SPACE/COSMOS

 

Superflares once per century

More often than previously thought, sun-like stars hurl huge amounts of radiation into space. The Sun, too, is capable of such outbursts

Max Planck Institute for Solar System Research

 

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Artist's impression of a Sun-like star exhibiting a superflare as seen in visible light

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Credit: MPS/Alexey Chizhik

There is no question that the Sun is a temperamental star, as alone this year’s unusually strong solar storms prove. Some of them led to remarkable auroras even at low latitudes. But can our star become even more furious? Evidence of the most violent solar “tantrums” can be found in prehistoric tree trunks and in samples of millennia-old glacial ice. However, from these indirect sources, the frequency of superflares cannot be determined. And direct measurements of the amount of radiation reaching the Earth from the Sun have only been available since the beginning of the space age.

Another way to learn about our Sun’s long-term behavior is to turn to the stars, as is the approach of the new study. Modern space telescopes observe thousands and thousands of stars and record their brightness fluctuations in visible light. Superflares, which release amounts of energy of more than one octillion joules within a short period of time, show themselves in the observational data as short, pronounced peaks in brightness. “We cannot observe the Sun over thousands of years,” Prof. Dr. Sami Solanki, Director at the MPS and coauthor, explained the basic idea behind the investigation. “Instead, however, we can monitor the behavior of thousands of stars very similar to the Sun over short periods of time. This helps us to estimate how frequently superflares occur,” he adds.

Looking for close relatives of the Sun

In the current study, the team including researchers from the University of Graz (Austria), the University of Oulu (Finland), the National Astronomical Observatory of Japan, the University of Colorado Boulder (USA) and the Commissariat of Atomic and Alternative Energies of Paris-Saclay and the University of Paris-Cité, analyzed the data from 56450 sun-like stars as seen by NASA’s space telescope Kepler between 2009 and 2013. “In their entirety, the Kepler data provide us with evidence of 220000 years of stellar activity,” said Prof. Dr. Alexander Shapiro from the University of Graz.

Crucial for the study was the careful selection of the stars to be taken into account. After all, the chosen stars should be particularly close “relatives” of the Sun. The scientists therefore only admitted stars whose surface temperature and brightness were similar to the Sun’s. The researchers also ruled out numerous sources of error, such as cosmic radiation, passing asteroids or comets, as well as non-sun-like stars that in Kepler images may by chance flare up in the vicinity of a sun-like star. To do this, the team carefully analyzed the images of each potential superflare - only a few pixels in size - and only counted those events that could reliably be assigned to one of the selected stars.

In this way, the researchers identified 2889 superflares on 2527 of the 56450 observed stars. This means that on average, one sun-like star produces a superflare approximately once per century.

“High performance dynamo computations of these solar-type stars easily explain the magnetic origins of the intense release of energy during such superflares”, said coauthor Dr. Allan Sacha Brun of the Commissariat of Atomic and Alternative Energies of Paris-Saclay and the University of Paris-Cité.

Surprisingly frequent

“We were very surprised that sun-like stars are prone to such frequent superflares”, said first author Dr. Valeriy Vasilyev from the MPS. Earlier surveys by other research groups had found average intervals of a thousand or even ten thousand years. However, earlier studies were unable to determine the exact source of the observed flare and therefore had to limit themselves to stars that did not have any too close neighbors in the telescope images. The current study is the most precise and sensitive to date.

Longer average time intervals between extreme solar events have also been suggested by studies looking for evidence of violent solar storms impacting Earth. When a particularly high flux of energetic particles from the Sun reaches the Earth's atmosphere, they produce a detectable amount of radioactive atoms such as the radioactive carbon isotope 14C. These atoms are then deposited in natural archives such as tree rings and glacial ice. Even thousands of years later, the sudden influx of high-energy solar particles can thus be deduced by measuring the amount of 14C using modern technologies. 

In this way, researchers were able to identify five extreme solar particle events and three candidates within the past twelve thousand years of the Holocene, leading to an average occurrence rate of once per 1500 years. The most violent is believed to have occurred in the year 775 AD. However, it is quite possible that more such violent particle events and also more superflares occurred on the Sun in the past. “It is unclear whether gigantic flares are always accompanied by coronal mass ejections and what is the relationship between superflares and extreme solar particle events. This requires further investigation”, co-author Prof. Dr. Ilya Usoskin from the University of Oulu in Finland pointed out. Looking at the terrestrial evidence of past extreme solar events could therefore underestimate the frequency of superflares.

Forecasting dangerous space weather

The new study does not reveal when the Sun will throw its next fit. However, the results urge caution. “The new data are a stark reminder that even the most extreme solar events are part of the Sun's natural repertoire,” said coauthor Dr. Natalie Krivova from the MPS. During the Carrington event of 1859, one of the most violent solar storms of the past 200 years, the telegraph network collapsed in large parts of northern Europe and North America. According to estimates, the associated flare released only a hundredth of the energy of a superflare. Today, in addition to the infrastructure on the Earth's surface, especially satellites would be at risk.

The most important preparation for strong solar storms is therefore reliable and timely forecasting. As a precaution, satellites, for example, could be switched off. From 2031, ESA’s space probe Vigil will help in the endeavor of forecasting. From its observation position in space, it will look at the Sun from the side and notice sooner than Earth-bound probes when processes that might drive dangerous space weather are brewing up on our star. The MPS is currently developing the Polarimetric and Magnetic Imager for this mission.

 

 

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Journal

Science

DOI

10.1126/science.adl5441 

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

Sun-like stars produce superflares roughly one per century

Article Publication Date

13-Dec-2024

NASA successfully integrates Roman mission’s telescope, instruments

NASA/Goddard Space Flight Center

 

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The telescope and instruments for NASA’s Nancy Grace Roman Space Telescope were recently integrated together on the observatory’s instrument carrier at the agency’s Goddard Space Flight Center in Greenbelt, Md. Next, the entire system will be joined to the Roman spacecraft. 

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Credit: NASA/Chris Gunn

NASA’s Nancy Grace Roman Space Telescope team has successfully integrated the mission’s telescope and two instruments onto the instrument carrier, marking the completion of the Roman payload. Now the team at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, will begin joining the payload to the spacecraft.

“We’re in the middle of an exciting stage of mission preparation,” said Jody Dawson, a Roman systems engineer at NASA Goddard. “All the components are now here at Goddard, and they’re coming together in quick succession. We expect to integrate the telescope and instruments with the spacecraft before the year is up.”

Engineers first integrated the Coronagraph Instrument, a technology demonstration designed to image exoplanets — worlds outside our solar system — by using a complex suite of masks and active mirrors to obscure the glare of the planets’ host stars.

Then the team integrated the Optical Telescope Assembly, which includes a 7.9-foot (2.4-meter) primary mirror, nine additional mirrors, and their supporting structures and electronics. The telescope will focus cosmic light and send it to Roman’s instruments, revealing billions of objects strewn throughout space and time. Roman will be the most stable large telescope ever built, at least 10 times more so than NASA’s James Webb Space Telescope and 100 times more than the agency’s Hubble Space Telescope. This will allow scientists to make measurements at levels of precision that can answer important questions about dark energy, dark matter, and worlds beyond our solar system.

With those components in place, the team then added Roman’s primary instrument. Called the Wide Field Instrument, this 300-megapixel infrared camera will give Roman a deep, panoramic view of the universe. Through the Wide Field Instrument’s surveys, scientists will be able to explore distant exoplanets, stars, galaxies, black holes, dark energy, dark matter, and more. Thanks to this instrument and the observatory’s efficiency, Roman will be able to image large areas of the sky 1,000 times faster than Hubble with the same sharp, sensitive image quality.

“It would be quicker to list the astronomy topics Roman won’t be able to address than those it will,” said Julie McEnery, the Roman senior project scientist at NASA Goddard. “We’ve never had a tool like this before. Roman will revolutionize the way we do astronomy.”

The telescope and instruments were mounted to Roman’s instrument carrier and precisely aligned in the largest clean room at Goddard, where the observatory is being assembled. Now, the whole assembly is being attached to the Roman spacecraft, which will deliver the observatory to its orbit and enable it to function once there.

At the same time, the mission’s deployable aperture cover — a visor that will shield the telescope from unwanted light — is being joined to the outer barrel assembly, which serves as the telescope’s exoskeleton.

“We’ve had an incredible year, and we’re looking forward to another one!” said Bear Witherspoon, a Roman systems engineer at NASA Goddard. “While the payload and spacecraft undergo a smattering of testing together, the team will work toward integrating the solar panels onto the outer barrel assembly.”

That keeps the observatory on track for completion by fall 2026 and launch no later than May 2027.

To virtually tour an interactive version of the telescope, visit:

https://roman.gsfc.nasa.gov/interactive

The Nancy Grace Roman Space Telescope is managed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with participation by NASA’s Jet Propulsion Laboratory and Caltech/IPAC in Southern California, the Space Telescope Science Institute in Baltimore, and a science team comprising scientists from various research institutions. The primary industrial partners are BAE Systems Inc. in Boulder, Colorado; L3Harris Technologies in Rochester, New York; and Teledyne Scientific & Imaging in Thousand Oaks, California.

Technicians install the primary instrument for NASA's Nancy Grace Roman Space Telescope, called the Wide Field Instrument (at left), in the biggest clean room at the agency's Goddard Space Flight Center in Greenbelt, Md. This marked the final step to complete the Roman payload, which also includes a Coronagraph instrument and the Optical Telescope Assembly.

Credit

NASA/Chris Gunn

 

Oldest modern human genomes sequenced

Genomes of seven early Europeans show they belonged to a small, isolated group that had recently mixed with Neandertals but left no present-day descendants

Max Planck Institute for Evolutionary Anthropology

 

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Illustration of Zlatý kůň, who belonged to the same population as the Ranis individuals and was closely related to two of them.

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Credit: © Tom Björklund for Max Planck Institute for Evolutionary Anthropology

After modern humans left Africa, they met and interbred with Neandertals, resulting in around two to three percent Neandertal DNA that can be found in the genomes of all people outside Africa today. However, little is known about the genetics of these first pioneers in Europe and the timing of the Neandertal admixture with non-Africans.

A key site in Europe is Zlatý kůň in Czechia, where a complete skull from a single individual who lived around 45,000 years ago was discovered and previously genetically analyzed. However, due to the lack of archaeological context, it was not possible to link this individual to any archaeologically defined group. A nearby site, the Ilsenhöhle in Ranis in Germany, about 230 km from Zlatý kůň, is known for a specific type of archaeology, the Lincombian-Ranisian-Jerzmanowician (LRJ), which dates to around 45,000 years ago. It has long been debated whether the LRJ culture was produced by Neandertals or early modern humans. Although mostly small fragments of bones are preserved in Ranis, a previous study was able to analyze mitochondrial DNA from thirteen of these remains and found that they belonged to modern humans and not Neandertals. However, since the mitochondrial sequence only constitutes a miniscule part of the genetic information, the relationships to other modern humans remained a mystery.

Linking Zlatý kůň and Ranis

A new study published today in Nature analyzed the nuclear genomes of the thirteen specimens from Ranis and found that they represented at least six individuals. The size of the bones indicated that two of these individuals were infants and, genetically, three were males and three were females. Interestingly, among these individuals were a mother and daughter, as well as other, more distant, biological relatives. The team also sequenced more DNA from the female skull found at Zlatý kůň, producing a high-quality genome for this individual. ”To our surprise, we discovered a fifth- or sixth-degree genetic relationship between Zlatý kůň and two individuals from Ranis.” says Arev Sümer, lead author of the study, ”This means that Zlatý kůň was genetically part of the extended family of Ranis and likely also made LRJ-type tools”.

Among the six individuals from Ranis, one bone was particularly well preserved, in fact it is the best preserved modern human bone from the Pleistocene for DNA retrieval. This allowed the team to obtain a high-quality genome from this male individual, referred to as Ranis13. Together, the Ranis13 and Zlatý kůň genomes represent the oldest high-quality modern human genomes sequenced to date. When analyzing genetic variants related to phenotypic traits, they found that Ranis and Zlatý kůň individuals carried variants associated with dark skin and hair color as well as brown eyes, reflecting the recent African origin of this early European population. 

By analyzing the segments inherited from the same ancestor in the Ranis and Zlatý kůň genomes, the researchers estimate that their population consisted of at most a few hundred individuals who may have been spread out over a larger territory. The authors found no evidence that this small early modern human population contributed to later Europeans or any other world-wide population.

A narrower timeframe for the shared Neandertal admixture

Members of the Zlatý kůň/Ranis population coexisted with Neandertals in Europe, raising the possibility that they may have had Neandertals among their recent ancestors after they migrated to Europe. Previous studies on modern humans from over 40,000 years ago, had found evidence of such recent admixture events between modern humans and Neandertals. However, no such evidence for recent Neandertal admixture was detected in the genomes of the Zlatý kůň/Ranis individuals. “The fact that modern human groups, which may have arrived in Europe later, carry such Neandertal ancestry while Ranis and Zlatý kůň do not could mean that the older Zlatý kůň/Ranis lineage may have entered Europe by a different route or did not overlap as extensively with the regions where Neandertals lived” speculates Kay Prüfer, who co-supervised the study.

The Zlatý kůň/Ranis population represents the earliest known divergence from the group of modern humans that migrated out of Africa and dispersed later across Eurasia. Despite this early separation, the Neandertal ancestry in Zlatý kůň and Ranis originated from the same ancient admixture event that can be detected in all people outside Africa today. By analyzing the length of the segments contributed from Neandertals in the high-coverage Ranis13 genome and using direct radiocarbon dates on this individual, the researchers dated this shared Neandertal admixture to between 45,000 and 49,000 years ago. Since all present-day non-African populations share this Neandertal ancestry with Zlatý kůň and Ranis, this means that around 45,000 to 49,000 years ago, a coherent ancestral non-African population must still have existed.

“These results provide us with a deeper understanding of the earliest pioneers that settled in Europe,” says Johannes Krause, senior author of the study. “They also indicate that any modern human remains found outside Africa that are older than 50,000 years could not have been part of the common non-African population that interbred with Neanderthals and is now found across much of the world.”

Illustration of the Zlatý kůň/Ranis group. Around 45,000 years ago, individuals from Ranis in Germany and Zlatý kůň in Czechia likely traveled together across the open steppe landscapes of Europe.

Credit

© Tom Björklund for Max Planck Institute for Evolutionary Anthropology

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Journal

Nature

DOI

10.1038/s41586-024-08420-x 

Article Title

Earliest modern human genomes constrain timing of Neanderthal admixture

Article Publication Date

12-Dec-2024

New timeline for Neandertal gene flow event

Scientists unravel timing and impact of Neandertal gene flow into early modern humans

Max Planck Institute for Evolutionary Anthropology

 

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The researchers identified regions with Neandertal ancestry in over 300 individuals. They assessed sharing of segments, inferred gene flow, and looked at variation to identify candidates for positive and negative selection.

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Credit: © Leonardo Iasi et al., Science (2024)

The study of ancient DNA has greatly advanced our knowledge of human evolution, including the discovery of gene flow from Neandertals into the common ancestors of modern humans. Neandertals and modern humans diverged about 500,000 years ago, with Neandertals living in Eurasia for the past 300,000 years. Then, sometime around 40,000 to 60,000 years ago, modern human groups left Africa and spread across Eurasia, encountering Neandertals along the way. As a result, most non-Africans harbor one to two percent Neandertal ancestry today. However, the precise timing and functional legacy of Neandertals remains elusive.

In a new study, researchers from the Max Planck Institute for Evolutionary Anthropology, Leipzig, and the University of California, Berkeley, examined the genomes of 300 present-day and ancient modern humans, including 59 individuals who lived between 2,000 and 45,000 years ago. "We set out to determine the timing and duration of Neandertal gene flow and the resulting impact on modern humans. To do this, we created a catalog of Neandertal ancestry segments. By comparing the segments among individuals from different time periods and geographic locations, we were able to show that the vast majority of Neandertal ancestry can be traced to a single, shared, extended period of gene flow into the common ancestors of all non-African individuals today," says Priya Moorjani from the University of California, Berkeley.

Neandertal ancestry revisited

By observing the length of the Neandertal DNA segments, which is related to the number of generations since the gene flow, the researchers inferred that the gene flow began about 50,000 years ago and continued for about 7,000 years. "This timeline closely matches the archaeological evidence for the overlap of Neandertals and modern humans in Europe. Some early modern humans - Oase, Ust'-Ishim, Zlatý kůň, and Bacho Kiro - possess substantial unique Neandertal ancestry that is not shared with modern humans after 40,000 years," says first author Leonardo Iasi from the Max Planck Institute for Evolutionary Anthropology.

These dates have several implications for human dispersal after the Out-of-Africa event, as they provide a lower bound on the timing of migration and the settlement of regions outside of Africa. For example, this suggests that the major migration out of Africa occurred no later than 43,500 years ago. Moreover, the population receiving Neandertal ancestry may have been highly structured during the gene flow event. "Diversification of humans outside of Africa may have begun during or soon after the Neandertal gene flow, which could partially explain the different levels of Neandertal ancestry among non-African populations and also reconcile our dates with archaeological evidence for the presence of modern humans in Southeast Asia and Oceania by about 47,000 years,“ says Benjamin Peter from the Max Planck Institute for Evolutionary Anthropology and the University of Rochester. "Studying more ancient genomes from Eurasia and Oceania could further our understanding of when humans spread to these regions.“

Functional impact of Neandertal ancestry

To understand the functional legacy of Neandertal ancestry, the researchers examined changes in Neandertal ancestry across the genome and over time. They identified some Neandertal regions that are present at high frequency, possibly because they were beneficial as early modern humans began to explore new environments outside of Africa. "These include genes related to immune function, skin pigmentation and metabolism," says Manjusha Chintalapati from the University of California, Berkeley. "On the other hand, there are also large regions of the genome that are completely devoid of Neandertal ancestry. These regions formed rapidly after the gene flow and were also absent from the earliest modern human genomes, 30,000 to 45,000-year-old individuals. Many Neandertal sequences may have been deleterious to humans and were therefore actively and rapidly selected against by evolution.“

This study sheds light on the complex history of gene flow from Neandertals into modern humans. It also highlights the power of genomic data to elucidate the legacy of human migrations and gene flow.

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Journal

Science

DOI

10.1126/science.adq3010 

Article Title

Neanderthal ancestry through time: Insights from genomes of ancient and present-day humans

Article Publication Date

13-Dec-2024

A new timeline for Neanderthal interbreeding with modern humans

Surviving Neanderthal genes in modern genome tell a story of thousands of years of interactions

University of California - Berkeley

 

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Illustration of an encounter between a group of Neanderthals (black) and a group of modern humans (red, top row) with offspring showing recent Neanderthal ancestry (red, bottom row), imagined as a cave art painting. DNA from bones and teeth of these early human ancestors is helping scientists understand the interactions between early Homo sapiens and the Neanderthals they encountered after migrating out of Africa.

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Credit: Leonardo Iasi, MPI-EVA. Figure created with Dall-E and BioRender.com

A new analysis of DNA from ancient modern humans (Homo sapiens) in Europe and Asia has determined, more precisely than ever, the time period during which Neanderthals interbred with modern humans, starting about 50,500 years ago and lasting about 7,000 years — until Neanderthals began to disappear.

That interbreeding left Eurasians with many genes inherited from our Neanderthal ancestors, which in total make up between 1% and 2% of our genomes today.

The genome-based estimate is consistent with archeological evidence that modern humans and Neanderthals lived side-by-side in Eurasia for between 6,000 and 7,000 years. The analysis, which involved present-day human genomes as well as 58 ancient genomes sequenced from DNA found in modern human bones from around Eurasia, found an average date for Neanderthal-Homo sapiens interbreeding of about 47,000 years ago. Previous estimates for the time of interbreeding ranged from 54,000 to 41,000 years ago.

The new dates also imply that the initial migration of modern humans from Africa into Eurasia was basically over by 43,500 years ago.

"The timing is really important because it has direct implications on our understanding of the timing of the out-of-Africa migration as most non-Africans today inherit 1-2% ancestry from Neanderthals," said Priya Moorjani, an assistant professor of molecular and cell biology at the University of California, Berkeley, and one of two senior authors of the study. "It also has implications for understanding the settlement of the regions outside Africa, which is typically done by looking at archeological materials or fossils in different regions of the world."

The genome analysis, also led by Benjamin Peter of the University of Rochester in New York and the Max Planck Institute for Evolutionary Anthropology (MPI-EVA) in Leipzig, Germany, will be published in the Dec. 13 print issue of the journal Science. The two lead authors are Leonardo Iasi, a graduate student at MPI-EVA, and Manjusha Chintalapati, a former UC Berkeley postdoctoral fellow now at the company Ancestry DNA.

The longer duration of gene flow may help explain, for example, why East Asians have about 20% more Neanderthal genes than Europeans and West Asians. If modern humans moved eastward about 47,000 years ago, as archeological sites suggest, they would already have had intermixed Neanderthal genes.

"We show that the period of mixing was quite complex and may have taken a long time. Different groups could have separated during the 6,000- to 7,000-year period and some groups may have continued mixing for a longer period of time," Peter said. "But a single shared period of gene flow fits the data best."

"One of the main findings is the precise estimate of the timing of Neanderthal admixture, which was previously estimated using single ancient samples or in present-day individuals. Nobody had tried to model all of the ancient samples together," Chintalapati said. “ This allowed us to build a more complete picture of the past”

Neanderthal deserts in the genome

In 2016, Moorjani pioneered a method for inferring the timing of Neanderthal gene flow using often incomplete genomes of ancient individuals. At that time, only five archaic Homo sapiens genomes were available. For the new study, Iasi, Chintalapati and their colleagues employed this technique with 58 previously sequenced genomes of ancient Homo sapiens who lived in Europe, Western and Central Asia over the past 45,000 years and the genomes of 275 worldwide contemporary humans to provide a more precise date — 47,000 years ago. Rather than assuming the gene flow occurred in a single generation, they tried more complex models developed by Iasi and Peter to establish that the interbreeding extended over about 7,000 years, rather than being intermittent.

The timing of the interbreeding between Neanderthals and modern humans was corroborated by another, independent study conducted by MPI-EVA researchers and scheduled to be published Dec. 12 in the journal Nature. That study, an analysis of two newly sequenced genomes of Homo sapiens that lived about 45,000 years ago, also found a date of 47,000 years ago.

"Although the ancient genomes were published in previous studies, they had not been analyzed to look at Neanderthal ancestry in this detailed way. We created a catalog of Neanderthal ancestry segments in modern humans. By jointly analyzing all these samples together, we inferred the period of gene flow was around 7,000 years," Chintalapati said. "The Max Planck group actually sequenced new ancient DNA samples that allowed them to date the Neanderthal gene flow directly. And they came up with a similar timing as us."

The UC Berkeley/MPI-EVA team also analyzed regions of the modern human genome that contain genes inherited from Neanderthals and some areas that are totally devoid of Neanderthal genes. They found that areas lacking any Neanderthal genes, so-called archaic or Neanderthal deserts, developed quickly after the two groups interbred, suggesting that some Neanderthal gene variants in those areas of the genome must have been lethal to modern humans.

Early modern human samples that are older than 40,000 years — samples from Oase cave in Romania, Ust'-Ishim in Russia, Zlatý kůň in the Czech Republic, Tianyuan in China and Bacho Kiro in Bulgaria  — already contained these deserts in their genomes.

"We find that very early modern humans from 40,000 years ago don't have any ancestry in the deserts, so these deserts may have formed very rapidly after the gene flow," said Iasi. "We also looked at the changes in Neanderthal ancestry frequency over time and across the genome and found regions that are present at high frequency, possibly because they carry beneficial variants that were introgressed from Neanderthals."

Most of the high-frequency Neanderthal genes are related to immune function, skin pigmentation and metabolism, as reported in some previous studies. One immune gene variant inherited from Neanderthals confers protective effects to coronavirus that causes COVID-19, for example. Some of the Neanderthal genes involved in the immune system and skin pigmentation actually increased in frequency in Homo sapiens over time, implying that they may have been advantageous to human survival.

"Neanderthals were living outside Africa in harsh, Ice Age climates and were adapted to the climate and to the pathogens in these environments. When modern humans left Africa and interbred with Neanderthals, some individuals inherited Neanderthal genes that presumably allowed them to adapt and thrive better in the environment," Iasi said.

"The fact that we find some of these regions already in 30,000-year-old samples shows that some of these regions were actually adapted immediately after the introgression," Chintalapati added.

Other genes, such as the gene conferring resistance to coronaviruses, may not have been immediately useful but became useful later on.

"The environment changes and then some genes become beneficial," Peter said.

Moorjani is currently looking at Neanderthal sequences in people of East Asian descent, who not only have a greater percentage of Neanderthal genes, but also somegenes — up to 0.1% of their genome — from another early hominin group, the Denisovans.

"It's really cool that we can actually peer into the past and see how variants inherited from our evolutionary cousins, Neanderthals and Denisovans, changed over time," Moorjani said. "This allows us to understand the dynamics of the mixture of Neanderthals and modern humans."

Other co-authors of the Science paper were postdoctoral fellow Laurits Skov of UC Berkeley and Alba Bossoms Mesa and Mateja Hajdinjak of MPI-EVA. Moorjani's research was supported by the Burroughs Wellcome Fund and the National Institutes of Health (R35GM142978).

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Journal

Science

DOI

10.1126/science.adq3010 

Subject of Research

People

Article Title

Neandertal ancestry through time: Insights from genomes of ancient and present-day humans

Article Publication Date

13-Dec-2024

Genomic analysis refines timing of Neandertal admixture – and its impact on modern humans

Summary author: Walter Beckwith

American Association for the Advancement of Science (AAAS)

A genomic study encompassing more than 300 genomes spanning the last 50,000 years has revealed how a single wave of Neandertal gene flow into early modern humans left an indelible mark on human evolution. Among other findings, the study reports that modern humans acquired several Neanderthal genes that ended up being advantageous to our lineage, including those involved in skin pigmentation, immune response, and metabolism. To date, sequencing of Neanderthal and Denisovan genomes has revealed substantial gene flow between these archaic hominins and modern human ancestors, even as scientists have also reported that Neanderthal ancestry is unevenly distributed across the genome. Moreover, certain regions of the genome – known as archaic deserts – completely lack Neandertal ancestry, while others exhibit high frequencies of Neanderthal variants, potentially due to beneficial adaptive mutations. However, much about the nature of this ancient admixture, including the role evolutionary forces like genetic drift or natural selection played in shaping these patterns, remains unclear. Using genomic data from 334 modern humans, including 59 ancient individuals ranging from 45,000 to 2,200 years old, and 275 present-day individuals from diverse global populations, Leonardo Iasi et al. performed a comprehensive evaluation of Neanderthal ancestry variation in modern humans over the last ~50,000 years. Iasi et al. discovered that the vast majority of Neanderthal gene flow is attributable to a single, shared extended period of gene flow that likely occurred 50,500 to 43,500 years ago, which is consistent with archeological evidence for the overlap of modern humans and Neandertals in Europe. Additionally, the findings demonstrate that Neanderthal ancestry underwent rapid natural selection – both positive and negative – within 100 generations after gene flow, especially on the X chromosome.

 

Nature is publishing a related paper, “Earliest modern human genomes constrain timing of Neanderthal admixture,” embargoed for the same time (Thursday, 12 December at 2pm US ET). To obtain a copy of this paper, please email press@nature.com or visit the Springer Nature press site. An online press briefing for the two papers will take place UNDER STRICT EMBARGO on Wednesday at 3pm London time (GMT) / 10 am US Eastern Time. To attend this briefing please pre-register here.

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Journal

Science

DOI

10.1126/science.adq3010 

Article Title

Neandertal ancestry through time: Insights from genomes of ancient and present-day humans

Article Publication Date

13-Dec-2024

 

Uncovering hidden consequences of catch-and-release sport fishing

UMass Amherst leads first study to examine effect of temporary halt in sportfishing, shows that giant trevally fishery in Seychelles is sensitive to angling pressure — despite being catch-and-release

University of Massachusetts Amherst

 

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Hook shyness can be especially concerning with a species like the giant trevally, a “bucket list” prized sport fish for many anglers.

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Credit: Fly Fishing Nation

AMHERST, Mass. – In an effort to conserve sensitive species of fish, some sport fishing is entirely catch-and-release, meaning that the fish are returned to the water once brought ashore. However, too much fishing may affect the behavior of the target species and the sustainability of the fishery. Now, for the first time, an international team of biologists co-led by the University of Massachusetts Amherst and University of South Florida, conservationists and industry partners in Seychelles, has tested whether this is indeed the case. In a paper recently published in the journal Canadian Journal of Fisheries and Aquatic Sciences, the team shows that a coveted sport-fishing species, the giant trevally, can be sensitive to too much fishing pressure. This result comes from a “natural experiment” presented by the COVID-era closure of the fishery and has widespread management implications for the species throughout its range in the Indian and Pacific oceans.

“A few years ago, both the Island Conservation Society, which promotes conservation in the Seychelles Islands, and the Alphonse Fishing Company, (now known as Blue Safari Seychelles Fly Fishing) a flyfishing guide service located in the Seychelles, approached my group concerned about the sustainability of sportfishing in the Seychelles,” says Andy Danylchuk, professor of fish conservation at UMass Amherst and the paper’s senior author. “It was the perfect convergence of a research question that my team cares deeply about — how recreational fishing can be a sustainable part of the ‘blue economy’— brought to us by stakeholders looking to implement policies and management guided by science.”

As opposed to harvest-orientated recreational fishing whose effects can be more easily gauged in terms of population numbers, catch-and-release should theoretically result in less mortality, meaning there should be more fish in the water for the anglers who are eager to catch them.

However, there are a host of unintended consequences that may be associated with catch-and-release, which can be difficult to quantify. These include increased mortality from hooking a fish in critical locations, such as the gills, post-release predation, altered movements and “hook shyness,” which occurs when some fish in a population are so used to being targeted that they no longer bite at the lures or flies anglers cast to them. Hook shyness can be especially concerning with a species like the giant trevally, a “bucket list” prized sport fish for many anglers who are willing to spend thousands of dollars on a once-in-a-lifetime trip to catch them. If catch rates decline because of hook shyness, anglers can become disappointed, which can ultimately affect the local tourist industry. In some locations, to protect against such a loss of income, local guides may resort to baiting the fish with chum in order to lure them closer to their paying customers — something that can exacerbate the problem of altering the behavior and movement patterns of giant trevally.

“The Island Conservation Society and the Alphonse Fishing Company wanted to know whether or not the current fishing practices for giant trevally in the Alphonse Group of islands in the Seychelles was sustainable,” says Lucas Griffin, the paper’s lead author who completed this research as part of a post-doctoral fellowship at UMass Amherst and is now an assistant professor of marine biology at the University of South Florida. “And so, we’ve been working with them on a series of studies to assess just that.”

The first, published in Ocean and Coastal Management in 2021, charted out what the giant trevally fishery looked like and how the Island Conservation Society and Alphonse Fishing Company have successfully managed it. The second, published in Fisheries Research in 2022, showed that catch-and-release has a minimal impact on the short-term activity and survival rate of giant trevally. “Our most recent published paper pulls more of the pieces together to shed light on whether angler presence alters the behavior of giant trevally,” says Griffin.

To conduct their research, they relied on a combination of acoustic telemetry (where a transmitter is surgically implanted in the giant trevally and receivers are placed throughout the coastal environment to rack individual fish as they move), and a mark-and-recapture program (where the team worked with anglers to implant microchips similar to what you’d put in your pet cat or dog that could be used to record how many times, and in which locations, individual fish were caught).

They had initially planned to work with the Alphonse Fishing Company and Island Conservation Society to use short-term closures of different fishing spots to see what happened to the giant trevally under “natural” conditions — and then COVID essentially shut recreational fishing down altogether for nearly two years. “It’s strange to say, but the pandemic created a once-in-a-lifetime natural experiment,” says Griffin. “The entire fishery shut down, so we could really see how giant trevally live in the total absence of fishing pressure.”

The team found that, while giant trevally can adapt their behaviors and movement patterns to fishing pressures, they don’t react to short-term closures — even those as total as the one during COVID. Furthermore, their data shows that over time, giant trevally may indeed become hook shy, and they point to evidence that some groups of giant trevally have shifted their home ranges away from prime fishing spots. Conversely, the mark-and-recapture program is showing a considerable population size of giant trevally, and that new giant trevally may be entering the fishery which may offset any issues of hook shyness.

Taken together, all of this evidence points to the conclusion that although giant trevally may be resilient to the acute effects of catch-and-release, they may indeed be sensitive to the overall extent of fishing pressure and that putting more anglers on the water may exacerbate the problems of hook shyness. A healthy ecosystem and high abundance of giant trevally may make fish more resilient to the effects of angling.

“We are part of the ecology of these fish,” says Griffin. “If we want to be catching more of them, we may need to consider limiting the number of anglers that target them in any given location.”

Funding for this research was provided by the Seychelles Conservation and Climate Adaptation Trust, the Alphonse Foundation and Bonefish & Tarpon Trust, while in-kind support was provided by Blue Safari Seychelles, Blue Safari Seychelles Fly Fishing (formerly Alphonse Fishing Company) the Islands Development Company, the Island Conservation Society, the Seychelles Fishing Authority, Patagonia Inc., Thomas & Thomas Fly Rods, Cortland Lines and Nautilus Reels.

A media kit, with photos, videos, and all credit and caption information, is available here.

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Journal

Canadian Journal of Fisheries and Aquatic Sciences

Article Title

Beyond the hook: Do angler-fish interactions in a catch-and-release recreational fishery modify fish space use and catchability?

Article Publication Date

12-Dec-2024