Evolutionary backing found in analysis of mammalian vertebrae

Two-toed sloth.

Differences in numbers of vertebrae are most extreme in mammals which do not rely on running and leaping, such as those adapted to suspensory locomotion like apes and sloths, a team of anthropologists has concluded in a study appearing in the journal Nature Ecology & Evolution.

Previous research had posited that running speed specifically determines variation in vertebral numbers -- a conclusion not supported by the new work.

"The classic body plan of many mammals is built on a mobile back and this body plan is conserved regardless of running speed," explains New York University anthropologist Scott Williams, the paper's senior author. "More specifically, we find that a particular type of locomotor behavior -- suspensory locomotion, which involves hanging below tree branches, rather than speed -- is associated with increases in variation in numbers of vertebrae across mammals."

The work centers on an effort to better understand why certain aspects of mammals remain consistent over time -- a phenomenon known as evolutionary stasis.

Despite the diversity evolution has yielded, there remain consistencies across a wide range of distantly related organisms. Of particular note is the number neck (cervical) and back (thoracic and lumbar) vertebrae of mammals.

"Nearly all mammals have the same number of cervical vertebrae, no matter how long or short their necks are -- humans, giraffes, mice, whales, and platypuses all have exactly seven cervical vertebrae," explains co-author Jeff Spear, an NYU doctoral student.

In fact, the majority of mammals possess 19 or 20 thoracic and lumbar vertebrae, for a total of 26 or 27 "CTL" vertebrae (for "cervical, thoracic, and lumbar" vertebrae). There is little variation in these numbers, either within species or across different species -- or even different species separated by over 160 million years of evolution. Humans, with 24 CTL, are one of the exceptions.

Earlier work had hypothesized that fast running constrains the number of CTL vertebrae in mammals and that slower mammals are freer to vary their CTL numbers, suggesting an association between speed and vertebrae count. However, this conclusion was based on data from a limited sample of mammalian diversity.

In order to learn what causes evolutionary stasis, and why there are exceptions, such as in humans, the scientists aimed to create a clearer picture using a larger and more diverse sample of mammals and phylogenetic methods -- those that account for evolutionary relatedness in analyses.

In their study, they counted the vertebrae of thousands of individuals for nearly 300 species of mammals. The researchers then compared variation in the number of CTL vertebrae to traits such as speed, habitat, locomotion, spine mobility, posture, and limb use.

The analyses did not seem to show an association between vertebrae count and running speed. Rather, this trend was primarily driven by animals adapted to suspensory and other "antipronograde" behaviors, where limbs are held in tension during slow climbing, clambering, and suspension.

This observation led the researchers to hypothesize that the classic body plan of certain mammals -- therian mammals, which give birth to live young -- is built on a mobile back and that this body plan is conserved regardless of running speed.

This was based on an existing understanding of genetic activity relevant to vertebrae.

"Changes in types of vertebrae are determined by Hox genes -- the genes that organize animal bodies along the head-tail axis, ensuring that your eyes go on your face and your legs go at the base of your torso," explains Spear. "But changes in Hox gene expression sometimes creates vertebrae that are intermediate in type, which can impinge the mobility of the spine."

For animals following the ancestral body plan, from possums to tigers, departures from the ancestral types of vertebrae in the back creates a risk of inefficient locomotion and are weeded out by natural selection, he adds.

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Small, hardy planets most likely to survive death of their stars

White dwarf illustration.

Small, hardy planets packed with dense elements have the best chance of avoiding being crushed and swallowed up when their host star dies, new research from the University of Warwick has found.

Astrophysicists from the Astronomy and Astrophysics Group have modelled the chances of different planets being destroyed by tidal forces when their host stars become white dwarfs and have determined the most significant factors that decide whether they avoid destruction.

Their 'survival guide' for exoplanets could help guide astronomers locate potential exoplanets around white dwarf stars, as a new generation of even more powerful telescopes is being developed to search for them. Their research is published in the Monthly Notices of the Royal Astronomical Society.

Most stars like our own Sun will run out of fuel eventually and shrink and become white dwarfs. Some orbiting bodies that aren't destroyed in the maelstrom caused when the star blasts away its outer layers will then be subjected to shifts in tidal forces as the star collapses and becomes super-dense. The gravitational forces exerted on any orbiting planets would be intense and would potentially drag them into new orbits, even pushing some further out in their solar systems.

By modelling the effects of a white dwarf's change in gravity on orbiting rocky bodies, the researchers have determined the most likely factors that will cause a planet to move within the star's 'destruction radius'; the distance from the star where an object held together only by its own gravity will disintegrate due to tidal forces. Within the destruction radius a disc of debris from destroyed planets will form.

Although a planet's survival is dependent on many factors, the models reveal that the more massive the planet, the more likely that it will be destroyed through tidal interactions.

But destruction is not certain based on mass alone: low viscosity exo-Earths are easily swallowed even if they reside at separations within five times the distance between the centre of the white dwarf and its destruction radius. Saturn's moon Enceladus -- often described as a 'dirty snowball' -- is a good example of a homogeneous very low viscosity planet.

High viscosity exo-Earths are easily swallowed only if they reside at distances within twice the separation between the centre of the white dwarf and its destruction radius. These planets would be composed entirely of a dense core of heavier elements, with a similar composition to the 'heavy metal' planet discovered by another team of University of Warwick astronomers recently. That planet has avoided engulfment because it is as small as an asteroid.

Dr Dimitri Veras, from the University of Warwick's Department of Physics, said: "The paper is one of the first-ever dedicated studies investigating tidal effects between white dwarfs and planets. This type of modelling will have increasing relevance in upcoming years, when additional rocky bodies are likely to be discovered close to white dwarfs."

"Our study, while sophisticated in several respects, only treats homogenous rocky planets that are consistent in their structure throughout. A multi-layer planet, like Earth, would be significantly more complicated to calculate but we are investigating the feasibility of doing so too."

Distance from the star, like the planet's mass, has a robust correlation with survival or engulfment. There will always be a safe distance from the star and this safe distance depends on many parameters. In general, a rocky homogenous planet which resides at a location from the white dwarf which is beyond about one-third of the distance between Mercury and the Sun is guaranteed to avoid being swallowed from tidal forces.

Dr Veras said: "Our study prompts astronomers to look for rocky planets close to -- but just outside of -- the destruction radius of the white dwarf. So far observations have focussed on this inner region, but our study demonstrates that rocky planets can survive tidal interactions with the white dwarf in a way which pushes the planets slightly outward.

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Treats might mask animal intelligence

Rat with cheese.

Rewards are frequently used to promote learning, but rewards may actually mask true knowledge, finds a new Johns Hopkins University study with rodents and ferrets.

The findings, published May 14 in Nature Communications, show a distinction between knowledge and performance, and provide insight into how environment can affect the two.

"Most learning research focuses on how humans and other animals learn 'content' or knowledge. Here, we suggest that there are two parallel learning processes: one for content and one for context, or environment. If we can separate how these two pathways work, perhaps we can find ways to improve performance," says Kishore Kuchibhotla, an assistant professor in The Johns Hopkins University's department of psychological and brain sciences and the study's lead author.

While researchers have known that the presence of reinforcement, or reward, can change how animals behave, it's been unclear exactly how rewards affect learning versus performance.

An example of the difference between learning and performance, Kuchibhotla explains, is the difference between a student studying and knowing the answers at home, and a student demonstrating that knowledge on a test at school.

"What we know at any given time can be different than what we show; the ability to access that knowledge in the right environment is what we're interested in," he says.

To investigate what animals know in hopes of better understanding learning, Kuchibhotla and the research team trained mice, rats and ferrets on a series of tasks, and measured how accurately they performed the tasks with and without rewards.

For the first experiment, the team trained mice to lick for water through a lick tube after hearing one tone, and to not lick after hearing a different, unrewarded tone. It takes mice two weeks to learn this in the presence of the water reward. At a time point early in learning, around days 3-5, the mice performed the task at chance levels (about 50%) when the lick tube/reward was present. When the team removed the lick tube entirely on these early days, however, the mice performed the task at more than 90% accuracy. The mice, therefore, seemed to understand the task many days before they expressed knowledge in the presence of a reward.

To confirm this finding with other tasks and animals, the team also had mice press a lever for water when they heard a certain tone; prompted rats to look for food in a cup if they heard a tone, but not if a light appeared before the tone; had rats press a lever for sugar water when a light was presented before a tone; had rats push lever for sugar water when they heard a certain tone, and prompted ferrets to differentiate between two different sounds for water. In all experiments, the animals performed better when rewards weren't available.

"Rewards, it seems, help improve learning incrementally, but can mask the knowledge animals have actually attained, particularly early in learning," says Kuchibhotla. Furthermore, the finding that all animals' performance improved across the board without rewards, suggest that variability in learning rates may be due to differences in the animals' sensitivity to reward context rather than differences in intelligence.

The dissociation between learning and performance, the researchers suggest, may someday help us isolate the root causes of poor performance. While the study involved only rodents and ferrets, Kuchibhotla says it may be possible to someday help animals and humans alike better access content when they need it if the right mechanisms within the brain can be identified and manipulated.

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Room for thought: Brain region that watches for walls identified

Illustration of human brain highlighting the occipital lobe.

To move through the world, you need a sense of your surroundings, especially of the constraints that restrict your movement: the walls, ceiling and other barriers that define the geometry of the navigable space around you. And now, a team of neuroscientists has identified an area of the human brain dedicated to perceiving this geometry. This brain region encodes the spatial constraints of a scene, at lightning-fast speeds, and likely contributes to our instant sense of our surroundings; orienting us in space, so we can avoid bumping into things, figure out where we are and navigate safely through our environment.

This research, published today in Neuron, sets the stage for understanding the complex computations our brains do to help us get around. Led by scientists at Columbia University's Mortimer B. Zuckerman Mind Brain Behavior Institute and Aalto University in Finland, the work is also relevant to the development of artificial intelligence technology aimed at mimicking the visual powers of the human brain.

"Vision gives us an almost instant sense where we are in space, and in particular of the geometry of the surfaces -- the ground, the walls -- which constrain our movement. It feels effortless, but it requires the coordinated activity of multiple brain regions," said Nikolaus Kriegeskorte, PhD, a principal investigator at Columbia's Zuckerman Institute and the paper's senior author. "How neurons work together to give us this sense of our surroundings has remained mysterious. With this study, we are a step closer to solving that puzzle."

To figure out how the brain perceives the geometry of its surroundings, the research team asked volunteers to look at images of different three-dimensional scenes. An image might depict a typical room, with three walls, a ceiling and a floor. The researchers then systematically changed the scene: by removing the wall, for instance, or the ceiling. Simultaneously, they monitored participants' brain activity through a combination of two cutting-edge brain-imaging technologies at Aalto's neuroimaging facilities in Finland.

"By doing this repeatedly for each participant as we methodically altered the images, we could piece together how their brains encoded each scene," Linda Henriksson, PhD, the paper's first author and a lecturer in neuroscience and biomedical engineering at Aalto University.

Our visual system is organized into a hierarchy of stages. The first stage actually lies outside brain, in the retina, which can detect simple visual features. Subsequent stages in the brain have the power to detect more complex shapes. By processing visual signals through multiple stages -- and by repeated communications between the stages -- the brain forms a complete picture of the world, with all its colors, shapes and textures.

In the cortex, visual signals are first analyzed in an area called the primary visual cortex. They are then passed to several higher-level cortical areas for further analyses. The occipital place area (OPA), an intermediate-level stage of cortical processing, proved particularly interesting in the brain scans of the participants.

"Previous studies had shown that OPA neurons encode scenes, rather than isolated objects," said Dr. Kriegeskorte, who is also a professor of psychology and neuroscience and director of cognitive imaging at Columbia. "But we did not yet understand what aspect of the scenes this region's millions of neurons encoded."

After analyzing the participants' brain scans, Drs. Kriegeskorte and Henriksson found that the OPA activity reflected the geometry of the scenes. The OPA activity patterns reflected the presence or absence of each scene component -- the walls, the floor and the ceiling -- conveying a detailed picture of the overall geometry of the scene. However, the OPA activity patterns did not depend on the components' appearance; the textures of the walls, floor and ceiling -- suggesting that the region ignores surface appearance, so as to focus solely on surface geometry. The brain region appeared to perform all the necessary computations needed to get a sense of a room's layout extremely fast: in just 100 milliseconds.

"The speed with which our brains sense the basic geometry of our surroundings is an indication of the importance of having this information quickly," said Dr. Henriksson. "It is key to knowing whether you're inside or outside, or what might be your options for navigation."

The insights gained in this study were possible through the joint use of two complementary imaging technologies: functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG). fMRI measures local changes in blood oxygen levels, which reflect local neuronal activity. It can reveal detailed spatial activity patterns at a resolution of a couple of millimeters, but it is not very precise in time, as each fMRI measurement reflects the average activity over a five to eight seconds. By contrast, MEG measures magnetic fields generated by the brain. It can track activity with millisecond temporal precision, but does not give as spatially detailed a picture.

"When we combine these two technologies, we can address both where the activity occurs and how quickly it emerges." said Dr. Henriksson, who collected the imaging data at Aalto University.

Moving forward, the research team plans to incorporate virtual reality technology to create more realistic 3D environments for participants to experience. They also plan to build neural network models that mimic the brain's ability to perceive the environment.

"We would like to put these things together and build computer vision systems that are more like our own brains, systems that have specialized machinery like what we observe here in the human brain for rapidly sensing the geometry of the environment," said Dr. Kriegeskorte.

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Matter around a young star helps astronomers explore our stellar history

Orion Nebula.

Astronomers map the substance aluminum monoxide (AlO) in a cloud around a distant young star -- Origin Source I. The finding clarifies some important details about how our solar system, and ultimately we, came to be. The cloud's limited distribution suggests AlO gas rapidly condenses to solid grains, which hints at what an early stage of our solar evolution looked like.

Professor Shogo Tachibana of the UTokyo Organization for Planetary and Space Science has a passion for space. From small things like meteorites to enormous things like stars and nebulae -- huge clouds of gas and dust in space -- he is driven to explore our solar system's origins.

"I have always wondered about the evolution of our solar system, of what must have taken place all those billions of years ago," he said. "This question leads me to investigate the physics and chemistry of asteroids and meteorites."

Space rocks of all kinds greatly interest astronomers as these rocks can remain largely unchanged since the time our sun and planets formed from a swirling cloud of gas and dust. They contain records of the conditions at that time -- generally considered to be 4.56 billion years ago -- and their properties such as composition can tell us about these early conditions.

"On my desk is a small piece of the Allende meteorite, which fell to Earth in 1969. It's mostly dark but there are some scattered white inclusions (foreign bodies enclosed in the rock), and these are important," continued Tachibana. "These speckles are calcium and aluminum-rich inclusions (CAIs), which were the first solid objects formed in our solar system."

Minerals present in CAIs indicate that our young solar system must have been extremely hot. Physical techniques for dating these minerals reveal a fairly specific age for the solar system. However, Tachibana and colleagues wished to expand on the details of this stage of evolution.

"There are no time machines to explore our own past, so we wanted to see a young star that could share traits with our own," said Tachibana. "With the Atacama Large Millimeter/submillimeter Array (ALMA), we found the emission lines -- a chemical fingerprint -- for AlO in outflows from the circumstellar disk (gas and dust surrounding a star) of the massive young star candidate Orion Source I. It's not exactly like our sun, but it's a good start."

ALMA was the ideal tool as it offers extremely high resolution and sensitivity to reveal the distribution of AlO around the star. No other instrument can presently make such observations.

"Thanks to ALMA, we discovered the distribution of AlO around a young star for the first time. The distribution of AlO is limited to the hot region of the outflow from the disk. This implies that AlO rapidly condenses as solid grains -- similar to CAIs in our solar system," explained Tachibana. "This data allows us to place tighter constraints on hypotheses that describe our own stellar evolution. But there's still much work to do."

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Research on repetitive worm behavior may have implications for understanding human disease

Caenorhabditis elegans.

Repetition can be useful if you're trying to memorize a poem, master a guitar riff, or just cultivate good habits. When this kind of behavior becomes compulsive, however, it can get in the way of normal life -- an impediment sometimes observed in psychiatric illnesses like Tourette's syndrome and autism spectrum disorders. Now, Rockefeller scientists have identified a brain circuit that underlies repetition in worms, a finding that may ultimately shed light on similar behavior in humans.

Studying the microscopic roundworm C. elegans, the researchers found that defects in one protein cause animals to reorient themselves over and over again. Described in Nature Communications, these observations are bolstered by previous research in mice, and suggest that similar mechanisms may drive repetitive behavior in a range of animals, including humans.

Chemical cleanup

The scientists initially set out to understand how astrocytes, star-shaped cells found in mammalian brains, help neurons do their job. Astrocytes are thought to be responsible for, among other things, disposing of excess neurochemicals at synapses, the connections between neurons. This task is vital because if chemicals are not removed in a timely fashion, they can stimulate neurons in unexpected ways, disrupting normal brain function. To better understand this process, Menachem Katz, a research associate in the lab of Shai Shaham, looked to C. elegans CEPsh glial cells, which he suspected to be the worm equivalents of astrocytes.

Confirming this suspicion, Katz, Shaham, and their colleagues, used mRNA sequencing to show that mouse astrocytes and CEPsh glia have similar genetic signatures. Among other commonalities, both cell types produce the protein GLT-1, the mammalian version of which is responsible for clearing the chemical glutamate away from synapses. This finding, says Shaham, afforded the researchers a unique opportunity to define how astrocytes and GLT-1 work.

"Scientists have been trying to understand the functions of astrocytes for many years, and in mammals it's not easy because these cells are essential for keeping neurons alive," he says. "But in C. elegans there are only four CEPsh glial cells, and they are not required for neuron survival. This allowed us to investigate the specific roles of glutamate transporters, without worrying about the side effects of neuron sickness."

To do so, the researchers created C. elegans lacking GLT-1. Surprisingly, this depletion did not result in glutamate accumulation at synapses, as was expected. Instead, the worms exhibited oscillations in synaptic glutamate levels -- and a peculiar behavioral defect.

"These animals changed their direction at a crazy rate. They just kept moving forward and going back, moving forward and going back," says Shaham, the Richard E. Salomon Family Professor. "And when we analyzed this behavior, we discovered that they did so in a really interesting pattern."

Turn, turn, turn

It's perfectly normal for C. elegans to change course every now and then. Typically, the worm reorients itself about once every 90 seconds. But worms lacking GLT-1, the researchers found, took this action to the extreme: at 90 second intervals the animals executed not one reversal, but bursts of them. "It's as if once they start the action, they can't stop repeating it," says Katz.

Further experiments revealed that removal of the glutamate receptor MGL-2 blocked both repetitive reversals and synaptic glutamate oscillations. The researchers concluded that when glutamate is not efficiently cleared, the chemical stimulates MGL-2, which in turn triggers the release of yet more glutamate. This process then repeats on a loop; and every time glutamate is released, it activates the neuron responsible for initiating reversals.

"These findings suggest a simple model for how repetition can occur in worms," says Katz. "And, it turns out, this model may hold up in more complex nervous systems."

Indeed, past experiments have shown that GLT-1 mutations cause repetitive grooming in mice, and that compounds blocking the mouse version of MGL-2 eliminate similar behavior in other contexts. Taken together with the new findings in C. elegans, this research suggests that abnormal glutamate secretion may underlie repetitive behaviors across the animal kingdom -- raising the possibility that they may be relevant to understanding pathological repetition in humans.

Consistent with this idea, human genetics studies have found mutations associated with glutamate signaling in patients with obsessive compulsive disorder and autism spectrum disorders, both of which can be accompanied by repetitive behavior.

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Tomato pan-genome makes bringing flavor back easier

Tomatoes.

Almost everyone agrees that most store-bought tomatoes don't have much flavor. Now, scientists from the Agricultural Research Service (ARS) and the Boyce Thompson Institute (BTI) may have spotlighted the solution in a paper just published in Nature Genetics.

Molecular biologist James Giovannoni with the ARS Plant, Soil and Nutrition Research Laboratory and BTI bioinformatics scientist Zhangjun Fei, both in Ithaca, New York, have finished constructing the pan-genome for the cultivated tomato and its wild relatives, mapping almost 5,000 previously undocumented genes.

A genome is a biological map of an organism's genes and their functions. But a genome is usually of a single variety, which then acts as a reference genome for the rest of the species. This pan-genome includes all of the genes from 725 different cultivated and closely related wild tomatoes, which revealed 4,873 genes that were absent from the original reference genome.

While cultivated tomatoes have a wide range of physical and metabolic variation, there have been several severe bottlenecks during its domestication and breeding. This means today's tomatoes have a narrow genetic base. The pan-genome helps identify what additional genes beyond the reference might be available for crop breeding and improvement.

In modern times, breeders have concentrated on traits such as yield, shelf life, disease resistance and stress tolerance, traits that have been economically important to growers. Tomatoes are one of the most eaten vegetables -- although they actually are fruit botanically -- with a worldwide annual production of 182 million tons, worth more than $60 billion.

U.S. tomato consumption per capita was 20.3 pounds for fresh tomatoes in 2017 plus an additional 73.3 pounds of processed tomatoes eaten per person. Tomatoes are the second most consumed vegetable in the United States after potatoes.

"One of the most important discoveries from constructing this pan-genome is a rare form of a gene labeled TomLoxC, which mostly differs in the version of its DNA gene promoter. The gene influences fruit flavor by catalyzing the biosynthesis of a number of lipid (fat)-involved volatiles -- compounds that evaporate easily and contribute to aroma," explained Giovannoni.

In addition, the researchers found a new role of TomLoxC. It also facilitates production of a group of apocarotenoids -- organic chemicals derived from carotenoids including vitamin A precursors -- that work as signaling molecules influencing a variety of responses in plants including environmental stresses. The compounds also have a variety of floral and fruity odors that are important in tomato taste.

The rare version of TomLoxC was found in only 2 percent of older or heirloom cultivated large tomato varieties, although the version was present in 91 percent of currant-sized wild tomatoes, primarily Solanum pimpinellifolium, the wild predecessor of the cultivated tomato. It is becoming more common in newer varieties.

"It appears that there may have been strong selection pressure against or at least no selection for the presence of this version of TomLoxC early in the domestication of tomatoes," Giovannoni added. "The increase in prevalence of this form in modern tomatoes likely reflects breeders' renewed interest in improved flavor."

With the availability of this wide array of specific genetic information, breeders should be able to work quickly to increase the flavor of store bought, mass production tomatoes while preserving the traits that make them an economically advantageous crop.

"These novel genes discovered from the tomato pan-genome added substantial information to the tomato genome repertoire and provide additional opportunities for tomato improvement. The presence and absence profiles of these genes in different tomato populations have shed important lights on how human selection of desired traits have reshaped the tomato genomes," said Fei.

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Shrinking moon may be generating moonquakes

The Moon.

The Moon is shrinking as its interior cools, getting more than about 150 feet (50 meters) skinnier over the last several hundred million years. Just as a grape wrinkles as it shrinks down to a raisin, the Moon gets wrinkles as it shrinks. Unlike the flexible skin on a grape, the Moon's surface crust is brittle, so it breaks as the Moon shrinks, forming "thrust faults" where one section of crust is pushed up over a neighboring part.

"Our analysis gives the first evidence that these faults are still active and likely producing moonquakes today as the Moon continues to gradually cool and shrink," said Thomas Watters, senior scientist in the Center for Earth and Planetary Studies at the Smithsonian's National Air and Space Museum in Washington. "Some of these quakes can be fairly strong, around five on the Richter scale."

These fault scarps resemble small stair-step shaped cliffs when seen from the lunar surface, typically tens of yards (meters) high and extending for a few miles (several kilometers). Astronauts Eugene Cernan and Harrison Schmitt had to zig-zag their lunar rover up and over the cliff face of the Lee-Lincoln fault scarp during the Apollo 17 mission that landed in the Taurus-Littrow valley in 1972.

Watters is lead author of a study that analyzed data from four seismometers placed on the Moon by the Apollo astronauts using an algorithm, or mathematical program, developed to pinpoint quake locations detected by a sparse seismic network. The algorithm gave a better estimate of moonquake locations. Seismometers are instruments that measure the shaking produced by quakes, recording the arrival time and strength of various quake waves to get a location estimate, called an epicenter. The study was published May 13 in Nature Geoscience.

Astronauts placed the instruments on the lunar surface during the Apollo 11, 12, 14, 15, and 16 missions. The Apollo 11 seismometer operated only for three weeks, but the four remaining recorded 28 shallow moonquakes -- the type expected to be produced by these faults -- from 1969 to 1977. The quakes ranged from about 2 to around 5 on the Richter scale.

Using the revised location estimates from the new algorithm, the team found that eight of the 28 shallow quakes were within 30 kilometers (18.6 miles) of faults visible in lunar images. This is close enough to tentatively attribute the quakes to the faults, since modeling by the team shows that this is the distance over which strong shaking is expected to occur, given the size of these fault scarps. Additionally, the new analysis found that six of the eight quakes happened when the Moon was at or near its apogee, the farthest point from Earth in its orbit. This is where additional tidal stress from Earth's gravity causes a peak in the total stress, making slip-events along these faults more likely.

"We think it's very likely that these eight quakes were produced by faults slipping as stress built up when the lunar crust was compressed by global contraction and tidal forces, indicating that the Apollo seismometers recorded the shrinking Moon and the Moon is still tectonically active," said Watters. The researchers ran 10,000 simulations to calculate the chance of a coincidence producing that many quakes near the faults at the time of greatest stress. They found it is less than 4 percent. Additionally, while other events, such as meteoroid impacts, can produce quakes, they produce a different seismic signature than quakes made by fault slip events.

Other evidence that these faults are active comes from highly detailed images of the Moon by NASA's Lunar Reconnaissance Orbiter (LRO) spacecraft. The Lunar Reconnaissance Orbiter Camera (LROC) has imaged over 3,500 of the fault scarps. Some of these images show landslides or boulders at the bottom of relatively bright patches on the slopes of fault scarps or nearby terrain. Weathering from solar and space radiation gradually darkens material on the lunar surface, so brighter areas indicate regions that are freshly exposed to space, as expected if a recent moonquake sent material sliding down a cliff. Examples of fresh boulder fields are found on the slopes of a fault scarp in the Vitello cluster and examples of possible bright features are associated with faults that occur near craters Gemma Frisius C and Mouchez L. Other LROC fault images show tracks from boulder falls, which would be expected if the fault slipped and the resulting quake sent boulders rolling down the cliff slope. These tracks are evidence of a recent quake because they should be erased relatively quickly, in geologic time scales, by the constant rain of micrometeoroid impacts on the Moon. Boulder tracks near faults in Schrödinger basin have been attributed to recent boulder falls induced by seismic shaking.

Additionally, one of the revised moonquake epicenters is just 13 kilometers (8 miles) from the Lee-Lincoln scarp traversed by the Apollo 17 astronauts. The astronauts also examined boulders and boulder tracks on the slope of North Massif near the landing site. A large landslide on South Massif that covered the southern segment of the Lee-Lincoln scarp is further evidence of possible moonquakes generated by fault slip events.

"It's really remarkable to see how data from nearly 50 years ago and from the LRO mission has been combined to advance our understanding of the Moon while suggesting where future missions intent on studying the Moon's interior processes should go," said LRO Project Scientist John Keller of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

Since LRO has been photographing the lunar surface since 2009, the team would like to compare pictures of specific fault regions from different times to see if there is any evidence of recent moonquake activity. Additionally, "Establishing a new network of seismometers on the lunar surface should be a priority for human exploration of the Moon, both to learn more about the Moon's interior and to determine how much of a hazard moonquakes present," said co-author Renee Weber, a planetary seismologist at NASA's Marshall Space Flight Center in Huntsville, Alabama.

The Moon isn't the only world in our solar system experiencing some shrinkage with age. Mercury has enormous thrust faults -- up to about 600 miles (1,000 kilometers) long and over a mile (3 kilometers) high -- that are significantly larger relative to its size than those on the Moon, indicating it shrank much more than the Moon. Since rocky worlds expand when they heat up and contract as they cool, Mercury's large faults reveal that is was likely hot enough to be completely molten after its formation. Scientists trying to reconstruct the Moon's origin wonder whether the same happened to the Moon, or if instead it was only partially molten, perhaps with a magma ocean over a more slowly heating deep interior. The relatively small size of the Moon's fault scarps is in line with the more subtle contraction expected from a partially molten scenario.

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Hummingbird robot uses AI to soon go where drones can't

Hummingbird.

What can fly like a bird and hover like an insect?

Your friendly neighborhood hummingbirds. If drones had this combo, they would be able to maneuver better through collapsed buildings and other cluttered spaces to find trapped victims.

Purdue University researchers have engineered flying robots that behave like hummingbirds, trained by machine learning algorithms based on various techniques the bird uses naturally every day.

This means that after learning from a simulation, the robot "knows" how to move around on its own like a hummingbird would, such as discerning when to perform an escape maneuver.

Artificial intelligence, combined with flexible flapping wings, also allows the robot to teach itself new tricks. Even though the robot can't see yet, for example, it senses by touching surfaces. Each touch alters an electrical current, which the researchers realized they could track.

"The robot can essentially create a map without seeing its surroundings. This could be helpful in a situation when the robot might be searching for victims in a dark place -- and it means one less sensor to add when we do give the robot the ability to see," said Xinyan Deng, an associate professor of mechanical engineering at Purdue.

The researchers will present their work on May 20 at the 2019 IEEE International Conference on Robotics and Automation in Montreal. A YouTube video is available at https://youtu.be/jhl892dHqfA.

Drones can't be made infinitely smaller, due to the way conventional aerodynamics work. They wouldn't be able to generate enough lift to support their weight.

But hummingbirds don't use conventional aerodynamics -- and their wings are resilient. "The physics is simply different; the aerodynamics is inherently unsteady, with high angles of attack and high lift. This makes it possible for smaller, flying animals to exist, and also possible for us to scale down flapping wing robots," Deng said.

Researchers have been trying for years to decode hummingbird flight so that robots can fly where larger aircraft can't. In 2011, the company AeroVironment, commissioned by DARPA, an agency within the U.S. Department of Defense, built a robotic hummingbird that was heavier than a real one but not as fast, with helicopter-like flight controls and limited maneuverability. It required a human to be behind a remote control at all times.

Deng's group and her collaborators studied hummingbirds themselves for multiple summers in Montana. They documented key hummingbird maneuvers, such as making a rapid 180-degree turn, and translated them to computer algorithms that the robot could learn from when hooked up to a simulation.

Further study on the physics of insects and hummingbirds allowed Purdue researchers to build robots smaller than hummingbirds -- and even as small as insects -- without compromising the way they fly. The smaller the size, the greater the wing flapping frequency, and the more efficiently they fly, Deng says.

The robots have 3D-printed bodies, wings made of carbon fiber and laser-cut membranes. The researchers have built one hummingbird robot weighing 12 grams -- the weight of the average adult Magnificent Hummingbird -- and another insect-sized robot weighing 1 gram. The hummingbird robot can lift more than its own weight, up to 27 grams.

Designing their robots with higher lift gives the researchers more wiggle room to eventually add a battery and sensing technology, such as a camera or GPS. Currently, the robot needs to be tethered to an energy source while it flies -- but that won't be for much longer, the researchers say.

The robots could fly silently just as a real hummingbird does, making them more ideal for covert operations. And they stay steady through turbulence, which the researchers demonstrated by testing the dynamically scaled wings in an oil tank.

The robot requires only two motors and can control each wing independently of the other, which is how flying animals perform highly agile maneuvers in nature.

"An actual hummingbird has multiple groups of muscles to do power and steering strokes, but a robot should be as light as possible, so that you have maximum performance on minimal weight," Deng said.

Robotic hummingbirds wouldn't only help with search-and-rescue missions, but also allow biologists to more reliably study hummingbirds in their natural environment through the senses of a realistic robot.

"We learned from biology to build the robot, and now biological discoveries can happen with extra help from robots," Deng said.

Simulations of the technology are available open-source at https://github.com/purdue-biorobotics/flappy.

Early stages of the work, including the Montana hummingbird experiments in collaboration with Bret Tobalske's group at the University of Montana, were financially supported by the National Science Foundation.

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Genetic therapy heals damage caused by heart attack

Heart illustration.

Researchers from King's College London have found that therapy that can induce heart cells to regenerate after a heart attack.

Myocardial infarction, more commonly known as a heart attack, caused by the sudden blocking of one of the cardiac coronary arteries, is the main cause of heart failure, a condition that now affects over 23 million population in the world, according to the World Health Organisation.

At present, when a patient survives a heart attack, they are left with permanent structural damage to their heart through the formation of a scar, which can lead to heart failure in the future. In contrast to fish and salamander, which can regenerate the heart throughout life.

In this study, published today in Nature, the team of investigators delivered a small piece of genetic material, called microRNA-199, to the heart of pigs, after a myocardial infarction which resulted in the almost complete recovery of cardiac function at one month later.

Lead author Professor Mauro Giacca, from King's College London said: "It is a very exciting moment for the field. After so many unsuccessful attempts at regenerating the heart using stem cells, which all have failed so far, for the first time we see real cardiac repair in a large animal."

This is the first demonstration that cardiac regeneration can be achieved by administering an effective genetic drug that stimulates cardiac regeneration in a large animal, with heart anatomy and physiology like that of humans.

"It will take some time before we can proceed to clinical trials" explained Professor Giacca.

"We still need to learn how to administer the RNA as a synthetic molecule in large animals and then in patients, but we already know this works well in mice."

From Science Daily