What guppy guts can teach us about evolution

On the list of scientific tools that help us understand health, evolution or the environment, the Trinidadian guppy doesn't often come to mind.

The fish are more often thought of as aquarium pets in the U.S. and, in their native Trinidad, wild guppies are so ubiquitous, they're almost taken for granted.

"In Trinidad, they're called drain fish and locals would ask us, 'Why are you studying drain fish?'" said Sarah Fitzpatrick, an assistant professor in Michigan State University's Department of Integrative Biology.

"Guppies in Trinidad are kind of like squirrels here," said Sarah Evans, an associate professor and Fitzpatrick's departmental colleague in the College of Natural Science.

But thanks to a unique combination of biology and ecology, the guppies have provided researchers with insights into evolution for decades. Evans and Fitzpatrick have pushed those insights a step further, showing the guppies' potential to help probe big questions about how microbes living in host organisms contribute to health, survival and quality of life.

A research team led by the Spartans, who are both based at the W.K. Kellogg Biological Station, published its results on May 25 in the journal Proceedings of the Royal Society B.

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As scientists learn more about the gut microbiome -- the collection of microbes that lives in a host organism's digestive tract -- it's becoming increasingly clear that it plays an important role in the well-being of its host. In fact, human health is intimately tied to our gut microbiome.

Evans and Fitzpatrick are interested in some of biology's big-picture questions and wanted to better understand how microbiomes change as organisms evolve.

"Because the microbiome affects fitness -- an organism's health and reproduction -- it can affect evolution," said Evans, who is a core faculty member of MSU's Ecology, Evolution and Behavior Program, or EEB.

Nature is full of interesting examples of this, among them termites. Along their evolutionary path, termites adapted to welcome populations of single-celled protozoans into their guts that enable them digest wood.

Giant pandas provide another example. Diet impacts a microbiome and pandas eat only leaves. Yet panda microbiomes can more closely resemble that of their carnivorous relatives than some of their plant-eating kin. That's likely due to the shape and size of the panda's gut itself, which evolved from a carnivorous ancestor.

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Evans and Fitzpatrick wanted to better investigate what are the biggest drivers of microbiomes as host organisms evolve. It could be things like gut shape, diet or characteristics of a new environment, which is likely to contain microbes that are foreign to the host. The researchers knew guppies could lend a fin from their unique "natural laboratory."

"Trinidad is a continental island," said Fitzpatrick, who is also a core faculty member of the EEB program and the coordinator of the Molecular Ecology and Genomics Lab at the Kellogg Biological Station. "It split off from South America a long time ago. It actually has a continuation of the northernmost part of the Andes mountain range."

Rivers and streams run down Trinidad's mountains in independent systems. Within each water system are independent ecosystems of guppies that naturally don't stray far from home.

In the 1950s, evolution researchers realized that they could take guppies from one ecosystem where the fish had lots of natural predators and put them in another where they didn't. Over time, the genes and traits of the fish would adapt to reflect the native populations in those low-predator environments. Likewise, fish transferred from low-predation sites would adapt when transferred to streams with high numbers of predators.

"And it's repeatable. They evolve in many of the same ways almost every time," Evans said. "That's why this system is in textbooks."

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Materials provided by Michigan State University. Original written by Matt Davenport. Note: Content may be edited for style and length.

#Nature | https://sciencespies.com/nature/what-guppy-guts-can-teach-us-about-evolution/

Air pollution linked to adverse outcomes in pregnancy

A new study in mice by UCLA scientists reveals how exposure to traffic-related air pollutants causes cellular changes in the placenta that can lead to pregnancy complications and affect the health of both mother and offspring.

The researchers found that the cellular changes caused by chronic exposure to air pollutants were related to immune activation by foreign substances entering the blood from the lungs. This immune response attacks some of the placental cells that are required to maintain the placenta structurally, and most importantly, the blood flow from mother to developing baby.

Although previous research has analyzed the effect of air pollution on pregnancy, those studies did not utilize cell-specific methods or focus on molecular signatures of the placenta. This study is the first to assess how such exposure can negatively affect the placenta, leading to adverse outcomes in pregnancy.

One group of female mice was exposed to environmental air pollutants nasally starting two months before conception and during pregnancy, while the control group of mice was exposed to saline. By the end of the study, tissue samples indicated that inhaled air pollutants had compromised the composition of the placental cells and molecular signatures. Researchers also identified inflammation in the mucosal lining of the uterus triggered by pollution.

The placenta is essential for a successful pregnancy and for maintaining the health of both the mother and the baby. These study findings suggest that maternal cells of immunity may be responsible for destruction of vital vascular cells in the placenta. This auto-destruction of placental structures can disrupt the maintenance of a healthy pregnancy or at least affect nutrient supply from the mother to the baby, with the potential for adverse pregnancy consequences or outcomes such as preterm labor or uteroplacental insufficiency as encountered in pre-eclampsia.

"The cellular changes we have observed could provide the missing link between exposure to air pollutants and adverse pregnancy outcomes, thereby helping to focus development of preventive strategies for at-risk pregnancies," said Dr. Sherin Devaskar, lead author of the study and physician-in-chief of UCLA Mattel Children's Hospital and distinguished professor of pediatrics at the David Geffen School of Medicine at UCLA.

The research also underscores the need to examine the timing of exposure and whether acute v. chronic exposures have different effects. The authors also plan to study dietary interventions to alleviate distress on placental molecular signatures, nutrient supply and development.

The collaborative study also involved Dr. Suhas G. Kallapur, chief of neonatology and developmental biology; Amit Ganguly, staff research associate; Shubhamoy Ghosh, PhD, assistant project scientist; Monica Cappelletti, PhD, adjunct assistant professor of pathology and laboratory medicine, all four in the department of Pediatrics-Neonatology at UCLA; Matteo Pellegrini, a professor of molecular, cell and developmental biology at UCLA and Anela Tosevska, PhD, bioinformatics scientist in the division of rheumatology, internal medicine at Medical University of Vienna, Austria.

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Materials provided by University of California - Los Angeles Health Sciences. Note: Content may be edited for style and length.

#Environment | https://sciencespies.com/environment/air-pollution-linked-to-adverse-outcomes-in-pregnancy/

A world first: for the first time, a human liver was treated in a machine and then successfully transplanted

The Liver4Life research team owes its perfusion machine, which was developed in house, to the fact that it became possible to implant a human organ into a patient after a storage period of three days outside a body. The machine mimics the human body as accurately as possible, in order to provide ideal conditions for the human livers. A pump serves as a replacement heart, an oxygenator replaces the lungs and a dialysis unit performs the functions of the kidneys. In addition, numerous hormone and nutrient infusions perform the functions of the intestine and pancreas. Like the diaphragm in the human body, the machine also moves the liver to the rhythm of human breathing. In January 2020, the multidisciplinary Zurich research team – involving the collaboration of University Hospital Zurich (USZ), ETH Zurich and the University of Zurich (UZH) – demonstrated for the first time that perfusion technology makes it possible to store a liver outside the body for several days (see press release USZ of January13, 2020call_made).

From poor to good in three days

The team prepared the liver in the machine with various drugs. In this way, it was possible to transform the liver into a good human organ, even though it was originally not approved for transplantation due to its poor quality. The multi-day perfusion, i.e. the mechanical circulation of the organ, enables antibiotic or hormonal therapies or the optimization of liver metabolism, for example. In addition, lengthy laboratory or tissue tests can be carried out without time pressure. Under normal circumstances, this is not possible because organs can only be stored for 12 hours if they are stored conventionally on ice and in commercially available perfusion machines.

Treatment attempt successful

As part of an approved individual treatment attempt, the doctors gave a cancer patient on the Swisstransplant waiting list the choice of using the treated human liver. Following his consent, the organ was transplanted in May 2021. The patient was able to leave hospital a few days after the transplantation and is now doing well: “I am very grateful for the life-saving organ. Due to my rapidly progressing tumor, I had little chance of getting a liver from the waiting list within a reasonable period of time.”

Saving more lives

The article on the first transplantation of a liver prepared in a perfusion machine was published in one of the most renowned scientific journals, Nature Biotechnology, on DATE. “Our therapy shows that by treating livers in the perfusion machine, it is possible to alleviate the lack of functioning human organs and save lives,” explains Prof. Pierre-Alain Clavien, Director of the Department of Visceral Surgery and Transplantation at the University Hospital Zurich (USZ). Prof. Mark Tibbitt, Professor of Macromolecular Engineering at ETH Zurich, adds: “The interdisciplinary approach to solving complex biomedical challenges embodied in this project is the future of medicine. This will allow us to use new findings even more quickly for treating patients.”

The next step in the Liver4Life project is to review the procedure on other patients and to demonstrate its efficacy and safety in the form of a multicenter study. Its success would mean that in the future, a liver transplantation, which usually constitutes an emergency procedure, would be transformed into a plannable elective procedure. At the same time, a next generation of machines is being developed. In addition, those involved in basic research continue to look for ways of treating other liver diseases outside the body with drugs, molecules or hormones.

Liver4Life: a Wyss Zurich project

The Liver4Lifecall_madeproject was launched in 2015 under the umbrella of the Wyss Zurich Translational Center (Wyss Zurich). It brings together the highly specialized technical know-how and biomedical knowledge of around ten medical professionals, biologists and engineers. The project is being financed with donations from the initiator of Wyss Zurich, Dr. h.c. mult. Hansjörg Wyss.

#News | https://sciencespies.com/news/a-world-first-for-the-first-time-a-human-liver-was-treated-in-a-machine-and-then-successfully-transplanted/

Study provides long-term look at ways to control wildfire in sagebrush steppe ecosystem

New research led by an Oregon State University scientist provides the first long-term study of methods to control the spread of wildfire in the sagebrush steppe ecosystem that dominates parts of the western United States.

In recent years, the number, size and intensity of wildfires in the sagebrush ecosystem -- which spans much of Nevada, Oregon and Utah, and portions of California, Idaho, Washington and Wyoming -- have significantly increased primarily due to climate change and the spread of invasive grasses.

Researchers studied several methods for decreasing fire intensity. They found application of herbicides had few long-term benefits; prescribed fire reduced the fire behavior metrics they tracked but led to more invasive grasses; and mechanical thinning reduced most fire behavior metrics without increasing invasive grasses as significantly.

"It's a pretty spectacular ecosystem, but it's incredibly fragile," said Lisa Ellsworth, lead author of the study and a range ecologist in Oregon State's College of Agricultural Sciences. "It was named as one of the most endangered ecosystems in North America because it is so fragile and is so impacted by climate change and by invasive species and by changing fire regimes."

Ellsworth and scientists and managers from the federal Bureau of Land Management, U.S. Forest Service, U.S. Department of Agriculture, U.S. Geological Survey, University of Idaho and Utah State University collaborated on a 10-year study of different methods to control fire in the ecosystem. Their findings were published today in the journal Ecosphere.

Publication of the research coincides with an effort by the Bureau of Land Management to construct and maintain fuel breaks along 435 miles of roads in sagebrush habitat in southeast Oregon, southwest Idaho and northern Nevada. The project is expected to take 10 to 15 years to complete.

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Ellsworth hopes the research can help inform the Bureau of Land Management project.

"I feel the pressure of time in these systems," she said. "We need to be implementing strategies that preserve our good condition sagebrush steppe areas and get ahead of this invasive grass and fire feedback cycle that we're in."

The research aims to address a gap in knowledge about the long-term effects of using different methods to reduce fire-induced losses in sagebrush ecosystems.

Historically, wildfire was estimated to occur every 50 to 100 years in this ecosystem because native plants grow slowly and are spread out, which limits the ability of fire to quickly spread. That historical cycle has been substantially disrupted due to the rise of invasive annual grasses, which cover more of the landscape and dry out more quickly than native grasses, facilitating the ignition and spread of more fire. This has resulted in fire frequencies that more than double historical averages.

The just-published study focused on fuel treatments, activities that reduce or redistribute burnable material with the ultimate goal of decreasing fire intensity. The researchers studied three fuel treatments: herbicide application, prescribed fire and mechanical thinning, ormowing, which involves removing the top growth of sagebrush and other shrubs.

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They then used a fire modeling program to test how the different treatments impacted fire behavior. They studied three fire behavior metrics: rate of spread, flame length and reaction intensity, a measure of the amount of heat per unit area of fire.

The study included six sites, ranging in size from about 50 acres to 200 acres, in five states: Oregon, Washington, Idaho, Nevada and Utah. They are all part of the Sagebrush Steppe Treatment Evaluation Project (SageSTEP), which started in 2005 to evaluate methods to restore the ecosystem in the Great Basin.

Among their findings:

• Prescribed fire resulted in the greatest reduction of the three fire behavior metrics, as this treatment was the only one to remove a large portion of the total fuel load from the sites. However, research by Ellsworth and others has found that after prescribed fire, invasive grasses often quickly establish in burned sites.


• Mechanical thinning reduced flame length, an important metric because it can mean easier access for firefighters. Surprisingly, the researchers found the method was nearly as effective as prescribed fire at reducing reaction intensity and rate of spread. However, the reduction in modeled fire spread and reaction intensity lessened in year three onward, whereas reduced modeled flame lengths were maintained the entire 10 years. Ellsworth called the mechanical method a "pretty solid trade off" for reducing most fire behavior metrics and not increasing invasive grasses, like prescribed fire often does.


• Herbicide treatments were ineffective at reducing fuels and or fire behavior metrics, the researchers concluded. Tebuthiuron, a herbicide that targeted broad-leaved shrubs, had no initial effects in the first two years and a minor effect after that. Dead shrubs remained standing through the 10 years, so fuel structure was not significantly altered. Imazapic, a herbicide intended to reduce annual grasses, only had a short term (two to three years) effect on reducing fuels for fire and thus only a slight reduction on modeled fire spread.

Co-authors of the paper were: Claire Williams, Oregon State's Department of Fisheries, Wildlife, and Conservation Sciences; Beth Newingham, Agricultural Research Service; Scott Shaff and David Pyke, U.S Geological Survey; Eva Strand, University of Idaho; Matt Reeves and Jeanne Chambers, U.S. Forest Service Rocky Mountain Research Station; and Eugene Schupp, Utah State University.

The research is part of the Sagebrush Steppe Treatment Evaluation Project, funded by the U.S. Joint Fire Science Program, the National Interagency Fire Center and the Bureau of Land Management.

#Nature | https://sciencespies.com/nature/study-provides-long-term-look-at-ways-to-control-wildfire-in-sagebrush-steppe-ecosystem/

Killer Asteroids Are Hiding in Plain Sight. A New Tool Helps Spot Them.

Researchers have built an algorithm that can scan old astronomical images for unnoticed space rocks, helping to detect objects that could one day imperil Earth.

Ed Lu wants to save Earth from killer asteroids.

Or at least, if there is a big space rock streaking our way, Dr. Lu, a former NASA astronaut with a doctorate in applied physics, wants to find it before it hits us — hopefully with years of advance warning and a chance for humanity to deflect it.

On Tuesday, B612 Foundation, a nonprofit group that Dr. Lu helped found, announced the discovery of more than 100 asteroids. (The foundation’s name is a nod to Antoine de Saint-Exupéry’s children’s book, “The Little Prince”; B612 is the home asteroid of the main character.)

That by itself is unremarkable. New asteroids are reported all the time by skywatchers around the world. That includes amateurs with backyard telescopes and robotic surveys systematically scanning the night skies.

What is remarkable is that B612 did not build a new telescope or even make new observations with existing telescopes. Instead, researchers financed by B612 applied cutting-edge computational might to years-old images — 412,000 of them in the digital archives at the National Optical-Infrared Astronomy Research Laboratory, or NOIRLab — to sift asteroids out of the 68 billion dots of cosmic light captured in the images.

“This is the modern way of doing astronomy,” Dr. Lu said.

The research adds to the “planetary defense” efforts undertaken by NASA and other organizations around the world.

Today, of the estimated 25,000 near-Earth asteroids at least 460 feet in diameter, only about 40 percent of them have been found. The other 60 percent — about 15,000 space rocks, each with the potential of unleashing the energy equivalent to hundreds of million of tons of TNT in a collision with Earth — remain undetected.

B612 collaborated with Joachim Moeyens, a graduate student at the University of Washington, and his doctoral adviser, Mario Juric, a professor of astronomy. They and colleagues at the university’s Institute for Data Intensive Research in Astrophysics and Cosmology developed an algorithm that is able to examine astronomical imagery not only to identify those points of light that might be asteroids, but also figure out which dots of light in images taken on different nights are actually the same asteroid.

In essence, the researchers developed a way to discover what has already been seen but not noticed.

Typically, asteroids are discovered when the same part of the sky is photographed multiple times during the course of one night. A swath of the night sky contains a multitude of points of light. Distant stars and galaxies remain in the same arrangement. But objects that are much closer, within the solar system, move quickly, and their positions shift over the course of the night.

Astronomers call a series of observations of a single moving object during a single night a “tracklet.” A tracklet provides an indication of the object’s motion, pointing astronomers to where they might look for it on another night. They can also search older images for the same object.

Many astronomical observations that are not part of systematic asteroid searches inevitably record asteroids, but only at a single time and place, not the multiple observations needed to put together tracklets.

The NOIRLab images, for example, were mainly taken by the Victor M. Blanco 4-Meter Telescope in Chile as part of a survey of almost one-eighth of the night sky to map the distribution of galaxies in the universe.

The additional specks of light were ignored, because they were not what the astronomers were studying. “They’re just random data in just random images of the sky,” Dr. Lu said.

But for Mr. Moeyens and Dr. Juric, a single point of light that is not a star or a galaxy is a starting point for their algorithm, which they named Tracklet-less Heliocentric Orbit Recovery, or THOR.

The motion of an asteroid is precisely dictated by the law of gravity. THOR constructs a test orbit that corresponds to the observed point of light, assuming a certain distance and velocity. It then calculates where the asteroid would be on subsequent and previous nights. If a point of light show up there in the data, that could be the same asteroid. If the algorithm can link together five or six observations across a few weeks, that is a promising candidate for an asteroid discovery.

A mosaic of images of one of the 104 discoveries. This object would not have been discoverable by traditional means.B612 Asteroid Institute/University of Washington DiRAC Institute/DECam

In principle, there are an infinite number of possible test orbits to examine, but that would require an impractical eternity to calculate. In practice, because asteroids are clustered around certain orbits, the algorithm needs to consider only a few thousand carefully chosen possibilities.

Still, calculating thousands of test orbits for thousands of potential asteroids is a humongous number-crunching task. But the advent of cloud computing — vast computational power and data storage distributed across the internet — makes that feasible. Google contributed time on its Google Cloud platform to the effort.

“It’s one of the coolest applications I’ve seen,” said Scott Penberthy, director of applied artificial intelligence at Google.

So far, the scientists have sifted through about one-eighth of the data of a single month, September 2013, from the NOIRLab archives. THOR churned out 1,354 possible asteroids. Many of them were already in the catalog of asteroids maintained by the International Astronomical Union’s Minor Planet Center. Some of them had been previously observed, but only during one night and the tracklet was not enough to confidently determine an orbit.

The Minor Planet Center has confirmed 104 objects as new discoveries so far. The NOIRLab archive contains seven years of data, suggesting that there are tens of thousands of asteroids waiting to be found.

“I think it’s awesome,” said Matthew Payne, director of the Minor Planet Center, who was not involved with developing THOR. “I think it’s hugely interesting and it also allows us to make good use of the archival data that already exists.”

The algorithm is currently configured to only find main belt asteroids, those with orbits between Mars and Jupiter, and not near-Earth asteroids, the ones that could collide with our planet. Identifying near-Earth asteroids is more difficult because they move faster. Different observations of the same asteroid can be separated farther in time and distance, and the algorithm needs to perform more number crunching to make the connections.

“It’ll definitely work,” Mr. Moeyens said. “There’s no reason why it can’t. I just really haven’t had a chance to try it.”

THOR not only has the ability to discover new asteroids in old data, but it could also transform future observations as well. Take, for example, the Vera C. Rubin Observatory, formerly known as the Large Synoptic Survey Telescope, currently under construction in Chile.

An algorithm known as Tracklet-less Heliocentric Orbit Recovery, or THOR, searches for asteroids by viewing observations from a vantage point of an object moving along a hypothetical “test orbit.” Viewed that way, previously hidden nearby asteroids become easily recognizable as nearly straight lines.University of Washington DiRAC Institute/B612 Asteroid Institute

Financed by the National Science Foundation, the Rubin Observatory is an 8.4-meter telescope that will repeatedly scan the night sky to track what changes over time.

Part of the observatory’s mission is to study the large-scale structure of the universe and spot distant exploding stars, also known as supernovas. Closer to home, it will also spot a multitude of smaller-than-a-planet bodies whizzing around the solar system.

Several years ago, some scientists suggested that the Rubin telescope’s observing patterns could be adjusted so that it could identify more asteroid tracklets and thus locate more of the dangerous, as-yet-undiscovered asteroids more quickly. But that change would have slowed down other astronomical research.

If the THOR algorithm proves to work well with the Rubin data, then the telescope would not need to scan the same part of the sky twice a night, allowing it to cover twice as much area instead.

“That in principle could be revolutionary, or at least very important,” said Zeljko Ivezic, the telescope’s director and an author on a scientific paper that described THOR and tested it against observations.

If the telescope could return to the same spot in the sky every two nights instead of every four, that could benefit other research, including the search for supernovas.

“That would be another impact of the algorithm that doesn’t even have to do with asteroids,” Dr. Ivezic said. “This is showing nicely how the landscape is changing. The ecosystem of science is changing because software now can do things that 20, 30 years ago you would not even dream about, you would not even think about.”

For Dr. Lu, THOR offers a different way to accomplish the same goals he had a decade ago.

Back then, B612 had its sights on an ambitious and far more expensive project. The nonprofit was going to build, launch and operate its own space telescope called Sentinel.

Another view of asteroid trajectories through the solar system, in green, with Earth’s orbit in blue. Venus’s and Mars’s orbits are in red, and Mercury’s and Jupiter’s orbits are in brownish-gray.B612 Asteroid Institute/University of Washington DiRAC Institute/OpenSpace Project

At the time, Dr. Lu and the other leaders of B612 were frustrated by the slow pace of the search for dangerous space rocks. In 2005, Congress passed a mandate for NASA to locate and track 90 percent of near-Earth asteroids with diameters of 460 feet or more by 2020. But lawmakers never provided the money NASA needed to accomplish the task, and the deadline passed with less than half of those asteroids found.

Raising $450 million from private donors to underwrite Sentinel was difficult for B612, especially because NASA was considering an asteroid-finding space telescope of its own.

When the National Science Foundation gave the go-ahead to construct the Rubin Observatory, B612 re-evaluated its plans. “We could quickly pivot and say, ‘What’s a different approach to solve the problem that we exist to solve?’” Dr. Lu said.

The Rubin Observatory is to make its first test observations in about a year and become operational in about two years. Ten years of Rubin observations, together with other asteroid searches could finally meet Congress’s 90 percent goal, Dr. Ivezic said.

NASA is accelerating its planetary defense efforts as well. Its asteroid telescope, named NEO Surveyor, is in the preliminary design stage, aiming for launch in 2026.

And later this year, its Double Asteroid Redirection Test mission will slam a projectile into a small asteroid and measure how much that changes the asteroid’s trajectory. China’s national space agency is working on a similar mission.

For B612, instead of wrangling a telescope project costing almost half a billion dollars, it can contribute with less expensive research endeavors like THOR. Last week, it announced that it had received $1.3 million of gifts to finance further work on cloud-based computational tools for asteroid science. The foundation also received a grant from Tito’s Handmade Vodka that will match up to $1 million from other donors.

B612 and Dr. Lu are now not just trying to save the world. “We’re the answer to a trivia question of how vodka is related to asteroids.” he said.

#Space | https://sciencespies.com/space/killer-asteroids-are-hiding-in-plain-sight-a-new-tool-helps-spot-them/

¿Cuándo empieza la pubertad? Últimamente, a menor edad

Actualmente, algunas niñas comienzan a desarrollar senos a los 6 o 7 años. Los investigadores indagan si en estos cambios inciden la obesidad, el estrés y las sustancias químicas.

A fines de la década de 1980, cuando trabajaba como directora del equipo dedicado a temas de maltrato infantil en el Centro Médico de la Universidad Duke, en Durham, Carolina del Norte, Marcia Herman-Giddens se dio cuenta de que algo estaba cambiando en las niñas. Durante las evaluaciones de las chicas que habían sido víctima de abusos, Herman-Giddens observó que a muchas de ellas los senos les habían empezado a crecer a edades tan tempranas como 6 o 7 años.

“Como que eso no estaba bien”, comentó Herman-Giddens, quien ahora es profesora adjunta en la Escuela de Salud Pública Global Gillings de la Universidad de Carolina del Norte. Llegó a pensar que las chicas con senos prematuros tenían más probabilidades de que abusaran sexualmente de ellas, pero no halló ninguna información que llevara el registro del inicio de la pubertad en las niñas estadounidenses. Así que decidió recabar los datos ella misma.

Una década después, publicó un estudio en el que participaron más de 17.000 niñas a las que se les practicaron exámenes físicos en los consultorios pediátricos de todo el país. Las cifras revelaron que a mediados de la década de 1990 las chicas habían comenzado a desarrollar senos —lo cual suele ser la primera señal de la pubertad— a la edad de 10 años, en promedio, más de un año antes de lo que se tenía registrado con anterioridad. Ese descenso fue todavía más notable en las niñas negras, a quienes les habían comenzado a crecer los senos a una edad promedio de 9 años.

La comunidad médica estaba desconcertada por el hallazgo y mucha gente cuestionó esa tendencia drástica que había sido identificada por una médica auxiliar que nadie conocía, recuerda Herman-Giddens. “Estaban desconcertados”, comentó.

No obstante, el estudio resultó ser un parteaguas en el ámbito del conocimiento médico sobre la pubertad. Los estudios de las décadas posteriores han confirmado que, en decenas de países, la edad en que inicia la pubertad en las niñas ha descendido cerca de tres meses por década desde los años setenta. En los niños también se ha observado una tendencia parecida, aunque menos acentuada.

Pese a que es difícil identificar causa y efecto, es posible que la pubertad precoz tenga consecuencias indeseables, sobre todo para las chicas. Las niñas que alcanzan la pubertad de manera prematura tienen un mayor riesgo de padecer depresión, ansiedad, drogadicción y otros problemas psicológicos en comparación con sus compañeras que llegan a la pubertad después. Asimismo, las chicas que comienzan a menstruar a temprana edad pueden tener más probabilidades de desarrollar cáncer de mama o de útero en la edad adulta.

Nadie sabe qué factor de riesgo —o mejor dicho qué combinación de factores— está provocando ese descenso en la edad de la pubertad ni por qué hay marcadas diferencias relacionadas con la raza y el sexo. Parece que la obesidad tiene algo que ver, pero no justifica en su totalidad este cambio. Los científicos también están investigando otras causas posibles, entre ellas, las sustancias químicas que se encuentran en algunos plásticos y el estrés. Además, por razones que resultan poco claras, los médicos de todo el mundo han informado sobre un aumento de casos de pubertad precoz durante la pandemia.

“Hemos visto estos cambios marcados en todos nuestros niños y si quisiéramos evitarlos, no sabríamos cómo hacerlo”, señaló Anders Juul, un pediatra endocrinólogo de la Universidad de Copenhague que ha publicado dos estudios recientes sobre este fenómeno. “No sabemos cuál sea la causa”.

La obesidad

Más o menos en la época en que Herman-Giddens publicó su notable estudio, el grupo de investigación de Juul analizó el crecimiento de senos en un grupo de 1100 niñas de Copenhague, Dinamarca. A diferencia de las niñas de Estados Unidos, el grupo de las danesas coincidió con el comportamiento descrito tradicionalmente en los libros de texto de medicina: las niñas comenzaban a desarrollar senos a una edad promedio de 11 años.

“Me hicieron muchas entrevistas sobre la explosión de la pubertad en Estados Unidos, como lo denominamos”, comentó Juul, “pero les dije que en Dinamarca no estaba ocurriendo lo mismo”.

En ese momento, Juul propuso que el inicio prematuro de la pubertad en Estados Unidos tal vez estuviera vinculado con un incremento de la obesidad infantil, algo que no había sucedido en Dinamarca.

La obesidad se ha asociado a la menstruación precoz de las niñas desde la década de 1970. Desde entonces, en muchos estudios se ha demostrado que las niñas con sobrepeso u obesidad tienden a comenzar a menstruar antes que las niñas que tienen un peso promedio.

En un estudio realizado durante décadas con casi 1200 niñas de Luisiana y publicado en 2003, se relacionó la obesidad infantil con el adelanto de la menstruación: cada desviación estándar por encima del peso medio en la infancia se asociaba a una probabilidad doble de tener la regla antes de los 12 años.

Y en 2021, investigadores británicos descubrieron que la leptina, una hormona liberada por las células grasas que limita el hambre, actuaba en una parte del cerebro que también regulaba el desarrollo sexual. Los ratones y las personas con ciertas mutaciones genéticas en esta región experimentaron un desarrollo sexual más tardío.

“No creo que haya mucha controversia en que la obesidad es una de las cosas que más contribuyen al adelanto de la pubertad en esta época”, señaló Natalie Shaw, endocrinóloga pediatra del Instituto Nacional de Ciencias de la Salud Ambiental que ha estudiado los efectos de la obesidad en la pubertad.

Sin embargo, añadió, muchas de las niñas que se desarrollan más pronto no tienen sobrepeso.

“No es posible justificar todo esto por medio de la obesidad”, comentó Shaw. “Simplemente ha ocurrido con demasiada rapidez”.

Las sustancias químicas

En la década posterior al estudio de Herman-Giddens, Juul empezó a notar un aumento en el número de derivaciones por pubertad precoz en Copenhague, sobre todo de niñas que desarrollaban los senos a los 7 u 8 años.

“Y entonces pensamos: ‘¿Es un fenómeno real?’”, dijo Juul. O, se preguntó, ¿se habían puesto “histéricos” los padres y los médicos por la cobertura informativa del estudio de Herman-Giddens?

En un estudio realizado en 2009 con casi 1000 niñas en edad escolar en Copenhague, su equipo descubrió que la edad media de desarrollo de los senos había descendido un año desde su anterior estudio, hasta algo menos de 10 años, y que la mayoría de las niñas los desarrollaban entre los 7 y 12 años. Las niñas también tenían la menstruación antes, alrededor de los 13 años, unos cuatro meses antes de lo que había reportado antes.

“Es un cambio muy marcado en un periodo de tiempo muy corto”, dijo Juul.

Pero, a diferencia de los médicos de Estados Unidos, no creía que la culpa fuera de la obesidad: el índice de masa corporal de los niños daneses de la cohorte de 2009 no era diferente al de los años 90.

Juul se ha pronunciado de manera muy abierta en favor de una teoría alternativa: que la culpa es de la exposición a sustancias químicas. En su estudio de 2009, las chicas que desarrollaban senos a edades más tempranas eran quienes tenían los niveles más elevados de ftalatos en la orina, los cuales son sustancias que se usan para que los plásticos duren más tiempo y que se encuentran en todo, desde los pisos de vinilo hasta los empaques para alimentos.

Los ftalatos pertenecen a una familia de sustancias químicas más amplia llamada “disruptores endocrinos”, que pueden afectar el comportamiento de las hormonas y que en las últimas décadas se han vuelto omnipresentes en el medioambiente. Pero las pruebas no muestran muy claramente que son los causantes de la pubertad precoz.

En una revisión de literatura publicada el mes pasado, Juul y su equipo de investigadores analizaron cientos de artículos que analizaban los disruptores endocrinos y sus efectos sobre la pubertad. Los métodos de estudio eran muy variados; algunos se hacían en niños, otros en niñas y buscaban muchas sustancias químicas diferentes en diferentes edades de exposición. Al final, el análisis incluyó 23 estudios que eran lo suficientemente similares como para compararlos, pero no se pudo demostrar ninguna relación clara entre una sustancia química determinada y la edad de inicio de la pubertad.

“La conclusión principal es que hay pocas publicaciones y una gran falta de información para profundizar en el tema”, explicó Russ Hauser, epidemiólogo medioambiental de la Escuela de Salud Pública T. H. Chan de la Universidad de Harvard y coautor del análisis.

Dicha falta de información ha ocasionado que muchos científicos tengan dudas sobre esta teoría, señaló Hauser, quien hace poco informó sobre la manera en que los disruptores endocrinos afectan la pubertad en el caso de los niños. “No contamos con la información suficiente para fundamentar respecto a alguna clase específica de sustancias químicas”.

Eleni Kalorkoti

El estrés y el estilo de vida

Es posible que en la pubertad precoz también intervengan otros factores, al menos en el caso de las niñas. El abuso sexual en la infancia temprana se ha relacionado con el inicio precoz de la pubertad; sin embargo, es difícil rastrear las causas. Podría ser que el estrés y el trauma sean la causa de un desarrollo precoz o, según la hipótesis de Herman-Giddens de hace algunas décadas, tal vez las chicas que se desarrollan más pronto sean más vulnerables a la violencia sexual.

También parece ser más probable que las chicas cuyas madres tienen antecedentes de trastornos en el estado de ánimo alcancen la pubertad más pronto, al igual que las niñas que no viven con sus padres biológicos. Asimismo, los cambios en la llegada a la pubertad se han vinculado a factores relacionados con el estilo de vida, como la falta de actividad física.

Además, durante la pandemia, los endocrinólogos pediátricos de todo el mundo observaron que estaban aumentando las consultas de niñas que alcanzaban la pubertad antes de lo normal. En un estudio publicado en Italia en febrero, se reveló que 328 niñas habían sido remitidas a cinco clínicas de todo el país durante un periodo de siete meses en 2020, a diferencia de 140 durante el mismo periodo de 2019. (En los varones no se encontró ninguna diferencia). Como anécdota, lo mismo podría estar pasando en India, Turquía y Estados Unidos.

“He preguntado a mis colegas de todo el mundo, y muchos de ellos me dicen que sí, que están observando una tendencia parecida”, comentó Paul Kaplowitz, profesor emérito de Pediatría en el Children’s National Hospital de Washington. No se sabe si la tendencia fue producto de un mayor estrés, de un estilo de vida más sedentario o de que los padres estaban lo suficientemente cerca de sus hijos como para notar cambios prematuros.

Lo más probable es que haya muchos factores que contribuyen al mismo tiempo. Y bastantes de estos problemas afectan de manera desproporcionada a las familias de bajos ingresos, lo cual, según los investigadores, puede explicar en parte las diferencias que hay en el inicio de la pubertad en Estados Unidos dependiendo del origen racial.

¿Una nueva normalidad?

Durante décadas, los libros de texto de medicina han definido las etapas de la pubertad utilizando la llamada Escala de Tanner, que se basó en observaciones minuciosas entre 1949 y 1971 de unos 700 niños y niñas que habían vivido en un orfanato de Inglaterra.

La escala establece que la pubertad normal comienza a los 8 años o después en el caso de las niñas y a los 9 años o después en el caso de los niños. Si la pubertad comienza antes de esos límites, los médicos deben examinar al niño para detectar un raro trastorno hormonal llamado pubertad precoz central, que puede provocar la pubertad ya en la primera infancia. Los niños con este trastorno suelen ser sometidos a escáneres cerebrales y toman medicamentos que bloquean la pubertad para retrasar el desarrollo sexual hasta una edad adecuada.

Pero algunos expertos sostienen que el umbral de edad para la alarma debería reducirse. De lo contrario, dicen, los niños sanos podrían ser remitidos a especialistas y someterse a procedimientos médicos innecesarios, que pueden resultar físicamente agotadores y costosos.

“Hay muchos más datos que indican que la edad de 8 años no es el límite óptimo para separar lo normal de lo anormal”, dijo Kaplowitz. En 1999, defendió que el límite de edad para la pubertad normal debía reducirse a los 7 años en las niñas blancas y a los 6 en las negras. “No fue muy bien recibido”, recuerda.

Sin embargo, esa postura se vio reforzada por un estudio reciente del grupo de Juul que mostraba que, de 205 niños puberales menores de 8 años que se sometieron a escáneres cerebrales, solo el 1,8 por ciento de las niñas y el 12,5 por ciento de los niños presentaban anomalías cerebrales que indicaban una pubertad precoz central.

Pero la reducción de la edad límite sigue siendo controvertida, ya que muchos pediatras sostienen que el riesgo de sufrir un trastorno sigue siendo lo suficientemente grande como para justificar las precauciones adicionales. Otros, como Herman-Giddens, afirman que los cambios son un signo de un problema legítimo de salud pública y que no deben aceptarse como normales.

“Puede que sea normal en el sentido de lo que muestran los datos”, dijo Herman-Giddens, “pero no creo que sea normal, a falta de una palabra mejor, para lo que pretendía la naturaleza”.

Azeen Ghorayshi cubre la intersección de sexo, género y ciencia para el Times. @azeen

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#News | https://sciencespies.com/news/cuando-empieza-la-pubertad-ultimamente-a-menor-edad/

Ecological functions of streams and rivers severely affected globally

Agriculture, loss of habitat or wastewater effluents -- human stressors negatively impact biodiversity in streams and rivers. Very little is known yet about the extent to which their capacity for self-purification and other essential ecosystem services are also impacted. An international research team lead by the Helmholtz Centre for Environmental Research (UFZ) has synthesised the globally available research on this topic in a meta-analysis recently published in Global Change Biology. This study provides new initiatives for improved water management.

Streams and rivers are the lifeblood of our planet, biodiversity hotspots and essential for human life: They provide drinking water, offer flood protection and are used to irrigate agricultural areas. But humans are impacting freshwaters and their ecological functions through actions such as altering the structure of waterbodies, agriculture or discharging wastewater. "Of course this leads to a variety of adverse ecological effects," says Dr. Mario Brauns, a scientist at the UFZ Department of River Ecology. "Most studies deal with the effects on biodiversity, but this may only be a part of the problem. Although a loss of biodiversity can be an indicator that freshwaters are affected by human stressors, the question of whether and to what extent its ecological functions suffer remains unanswered."

An essential ecosystem service of streams and rivers is their natural self-purification service. This can be assessed based on ecological functions such as nutrient retention or leaf litter decomposition. But how do human stressors affect these ecological functions that are essential for the natural self-purification capacity of a river or stream? "In this meta-analysis, we compiled the current status of research on this question," says Brauns. The international research team evaluated the published literature for studies investigating the effects of human stressors on the ecological functions of rivers and streams. "We reviewed the research available worldwide and found a total of 125 studies -- which is not much given the global scale," says Brauns. "This again underscores how little research has been done to date in this area. And: The studies found were conducted primarily in Europe or North America. Hardly anything is known to date for Asia or Africa and we see an urgent need for research and action in these geographical areas."

Evaluation of the data revealed that the efficiency at which streams retain nitrates is nearly five times lower for streams draining agriculture catchments than for streams in pristine catchments. "This is surprising," says Brauns and explains: "Rivers and streams affected by agriculture are impacted by high nutrient concentrations and a degraded structure and can no longer adequately fulfil their ecological function and lose a major portion of their purification service." Another important result is the comparative stressor analysis: Which stressors have the greatest impact across all ecological functions? Wastewater ranks first and is followed by agriculture and urbanization. "These stressors are areas where we must take urgent action," says Brauns. "The ecological functions of rivers and streams are reliable indicators that allow a functional assessment of streams and rivers and implementation of appropriate management strategies, as demonstrated by our study. We advocate for more studies on the ecological functions of streams and rivers, preferably over a broader geographical area. If the stressors persist in contemporary intensity, we will lose the functional backbone of streams and rivers and ecosystem services essential to humans."

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Tooth of an Ancient Girl Fills Gap in Human Family Tree

A molar discovered in a cave in Laos shows where the enigmatic Denisovans could have interbred with the ancestors of modern humans.

A tooth found inside of a mountain cave in Laos has solved one of the biggest scientific mysteries of the Denisovans, a branch of ancient humans that disappeared roughly 50,000 years ago.

Since 2010, when Denisovan teeth and finger bones were first discovered, DNA testing has revealed that the enigmatic hominins were among the ancestors of people alive today in Australia and the Pacific.

But scientists didn’t understand how the Denisovans, whose scant remains had been found only in Siberia and Tibet, would have been able to interbreed with the group of humans who expanded east from Africa through Southeast Asia before reaching Australia, New Guinea and other islands in the Pacific.

Now, the discovery of a girl’s molar in Laos, published on Tuesday in the journal Nature Communications, puts Denisovans right in the path of modern humans who arrived in Southeast Asia tens of thousands of years later.

“We knew that Denisovans should be here,” said Laura Shackelford, a paleoanthropologist at the University of Illinois and a co-author of the new study. “It’s nice to have some tangible evidence of their existence in this area.”

Dr. Shackelford joined a team of French and Laotian colleagues on an expedition to the Annamite Mountains in northern Laos in 2008, and they have been digging up fossils ever since. In one of the many caves that riddle the mountains, they have unearthed human skull fragments dating back about 75,000 years, making them the oldest evidence of modern humans in Southeast Asia.

At the end of the researchers’ 2018 field season, children from a nearby village told Dr. Shackelford and her colleagues of another cave that contained bones. Her Laotian colleagues warned her that the cave was a favorite spot for cobras, but she decided a trip inside was worth the risk.

Laura Shackelford, right, a paleoanthropologist at the University of Illinois, and Fabrice Demeter of the University of Copenhagen, were co-authors of a study regarding the tooth they found in the Laotian cave.A. Zachwieja

A team of caving experts scouted the site first, and then Dr. Shackelford made her way into a closet-sized cavity where the children claimed to have found bones. When she inspected the cave floor, she saw nothing.

“But then I turned my flashlight on, and I looked up,” she recalled. “All you could see were bones and teeth, embedded in the walls and in the ceiling of this cave. They were just sort of everywhere.”

Dr. Shackelford and her colleagues started working full-time in the new cave, which they dubbed Cobra Cave ( despite never encountering a snake). They chiseled rocks the size of soccer balls out of the walls and soaked them in a mild acid. The rock gradually disintegrated, leaving the harder fossils behind.

On close inspection, most of the fossils turned out to be bones from extinct mammals, such as pigs, deer and pygmy elephants. Gnaw marks on the bones revealed how they all ended up in a jumble in Cobra Cave: Porcupines likely carried them there and chewed on the bones to hone their teeth.

Sorting through the gnawed bones, the scientists found a surprise: a molar that resembled a human child’s tooth. But some features of the molar suggested it was not quite human. “We were so amazed and so excited,” Dr. Shackelford said.

They were even more delighted when geologists examined the cave wall to determine the age of the tooth. The tooth itself was too small to analyze, but the researchers found fossils and minerals nearby that contained radioactive elements that broke down at a regular pace. By measuring those elements, the researchers estimated the tooth was between 164,000 and 131,000 years old.

In other words, the Cobra Cave tooth is about twice as old as the oldest modern humans that Dr. Shackelford and her colleagues have found in the region. The tooth’s great age hinted that it belonged to an extinct relative of modern humans. But which one?

Researchers discovered the Denisovan tooth in a cave on P’ou Loi Mountain in northern Laos.F. Demeter

Humanity’s lineage split from the ancestors of chimpanzees about six million years ago in Africa. Over the next four million years, they evolved into upright, big-brained meat-eaters. At that point, some relatives began moving to Europe and Asia from Africa. One species, called Homo erectus, spread east as far as Indonesia.

Evidence from fossils and ancient DNA indicate that another wave of early humans traveled out of Africa even later. As the population spread across Europe and Asia, it split about half a million years ago. The western population became Neanderthals, and the eastern one became Denisovans.

Paleoanthropologists first discovered Neanderthal fossils in the mid-1800s in Germany and Belgium and have since found an abundance of bones marking the group’s range across Europe, the Middle East and Siberia. The fossils revealed Neanderthals as stocky, chinless humans. Tools and other remains offered glimpses into their minds: They were adept hunters who could stalk both rhinos and dolphins. They buried their dead and fashioned necklaces from eagle talons.

DNA in Neanderthal fossils also linked them to living humans. Soon after modern human ancestors moved out of Africa, they encountered Neanderthals in the Middle East and interbred with them — probably on several occasions.

Scientists have had a much harder time reconstructing the ancient migration of the Denisovans. For years, the only place where they fond these ancient humans was the Denisova Cave in Siberia. It was hard to see how people several thousand miles away, in Australia, New Guinea and nearby islands, could have ended up with Denisovan DNA.

The Denisovan samples from Siberia were limited to a few teeth and finger bones. Fortunately, scientists found an abundance of DNA in these specimens, and even extracted Denisovan DNA from dirt on the cave floor.

The evidence gathered so far indicates that Denisovans occupied the cave 300,000 years ago and inhabited the surrounding area off and on until about 50,000 years ago. They also appear to have left behind stone tools in the cave.

The Denisova Cave in Siberia yielded the first fossils and DNA of Denisovans.Bence Viola/University of Toronto, Max Planck Institute for Evolutionary Anthropology, via Associated Press

Given that Denisovans endured for hundreds of thousands of years, scientists were confident that they’d find Denisovan fossils elsewhere. In 2019, that proved to be the case. Chinese researchers announced the discovery of a 160,000-year-old jaw in a Tibetan cave with teeth matching those found at the Siberian site. That discovery in Tibet, more than 1,400 miles south of Siberia, drastically expanded the known range of Denisovans.

The jaw also provided a few more clues about the Denisovans themselves. For one thing, the proportions of the jaw and teeth implied they might have been tall and solidly built, like football players. To survive in the harsh environment of the Tibetan plateau, they would have had to withstand low oxygen in the air and cold weather.

Still, some 1,100 miles would have separated Denisovans in Tibet from modern human ancestors in Southeast Asia, leaving scientists to wonder how the two groups could have interbred.

Examining the tooth from the Cobra Cave in Laos, Dr. Shackelford and her colleagues did not know if it had come from Denisovans, Neanderthals, Homo erectus or some other unknown species of human. Over the past four years, they have been analyzing the tooth for clues.

Initially, they hoped that it would contain ancient DNA. But before destroying part of the tooth to find out, they had colleagues at the University of Copenhagen look at other mammal fossils found from the same sample of the Cobra Cave wall. Those specimens yielded no DNA, so they decided not to look for any in it.

But they had better luck when they searched for protein fragments in the molar’s enamel. The chemical makeup of the fragments has only been found in the teeth of modern humans, Neanderthals and Denisovans — but not those of other mammals.

Unfortunately, the protein composition is the same in all three groups of hominins, leaving the researchers unable to say which one the molar came from.

Fossilized teeth and bones were embedded in the ceiling of Cobra Cave, many of which were gnawed on by porcupines.F. Demeter

But the enamel of the juvenile tooth had one more piece of information to offer: It belonged to a girl. It lacked a specific enamel protein encoded by a gene on the Y chromosome, which is only carried by males.

The scientists made a high-resolution scan of the molar’s surface and interior, allowing them to compare its fine anatomical structure to more than 400 molars from living and extinct humans. Of those teeth, the Cobra Cave specimen most closely resembled a molar lodged in the Denisovan jaw from Tibet.

Shara Bailey, a paleoanthropologist at New York University who has studied the Tibetan jaw but was not involved in the new study, said this conclusion was sound. “I agree 100 percent with the analysis,” she said.

Dr. Bailey acknowledged that some people may wonder how a single tooth could reveal so much about its Paleolithic owner. But the cusps and ridges of teeth are complex landscapes, and the shape of those landscape is largely determined by genes, making teeth a rich trove of information about evolution.

“Teeth are the unsung heroes of paleoanthropology,” Dr. Bailey said.

The discovery of Denisovans in Laos shows that they were exactly where they needed to be to interbreed with modern humans who arrived in Southeast Asia thousands of years later.

Dr. Bailey and Dr. Shackelford agreed that more Denisovan fossils wait to be discovered elsewhere. Recent studies have found a small amount of Denisovan DNA in East Asians, for example, which their ancestors may have acquired through a separate interbreeding. And some ancient teeth that were already discovered in China and Taiwan seem now like they might have a Denisovan shape, warranting a fresh look.

But Bence Viola, a paleoanthropologist at the University of Toronto who was not involved in the study, said the Cobra Cave tooth itself provided some fresh clues about the Denisovans.

“These guys were able to deal with extensive snow cover and very low winter temperatures but at the same time with humid tropical environments,” he said. “Denisovans were very adaptable — likely more so than Neanderthals. They were most similar to modern humans in the end.”

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First animals developed complex ecosystems before the Cambrian explosion

Early animals formed complex ecological communities more than 550 million years ago, setting the evolutionary stage for the Cambrian explosion, according to a study by Rebecca Eden, Emily Mitchell, and colleagues at the University of Cambridge, UK, publishing May 17 in the open-access journal PLOS Biology.

The first animals evolved towards the end of the Ediacaran period, around 580 million years ago. However, the fossil record shows that after an initial boom, diversity declined in the run-up to the dramatic burgeoning of biodiversity in the so-called "Cambrian explosion" nearly 40 million years later. Scientists have suggested this drop in diversity is evidence of a mass extinction event roughly 550 million years ago -- possibly caused by an environmental catastrophe -- but previous research has not investigated the structure of these ancient ecological communities.

To evaluate the evidence for an Ediacaran mass extinction, researchers analyzed the metacommunity structure of three fossil assemblages that span the last 32 million years of this geological period (between 575 to 543 million years ago). They used published paleoenvironmental data, such as ocean depth and rock characteristics, to look for metacommunity structure indicative of environmental specialization and interactions between species. The analysis revealed increasingly complex community structure in the later fossil assemblages, suggesting that species were becoming more specialized and engaging in more inter-species interactions towards the end of the Ediacaran era, a trend often seen during ecological succession.

The results point to competitive exclusion, rather than mass extinction, as the cause of the diversity drop in the late Ediacaran period, the authors say. The analysis indicates that the features of ecological and evolutionary dynamics commonly associated with the Cambrian explosion -- such as specialization and niche contraction -- were established by the first animal communities in the late Ediacaran.

Mitchell adds, "We found that the factors behind that explosion, namely community complexity and niche adaptation, actually started during the Ediacaran, much earlier than previously thought. The Ediacaran was the fuse that lit the Cambrian explosion."

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First animals developed complex ecosystems before the Cambrian explosion

Early animals formed complex ecological communities more than 550 million years ago, setting the evolutionary stage for the Cambrian explosion, according to a study by Rebecca Eden, Emily Mitchell, and colleagues at the University of Cambridge, UK, publishing May 17 in the open-access journal PLOS Biology.

The first animals evolved towards the end of the Ediacaran period, around 580 million years ago. However, the fossil record shows that after an initial boom, diversity declined in the run-up to the dramatic burgeoning of biodiversity in the so-called "Cambrian explosion" nearly 40 million years later. Scientists have suggested this drop in diversity is evidence of a mass extinction event roughly 550 million years ago -- possibly caused by an environmental catastrophe -- but previous research has not investigated the structure of these ancient ecological communities.

To evaluate the evidence for an Ediacaran mass extinction, researchers analyzed the metacommunity structure of three fossil assemblages that span the last 32 million years of this geological period (between 575 to 543 million years ago). They used published paleoenvironmental data, such as ocean depth and rock characteristics, to look for metacommunity structure indicative of environmental specialization and interactions between species. The analysis revealed increasingly complex community structure in the later fossil assemblages, suggesting that species were becoming more specialized and engaging in more inter-species interactions towards the end of the Ediacaran era, a trend often seen during ecological succession.

The results point to competitive exclusion, rather than mass extinction, as the cause of the diversity drop in the late Ediacaran period, the authors say. The analysis indicates that the features of ecological and evolutionary dynamics commonly associated with the Cambrian explosion -- such as specialization and niche contraction -- were established by the first animal communities in the late Ediacaran.

Mitchell adds, "We found that the factors behind that explosion, namely community complexity and niche adaptation, actually started during the Ediacaran, much earlier than previously thought. The Ediacaran was the fuse that lit the Cambrian explosion."

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#Nature | https://sciencespies.com/nature/first-animals-developed-complex-ecosystems-before-the-cambrian-explosion/

How to Watch Tau Herculids, a Potential New Meteor Shower

A comet’s breakup three decades ago could produce a seldom-seen meteor storm on Monday night. Or it could be a complete dud.

A never-before-seen meteor shower may light up the skies with untold numbers of brilliant streaks the evening of Monday night into Tuesday morning.

Or the event could fizzle out and be a dud.

Those are the best predictions that meteor watchers have for the Tau Herculids, a potential celestial spectacle that has sky-watching enthusiasts eager with anticipation.

Meteor showers can happen when the Earth plows into debris produced by a comet (or, occasionally, asteroids). The source of the Tau Herculids is Comet 73P/Schwassmann-Wachmann 3, or SW3 for short. Discovered in 1930, the trifling ice ball originally clocked in at about two-thirds of a mile in diameter, so it rarely produced enough material to generate major nighttime fireworks. But in 1995, SW3 crumbled, producing a large fragment field that our planet is about to encounter.

When and where can I see the potential shower?

If the Tau Herculids happen, they will be most visible throughout the lower 48 United States on the evening of Monday, May 30, and the early morning of Tuesday, May 31, likely around 1 a.m. Eastern time. The further south you live, the better your view. Skywatchers in West Africa, the Caribbean and South America are also favored to see some action. Those in high latitude places like Alaska are out of luck.

To catch the shower, get away from bright city lights and find the darkest and clearest location you can, one with few hills or other obstacles on the horizon. The moon will be new that night, so its light w ill not interfere with the display. Allow about half an hour for your eyes to adjust to the darkness.

“The best piece of equipment is to go to your attic and haul out that beach chair,” said Joe Rao, an associate astronomer at the Hayden Planetarium in New York. “Then just lay back and look up.”

Meteor showers appear to emanate from a point in the sky known as their radiant. The Tau Herculids, the meteor shower from SW3, was predicted to come from the constellation Hercules — hence the shower’s name — a forecast that has since turned out to be incorrect.

The Tau Herculids will actually originate from the constellation Boötes, radiating from just above the star Arcturus, a ruddy orange-yellow entity that will be the brightest star in the sky of the Northern Hemisphere at that time. Locating Arcturus is easy if you can find the Big Dipper: Simply trace a line from the last two stars in the Dipper’s handle in a direction away from its bowl. The first bright star you see should be Arcturus.

Unlike meteor showers that are visible for days before and after a peak night, this show will not last long, if it occurs at all.

“This is not a long-term event,” said Robert Lunsford, the secretary-general of the International Meteor Organization. “I would certainly try to be out at 10 o’clock Pacific time or 1 a.m. Eastern, because if nothing’s happening then, then it’s a nonevent.”

How many meteors might the Tau Herculids produce?

“That’s the $64,000 question,” said Mr. Rao. “There’s no consensus. The predictions are absolutely all over the place.”

NASA models are on the pessimistic side, suggesting few or potentially no meteors will be visible. But Mr. Rao points to estimates from reputable meteor watchers at the opposite end of the spectrum who predict seeing as many as 10,000 meteors to 100,000 meteors per hour. If those are true, the Tau Herculids will be a meteor storm and possibly one of the biggest displays in recorded history.

“I’d be happy just to see one in the entire hour,” Mr. Lunsford said. “But there’s a possibility we could see one per second.”

Much will depend on the size and the speed of the debris as it hits the atmosphere and how big the comet’s leftover particles are.

“The particles may be sand-grain-sized,” said Mr. Rao. “I maintain that there must be stuff out there at least as big as pebbles, or nuggets, or even ping-pong-ball-size.”

If the fragments are on the smaller side, they may produce many slow streaks that are too dim for the human eye to see. Night sky devotees have been burned before when announcing possible wonders like the supposedly once-in-a-lifetime sighting of Comet Kohoutek in 2020 that failed to live up to expectations.

“We’ve gotten a lot of black eyes over predicting some marvelous event, and then nothing happens,” said Mr. Lunsford. “We need a certain set of circumstances to occur for this meteor shower, and the likelihood is remote. But we owe it to the general public to let them know this is a possibility.”

Why might the Tau Herculids appear for the first time?

Fragment B of Comet 73P/Schwassmann-Wachmann 3 over the course of three days as observed by the Hubble Space Telescope’s Advanced Camera for Surveys.NASA, ESA, H. Weaver (APL/JHU), M. Mutchler and Z. Levay (STScI)

New meteor showers are rare events, Mr. Lunsford said, “happening only a couple times a century.”

But in October 1995, astronomers began getting phone calls from people claiming to have discovered a new comet, Mr. Rao said. The comet wasn’t new: It was SW3 falling apart and becoming hundreds of times as bright as normal, he added.

“It was like breaking open an egg,” he said. “All this dusty debris suddenly emerged.”

While our planet has already hit bits of SW3’s dust, this will be the first time the Earth’s orbit meets all the material that burst out in 1995.

No one is exactly sure what caused SW3’s collapse, but NASA’s Hubble and Spitzer space telescopes watched the comet fragment for years. It was possible that the icy object made too many close passes to both the hot sun and the powerful gravitational pull of Jupiter.

“Maybe after countless numbers of times of having its orbit perturbed, it’s like the comet finally said, ‘I can’t deal with this anymore,’ and broke up into pieces,” Mr. Rao said.

When did we learn what caused meteor showers?

Humans have been spotting “shooting stars” for millenniums. It is unknown when ancient skygazers first associated them with a particular point in the sky. Mark Littman, author of “The Heavens on Fire: The Great Leonid Meteor Storms,” says that some Indigenous traditions in the Americas may indicate an early understanding of radiants.

The Kiliwa, who are Indigenous people in Baja California, Mexico, for instance, describe meteor showers as a kind of fiery celestial urine coming from a constellation they call Xsmii.

“​​If you think of a meteor shower, and you have, excuse me, the spray coming out, it suggests that they noticed there was a radiant,” Dr. Littman said. “That would be the most ancient observation of a radiant that we have.”

The oldest-known written observation of a radiant came from Islamic sky watchers who recorded a great shower after the death of the conqueror Abu Ishaq Ibrahim II ibn Ahmad in A.D. 902. They noted that the meteors were coming from one spot as they rained, Dr. Littman said.

Our modern understanding of meteor showers can be traced to the late 18th century, when people noted a major comet passing by a year before a large meteor storm from the direction of the constellation Leo. Then on Nov. 12, 1833, the Leonids shower put on a display so spectacular that thousands of shooting stars fell every minute.

“There were reports of people falling to the ground in prayer and rushing to church to repent their sins,” Dr. Littman said.

Denison Olmsted, who was an astronomer in Connecticut, was awakened by his neighbors that night and went out to see the storm. Olmsted wrote to a local newspaper asking viewers to send him their own accounts, a request that was reprinted in newspapers across the country.

After collecting many replies and conducting further investigations, Olmsted concluded that meteor showers originate beyond our planet, contradicting a long-held belief expressed by Aristotle that meteors were exhalations from Earth’s surface.

“He really should be credited as the father of meteor science,” Dr. Littman said.

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