected in wastewater samples from as early as May . The virus’s continued presence in wastewater suggests people are still getting infected and passing it on to others.
Yes. “If you don’t know if you received polio shots, then you should probably get your polio shots,” Lauring says. “If you didn’t [get vaccinated], you should get a polio shot.”
Vaccine-derived polioviruses are largely a problem in communities where not enough people are vaccinated. “That’s one piece of the puzzle of what’s been going on in New York,” Lauring says. Low immunization rates mean vaccine-derived viruses can spread, largely among unvaccinated people, and circulate silently before someone gets sick.
Places that have sanitation issues or struggle with other intestinal diseases are also hot spots for vaccine-derived polioviruses. When there’s not enough immunity to stop poliovirus from circulating, the virus can evolve further.
People who got vaccinated, even decades ago, are likely still protected.
Adults who have a high risk of exposure to the virus are eligible for one lifetime booster shot, according to the CDC. Otherwise, people should make sure they received all the recommended doses.
It’s unknown exactly how durable childhood polio vaccines are at protecting against severe disease in adults. With little polio circulating around the world, it’s a hard question to study, Lauring says. Still, for years there haven’t been any cases of polio in the United States, and we’ve largely had immunity from the inactivated vaccine, he says. “I’m not sounding the alarm bells.”
Erin I. Garcia de Jesus is a staff writer at Science News . She holds a Ph.D. in microbiology from the University of Washington and a master’s in science communication from the University of California, Santa Cruz.
Aimee Cunningham is the biomedical writer. She has a master’s degree in science journalism from New York University.
Science News was founded in 1921 as an independent, nonprofit source of accurate information on the latest news of science, medicine and technology. Today, our mission remains the same: to empower people to evaluate the news and the world around them. It is published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education (EIN 53-0196483).
A single, doomed moon could clear up a couple of mysteries about Saturn.
This hypothetical missing moon, dubbed Chrysalis, could have helped tilt Saturn over , researchers suggest September 15 in Science . The ensuing orbital chaos might then have led to the moon’s demise, shredding it to form the iconic rings that encircle the planet today.
“We like it because it’s a scenario that explains two or three different things that were previously not thought to be related,” says study coauthor Jack Wisdom, a planetary scientist at MIT. “The rings are related to the tilt, who would ever have guessed that?”
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Saturn’s rings appear surprisingly young , a mere 150 million years or so old ( SN: 12/14/17 ). If the dinosaurs had telescopes, they might have seen a ringless Saturn. Another mysterious feature of the gas giant is its nearly 27-degree tilt relative to its orbit around the sun. That tilt is too large to have formed when Saturn did or to be the result of collisions knocking the planet over.
When Saturn formed, its spin axis was probably close to straight up and down (1). But as the moon Titan moved away from Saturn, interactions between Titan, another moon called Chrysalis and the planet Neptune could have helped tilt Saturn over by 36 degrees (2). Chaos ensued, leading to the destruction of Chrysalis. The shredded moon formed Saturn’s rings, and its loss let Saturn’s tilt angle relax a bit to its present-day value of about 27 degrees (3).
Planetary scientists have long suspected that the tilt is related to Neptune, because of a coincidence in timing between the way the two planets move. Saturn’s axis wobbles, or precesses, like a spinning top. Neptune’s entire orbit around the sun also wobbles, like a struggling hula hoop.
The periods of both precessions are almost the same, a phenomenon known as resonance. Scientists theorized that gravity from Saturn’s moons — especially the largest moon, Titan — helped the planetary precessions line up. But some features of Saturn’s internal structure were not known well enough to prove that the two timings were related.
Wisdom and colleagues used precision measurements of Saturn’s gravitational field from the Cassini spacecraft, which plunged into Saturn in 2017 after 13 years orbiting the gas giant, to figure out the details of its internal structure ( SN: 9/15/17 ). Specifically, the team worked out Saturn’s moment of inertia, a measure of how much force is needed to tip the planet over. The team found that the moment of inertia is close to, but not exactly, what it would be if Saturn’s spin were in perfect resonance with Neptune’s orbit.
“We argue that it’s so close, it couldn’t have occurred by chance,” Wisdom says. “That’s where this satellite Chrysalis came in.”
After considering a volley of other explanations, Wisdom and colleagues realized that another smallish moon would have helped Titan bring Saturn and Neptune into resonance by adding its own gravitational tugs. Titan drifted away from Saturn until its orbit synced up with that of Chrysalis. The enhanced gravitational kicks from the larger moon sent the doomed smaller moon on a chaotic dance. Eventually, Chrysalis swooped so close to Saturn that it grazed the giant planet’s cloud tops. Saturn ripped the moon apart, and slowly ground its pieces down into the rings.
Calculations and computer simulations showed that the scenario works, though not all the time. Out of 390 simulated scenarios, only 17 ended with Chrysalis disintegrating to create the rings. Then again, massive, striking rings like Saturn’s are rare, too.
The name Chrysalis came from that spectacular ending: “A chrysalis is a cocoon of a butterfly,” Wisdom says. “The satellite Chrysalis was dormant for 4.5 billion years, presumably. Then suddenly the rings of Saturn emerged from it.”
The story hangs together, says planetary scientist Larry Esposito of the University of Colorado Boulder, who was not involved in the new work. But he’s not entirely convinced. “I think it’s all plausible, but maybe not so likely,” he says. “If Sherlock Holmes is solving a case, even the improbable explanation may be the right one. But I don’t think we’re there yet.”
Lisa Grossman is the astronomy writer. She has a degree in astronomy from Cornell University and a graduate certificate in science writing from University of California, Santa Cruz. She lives near Boston.
Science News was founded in 1921 as an independent, nonprofit source of accurate information on the latest news of science, medicine and technology. Today, our mission remains the same: to empower people to evaluate the news and the world around them. It is published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education (EIN 53-0196483).
