Learning Disorders And Parkinson’s Disease: Tremor Predicts Effects Of Medication (Neuroscience)

The effect of dopaminergic medication on the learning abilities of patients with Parkinson’s disease turns out to be linked to the presence of tremor symptoms. In patients who do not experience tremor, dopaminergic medication improves the ability to learn from rewards (reinforcement learning). Remarkably, the medication brings no benefit in reward learning to patients who do exhibit tremor. These were the results from a new study by brain researchers at the Donders Institute of Radboud University and Radboud university medical center, published on 6 November in the scientific journal Brain.

“It is somewhat surprising that until now, studies of cognition in Parkinson’s disease never assessed the distinction between patients who exhibit tremor and those who do not”, says Hanneke den Ouden, brain researcher at Radboud University. “Our study shows that there is a link between problems with motor skills and problems with cognition in patients with Parkinson’s disease.”

Learning abilities and Parkinson’s disease

Most patients with Parkinson’s disease experience tremor –shaking in an arm or leg. Only one in four patients does not experience these symptoms. In addition, many patients experience mental issues. Due to a decrease in dopamine, a chemical messenger molecule that occurs in the brain, patients with Parkinson’s disease become less sensitive to learning through rewards.

A large number of prior studies have shown that this learning disorder can be remedied by administering dopaminergic medication. It remained a mystery, however, why medication had no effect in many patients. The study of the Radboud researchers reveals that this improvement through medication only occurs in patients who experience tremor.

Presence and absence of tremor

“The fact that we only observe results from earlier studies in patients without tremor suggests that prior studies only included with these patients. This would make sense, as it is easier for patients without tremor to participate in an experiment. However, it is important to realise that three out of four patients actually do experience tremor, and our study shows that the medication has a different effect on these patients. We see this as a major warning: Always be aware of the diversity of patients in your study, as you might otherwise draw the wrong conclusions.”

Predictive value

According to the researchers, it is crucial to improve our understanding of such patient diversity. “This study tells us that the dopamine systems of Parkinson’s disease patients with and without tremor are affected in different ways, and that this goes beyond the level of just motor problems, affecting cognition as well”, according to co-author Rick Helmich, neurologist at Radboud university medical center. “Whether someone experiences tremor or not might therefore potentially have a significant predictive value regarding the effectiveness of medication in the cognitive domain. However, more and larger studies are needed before this can be confirmed.”

References: Annelies J van Nuland, Rick C Helmich, Michiel F Dirkx, Heidemarie Zach, Ivan Toni, Roshan Cools, Hanneke E M den Ouden, Effects of dopamine on reinforcement learning in Parkinson’s disease depend on motor phenotype, Brain, , awaa335, https://doi.org/10.1093/brain/awaa335 link: https://academic.oup.com/brain/advance-article/doi/10.1093/brain/awaa335/5956227

Provided by Radboud University

Explaining Gravity, Without Strings Attached? (Physics)

For decades, most physicists have agreed that string theory is the missing link between Einstein’s theory of general relativity, describing the laws of nature at the largest scale, and quantum mechanics, describing them at the smallest scale. However, an international collaboration headed by Radboud physicists has now provided compelling evidence that string theory is not the only theory that could form the link. They demonstrated that it is possible to construct a theory of quantum gravity that obeys all fundamental laws of physics, without strings. They described their findings in Physical Review Letters last week.

©Radboud University

When we observe gravity at work in our universe, such as the motion of planets or light passing close to a black hole, everything seems to follow the laws written down by Einstein in his theory of general relativity. On the other hand, quantum mechanics is a theory that describes the physical properties of nature at the smallest scale of atoms and subatomic particles. Though these two theories have allowed us to explain every fundamental physical phenomenon observed, they also contradict each other. As of today, physicists have severe difficulties to reconcile the two theories to explain gravity on both the largest and smallest scale.

No strings attached

In the 1970s, physicists proposed a new set of physics principles to address this problem, extending the laws proposed by the general theory of relativity. According to this so-called ‘string theory’, everything around us is formed not by point particles, but by strings: one dimensional objects that vibrate. Since its introduction, string theory has been the most widespread theoretical framework that is thought to complete Einstein’s general theory of relativity to a theory of quantum gravity.

However, a new demonstration by theoretical physicists at Radboud University now shows that string theory is not the only way to do this. ‘We show that it is still possible to explain gravity using quantum mechanics without using the laws of string theory at all’, says theoretical physicist Frank Saueressig. ‘We demonstrate that the idea that everything consists of point particles could still fit with quantum gravity, without including strings. This particle physics framework is also verified experimentally, for example, at the Large Hadron Collider (LHC) at CERN.’

Seen in experiments

‘For scientists, this alternate theory is attractive to use because it has been extremely difficult to connect string theory to experiments. Our idea uses the physical principles that are already tested experimentally. In other words: nobody ever observed strings in experiments, but particles are things that people definitely see at LHC experiments. This lets us bridge the gap between theoretical predictions and experiments more easily.’

Only one set of laws

After having demonstrated that their ideas are capable of resolving long-standing problems in particle physics, the consortium is currently exploring the resulting implications of their new laws at the level of black holes. ‘After all, there is only one set of laws of nature and this set should be able to apply to all kinds of questions including what happens when we collide particles at fantastically high energies or what happens when particles fall into a black hole. It would be fantastic to demonstrate that there is actually a link between these seemingly disconnected questions which allows to resolve the puzzles appearing at both sides.’

References: Tom Draper, Benjamin Knorr, Chris Ripken, and Frank Saueressig, “Finite Quantum Gravity Amplitudes: No Strings Attached”, Physical Review Letters 125, 181301. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.181301

Provided by Radboud University

Feeding A Galaxy’s Nuclear Black Hole (Astronomy)

A galactic bar is the approximately linear structure of stars and gas that stretches across the inner regions of some galaxies. The bar stretches from one inner spiral arm, across the nuclear region, to an arm on the other side. Found in about half of spiral galaxies, including the Milky Way, bars are thought to funnel large amounts of gas into the nuclear regions, with profound consequences for the region including bursts of star formation and the rapid growth of the supermassive black hole at the center. Quasars, for example, have been suggested as one result of this kind of activity. Eventually, however, feedback from such energetic events (supernovae, for example) terminates the inflow and stalls the black hole’s growth. How bars and gas inflows form and evolve are not well understood—galaxy mergers are thought to play a role—nor are the physical properties of galactic nuclei that are still actively accumulating gas. A serious difficulty is that dust in the dense material around the nucleus is opaque to optical radiation and, depending in part on the geometry, can obscure observations. Infrared and submillimeter wavelength measurements that can peer through the dust offer the best way forward.

A near-infrared Hubble image of the luminous, barred spiral galaxy ESO320-G030. Infrared observations and modeling of over a dozen molecular species at its center reveal massive inflows of gas to a nuclear region undergoing a burst of star formation and dominated by three-components, a small warm core, a disk, and an outer envelope. Credit: NASA/HST; Alonso-Herrero et al.

The luminous, barred galaxy ESO 320-G030 is about one hundred and fifty million light-years away and shows no signs of having been in a merger, yet this galaxy has a bar nearly sixty thousand light-years long, as well as a second bar about ten times smaller perpendicular to it. This galaxy shows high star formation activity in the nuclear region, but no clear evidence of an active nucleus, perhaps because of the high extinction. The galaxy is also seen with inflowing gas (and evidence of outflows simultaneously), making it a nearby prototype of isolated, rapidly evolving galaxies driven by their bars.

CfA astronomers Eduardo Gonzalez-Alfonso, Matt Ashby, and Howard Smith led a program of far infrared Herschel spectroscopy of this object coupled with ALMA submillimeter observations of the gas. By carefully modeling the shapes of the infrared absorption lines of water and several of its ionized and isotopic variations, with fifteen other molecular species including ammonia, OH and NH, they conclude that a nuclear starburst of about twenty solar-masses of stars per year is being sustained by gas inflow with short (twenty million year) lifetime. They find evidence for three structural components: an envelope about five hundred light-years across, a dense circumnuclear disk about one hundred twenty light-years in radius, and a compact core or torus forty light-years in size and characterized by its very warm dust. These three components are responsible for about 70% of the galaxy’s luminosity. Although ESO 320-G030 is an exceptional example, being both bright and nearby, the results suggest that similar complex nuclear structures, with inflows and outflows, may be common in luminous galaxies in the more distant universe including those during its most active epoch of star formation.

References: Gonzalez-Alfonso et al., A proto-pseudobulge in ESO 320-G030 fed by a massive molecular inflow driven by a nuclear bar. arXiv:2011.00347 [astro-ph.GA]. arxiv.org/abs/2011.00347

Provided by Harvard-Smithsonian Center for Astrophysics

Do You Know About The Eternal Young White Dwarfs? (Planetary Science)

White dwarfs are the most common fossil stars within the stellar graveyard. It is well known that more than 95% of all main-sequence stars will finish their lives as white dwarfs, earth-sized objects less massive than ~1.4 Mo—the Chandrasekhar limiting mass— supported by electron degeneracy. A remarkable property of the white-dwarf population is its mass distribution, which exhibits a main peak at ~0.6 Mo, a smaller peak at the tail of the distribution around ~0.82 Mo, and a low-mass excess near ~0.4 Mo. White dwarfs with masses lower than 1.05 Mo are expected to harbour carbon(C)-oxygen(O) cores, enveloped by a shell of helium which is surrounded by a layer of hydrogen. Traditionally, white dwarfs more massive than 1.05 Mo (ultra-massive white dwarfs) are thought to contain an oxygen-neon(Ne) core, and their formation is theoretically predicted as the end product of the isolated evolution of intermediate-mass stars with an initial mass larger than 6-9 Mo, depending on the metallicity and the treatment of convective boundaries during core hydrogen burning. Once the helium in the core has been exhausted, these stars evolve to the super asymptotic giant branch (SAGB) phase, where they reach temperatures high enough to start off-centre carbon ignition under partially degenerate conditions. A violent carbon ignition eventually leads to the formation of an ONe core, which is not hot enough to develop further nuclear burning. During the SAGB phase, the star loses most of its outer envelope by the action of stellar winds, ultimately becoming an ultra-massive ONe-core white dwarf star.

Artist impression of white dwarf ©gettyimages

On the other hand, the existence of a fraction of ultra-massive white dwarfs harbouring CO cores is supported by different piece of evidence. This population could be formed through binary evolution channels, involving the merger of two white dwarfs. Assuming that C is not ignited in the merger event, the merger of two CO-core white dwarfs with a combined mass below the Chandrasekhar limit is expected to lead to the formation of a single CO-core white dwarf substantially more massive than any CO-core white dwarf that can form from a single evolution ( 1.05 M ∼1.05 Mo). To the date, it has not been possible to distinguish a CO-core from a ONe-core ultra-massive white dwarf from their observed properties, although a promissory avenue to accomplish this is by means of white dwarf asteroseismology. Recent studies reveal that 10% -30% of all white dwarfs are expected to be formed as a result of merger events of any kind, and that this percentage raises up to 50 % for massive white dwarfs (M>0.9Mo). In particular, double white dwarf mergers contribute to the formation of massive white dwarfs in 20-30%. These results are in line with the existence of an excess of massive white dwarfs in the mass distribution. However, the existence of ultra-massive CO white dwarfs remains to be proven, and their exact percentage is still unclear.

The formation of white dwarfs as a result of stellar mergers is particularly important given the persistent historical interest in the study of the channels that lead to the occurrence of type Ia Supernovae, which are thought to be the violent explosion of a white dwarf exceeding the Chandrasekhar limiting mass. The main pathways to type Ia Supernovae involve binary evolution, namely the single-degenerate channel in which a white dwarf gains mass from a non-degenerate companion, or the double-degenerate channel involving the merger of two white dwarfs. Moreover, ultra-massive white dwarfs resulting from merger episodes are of utmost importance in connection with the formation of rapidly spinning neutron stars/magnetars. Mergers of white dwarfs have also been invoked as the most likely mechanism for the formation of Fast Radio Bursts, which are transient intense radio pulses with duration of milliseconds. Since they have been localized at redshifts z > 0.3, it is thought that Fast Radio Bursts could replace Supernovae of type Ia to probe the expansion of the universe to higher redshifts.

Recent observations provided by Gaia space mission, indicate that a fraction of the ultra-massive white dwarfs experience a strong delay in their cooling, which cannot be attributed only to the occurrence of crystallization, thus requiring an unknown energy source able to prolong their life for long periods of time.

In this study, Maria Camisassa and colleagues showed that these strong delays in the cooling times reported for a selected population of the ultra-massive white dwarfs are caused by the energy released by the sedimentation process of ²²Ne occurring in the interior of CO-core ultra-massive white dwarfs with high ²²Ne content, providing strong sustain to the formation of CO-core ultra-massive white dwarfs through merger events.

In order to demonstrate the possible existence of these eternal youth ultra-massive CO-core white dwarfs, they have analyzed the effect of ²²Ne sedimentation on the local white dwarf population revealed by Gaia observations by means of an up-to date population synthesis code. The code, based on Monte Carlo techniques, incorporates the different theoretical white dwarf cooling sequences under study, as well as an accurate modeling of the local white dwarf population and observational biases. They have performed a population synthesis analysis of the Galactic thin disk white dwarf population within 100 pc from the Sun under different input models. In order to minimize the selection effects, they chose the 100 pc sample, given that it represents the maximum size that the sample can be considered volume-limited and thus practically complete sample.

First, they considered that all the ultra-massive white dwarfs in the simulated sample have ONe core composition. This first synthetic population is shown in the Gaia HR diagram in the upper left panel of Figure 1. The histogram of this synthetic population is shown in the upper right panel (black steps), together with the Gaia 100 pc white dwarf sample (red steps). The Q branch can easily be regarded as the main peak in the histogram of the Gaia 100 pc white dwarf sample, between 13.0 and 13.4. A first glance at these three histograms reveals that ultra-massive ONe white dwarfs fail to account for the pile-up in the Q branch, even though the ONe white dwarf sequences used include all the energy sources resulting from the crystallization process. A quantitative statistical reduced x²-test analysis of the synthetic population distribution in the Q branch reveals a value of 11.18 when compared to the observed distribution.

Figure 1: Left panels: Synthetic white dwarf populations (gray points) in the Gaia Hertzsprung-Russell diagram considering different prescriptions. The ultra-massive Q branch is delimited by solid red lines. Dashed red lines mark the region where they have counted white dwarfs to prepare the histograms. Right panels: synthetic (black line) and observed (red line) histograms for the 100pc white dwarf population. The observed Q branch can be regarded as the red peak between 13.0 and 13.4 in the 100 pc white dwarf sample observed by Gaia. Note that, in order to theoretically reproduce the peak in the observed population, it is necessary to assume a high merger fraction leading to ultra massive white dwarfs with CO core composition and a high ²²Ne abundance. ©Maria Camisassa et al.

The middle left panel of Figure 1 illustrates the HR diagram of a typical synthetic white dwarf population realization, considering that 20% of the ultra-massive white dwarfs come from merger events. That is, 20% of the ultra-massive white dwarfs harbour a CO-core. In this model they also have assumed white dwarfs with high ²²Ne abundance, X²²Ne=0.06. The histogram of this synthetic population, shown in black steps in the middle right panel, reveals that, although a mixed white dwarf population with both CO-core and ONe-core white dwarfs is in better agreement with the observations, the pile-up is still not fully reproduced. The reduced x² value of this synthetic population is 2.60.

Finally, they have also performed a population synthesis realization in which 50% of the ultra-massive white dwarfs have a merger origin and their core-chemical composition is CO. As in the previous model, the ²²Ne content of the white dwarf sequences with merger origin was set to X²²Ne=0.06. The results of this synthetic population are shown in the lower panels of Figure 1. They found that this simulation is in perfect agreement with the observed white dwarf sample, being its reduced x²-test value 1.36.

The better agreement with the observations revealed by Gaia of the synthetic populations that include CO-core ultra-massive white dwarf sequences is in line with the longer cooling times that characterize these stars due to ²²Ne sedimentation process. They have also simulated a synthetic population that considers a fraction of merger of 50% and a ²²Ne abundance of 0.02, finding a better agreement when compared to simulations computed with only ONe-core white dwarfs, but not as good as the agreement they found for a population with high ²²Ne content (The reduced x² value of this synthetic population is 4.86). They have also generated synthetic populations considering different ²²Ne abundances in the white dwarf models and found that the best fit models are obtained for a high ²²Ne abundance (X²²Ne=0.06), as the one shown in the middle and lower panels of Figure 1. Such a high ²²Ne abundance is not consistent with the isolated standard evolutionary history channel, because it would imply that these white dwarfs come from high-metallicity progenitors. However, merger events provide a possible scenario to create such a high ²²Ne abundance. If H were burnt in C-rich layers during the merger event, it would create a high amount of ¹⁴N that could later capture He ions, creating a high ²²Ne abundance before the ultra-massive white dwarf is born.

The analysis of the ultra-massive white dwarf population revealed by Gaia shows that ONe-core white dwarfs alone are not able to account for the pile-up in the ultra-massive Q branch. Indeed, energy sources as latent heat and phase separation process due to crystallization, and ²²Ne sedimentation can not prevent the fast cooling of these stars. Their study finds that CO-core ultra-massive white dwarfs with high ²²Ne content are long-standing living objects, that should stay on the Q branch for long periods of time. Indeed, their CO core composition, combined with a high ²²Ne abundance, provides a favorable scenario for ²²Ne sedimentation to effectively operate, producing strong delays in the cooling times due to the combination of three effects: crystallization, ²²Ne sedimentation and higher thermal content, and leading to an eternal youth source.

Their study indicates that the observed evidence of these delays from Gaia provides valuable sustain on their CO chemical composition, and their past history involving merger events, whilst ONe core white dwarfs are unable to predict these delays. Moreover, the high percentage of observed carbon-rich atmosphere stars (DQ white dwarfs) on the Q branch 20 supports the hypothesis that a large fraction of the white dwarfs on the Q branch would certainly have been formed through merger events.

References: María E. Camisassa, Leandro G. Althaus, Santiago Torres, Alejandro H. Córsico, Sihao Cheng, Alberto Rebassa-Mansergas, “Forever young white dwarfs: when stellar ageing stops”, ArXiv, pp. 1-27, 2020. https://arxiv.org/abs/2008.03028

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Indian Fossils Support New Hypothesis For Origin Of Hoofed Mammals (Paleontology)

New research published today in the Journal of Vertebrate Paleontology describes a fossil family that illuminates the origin of perissodactyls—the group of mammals that includes horses, rhinos and tapirs. It provides insights on the controversial question of where these hoofed animals evolved, concluding that they arose in or near present day India.

Life reconstruction of Cambaytherium. Credit: Elaine Kasmer

With more than 350 new fossils, the 15-year study pieces together a nearly complete picture of the skeletal anatomy of the Cambaytherium—an extinct cousin of perissodactyls that lived on the Indian subcontinent almost 55 million years ago.

The findings include a sheep-sized animal with moderate running ability and features that were intermediate between specialized perissodactyls and their more generalized mammal forerunners. Comparing its bones with many other living and extinct mammals revealed that Cambaytherium represents an evolutionary stage more primitive than any known perissodactyl, supporting origin for the group in or near India—before they dispersed to other continents when the land connection with Asia formed.

This new landmark article was selected for publication as a part of the prestigious Society of Vertebrate Paleontology Memoir Series, a special yearly publication that provides a more in-depth analysis of the most significant vertebrate fossils.

Cambaytherium, first described in 2005, is the most primitive member of an extinct group that branched off just before the evolution of perissodactyls, providing scientists with unique clues to the ancient origins and evolution of the group.

“The modern orders artiodactyla (even-toed ungulates), perissodactyla, and primates appeared abruptly at the beginning of the Eocene around 56 million years ago across the Northern Hemisphere, but their geographic source has remained a mystery,” explained Ken Rose, emeritus professor at Johns Hopkins University and lead author of the study.

Prof. Rose became intrigued by a new hypothesis suggesting that perissodactyls may have evolved in isolation in India. Then India was an island continent drifting northwards, but it later collided with the continent of Asia to form a continuous landmass.

“In 1990, Krause and Maas proposed that these orders might have evolved in India, during its northward drift from Madagascar, dispersing across the northern continents when India collided with Asia.”

Armed with this new hypothesis, Rose and colleagues obtained funding from the National Geographic Society to explore India for rare fossil-bearing rocks of the correct age that might provide critical evidence for the origin of perissodactyls and other groups of mammals.

Hot and dusty work in vast open-pit lignite mines in India provide evidence for origins of Perissodactyls. Credit: Ken Rose

The first trip to Rajasthan in 2001 had little success, “Although we found only a few fish bones on that trip, the following year our Indian colleague, Rajendra Rana, continued exploring lignite mines to the south and came upon Vastan Mine in Gujarat.”

This new mine proved much more promising. Rose added: “In 2004 our team was able to return to the mine, where our Belgian collaborator Thierry Smith found the first mammal fossils, including Cambaytherium.”

Encouraged, the team returned to the mines and collected fossilized bones of Cambaytherium and many other vertebrates, despite challenging conditions.

“The heat, the constant noise and coal dust in the lignite mines were tough—basically trying to work hundreds of feet down near the bottom of open-pit lignite mines that are being actively mined 24/7,” he said.

Through the cumulation of many years of challenging fieldwork, the team can finally shed light on a mammal mystery. Despite the abundance of perissodactyls in the Northern Hemisphere, Cambaytherium suggests that the group likely evolved in isolation in or near India during the Paleocene (66-56 million years ago), before dispersing to other continents when the land connection with Asia formed.

References: Kenneth D. Rose et al, Anatomy, Relationships, and Paleobiology of Cambaytherium (Mammalia, Perissodactylamorpha, Anthracobunia) from the lower Eocene of western India, Journal of Vertebrate Paleontology (2020). DOI: 10.1080/02724634.2020.1761370

Provided by Taylor & Francis

How Cell Processes Round Up And Dump Damaged Proteins? (Biology)

UMass Amherst research chemists discover cells’ unexpected clean-up techniques.

In a new paper with results that senior author Eric Strieter at the University of Massachusetts Amherst calls “incredibly surprising,” he and his chemistry lab group report that they have discovered how an enzyme known as UCH37 regulates a cell’s waste management system.

©Kirandeep Deol et al.

Strieter says, “It took us eight years to figure it out, and I’m very proud of this work. We had to develop a lot of new methods and tools to understand what this enzyme is doing.”

As he explains, a very large protease called a proteasome is responsible for degrading the vast majority of proteins in a cell; it may be made up of as many as 40 proteins. It has been known for more than 20 years that UCH37 is one of the regulatory enzymes that associates with the proteasome, he adds, “but no one understood what it was doing.”

It turns out that the crux of the whole process, he adds, is how complicated modifications in a small protein called ubiquitin can be. “In addition to modifying other proteins, ubiquitin modifies itself resulting in a wide array of chains. Some of these chains can have extensive branching. We found that UCH37 removes branchpoints from chains, allowing degradation to proceed.”

Writing this week in Molecular Cell, he and first author and Ph.D. candidate Kirandeep Deol, who led and conducted the experiments, with co-authors Sean Crowe, Jiale Du, Heather Bisbee and Robert Guenette, discuss how they answered the question. The work was supported by the NIH’s National Institute of General Medical Sciences.

This advance could eventually lead to a new cancer treatment, Strieter says, because cancer cells need the proteasome to grow and proliferate. “Many cancer cells are essentially addicted to proteasome function,” he points out. “Its cells produce proteins at such a fast rate that mistakes are made, and if these are not cleared out, cells can’t function. Since UCH37 aids in clearing out proteins, it could be a useful therapeutic target to add to the proteasome inhibitors that have already been successful in the clinic.”

To begin their years-long process, Strieter says, “we had to come up with a way to generate a wide variety of ubiquitin chains that would represent the potential diversity in a cell. Using that new library of ubiquitin chains allowed us to interrogate the activity of UCH37 in a controlled setting. That series of experiments gave us the first clue that this enzyme was doing something unique.”

Another new method they developed uses mass spectrometry to characterize the architecture of ubiquitin chains in complex mixtures. “This allowed us to see that the activity we discovered with our library of substrates was also present in a more heterogenous mixture,” Strieter says. Finally, the chemists used the CRISPR gene editing tool to remove UCH37 from cells to measure the impact of UCH37 on proteasome-mediated degradation in vitro and in cells.

This technique led to one more surprise. “Instead of acting as expected and opposing the degradation process, it turned out that UCH37 was removing branchpoints from ubiquitin chains to help degrade proteins,” Strieter says. “You would think that by removing the signal for degradation that degradation would be impaired,” he adds, “but it didn’t work that way.”

In future experiments, Strieter and colleagues hope to further explore the degradation process and learn in more detail how UCH37 manages to regulate cellular function.

References: Kirandeep K. Deol, Sean O. Crowe, Jiale Du, Heather A. Bisbee, Robert G. Guenette, Eric R. Strieter, “Proteasome-Bound UCH37/UCHL5 Debranches Ubiquitin Chains to Promote Degradation”, Molecular Cell, 2020. DOI: https://doi.org/10.1016/j.molcel.2020.10.017 https://www.cell.com/molecular-cell/fulltext/S1097-2765(20)30724-3

Provided by University of Massachusetts Amherst

Migration And Molt Affect How Birds Change Their Colors (Ornithology / Biology)

In late summer and autumn, millions of birds fly above our heads, often at night, winging their way toward their wintering grounds.

Before the journey, many birds molt their bright feathers, replacing them with a more subdued palette. Watching this molt led scientists to wonder how feather color changes relate to the migrations many birds undertake twice each year. Molt matters — not only because replacing worn feathers is necessary for flight, but because molt is the catalyst for plumage changes that affect whether birds find mates and reproduce.

Indigo buntings and other migratory birds molt before making the long trek south every fall. ©Eric Liffmann.

“We’re really blessed here, as nature lovers and birdwatchers, that we have lots of species of warblers here, which come in blues, greens, red and yellows,” said Jared Wolfe, assistant professor in Michigan Technological University’s College of Forest Resources and Environmental Science and one of the founders of the Biodiversity Initiative. “These brightly colored birds migrate and nest here and then leave for the winter. Everyone is so focused on the coloration, but the mechanism of the change of coloration is the process of molt, of replacing feathers.”

While migration distances vary, many species fly thousands of miles each year, chasing summer as the planet tilts toward and away from winter. These lengthy journeys tend to wear out feathers. In research published in the journal Ecology and Evolution, Wolfe and co-authors analyzed the variation in distances traveled against the extent of molt in a particular species. “Birds that go farther distances replace more feathers,” said Wolfe.

“Sun is the primary reason feathers degrade, and harsh environments,” he said. “In northerly latitudes in the summer, it’s sunny all day. As the birds move south, tracking the sun, they are maximally exposing themselves to sun all year.”

A golden-crowned Kinglet in Bluebonnet Swamp, Louisiana. Image Credit: John Hartgerink

Feathers must be replaced because of wear and tear; what’s the significance of brightly colored plumage? Wouldn’t black be more protective against sunburn, or white better at deflecting heat?

For birds, like many animals, an attention-getting physical appearance plays a crucial role in attracting a mate. As stylish haircuts and makeup are to humans, beautiful feathers are to birds. But a spectacular plumage is also pragmatic; it broadcasts age and health, which determine who gets to mate and who doesn’t.

“Bright plumages are signals of habitat quality in the tropics,” Wolfe said. “Acquiring mates is based on a signal of habitat quality from the wintering grounds. Undergoing a second molt on the wintering grounds before migrating north allows the birds to become colorful. Color is a signal to potential mates in places like the Midwest what jungle wintering habitats are like.”

Experiences during the winter months affect how colorful birds become, which affects how successful they are at finding mates and breeding in North America. Scientists call these carryover effects. “It’s so elegant, but we’re just now starting to understand it,” Wolfe said.

Growing vibrant feathers is a physically taxing activity, and the easier a bird has it during the winter, the more brightly colored their plumage during the summer. This makes quality and availability of food, places to shelter and safety from predators important components of a wintering habitat.

Like humans seeking out coveted locations to live, birds flock to the best habitats. In both cases, resources are finite. What might have been an ideal wintering ground one year might be depleted of food sources or other important attributes the next.

“The best habitats offer resource stability over time, versus poorer quality habitats which are variable month-to-month, year-to-year,” he said.

But what about birds that don’t migrate, preferring to spend their lives within a single home range? For them, it turns out molt is comparable to changing one’s clothes on a regular basis rather than changing appearances to impress someone. Molting and breeding are constricted by multiple factors: Seasons, food abundance and size of home range play major roles in plumage and feather replacement.

From left, Kristin Brzeski, Luke Powell, Jared Wolfe and Ammoet Motove Etinge band birds in Equatorial Guinea. Image Credit: Tristan Spinski

“Birds here in the temperate zones are restricted in when they can breed and undergo their annual molt by winter,” Wolfe said. “In the tropics, there are wet and dry seasons, but there is less constraint from a real absence of food sources. Molt is an expensive process calorically; birds need lots and lots of food while they’re molting.”

Wolfe and his collaborators found that adjusting the time it takes Amazonian birds to complete their annual molt affects how they go about making a living. For example, ant-following birds in Brazil eat insects that are trying to outrun army ants. One tiny species, the white-plumed antbird, opportunistically darts ahead of the ants — not your garden variety ant but a species that can overpower and eat lizards, birds and small mammals in addition to insects — to take advantage of a moveable feast.

“Its molt is crazy slow; it takes an entire year,” Wolfe said, noting that the bird essentially lives in a constant state of molt, dropping one feather at a time.

Obligate antbirds have huge home ranges that overlap with multiple army ant colonies, which means they spend a large part of their day flying around the jungle in search of army ants. The bird’s lengthy daily commute is a problem when they molt wing feathers, which creates gaps in their wings and compromises their ability to fly. How do they get around this problem? A very slow molt.

“A single feather at a time to minimize gaps thereby improving their ability to fly and maintain large home ranges,” Wolfe said. “This unique adaptation has made the white-plumed antbird the slowest-molting songbird on Earth.”

A white-plumed antbird from Amazonas, Brazil. Image Credit: Philip Stouffer

Despite the predilection of migrant birds to return to the same breeding territory year after year, Wolfe and collaborators note that not all birds return to the same molting grounds. This finding confounds the assumption of home field advantage, where birds benefit from completing their annual molt in a familiar location. But it appears there isn’t much of a relationship between molting activity and what Wolfe calls “site fidelity.”

“Until our research, it had remained a mystery whether or not migratory songbirds return to the same site to molt,” Wolfe said. “This is an important question because there is growing evidence that mortalities accrued after the breeding season – during molt, migration and overwintering periods – is responsible for the continued loss of migratory songbirds. In fact, bird abundance has decreased by 29% since 1970. Understanding where and why birds molt is an important step towards protecting vulnerable populations of songbirds.”

Wolfe and colleagues used 31 years of bird banding data from northern California and southern Oregon to measure the site fidelity of 16 species of songbird during molt. While the researchers did find that breeding activity strongly correlated with site fidelity, molt did not appear to influence a bird’s decision to return to a particular place or not. It appears that birds, like humans, tend to splurge on fine feathers — and then go home to show them off.

References: Terrill, R., Seeholzer, G., & Wolfe, J. (2020). Evolution of breeding plumages in birds: A multiple-step pathway to seasonal dichromatism in New World warblers (Aves: Parulidae). Ecology and Evolution. http://doi.org/10.1002/ece3.6606
Retrieved from: https://digitalcommons.mtu.edu/michigantech-p/2760

Provided by Michigan Technological University

Mystery Of Glacial Lake Floods Solved (Earth Science)

A long-standing mystery in the study of glaciers was recently — and serendipitously — solved by a team led by University of Hawai’i at Mānoa astrobiologist and earth scientist Eric Gaidos. Their findings were published this week in the journal Geophysical Research Letters.

The hot water drill used to drill through the glacier to the subglacial lakes. The drill stem is hundreds of meters below in the ice, suspended on a rubber hose through which hot water is pumped down. ©Eric Gaidos.

The mystery involves floods or “jokulhlaups” that emerge suddenly and unpredictably from glaciers or ice caps like those in Iceland where volcanic heat melts the ice and water accumulates in lakes underneath the glaciers. Scientists have long studied the development of these floods, which are some of the largest on Earth.

“These floods may affect the motion of some glaciers and are a significant hazard in Iceland,” said Gaidos, professor at the UH Mānoa School of Ocean and Earth Science and Technology (SOEST). “But the mechanism and timing of the initiation of these floods has not been understood.”

Then, in June 2015, an unexpected series of events revealed how these floods start.

That summer, Gaidos and colleagues drilled a hole to one of the Icelandic lakes to study its microbial life. While collecting samples through the borehole, the team noticed a downwards current, like a bathtub drain, in the hole.

“The flow was so strong we nearly lost our sensors and sampling equipment into the hole,” said Gaidos. “We surmised that we had accidentally connected a water mass inside the glacier to the lake beneath. That water mass was rapidly draining into the lake.”

In June 2015, a team led by Gaidos used hot water to melt a hole through 250 meters of ice to sample a lake beneath a glacier in Iceland. ©Eric Gaidos.

A few days later, after the team had left the glacier, the lake drained in a flood. Fortunately, the flood was small and Icelanders have an elaborate early-warning system on their rivers so no people were hurt, nor infrastructure damaged in this event, Gaidos assured.

The researchers used a computer model of the draining of the flow through the hole , and its effect on the lake, to show that this could have triggered the flood.

“We discovered that the glacier can contain smaller bodies of water above the lakes fed by summer melting,” said Gaidos. “If this water body is hydraulically connected to the lake then the pressure in the lake rises and that allows water to start draining out underneath the glacier.”

Illustration of the water movement that may have triggered the flood of June 2015 (arrows indicate flow direction): the subglacial lake, warmed to 4?C by geothermal input, the perched reservoir fed by summer melt through the firn layer, a water-filled system of crevasses and conduits (moulins), our borehole, and the outlet under the ice dam. ©Gaidos, et al. (2020).

While the team made an artificial connection to the lake in 2015, natural connections can form when water from rain or melting snow accumulates in crevasses and the pressure eventually forces a crack through the glacier to the lake. This discovery provides a new understanding of how these floods can start and how this depends on weather and the season.

Collaborators in Iceland are continuing to research this phenomenon using radio echo-sounding to search for water bodies within the ice, as well as study the larger lake below it.

This work was partly funded by the Sloan Foundation with significant assistance from the Icelandic government agencies, including the Meteorological Office.

References: Gaidos, E., Jóhannesson, T., Einarsson, B., Thorsteinsson, T., Amend, J. P., & Skidmore, M. (2020). Après Nous, le Déluge: A Human‐Triggered Jökulhlaup from a Subglacial Lake. Geophysical Research Letters, 47, e2020GL089876. Accepted Author Manuscript. https://doi.org/10.1029/2020GL089876 link: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL089876

Provided by University of Hawaii at Manoa