Matabele ants: Travelling faster with detours

These are Matabele ants carrying a termite prey back to the nest.

Termites are the African Matabele ants' (Megaponera analis) favourite dish. Proceeding in long files of 200 to 600, they raid termites at their foraging sites and haul the prey back to their nest where they are ultimately eaten.

Before starting their raids, the ants send out scouts to look for the termites' foraging sites. Once they have spotted them, the scout ants return to the nest to mobilize their comrades. On their way back to the nest, the scouts show astonishing navigational abilities: They take the quickest route rather than the shortest.

Travelling faster in open country

If the direct way back passes through an area densely grown with grass, for example, the scouts prefer taking detours through open terrain which enables them to double their pace -- and this is worth it: They travel much faster although they are not taking the shortest route. This reduces their time back to the nest by 35 percent on average as Erik T. Frank, Philipp Hönle, and Karl Eduard Linsenmair from Julius-Maximilians-Universität Würzburg (JMU) in Bavaria, Germany, discovered. The biologists' results have been published in the Journal of Experimental Biology.

Individual ants make decisions

"Other ant species are known to rely on various navigational aids to determine the shortest way back to the nest from a foraging site," Erik Franks says. The navigational skills of the Matabele ants seem to be even more complex, a finding the researchers want to explore in greater detail now.

Moreover, the JMU scientists were surprised that the decision which way to take is made by individual ants and not collectively. "We have thus provided the first proof of time optimized path integration by individuals in the ant kingdom," says Frank who is currently conducting postdoc research at the University of Lausanne.

From Science Daily

Can a quantum drum vibrate and stand still at the same time?

Researchers have studied how a 'drumstick' made of light could make a microscopic 'drum' vibrate and stand still at the same time.

A team of researchers from the UK and Australia have made a key step towards understanding the boundary between the quantum world and our everyday classical world.

Quantum mechanics is truly weird. Objects can behave like both particles and waves, and can be both here and there at the same time, defying our common sense. Such counterintuitive behaviour is typically confined to the microscopic realm and the question "why don't we see such behaviour in everyday objects?" challenges many scientists today.

Now, a team of researchers have developed a new technique to generate this type of quantum behaviour in the motion of a tiny drum just visible to the naked eye. The details of their research are published today in New Journal of Physics.

Project principal investigator, Dr Michael Vanner from the Quantum Measurement Lab at Imperial College London, said: "Such systems offer significant potential for the development of powerful new quantum-enhanced technologies, such as ultra-precise sensors, and new types of transducers.

"Excitingly, this research direction will also enable us to test the fundamental limits of quantum mechanics by observing how quantum superpositions behave at a large scale."

Mechanical vibrations, such as those that create the sound from a drum, are an important part of our everyday experience. Hitting a drum with a drumstick causes it to rapidly move up and down, producing the sound we hear.

In the quantum world, a drum can vibrate and stand still at the same time. However, generating such quantum motion is very challenging. lead author of the project Dr Martin Ringbauer from the University of Queensland node of the Australian Research Council Centre for Engineered Quantum Systems, said: "You need a special kind of drumstick to make such a quantum vibration with our tiny drum."

In recent years, the emerging field of quantum optomechanics has made great progress towards the goal of a quantum drum using laser light as a type of drumstick. However, many challenges remain, so the authors' present study takes an unconventional approach.

Dr Ringbauer continues: "We adapted a trick from optical quantum computing to help us play the quantum drum. We used a measurement with single particles of light -- photons -- to tailor the properties of the drumstick.

"This provides a promising route to making a mechanical version of Schrodinger's cat, where the drum vibrates and stands still at the same time."

These experiments have made the first observation of mechanical interferences fringes, which is a crucial step forward for the field.

In the experiment, the fringes were at a classical level due to thermal noise, but motivated by this success, the team are now working hard to improve their technique and operate the experiments at temperatures close to absolute zero where quantum mechanics is expected to dominate.

Read more at Science Daily

Limiting warming to 1.5 degree C would save majority of global species from climate change

Can we keep global warming to 1.5 degrees Celsius?

Limiting global warming to 1.5oC would save the vast majority of the world's plant and animal species from climate change -- according to new research led by the University of East Anglia.

A new report published today in Science reveals that limiting warming to the ultimate goal of the Paris Agreement would avoid half the risks assoCiated with warming of 2oC for plants and animals, and two thirds of the risks for insects.

Species across the globe would benefit -- but particularly those in Southern Africa, the Amazon, Europe and Australia.

Reducing the risk to insects is particularly important, the team say, because they are so vital for 'ecosystem services' such as pollinating crops and flowers, and being part of the food chain for other birds and animals.

Previous research focused on quantifying the benefits of limiting warming to 2oC above pre-industrial times -- the upper limit for temperature as set out in the Paris Agreement -- and did not look at insects.

This is the first study to explore how limiting warming to 1.5oC would benefit species globally.

Researchers at UEA and James Cook University in Australia studied some 115,000 species including 31,000 insects, 8,000 birds, 1,700 mammals, 1,800 reptiles, 1,000 amphibians and 71,000 plants in this, the largest scale study of its kind.

Lead researcher Prof Rachel Warren, from the Tyndall Centre for Climate Change Research at UEA, said: "We wanted to see how different projected climate futures caused areas to become climatically unsuitable for the species living there.

"We measured the risks to biodiversity by counting the number of species projected to lose more than half their geographic range due to climate change.

"We found that achieving the ultimate goal of the Paris Agreement, to limit warming to 1.5oC above pre-industrial levels, would reap enormous benefits for biodiversity -- much more so than limiting warming to 2oC.

"Insects are particularly sensitive to climate change. At 2oC warming, 18 per cent of the 31,000 insects we studied are projected to lose more than half their range.

"This is reduced to 6 per cent at 1.5oC. But even at 1.5oC, some species lose larger proportions of their range.

"The current global warming trajectory, if countries meet their international pledges to reduce CO2, is around 3oC. In this case, almost 50 per cent of insects would lose half their range.

"This is really important because insects are vital to ecosystems and for humans. They pollinate crops and flowers, they provide food for higher-level organisms, they break down detritus, they maintain a balance in ecosystems by eating the leaves of plants, and they help recycle nutrients in the soil.

"We found that the three major groups of insects responsible for pollination are particularly sensitive to warming.

"If temperatures rise by 3oC, ecosystem services provided by insects would be greatly reduced. Other research has already shown that insects are already in decline for other reasons, and this research shows that climate change would really compound the problem."

The study includes the ability of species to reloCate to more suitable loCations as the world warms. Birds, mammals and butterflies have the greatest ability to disperse. The dispersal means that a small number of species can gain in range by 2100.

Prof Warren added: "If warming is limited to 1.5oC by 2100 then more species can keep up or even gain in range, whereas if warming reached 2oC by 2100 many species cannot keep up and far more species lose large parts of their range."

Co-author Dr Jeff Price, also from UEA, added: "Examples of animals to really benefit from limiting warming to 1.5 include the critically endangered Black RhinoCeros, which is already highly threatened by poaching and habitat loss.

Read more at Science Daily

New genes found that determine how the heart responds to exercise

A new study by researchers at Queen Mary University of London and University College London (UCL) has discovered 30 new gene locations that determine how the heart responds to and recovers from exercise.

The study, published in the journal Nature Communications, was conducted using the genetic and electrocardiogram data of 67,000 people from UK Biobank.

The findings could be used to improve the identification of people with impaired heart rate during recovery and those at higher risk of heart disease mortality.

The difference in heart rate response to exercise was as much as 3.15 beats per minute, depending on the genetic risk score of an individual, while the difference in heart rate response to recovery differed by as much as 10.4 beats per minute.

Lead researcher Patricia Munroe, Professor of Molecular Medicine at Queen Mary's William Harvey Research Institute said: "Our findings advance our knowledge on key pathways controlling heart rate response to exercise and recovery, information which may be valuable in the future for cardiovascular risk prediction."

Co-lead researcher Pier Lambiase, Professor of Cardiology at UCL said: "This first study by our "Electrogenomics" group is a wonderful example of the power of the collaboration between UCL Electrophysiology & QMUL Genomics, opening new avenues to dissect the mechanistic links between heart control and cardiovascular outcomes."

The results have implications to target new therapies to treat abnormal heart rhythms and potentially increase heart health.

From Science Daily

Giraffes surprise biologists yet again

This is a group of juvenile giraffes.

New research from the University of Bristol has highlighted how little we know about giraffe behaviour and ecology.

It is commonly accepted that group sizes of animals increase when there is a risk of predation, since larger group sizes reduce the risk of individuals being killed, and there are 'many eyes' to spot any potential predation risk.

Now, in the first study of its kind, Bristol PhD student Zoe Muller from the School of Biological Sciences has found that this is not true for giraffes, and that the size of giraffe groups is not influenced by the presence of predators.

Zoe Muller said: "This is surprising, and highlights how little we know about even the most basic aspects of giraffe behaviour."

This study investigates how the grouping behaviour of giraffes differed in response to numerous factors, such as predation risk, habitat type and the characteristics of individuals.

Habitat type had some effect on group size, but the main effect on group size was in the behaviour of adult females, who were found to be in smaller groups when they had calves.

This is contrary to another popular belief that female giraffes form large groups to communally care for their young -- this study, published this week in the Journal of Zoology presents the first evidence to show that actually, the opposite is true.

Giraffe populations have declined by 40 percent in the last 30 years, and there are now thought to be fewer than 98,000 individuals remaining in the wild.

In recognition of their drastic decline in the wild, they have recently been listed as "Vulnerable" on the International Union for Conservation in Nature's Red List of Threatened Species.

However, conservation review is ongoing due to current debate over their taxonomic status, since some subspecies may be even more at risk of extinction than is currently recognised.

Zoe Muller added: "This research adds another important piece to the puzzle of understanding how giraffes live in the wild.

"Giraffes are a threatened species, suffering ongoing decline across Africa, and this research highlights how they are actually an incredibly misunderstood species. We can only manage and conserve giraffe populations effectively if we properly understand their behaviour and ecology, which we are only just beginning to do.

"Despite their prominence, giraffes have been significantly understudied in comparison to other charismatic African mammals. "The common misconception is that giraffes are 'everywhere' in Africa, yet recent research efforts have highlighted the fragmented and rapidly declining nature of their populations.

"Their recent listing as 'Vulnerable' on the IUCN red list is a valuable step towards recognising their potential to become extinct, and more research is sorely needed to understand the threats and challenges they face in the wild."

Read more at Science Daily

Smarter brains run on sparsely connected neurons

Erhan Genc investigates how intelligence is reflected in brain structures.

The more intelligent a person, the fewer connections there are between the neurons in his cerebral cortex. This is the result of a study conducted by neuroscientists working with Dr Erhan Genç and Christoph Fraenz at Ruhr-Universität Bochum; the study was performed using a specific neuroimaging technique that provides insights into the wiring of the brain on a microstructural level.

Together with colleagues from the University of New Mexico in Albuquerque, Humboldt University of Berlin and the Lovelace Biomedical and Environmental Research Institute in Albuquerque, the team from the biopsychology research unit in Bochum published their report in the journal Nature Communications on May 15, 2018.

Intelligence is determined by the number of dendrites

The researchers analysed the brains of 259 men and women using neurite orientation dispersion and density imaging. This method enabled them to measure the amount of dendrites in the cerebral cortex, i.e. extensions of nerve cells that are used by the cells to communicate with each other. In addition, all participants completed an IQ test. Subsequently, the researchers associated the gathered data with each other and found out: the more intelligent a person, the fewer dendrites there are in their cerebral cortex.

Using an independent, publicly accessible database, which had been compiled for the Human Connectome Project, the team confirmed these results in a second sample of around 500 individuals.

Previously conflicting results are thus explained

The new findings provide an explanation of conflicting results gathered in intelligence research to date. For one, it had been previously ascertained that intelligent people tend to have larger brains. "The assumption has been that larger brains contain more neurons and, consequently, possess more computational power," says Erhan Genç. However, other studies had shown that -- despite their comparatively high number of neurons -- the brains of intelligent people demonstrated less neuronal activity during an IQ test than the brains of less intelligent individuals.

"Intelligent brains possess lean, yet efficient neuronal connections," concludes Erhan Genç. "Thus, they boast high mental performance at low neuronal activity."

From Science Daily

More than a living syringe: Mosquito saliva alone triggers unexpected immune response

Aedes aegypti mosquitoes after a blood meal.

Mosquito season is around the corner, bringing with it a higher risk of catching potentially serious diseases transmitted by their bite. Mosquitoes also may increase the severity of the diseases they transmit, and researchers think that mosquito saliva plays an active role in this process. A team of researchers at Baylor College of Medicine has taken a closer look at the effect of mosquito saliva alone and found that it can trigger an unexpected variety of immune responses in an animal model of the human immune system. These results offer an opportunity to develop effective strategies to prevent mosquito-based transmission of disease. The study appears in the journal PLOS Neglected Tropical Diseases.

"Billions of people worldwide are exposed to diseases transmitted by mosquitoes, and many of these conditions do not have effective treatments," said corresponding author Dr. Rebecca Rico-Hesse, professor of molecular virology and microbiology at Baylor College of Medicine. "One of the interests of my lab is to study the development of dengue fever, which is caused by the dengue virus transmitted by mosquito Aedes aegypti."

The World Health Organization has estimated that 100 million dengue virus infections and 22,000 deaths occur yearly worldwide, mostly among children. According to the Centers for Disease Control and Prevention, more than one-third of the world's population lives in areas at risk of infection, making the dengue virus a leading cause of illness and death in the tropics and subtropics.

"One of the main limitations for studying dengue fever is that the dengue virus only causes the disease in humans; no other animals can be used as models of the condition to develop preventive and therapeutic measures," Rico-Hesse said. "To overcome this challenge, we have been working with a mouse model of the human immune system."

These 'humanized mice' were developed by other research groups from mice naturally born without their own immune system. These severely immunodeficient mice received human stem cells that gave rise to many of the components of the human immune system, creating a living humanized animal model in which Rico-Hesse and her colleagues can study factors that may affect the development of dengue fever.

"In 2012, we demonstrated in these humanized mice that mosquito-bite delivery and needle-injection delivery of dengue virus led to significantly different disease developments," Rico-Hesse said. "Importantly, mosquito-bite delivery of the virus resulted in a more human-like disease than the one we observed after needle-injection delivery of the virus. When the mosquitoes delivered the virus, the mice had more of a rash, more fever and other characteristics that mimic the disease presentation in humans."

These observations support the idea that mosquitoes are not just acting like 'syringes,' merely injecting viruses into the animals they feed on. Their saliva seems to contribute significantly to the development of the disease, which has prompted Rico-Hesse and her colleagues to investigate what this role might be. They began by determining the effect of bites from virus-free mosquitoes on the human immune response of humanized mice.

An unexpected complex response

To test the effect of virus-free mosquito saliva on humanized mice, the researchers held a vial containing mosquitoes against a footpad of anesthetized humanized mice, allowing a total of four mosquitoes to feed on both footpads.

The researchers then took blood and a number of other tissue samples six hours, 24 hours and seven days after the mosquitoes bit the mice, and determined the levels of cytokines, molecules that modulate the immune response, as well as the number and activity of different types of immune cells. They compared these results with those obtained from humanized mice that had not been bitten by mosquitoes.

To make the above determinations, the researchers used highly-sensitive techniques -- flow cytometry for immune cell analysis and multiplex cytokine bead array analysis for cytokines -- that allowed them to dissect the immune responses in great detail. This approach produced surprising results.

"We found that mosquito-delivered saliva induced a varied and complex immune response we were not anticipating," said co-author Dr. Silke Paust, assistant professor of pediatrics at Baylor and Texas Children's Hospital. "For instance, both the immune cell responses and the cytokine levels were affected. We saw activation of T helper cells 1, which generally contribute to antiviral immunity, as well as activation of T helper cells 2, which have been linked to allergic responses."

At various time points, the levels and activities of other types of immune cells also increased as others decreased. Overall, the researchers found evidence that mosquito saliva alone can trigger long-lasting immune responses -- up to seven days post-bite -- in multiple tissue types, including blood, skin and bone marrow.

"The diversity of the immune response was most striking to me. This is surprising given that no actual infection with any type of infectious agent occurred," said Paust, who also is a member of the Dan L Duncan Comprehensive Cancer Center at Baylor College of Medicine. "These results are evidence that components in the mosquito saliva can modulate the immune response in humanized mice."

The researchers will continue this study by investigating which of the more than 100 proteins in mosquito saliva are mediating the effects on the immune system, or may help the virus become more infectious. Identifying these proteins could help design strategies to fight transmission of dengue fever, as well as other diseases caused by viruses also transmitted by Aedes aegypti, such as Zika virus, chikungunya virus and yellow fever virus.

Read more at Science Daily

Quarks feel the pressure in the proton

Nuclear physicists have found that the proton's building blocks, the quarks, are subjected to a pressure of 100 decillion Pascal (1035) near the center of a proton, which is about 10 times greater than the pressure in the heart of a neutron star.

Inside every proton in every atom in the universe is a pressure cooker environment that surpasses the atom-crushing heart of a neutron star. That's according to the first measurement of a mechanical property of subatomic particles, the pressure distribution inside the proton, which was carried out by scientists at the Department of Energy's Thomas Jefferson National Accelerator Facility.

The nuclear physicists found that the proton's building blocks, the quarks, are subjected to a pressure of 100 decillion Pascal (1035) near the center of a proton, which is about 10 times greater than the pressure in the heart of a neutron star. The result was recently published in the journal Nature.

"We found an extremely high outward-directed pressure from the center of the proton, and a much lower and more extended inward-directed pressure near the proton's periphery," explains Volker Burkert, Jefferson Lab Hall B Leader and a co-author on the paper.

Burkert says that the distribution of pressure inside the proton is dictated by the strong force, the force that binds three quarks together to make a proton.

"Our results also shed light on the distribution of the strong force inside the proton," he said. "We are providing a way of visualizing the magnitude and distribution of the strong force inside the proton. This opens up an entirely new direction in nuclear and particle physics that can be explored in the future."

Once thought impossible to obtain, this measurement is the result of a clever pairing of two theoretical frameworks with existing data.

First, there are the generalized parton distributions. GPDs allow researchers to produce a 3D image of the proton's structure as probed by the electromagnetic force. The second are the gravitational form factors of the proton. These form factors describe what the mechanical structure of the proton would be if researchers could probe the proton via the gravitational force.

The theorist who developed the concept of gravitational form factors in 1966, Heinz Pagels, famously observed in the paper detailing them that there was "very little hope of learning anything about the detailed mechanical structure of a particle, because of the extreme weakness of the gravitational interaction."

Recent theoretical work, however, has connected GPDs to the gravitational form factors, allowing the results from electromagnetic probes of protons to substitute for gravitational probes.

"This is the beauty of it. You have this map that you think you will never get," said Latifa Elouadrhiri, a Jefferson Lab staff scientist and co-author on the paper. "But here we are, filling it in with this electromagnetic probe."

The electromagnetic probe consists of beams of electrons produced by the Continuous Electron Beam Accelerator Facility, a DOE Office of Science User Facility. These electrons are directed into the nuclei of atoms, where they interact electromagnetically with the quarks inside protons via a process called deeply virtual Compton scattering.

In the DVCS process, an electron enters a proton and exchanges a virtual photon with a quark, transferring energy to the quark and proton. A short time later, the proton releases this energy by emitting another photon and continues on intact. This process is analogous to the calculations Pagels performed for how it would be possible to probe the proton gravitationally via a hypothetical beam of gravitons. The Jefferson Lab researchers were able to exploit a similarity between the well-known electromagnetic and hypothetical gravitational studies to get their result.

"There's a photon coming in and a photon coming out. And the pair of photons both are spin-1. That gives us the same information as exchanging one graviton particle with spin-2," says Francois-Xavier Girod, a Jefferson Lab staff scientist and co-author on the paper. "So now, one can basically do the same thing that we have done in electromagnetic processes -- but relative to the gravitational form factors, which represent the mechanical structure of the proton."

Read more at Science Daily

How the gut influences neurologic disease

Scientists examined gut microbes and the influence of changes in diet in mice.

A study published this week in Nature sheds new light on the connection between the gut and the brain, untangling the complex interplay that allows the byproducts of microorganisms living in the gut to influence the progression of neurodegenerative diseases. Investigators from Brigham and Women's Hospital (BWH) have been using both animal models and human cells from patients to tease out the key players involved in the gut-brain connection as well as in the crosstalk between immune cells and brain cells. Their new publication defines a pathway that may help guide therapies for multiple sclerosis and other neurologic diseases.

"These findings provide a clear understanding of how the gut impacts central nervous system resident cells in the brain," said corresponding author Francisco Quintana, PhD, of the Ann Romney Center for Neurologic Diseases at BWH. "Now that we have an idea of the players involved, we can begin to go after them to develop new therapies."

The new research focuses on the influence of gut microbes on two types of cells that play a major role in the central nervous system: microglia and astrocytes. Microglia are an integral part of the body's immune system, responsible for scavenging the CNS and getting rid of plaques, damaged cells and other materials that need to be cleared. But microglia can also secrete compounds that induce neurotoxic properties on the star-shaped brain cells known as astrocytes. This damage is thought to contribute to many neurologic diseases, including multiple sclerosis.

Brigham researchers have previously explored the gut-brain connection to gain insights into multiple sclerosis. Although some studies have examined how byproducts from organisms living in the gut may promote inflammation in the brain, the current study is the first to report on how microbial products may act directly on microglia to prevent inflammation. The team reports that the byproducts that microbes produce when they break down dietary tryptophan -- an amino acid found in turkey and other foods -- may limit inflammation in the brain through their influence on microglia.

To conduct their study, the research team examined gut microbes and the influence of changes in diet in a mouse model of multiple sclerosis. They found that compounds resulting from the breakdown of tryptophan can cross the blood-brain barrier, activating an anti-inflammatory pathway that limits neurodegeneration. The researchers also studied human multiple sclerosis brain samples, finding evidence of the same pathway and players.

Activation of this same pathway has recently been linked to Alzheimer's disease and glioblastoma. The Ann Romney Center for Neurologic Diseases, of which Quintana is a part, brings experts together to accelerate treatment for these diseases, as well as multiple sclerosis Parkinson's disease and ALS (Lou Gehrig's disease).

"It is likely the mechanisms we've uncovered are relevant for other neurologic diseases in addition to multiple sclerosis," said Quintana. "These insights could guide us toward new therapies for MS and other diseases."

Read more at Science Daily

Critically endangered South American forests were planted by ancient peoples

Campos da Serra y Floresta de Araucari.

Critically endangered South American forests thought to be the result of climate change were actually spread by ancient communities, archaeologists have found.

Huge swathes of land in Chile, Brazil and Argentina are covered with millions of Araucaria, or monkey puzzle trees, thanks to people planting or cultivating them more than a thousand years ago, a new study shows. Recent logging means the landscape is now one of the world's most at-risk environments.

It had been thought the forests expanded due to wetter and warmer weather. But the research shows the rapidly expanding pre-Columbian population of South America, Southern Jê communities, were really responsible.

New excavations and soil analysis shows the forests, still hugely culturally and economically important to people living in South America, expanded between 1,410 and 900 years ago because of population growth and cultural changes.

Dr Mark Robinson, from the University of Exeter, who led the British Academy and AHRC-FAPESP-funded research, said: "Our research shows these landscapes were human-made. Communities settled on grassland, and then -- perhaps because they modified the soil, protected seedlings or even planted trees -- established these forests in places where geographically they shouldn't have flourished."

The forests date back to the period when dinosaurs roamed. The iconic monkey puzzle tree, or Parana pine, has grown in the region for thousands of years. Its nuts were one of the most important food sources for ancient communities, attracted game for hunting when nuts were ripe. They were also a valuable source of timber, fuel and resin, and became an integral part of southern Jê cosmology. Communities still call themselves "people of the Araucaria," and hold festivals to celebrate the forests.

Of the 19 species of Araucaria tree, five are classified as endangered and two, including the Brazilian Araucaria angustifolia, are critically endangered. Reports from the late 1800s describe trees with diameters of over 2 m, reaching 42 m in height. Modern trees are only around 17.7 m tall.

The archaeological analysis began because the experts, from the University of Exeter, University of Reading, University of São Paulo, University of New Mexico, Universidade Federal de Pelotas and Universidade do Sul de Santa Catarina, noticed that in areas of low human activity forests are limited to south-facing slopes, whereas in areas of extensive archaeology, forests cover the entire landscape. They were able to analyse soil isotopes reflecting vegetation and archaeological evidence from Campo Belo do Sul, Santa Catarina State, Brazil, to test whether this pattern was directly related to past human activity.

The study shows the forests first expanded around 4,480 to 3,200 years ago, most likely near streams, and this may have been caused by a wetter climate. But a more rapid and extensive expansion across the whole region later happened between 1,410 and 900 years ago, when forests expanded into highland areas. The weather during this time was dry and less humid. This expansion of the forests coincides with population growth and increasingly complex and hierarchical societies in South America.

The expansion in forests reached a peak around 800 years ago. The number of people in South America declined 400 years ago when European settlers arrived in the area. The population did not begin to recover until the 19 century, when loggers began exploiting the Araucaria forests for timber.

Professor José Iriarte, from the University of Exeter, another member of the research team, said: "This study shows the Araucaria forests were expanded beyond their natural boundaries, they were used sustainably for hundreds of years, and conservation strategies must reflect this so they balance protection, heritage and economic development."

Read more at Science Daily