Humans are remarkably good at guessing a person’s age just by hearing their voice. But this is the first time the phenomenon has been demonstrated in wild animals, said Duke biology professor and study co-author Steve Nowicki.

The findings were published on January 7 in the journal Behavioral Ecology.

During the early spring, a male swamp sparrow stakes out a breeding territory and threatens any male who dares to trespass on his turf. If a potential rival enters another male’s territory and starts to sing, the resident male says “Get out!” by singing back with a rapid weet-weet-weet and flying toward the intruder. Eventually, if all else fails, he attacks.

Previous research by this team showed that male swamp sparrows reach their peak as vocalists at age two, and start to decline after that, singing less frequently and less consistently as they get older.

To find out if other males take note of such changes, the team set up a speaker in the territories of 35 male swamp sparrows in a Pennsylvania marsh and played them 5-minute audio clips of stranger males recorded at age two and again at age 10.

The team measured the birds’ responses, noting how closely each male approached the speaker. They found that males approached seven feet closer when they heard a potential rival’s song recorded at age two than at age 10. This suggests that males are more aggressive towards younger-sounding rivals.

Males in their prime pose an obvious threat: if a resident male isn’t assertive, there’s a good chance that the other guy could steal his mates, said first author Matthew Zipple, a doctoral student at Duke. But apparently the song of a 10-year-old — a centenarian in bird years — doesn’t warrant getting as worked up over.

If decreases in song quality in later life reflect the inevitable consequences of physical decline, the researchers believe that such changes could indicate to other males that a once-formidable male is no longer a match.

Whether song changes after mid-life make males more or less attractive to females is still unknown. “One interesting question would be, is the equation a little different from the female’s point of view?” Nowicki said.

Males accumulate genetic mutations in their sperm as they age that could make them less desirable mates. On the flip side, Nowicki said, “The mere fact that he’s lived this long means he must be doing something right.”

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Materials provided by Duke University. Original written by Robin Ann Smith. Note: Content may be edited for style and length.

The new approach is based on a light-sensitive hydrogel that the researchers designed. Incorporating this material into medical devices could avoid many endoscopic procedures and would give doctors a faster and easier way to remove devices when they are no longer needed or are not functioning properly, the researchers say.

“We are developing a set of systems that can reside in the gastrointestinal tract, and as part of that, we’re looking to develop different ways in which we can trigger the disassembly of devices in the GI tract without the requirement for a major procedure,” says Giovanni Traverso, an assistant professor of mechanical engineering, a gastroenterologist at Brigham and Women’s Hospital, and the senior author of the study.

In a study in pigs, the researchers showed that devices made with this light-sensitive hydrogel can be triggered to break down after being exposed to blue or ultraviolet light from a small LED.

Ritu Raman, a postdoc at MIT’s Koch Institute for Integrative Cancer Research, is the lead author of the paper, which appears today in Science Advances. Other authors of the paper are former technical associates Tiffany Hua, Jianlin Zhou, Tina Esfandiary, and Vance Soares; technical associates Declan Gwynne, Joy Collins, and Siddartha Tamang; graduate student Simo Pajovic; Division of Comparative Medicine veterinarian Alison Hayward; and David H. Koch Institute Professor Robert Langer.

Controlled breakdown

Over the past several years, Traverso and Langer have developed many ingestible devices designed to remain in the GI tract for extended periods of time. They have also worked on a variety of strategies to control the breakdown of such devices, including methods based on changes in pH or temperature, or exposure to certain chemicals.

“Given our interests in developing systems that can reside for prolonged periods in the gastrointestinal tract, we continue to investigate a range of approaches to facilitate the removal of these systems in the setting of adverse reaction or when they are no longer needed,” Traverso says. “We’re really looking at different triggers and how they perform, and whether we can apply them to different settings.”

In this study, the researchers explored a light-based trigger, which they believed could offer some advantages over their earlier approaches. One potential advantage is that light can act at a distance and doesn’t need to come into direct contact with the material being broken down. Also, light normally does not penetrate the GI tract, so there is no chance of accidental triggering.

To create the new material, Raman designed a light-sensitive hydrogel based on a material developed in the lab of Kristi Anseth, a former Langer lab postdoc who is now a professor of chemical and biological engineering at the University of Colorado at Boulder. This polymer gel includes a chemical bond that is broken when exposed to a wavelength of light between 405 and 365 nanometers (blue to ultraviolet).

Raman decided that instead of making a material composed exclusively of that light-sensitive polymer, she would use it to link together stronger components such as polyacrylamide. This makes the overall material more durable but still allows it to break apart or weaken when exposed to the right wavelength of light. She also constructed the material as a “double network,” in which one polymer network surrounds another.

“You’re forming one polymer network and then forming another polymer network around it, so it’s really entangled. That makes it very tough and stretchy,” Raman says.

The material’s properties can be tuned by varying the composition of the gel. When the light-sensitive linker makes up a higher percentage of the material, it breaks down faster in response to light but is also mechanically weaker. The researchers can also control how long it takes to break down the material by using different wavelengths of light. Blue light works more slowly but poses less risk to cells that are sensitive to damage from ultraviolet light.

Deflated by light

The gel and its breakdown products are biocompatible, and the gel can be easily molded into a variety of shapes. In this study, the researchers used it to demonstrate two possible applications: a seal for a bariatric balloon and an esophageal stent. Standard bariatric balloons, which are sometimes used to help treat obesity, are inflated in a patient’s stomach and filled with saline. After about six months, the balloon is removed by endoscopic surgery.

In contrast, the bariatric balloon that the MIT team designed can be deflated by exposing the seal to a tiny LED light, which would in principle be swallowed and then pass out of the body. Their balloon is made of latex and filled with sodium polyacrylate, which absorbs water. In this study, the researchers tested the balloons in pigs and found that the balloons swelled up as soon as they were placed in the stomach. When a small, ingestible LED emitting blue light was placed in the stomach for about six hours, the balloons slowly deflated. With a higher-power light, the material broke down within 30 minutes.

The researchers also molded the light-sensitive gel into an esophageal stent. Such stents are sometimes used to help treat esophageal cancer or other disorders that cause a narrowing of the esophagus. A light-triggerable version could be broken down and passed through the digestive tract when no longer needed.

In addition to those two applications, this approach could be used to create other kinds of degradable devices, such as vehicles for delivering drugs to the gastrointestinal tract, according to the researchers.

“This study is a proof of concept that we can create this kind of material, and now we’re thinking about what are the best applications for it,” Traverso says.

The research was funded by the National Institutes of Health, the Bill & Melinda Gates Foundation, the Koch Institute Support (core) Grant from the National Cancer Institute, and an AAAS L’Oréal USA for Women in Science Fellowship.

The challenge is that lengths of chemical bonds are between 0.1 — 0.3 nm, about half a million times smaller than the width of a human hair, making direct imaging of bonding between a pair of atoms difficult. Advanced microscopy methods, such as atomic force microscopy (AFM) or scanning tunnelling microscopy (STM), can resolve atomic positions and measure bond lengths directly, but filming chemical bonds to break or to form, with spatiotemporal continuity, in real time, still remains one of the greatest challenges of science.

This challenge has been met by a research team from the UK and Germany led by Professor Ute Kaiser, head of the Electron Microscopy of Materials Science in the University of Ulm, and Professor Andrei Khlobystov in the School of Chemistry at the University of Nottingham they have published ‘Imaging an unsupported metal-metal bond in dirhenium molecules at the atomic scale’ in Science Advances, a journal of the American Association for the Advancement of Science covering all aspects of scientific endeavour.

Atoms in a nano test tube

This group of researchers are known for their pioneering use of transmission electron microscopy (TEM) to film ‘movies’ of chemical reactions at the single-molecule level, and dynamics of tiny clusters of metal atoms in nanocatalysts utilise carbon nanotubes — atomically thin hollow cylinders of carbon with diameters at the molecular scale (1-2 nm) as miniature test tubes for atoms.

Professor Andrei Khlobystov, said: “Nanotubes help us to catch atoms or molecules, and to position them exactly where we want. In this case we trapped a pair of rhenium (Re) atoms bonded together to form Re2. Because rhenium has a high atomic number it is easier to see in TEM than lighter elements, allowing us to identify each metal atom as a dark dot.”

Professor Ute Kaiser, added: “As we imaged these diatomic molecules by the state of the art chromatic and spherical aberration corrected SALVE TEM, we observed the atomic-scale dynamics of Re2 adsorbed on the graphitic lattice of the nanotube and discovered that the bond length changes in Re2 in a series of discrete steps.”

A dual use of electron beam

The group have rich track record of using electron beam as a tool for dual-purpose: precise imaging of atomic positions and activation of chemical reactions due to energy transferred from fast electrons of the electron beam to the atoms. The “two-in-one” trick with TEM allowed these researchers to record movies of molecules reacting in the past, and now they were able to film two atoms bonded together in Re2 ‘walking’ along the nanotube in a continuous video. Dr Kecheng Cao, Research Assistant at Ulm University who discovered this phenomenon and performed the imaging experiments, said: ‘It was surprisingly clear how the two atoms move in pairs, clearly indicating a bond between them. Importantly, as Re2 moves down the nanotube, the bond length changes, indicating that the bond becomes stronger or weaker depending on the environment around the atoms.’

Breaking the bond

After a period of time, atoms of Re2 exhibited vibrations distorting their circular shapes onto ellipses and stretching the bond. As the bond length reached a value exceeding the sum of atomic radii, the bond snapped and vibration ceased, indicating that the atoms became independent of one another. A little later the atoms joined together again, reforming a Re2 molecule.

Dr Stephen Skowron, Postdoctoral Research Assistant at University of Nottingham who carried out the calculations for Re2 bonding, said: ‘Bonds between metal atoms are very important in chemistry, particularly for understanding magnetic, electronic, or catalytic properties of materials. What makes it challenging is that transition metals, such as Re, can form bonds of different order, from single to quintuple bonds. In this TEM experiment we observed that the two rhenium atoms are bonded mainly through a quadruple bond, providing new fundamental insights into transition metal chemistry’.

Electron microscope as a new analytical tool for chemists

Andrei Khlobystov, said: ‘To our knowledge, this is the first time when bond evolution, breaking and formation was recorded on film at the atomic scale. Electron microscopy is already becoming an analytical tool for determining structures of molecules, particularly with the advance of the cryogenic TEM recognised by 2017 Nobel Prize in Chemistry. We are now pushing the frontiers of molecule imaging beyond simple structural analysis, and towards understanding dynamics of individual molecules in real time.’ The team believe that one day in future electron microscopy may become a general method for studying chemical reactions, similar to spectroscopic methods widely used in chemistry labs.

To put a fine point on it, what is an endangered species? The quick answer: An endangered species is at risk of extinction. Fine, except questions about risk always come in shades and degrees, more risk and less risk.

Extinction risk increases as a species is driven to extinction from portions of its natural range. Most mammal species have been driven to extinction from half or more of their historic range because of human activities.

The query “What is an endangered species?” is quickly transformed into a far tougher question: How much loss should a species endure before we agree that the species deserves special protections and concerted effort for its betterment? My colleagues and I put a very similar question to nearly 1,000 (representatively sampled) Americans after giving them the information in the previous paragraph. The results, “What is an endangered species?: judgments about acceptable risk,” are published today in Environmental Research Letters.

Three-quarters of those surveyed said a species deserves special protections if it had been driven to extinction from any more than 30% of its historic range. Not everyone was in perfect agreement. Some were more accepting of losses. The survey results indicate that people more accepting of loss were less knowledgeable about the environment and self-identify as advocates for the rights of gun and land owners. Still, three-quarters of people from the group of people who were more accepting of loss thought special protections were warranted if a species had been lost from more than 41% of their former range.

These attitudes of the American public are aligned with the language of the U.S. Endangered Species Act — the law for preventing species endangerment in the U.S. That law defines an endangered species as one that is “in danger of extinction throughout all or a significant portion of its range.”

But There Might Be A Problem

Government decision-makers have tended to agree with the scientists they consult in judging what counts as acceptable risk and loss. These scientists express the trigger point for endangerment in very different terms. They tend to say a species is endangered if its risk of total and complete extinction exceeds 5% over 100 years.

Before human activities began elevating extinction risk, a typical vertebrate species would have experienced an extinction risk of 1% over a 10,000-year period. The extinction risk that decision-makers and their consultant experts have tended to consider acceptable (5% over 100 years) corresponds to an extinction risk many times greater that the extinction risk we currently impose on biodiversity! Experts and decision-makers — using a law designed to mitigate the biodiversity crisis — tend to allow for stunningly high levels of risk. But the law and the general public seem accepting of only lower risk that would greatly mitigate the biodiversity crisis. What’s going on?

One possibility is that experts and decision-makers are more accepting of the risks and losses because they believe greater protection would be impossibly expensive. If so, the American public may be getting it right, not the experts and decision-makers. Why? Because the law allows for two separate judgements. The first judgement is, is the species endangered and therefore deserving of protection? The second judgment is, can the American people afford that protection? Keeping those judgements separate is vital because making a case that more funding and effort is required to solve the biodiversity crisis is not helped by experts and decision-makers when they grossly understate the problem — as they do when they judge endangerment to entail such extraordinarily high levels of risk and loss.

Facts and Values

Another possible explanation for the judgments of experts and decision-makers was uncovered in an earlier paper led by Jeremy Bruskotter of Ohio State University (also a collaborator on this paper). They showed that experts tended to offer judgments about grizzly bear endangerment — based not so much their own independent expert judgement — but on basis of what they think (rightly or wrongly) their peers’ judgement would be.

Regardless of the explanation, a good answer to the question, “What an endangered species?” is an inescapable synthesis of facts and values. Experts on endangered species have a better handle on the facts than the general public. However, there is cause for concern when decision-makers do not reflect the broadly held values of their constituents. An important possible explanation for this discrepancy in values is the influence of special interests on decision-makers and experts charged with caring for biodiversity.

Getting the answer right is of grave importance. If we do not know well enough what an endangered species is, then we cannot know well enough what it means to conserve nature, because conserving nature is largely — either directly or indirectly — about giving special care to endangered species until they no longer deserve that label.

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Materials provided by Michigan Technological University. Note: Content may be edited for style and length.