By Natalia Mesa If a longtime friend suddenly becomes a foe, like Brutus to Caesar or Iago to Othello, the brain must update the person’s feelings about the betrayer without altering memories of who that companion is. The hippocampus may sometimes store both pieces of information, but when it comes to updating feelings, it keeps identity and emotional valence separate, according to a mouse study published today in Science. “We found the neural mechanisms that underlie emotion toward others,” says study investigator Teruhiro Okuyama, professor at the Institute of Quantitative Biosciences at the University of Tokyo: Memory-storing neurons in the hippocampus remain relatively stable, but the strength of their connections to the basolateral amygdala neurons shift, the study shows. Okuyama and his colleagues used chemogenetics to induce aggression in previously docile mice and optogenetics to trace how hippocampal circuits change in the animal’s cagemate. They found that they could both “write and erase social memories” by targeting specific neuron populations. “It’s truly unbelievable how much they did in this paper,” says Robert Malenka, professor of psychiatry and behavioral sciences at Stanford University, who was not involved in the work. “They did a beautiful job of taking three brain areas and defining the connectivity and the cell-type-specific connections that are responsible for the phenomenon they’re studying.” Neurons in the hippocampus store social memories and segregate positive and negative ones, previous work shows. But most past work has studied how negative run-ins with unfamiliar animals affect behavior. © 2026 Simons Foundation

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress; Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress; Chapter 8: Hormones and Sex
Link ID: 30318 - Posted: 07.11.2026

By Libby Riddle A bear might seem like the scariest thing you could run into in a national park. But a new study suggests maybe you should be more worried about elk. Out of nearly 3,000 wildlife incidents in Canadian national parks, more than half involved an elk, researchers report July 2 in Frontiers in Conservation Science. But the risk of tangling with a given species also depended on what people were doing, say Holly Landles and conservation biologist Shashank Balakrishna of the University of York in England. Camping out? Be wary of elk grazing near your campsite. Quietly hiking or wildlife watching? Watch out for bears using the same trails. “By identifying situations where a potential conflict scenario is more likely, we can help visitors make informed decisions that improve safety whilst also reducing unnecessary disturbance to wildlife,” says Landles, who conducted this research as an undergraduate at York. Landles and Balakrishna analyzed 2,878 aggressive wildlife incidents from 2010 to 2023 involving five animals: black bears, grizzly bears, elk, coyotes and mule deer. Aggressive behaviors included chasing, attacking or bluffing a charge. The analysis identified which animal–human activity combinations were especially risky. Elk topped the list, involved in 62 percent of all the incidents. One of the riskiest combos was elk and camping — the animals turned up in 84 percent of campground incidents. This may be because Canada’s peak camping season aligns with when the animals mate and give birth — times of heightened aggression for the species. “Elk are herbivorous herd animals that don’t immediately inspire fear like a carnivore does,” Balakrishna says. Visitors may underestimate how aggressive they can be. © Society for Science & the Public 2000–2026.

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress
Link ID: 30308 - Posted: 07.04.2026

By Hannah Thomasy Prairie voles have a reputation as one of the most social rodents, but when Aubrey Kelly tried to use them to study the neurobiology of group dynamics, she discovered limits to their sociability. “Prairie voles are indeed super social with their pair-bond partner and with their offspring,” says Kelly, associate professor of psychology at Emory University. “But if an adult prairie vole encounters a stranger, they’re going to fight—oftentimes to the death.” She shifted her focus to paternal care in the voles but stayed on the lookout for a truly social rodent that lived in rich, complex communities. As a graduate student, she had studied the neural circuitry that contributes to such societies in zebra finches, and she hoped to make similar inroads in mammalian brains. “I got really into the idea of animal societies and how individuals can just get along in big groups, which is something that we do ourselves,” Kelly says. About four years later, a colleague introduced her to spiny mice. Despite their name, these animals are more closely related to gerbils than to laboratory mice. They live in large, flexible, mixed-sex groups and rarely brawl, the colleague told her. Kelly was intrigued—perhaps these groups were the miniature mammal societies she had been searching for. Her subsequent work has demonstrated that, indeed, these critters not only tolerate groups but actually prefer them: When given a choice between associating with two peers or eight peers, they spend the majority of their time with the larger group. Now Kelly is digging into the neural mechanisms underlying this communal lifestyle. Kelly spoke with The Transmitter about spiny mouse “friendships,” custom CRISPR tools and the neurobiology of coexistence. © 2026 Simons Foundation

Related chapters from BN: Chapter 5: Hormones and the Brain; Chapter 15: Emotions, Aggression, and Stress
Related chapters from MM:Chapter 8: Hormones and Sex; Chapter 11: Emotions, Aggression, and Stress
Link ID: 30266 - Posted: 06.03.2026

By Elizabeth Preston On the island of Golem Grad in North Macedonia, visitors may see a chain of tortoises mounting each other like a slow-moving, libidinous locomotive. It used to strike Dragan Arsovski, an ecologist at the Macedonian Ecological Society, as funny. Now that he knows what’s really going on, he isn’t laughing. This uninhabited island in a country that once was part of Yugoslavia is crawling with around 1,000 Hermann’s tortoises — especially males. They pursue mates aggressively, making life unhealthy and short for the island’s scarce females. Some of those females even die by walking off the island’s cliffs. In a paper published last month in the journal Ecology Letters, researchers have found that the relentless males are driving their population to extinction. The island, in Lake Prespa, has a forested plateau encircled by sheer cliffs. When Dr. Arsovski started studying the salad-plate-size tortoises in 2008, “it was quite a dense and seemingly prosperous population,” he said. But for some reason, there were far more adult males than females — 19 males for every female on the plateau, at the latest count. He and his colleagues documented how the males seemed to manage their carnal instincts by mounting each other. Then, after many years of study, Dr. Arsovski realized that the females were undersized and dying young. He also realized those once-comical copulatory trains were made up of many males pursuing just one female. When the female tired, the train would become a frenzied heap of reptiles. “She’s literally buried by males,” Dr. Arsovski said. He and his co-authors wrote that as part of the tortoises’ courtship, they “bump, bite (sometimes to the point of blood loss), mount and finally vigorously poke fleeing females” with a sharp tail tip. Three-quarters of the island’s females had genital injuries. © 2026 The New York Times Company

Related chapters from BN: Chapter 6: Evolution of the Brain and Behavior; Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 30125 - Posted: 02.18.2026

By Carl Zimmer If you live in the United States, chances are you’re familiar with the game rock-paper-scissors. You put out your hand in one of three gestures: clenching it in a fist (rock), holding it out flat (paper) or holding up two fingers in a “V” (scissors). Rock beats scissors, scissors beat paper and paper beats rock. Americans by no means have a monopoly on the game. People play it around the world in many variations, and under many names. In Japan, where the game has existed for thousands of years, it’s known as janken. In Indonesia, it’s known as earwig-man-elephant: The elephant kills the man, the man kills the earwig and the earwig crawls up through the elephant’s trunk and eats its brain. The game is so common that it exists beyond our own species. Over millions of years, animals have evolved their own version of rock-paper-scissors. For them, winning the game means passing down their genes to future generations. A study published on Thursday in the journal Science reveals the hidden biology that makes the game possible — and shows how it may be an important source of nature’s diversity. The first clues that nature also played rock-paper-scissors emerged three decades ago in the dry hills outside Merced, Calif. Barry Sinervo, a biologist then at Indiana University, studied the common side-blotched lizard there. He would mark the lizards — named for the dark blue or black spot on their side, just behind the front leg — release them into the tall grass and catch the survivors to check up on them in later years. Dr. Sinervo, who later joined the faculty at the University of California, Santa Cruz, and who died in 2021, grew fascinated by the strange mating habits of the lizards. At the start of every breeding season, the males developed one of three colors on their throats: blue, orange or yellow. And depending on their color, the males behaved differently. © 2026 The New York Times Company

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress
Link ID: 30071 - Posted: 01.07.2026

Steven Morris Some people respond to the unwanted attentions of a gull eyeing up a bag of chips or a Cornish pasty by frantically flapping their hands at the hungry bird while others beat a rapid retreat into the nearest seaside shelter. But researchers have found that a no-nonsense yell – even a relatively quiet one – may be the best way to get rid of a pesky herring gull. Animal behaviourists from the University of Exeter tried to establish the most effective method of countering a feathery threat by placing a portion of chips in a place where gulls were bound to find them. Once a gull approached, they played three recordings. First, a male voice shouting: “No, stay away, that’s my food, that’s my pasty!” Then, the same voice speaking the same words was played, followed by the “neutral” birdsong of a robin. Study finds shouting is best way to get rid of pesky seagulls – video They tested 61 gulls across nine seaside towns in Cornwall and found nearly half of the birds exposed to the shouting voice flapped away within a minute. Only 15% of the gulls exposed to the speaking male voice flew off, though the rest walked away from the food, still apparently sensing danger. In contrast, 70% of gulls exposed to the robin song stayed put. The volume of the “shouting” and “speaking” voices was the same, meaning the gulls seemed to be responding to the acoustic properties of the message rather than the loudness. © 2025 Guardian News & Media Limited

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress
Link ID: 30008 - Posted: 11.12.2025

By Annie Liontas In 2016, Marchell Taylor lay in his windowless, six-by-eight cell in the Denver County Jail. Only 36 days after being released after serving time for drug and robbery convictions, he robbed a Papa John’s and assaulted an employee. Because of his record, Mr. Taylor faced 300 years of imprisonment. He asked himself: Why am I back here? Answering his question may require looking back to 1978, when he was 9 years old and his family’s car slammed into a wall. He woke up to blood on his face. The brain injury he sustained went untreated. Shortly after that, his behavior changed, and he became, in his words, “snappy and violent.” By age 10, he was regularly turning to marijuana and alcohol. At 13, he was breaking into houses. At 14, he robbed a 7-Eleven. In 1993 he was picked up for aggravated robbery and ended up in a maximum security facility. For the next two decades, Mr. Taylor was in and out of institutions like this. That is until the Brain Injury Alliance of Colorado diagnosed him with a brain injury in 2016 while he was awaiting trial. After administering a screening, psychologists at the Men’s Mental Health Transition Unit — a pioneering mental health program in the Denver County Jail — gave Mr. Taylor access to therapies for mental health, including cognitive behavioral therapy and eye movement desensitization and reprocessing therapy, which helps process traumatic memories and experiences. These treatments taught him about his brain, and he says it has made all the difference. It is tempting to dismiss brain injury at an early age as the cause of years of criminal behavior. It’s certainly true in Mr. Taylor’s case that there were other contributing factors, including ongoing substance abuse, a lack of money and weak social and psychological support. But after spending years researching brain injuries in an effort to understand my own recovery from several and as a friend of Mr. Taylor’s, I’m reckoning with the fact that experts are only now beginning to recognize the connection between brain injury and incarceration. While such trauma may not offer a tidy explanation for histories like his, growing insight into this connection offers an opportunity to change the grim legacy of incarceration and mental illness in this country by treating an underlying factor that can fuel recidivism. © 2024 The New York Times Company

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress; Chapter 19: Language and Lateralization
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress; Chapter 15: Language and Lateralization
Link ID: 29585 - Posted: 12.04.2024

By Claudia López Lloreda Success tends to breed success. For instance, when a mouse dominates its opponents over and over, it becomes increasingly aggressive—helping to ensure victory in future fights. This “winner effect” takes hold thanks to multiple changes in synaptic plasticity, according to new findings published today in Cell. The results begin to reveal the mechanisms behind various forms of aggression seen in animals, says Jacob Nordman, assistant professor of molecular and integrative physiology at Southern Illinois University, who was not involved in the work. “There’s some aggression that is defensive; there’s some aggression that is pathological; there’s some aggression that’s territorial,” he says. “There might be a set of behaviors and, in turn, a set of circuits and possibly plasticity within those circuits, that speak to that.” Innate aggression is controlled by the ventromedial hypothalamus (VMH)—also known as the “attack” center—which shapes an animal’s social behaviors and fear response. But aggression can be learned, too. When paired with a mouse that is naturally docile, a more dominant mouse will eventually attack the other—and if it prevails, it tends to pick even longer fights with rivals over the coming days, thanks to synapse strengthening and increased activity in the VMH, a 2020 study reported. Full-blown and more generalized aggression emerges after even longer winning streaks, and it involves additional mechanisms, the new study suggests: Changes to neuronal excitability and dendritic spine morphology help cement the animal’s hawkishness. “Aggression is malleable—you can shape it,” says Scott Russo, professor of neuroscience at the Icahn School of Medicine at Mount Sinai, who was not involved with the study. “It’s not something that’s defined only by genetics, but that actually these circuits that support aggressive social behavior can change as a consequence of experience.” © 2024 Simons Foundation

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress; Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress; Chapter 8: Hormones and Sex
Link ID: 29524 - Posted: 10.19.2024

By Dana G. Smith In July 2016, a heat wave hit Boston, with daytime temperatures averaging 92 degrees for five days in a row. Some local university students who were staying in town for the summer got lucky and were living in dorms with central air-conditioning. Other students, not so much — they were stuck in older dorms without A.C. Jose Guillermo Cedeño Laurent, a Harvard researcher at the time, decided to take advantage of this natural experiment to see how heat, and especially heat at night, affected the young adults’ cognitive performance. He had 44 students perform math and self-control tests five days before the temperature rose, every day during the heat wave, and two days after. “Many of us think that we are immune to heat,” said Dr. Cedeño, now an assistant professor of environmental and occupational health and justice at Rutgers University. “So something that I wanted to test was whether that was really true.” It turns out even young, healthy college students are affected by high temperatures. During the hottest days, the students in the un-air-conditioned dorms, where nighttime temperatures averaged 79 degrees, performed significantly worse on the tests they took every morning than the students with A.C., whose rooms stayed a pleasant 71 degrees. A heat wave is once again blanketing the Northeast, South and Midwest. High temperatures can have an alarming effect on our bodies, raising the risk for heart attacks, heatstroke and death, particularly among older adults and people with chronic diseases. But heat also takes a toll on our brains, impairing cognition and making us irritable, impulsive and aggressive. Numerous studies in lab settings have produced similar results to Dr. Cedeño’s research, with scores on cognitive tests falling as scientists raised the temperature in the room. One investigation found that just a four-degree increase — which participants described as still feeling comfortable — led to a 10 percent average drop in performance across tests of memory, reaction time and executive functioning. © 2024 The New York Times Company

Related chapters from BN: Chapter 13: Homeostasis: Active Regulation of the Internal Environment; Chapter 15: Emotions, Aggression, and Stress
Related chapters from MM:Chapter 9: Homeostasis: Active Regulation of the Internal Environment; Chapter 11: Emotions, Aggression, and Stress
Link ID: 29370 - Posted: 06.26.2024

By Carl Zimmer In the early 1900s, primatologists noticed a group of apes in central Africa with a distinctly slender build; they called them “pygmy chimpanzees.” But as the years passed, it became clear that those animals, now known as bonobos, were profoundly different from chimpanzees. Chimpanzee societies are dominated by males that kill other males, raid the territory of neighboring troops and defend their own ground with border patrols. Male chimpanzees also attack females to coerce them into mating, and sometimes even kill infants. Among bonobos, in contrast, females are dominant. Males do not go on patrols, form alliances or kill other bonobos. And bonobos usually resolve their disputes with sex — lots of it. Bonobos became famous for showing that nature didn’t always have to be red in tooth and claw. “Bonobos are an icon for peace and love, the world’s ‘hippie chimps,’” Sally Coxe, a conservationist, said in 2006. But these sweeping claims were not based on much data. Because bonobos live in remote, swampy rainforests, it has been much more difficult to observe them in the wild than chimpanzees. More recent research has shown that bonobos live a more aggressive life than their reputation would suggest. In a study based on thousands of hours of observations in the wild published on Friday, for example, researchers found that male bonobos commit acts of aggression nearly three times as often as male chimpanzees do. “There is no ‘hippie ape,’” said Maud Mouginot, a biological anthropologist at Boston University who led the analysis. As our closest living relatives, bonobos and chimpanzees can offer us clues about the roots of human behavior. We and the two species share a common ancestor that lived about 7 million years ago. About 5 million years later, bonobos split off from chimpanzees. © 2024 The New York Times Company

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress
Link ID: 29256 - Posted: 04.13.2024

Ian Sample Science editor Human tears carry a substance that dampens down aggression, according to researchers, who believe the drops may have evolved over time to protect wailing babies from harm. Sniffing emotional tears from women reduced male aggression by more than 40% in computerised tests, and prompted corresponding changes in the brain, though the scientists behind the study think all human tears would have a similar effect. “The reduction in aggression was impressive to us, it seems real,” said Noam Sobel, a professor of neurobiology at the Weizmann Institute of Science in Israel. “Whatever is in tears actually lowers aggression.” Charles Darwin puzzled over the point of weeping. Writing in The Expression of Emotions in Man and Animals in 1872, the great naturalist declared sobbing as “purposeless as the secretion of tears from a blow outside the eye”. But in the 150 years since, researchers have proposed all manner of roles, from signalling vulnerability and helplessness to clearing bacteria from the eyes. Previous work at Sobel’s lab found that sniffing women’s tears reduced male testosterone but it was unclear whether this affected behaviour. In animals, the picture is clearer: subordinate mole rats, for example, cover themselves in tears to protect themselves from aggressors. For the latest study, Dr Shani Agron and others in Sobel’s lab collected tears rolling down women’s faces as they watched sad movies. The researchers did not specifically advertise for female tear donors but nearly all who came forward were women, of whom six were selected because they produced tears in such quantities. The experiments involved 31 men who sniffed either saline or women’s tears before having swabs dabbed with the droplets stuck to their upper lip. The men then took part in a computerised game used in psychology to provoke aggressive behaviour by unfairly deducting players’ points. © 2023 Guardian News & Media Limited

Related chapters from BN: Chapter 16: Psychopathology: Biological Basis of Behavior Disorders; Chapter 5: Hormones and the Brain
Related chapters from MM:Chapter 12: Psychopathology: The Biology of Behavioral Disorders; Chapter 8: Hormones and Sex
Link ID: 29063 - Posted: 12.22.2023

Max Kozlov A group of brain cells in mice becomes active both when the animals fight and when they watch other mice fight, a study1 shows. The work hints that such ‘mirror neurons’, which fire when an animal either observes or takes part in a particular activity, could shape complex social behaviours, such as aggression. The mirror neurons described in the study are the first to be found in the hypothalamus, an evolutionarily ancient brain region — suggesting that mirror neurons’ original purpose might have been to enhance defence and, ultimately, reproductive success, the authors speculate. The study was published in Cell on 15 February. “We’ve now shown that mirror neurons functionally participate in the behaviours they’re mirroring,” says Nirao Shah, a neuroscientist at Stanford University in California who co-authored the study. “That changes what we think about mirror neurons.” First identified in monkeys in the 1990s, mirror neurons generally fire when an animal takes a certain action, but they also fire when it sees another animal perform the same action. Previous work has linked mirror neurons’ activity to simple behaviours, such as reaching for an object, but not to complex social behaviours, such as fighting. But exactly how mirror-neuron activity contributes to cognitive functions has been controversial, says Pier Francesco Ferrari, a neuroethologist at the Institute of Cognitive Science Marc Jeannerod in Lyon, France. Some researchers have argued that the fact that mirror neurons fire both when an animal observes a behaviour and when it performs that behaviour itself shows that these neurons are involved in a higher-order awareness of others’ actions — and perhaps even contribute to empathy. But others say that there is little evidence to support this theory. © 2023 Springer Nature Limited

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress; Chapter 11: Motor Control and Plasticity
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress; Chapter 5: The Sensorimotor System
Link ID: 28674 - Posted: 02.18.2023

ByEmily Underwood When two male mice meet in a confined space, the rules of engagement are clear: The lower ranking mouse must yield. But when these norms go out the window—say, when researchers rig such an encounter to favor the weakling—it sends the higher ranking male into a depressionlike spiral. That’s the conclusion of a new neuroimaging study that reveals how the mouse brain responds to an unexpected loss of social status, which has been shown to be a major risk factor for depression in humans, particularly men. The new study’s approach is “clever and powerful,” says Neir Eshel, a neuroscientist and psychiatrist at Stanford University who wasn’t involved in the work. But he cautions more work is needed to extend the results to our own species. Groups of mice live in hierarchies, both in the lab and the wild. In the lab, though, the highest ranking males form particularly despotic regimes. One or more dominant “alpha mice” will have privileged access to food and females. They can pee wherever they please, rather than in the designated corner reserved for commoners. Hailan Hu, a neuroscientist at the Zhejiang University School of Medicine, wanted to know what would happen in the brains of these mousy muckety-mucks when their pecking order was upended. She and colleagues set up a battle of wills, designed to avoid any actual fighting or bloodshed. Ten times a day, over 4 days, the researchers put a dominant mouse nose-to-nose with a subordinate in a clear, narrow tube. Then they blocked the lower ranked rodent’s exit, leaving it no choice but to advance on its superior. At first, the dominant mice resisted the upstarts and held their ground. But by the fourth day, they were retreating voluntarily from their opponents after only a few seconds. In doing so, the mouse kings also fell in social status and lost their high-ranking perks, including VIP access to a warm nest in the corner.

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress; Chapter 16: Psychopathology: Biological Basis of Behavior Disorders
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress; Chapter 12: Psychopathology: The Biology of Behavioral Disorders
Link ID: 28651 - Posted: 02.01.2023

By Tom Siegfried Survival of the fittest often means survival of the fastest. But fastest doesn’t necessarily mean the fastest moving. It might mean the fastest thinking. When faced with the approach of a powerful predator, for instance, a quick brain can be just as important as quick feet. After all, it is the brain that tells the feet what to do — when to move, in what direction, how fast and for how long. And various additional mental acrobatics are needed to evade an attacker and avoid being eaten. A would-be meal’s brain must decide whether to run or freeze, outrun or outwit, whether to keep going or find a place to hide. It also helps if the brain remembers where the best hiding spots are and recalls past encounters with similar predators. All in all, a complex network of brain circuitry must be engaged, and neural commands executed efficiently, to avert a predatory threat. And scientists have spent a lot of mental effort themselves trying to figure out how the brains of prey enact their successful escape strategies. Studies in animals as diverse as mice and crabs, fruit flies and cockroaches are discovering the complex neural activity — in both the primitive parts of the brain and in more cognitively advanced regions — that underlies the physical behavior guiding escape from danger and the search for safety. Lessons learned from such studies might not only illuminate the neurobiology of escape, but also provide insights into how evolution has shaped other brain-controlled behaviors. This research “highlights an aspect of neuroscience that is really gaining traction these days,” says Gina G. Turrigiano of Brandeis University, past president of the Society for Neuroscience. “And that is the idea of using ethological behaviors — behaviors that really matter for the biology of the animal that’s being studied — to unravel brain function.” © 2022 Annual Reviews

Related chapters from BN: Chapter 11: Motor Control and Plasticity; Chapter 18: Attention and Higher Cognition
Related chapters from MM:Chapter 5: The Sensorimotor System; Chapter 14: Attention and Higher Cognition
Link ID: 28609 - Posted: 12.24.2022

ByErik Stokstad Toxoplasma gondii is sometimes called the “mind control” parasite: It can infect the brains of animals and mess with their behavior in ways that may kill the host but help ensure the parasite’s spread. But now, researchers have found that infected wolves may actually benefit from those mind-altering tricks. A Toxoplasma infection, they found, makes wolves bolder and more likely to become pack leaders or disperse into other habitats, giving them more opportunity to reproduce. "We’ve really underestimated some of the consequences this parasite has,” says Eben Gering, a biologist at Nova Southeastern University who was not involved in the work. “The findings probably represent the tip of the iceberg concerning the parasite’s significance to the dynamics of wild ecosystems.” T. gondii, a single-celled parasite, only reproduces in domesticated cats and other felids. Infected cats excrete spore-packed oocysts in their feces, which can survive on plants or in soil or water. They can also persist in undercooked meat of livestock or game. When a host—humans included—consumes an oocyst, the spores are released and spread into the brain and muscles, forming new cysts. Worldwide, about one in four people is infected. Usually, the immune system keeps the parasite in check, but it can cause spontaneous abortion and other serious problems during pregnancy. It's long been known that rodents infected with Toxoplasma lose their fear of predators. Cysts in the brain somehow increase dopamine and testosterone, boosting boldness and risk-taking and increasing the chance the host will be eaten by cats. "These parasites are using some generic mind control or personality control that helps them fulfill their lifecycle," says Jaap de Roode, a biologist at Emory University who was not involved in the new study. "And that has all sorts of interesting consequences that we may not even have thought of before.” The consequences aren’t limited to rodents. In 2016, researchers in Gabon found that Toxoplasma-infected captive chimpanzees lost their aversion to leopard urine. And last year, another team described how Toxoplasma-infected hyena cubs in Kenya venture closer to lions, making them more likely to be killed.

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress
Link ID: 28583 - Posted: 12.06.2022

By Virginia Morell In the summer of 2013, dolphin researcher Nicole Danaher-Garcia spotted something rare and remarkable in the animal world. As she stood on top of the bridge of a sport fishing yacht near Bimini in the Bahamas, she spied 10 adult Atlantic spotted dolphins she had never seen before—speeding into the waters of another group of dolphins. Most mammals attack intruders, but war wasn’t on the menu that day. Instead, the newcomers—eventually 46 in all—joined up with the resident dolphins, some 120 in number. Today, the two groups of Atlantic spotted dolphins (Stenella frontalis) have partially integrated, diving and swimming together, forming fast friendships, and likely even mating. It’s a “striking” display of tranquility between animals scientists usually consider rivals, says Richard Wrangham, a primatologist at Harvard University who was not involved with the study. Most mammals fight to protect mates and other resources if they encounter strangers entering their territory, he notes. This research, he says, may ultimately lead to a better understanding of the evolution of peacefulness. Danaher-Garcia, a behavioral ecologist, and her colleagues at the Dolphin Communication Project observed the two groups of dolphins in Bimini for 5 years, carrying out nearly 300 surveys. At first, the scientists only saw one small group of mixed Bimini and newcomer dolphins. But the next year, the scientists spotted a larger group of males and females of all ages from both communities mixing without “any signs of aggression,” she says. The dolphins continued their friendly behaviors through 2018, leading the team to suspect the two groups were merging. (Because of COVID-19 concerns, the scientists put their studies on hold in 2020.) The scientists discovered the newcomers had migrated from Little Bahama Bank, an area some 160 kilometers to the north known for its shallow seas, coral reefs, and sand banks. They were part of the White Sand Ridge (WSR) spotted dolphin community that another scientific team has been studying since the mid-1980s. © 2022 American Association for the Advancement of Science.

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress; Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress; Chapter 8: Hormones and Sex
Link ID: 28419 - Posted: 08.03.2022

Meghan Hoyer and Tim Meko When Vanderbilt University psychiatrist Jonathan Metzl learned that the perpetrator of the Uvalde, Tex., school massacre was a young man barely out of adolescence, it was hard not to think about the peculiarities of the maturing male brain. Salvador Rolando Ramos had just turned 18, eerily close in age to Nikolas Cruz, who had been 19 when he shot up a school in Parkland, Fla. And to Adam Lanza, 20, when he did the same in Newtown, Conn. To Seung-Hui Cho, 23, at Virginia Tech. And to Eric Harris, 18, and Dylan Klebold, 17, in Columbine, Colo. Teen and young adult males have long stood out from other subgroups for their impulsive behavior. They are far more reckless and prone to violence than their counterparts in other age groups, and their leading causes of death includes fights, accidents, driving too fast, or, as Metzl put it, “other impulsive kinds of acts.” “There’s a lot of research about how their brains are not fully developed in terms of regulation,” he said. Perhaps most significantly, studies show, the prefrontal cortex, which is critical to understanding the consequences of one’s actions and controlling impulses, does not fully develop until about age 25. In that context, Metzl said, a shooting “certainly feels like another kind of performance of young masculinity.” In coming weeks and months, investigators will dissect Ramos’s life to try to figure out what led him to that horrific moment at 11:40 a.m. Tuesday, May 24 when he opened fire on a classroom full of 9- and-10-year-olds at Robb Elementary School. Although clear answers are unlikely, the patterns that have emerged about mass shooters in the growing databases, school reports, medical notes and interview transcripts show a disturbing confluence between angry young men, easy access to weapons and reinforcement of violence by social media. © 1996-2022 The Washington Post

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress; Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress; Chapter 8: Hormones and Sex
Link ID: 28352 - Posted: 06.04.2022

By Sabrina Imbler Sign up for Science Times Get stories that capture the wonders of nature, the cosmos and the human body. Get it sent to your inbox. One morning in the Panamanian rainforest, a small fruit bat sized up his competition. The odds did not appear to be in his favor. The winged mammal, a Seba’s short-tailed bat, weighed about half an ounce. But his six opponents, fringe-lipped bats, were twice as heavy and occupying the shrouded corner where the small bat wanted to roost. Even worse, the larger bats are known to feast on small animals, such as frogs, katydids and smaller bats — including Seba’s short-tailed bats. None of this fazed the Seba’s short-tailed bat, which proceeded to scream, shake his wings and hurl his body at the posse of bigger bats, slapping one in the face more than 50 times. “I’ve never seen anything like it,” said Ahana Aurora Fernandez, a behavioral biologist at the Natural History Museum, Berlin, who viewed a recording of the bats but was not involved in the research that produced it. “It’s one bat against six,” Dr. Fernandez said. “He shows no fear at all.” The tiny bat’s belligerence paid off as the big bats fled. The corner clear, the Seba’s short-tailed bat moved in, joined a minute later by his female companion, who had nonchalantly watched the fight from nearby. This fun-size brawl and two similar bat bullying incidents in other roosts were observed by Mariana Muñoz-Romo, a biologist at the Smithsonian Tropical Research Institute, and her colleagues, who had been monitoring the sexual preferences of the larger fringe-lipped bats. In a paper published in March in the journal Behaviour, they asked how often tiny bats antagonize bigger ones. When it comes with a risk of being eaten, why pick a fight? The researchers originally set out to study fringe-lipped bats, who were recently discovered to smear a sticky, fragrant substance on their arms, potentially to attract mates. The animals also have impressive appetites, and have been observed eating sizable frogs. © 2022 The New York Times Company

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress; Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress; Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 28287 - Posted: 04.16.2022

By Annie Roth and Hisako Ueno The reign of Japan’s monkey queen has just begun. Last year, Yakei, a 9-year-old female Japanese macaque, fought several other macaques, including her own mother, to become the alpha of her troop. That made Yakei the first known female troop leader in the history of Takasakiyama Natural Zoological Garden in Southern Japan, which was established in 1952 and is home to over 1,000 macaques. But during her first breeding season as queen, which began in November 2021 and concluded in March 2022, a messy love triangle threatened to weaken her grip on power. According to officials at the park, the macaque that Yakei showed interest in mating with, a 15-year-old male named Goro, rejected her advances despite their coupling during a previous breeding season. Meanwhile, an 18-year-old macaque named Luffy did his best to woo Yakei, much to her displeasure. Japanese macaques are polyamorous and scientists were worried that Yakei would not be able to maintain her status while pursuing and rejecting potential mates. Tensions run high during breeding season, and a challenge from a spurned male could easily rob Yakei, an average-sized female, of her rank. Yakei rose to power by defeating her troop’s alpha male, but he was elderly and less formidable than the average young male. Fortunately for Yakei, no other macaques attempted to usurp her throne this season and the queen remained the troop’s alpha at the end of March, according to reserve officials. Her continued rule has surprised scientists and given them an opportunity to observe how macaque society functions under a matriarchy. Despite having to maintain her supremacy, Yakei managed to have a successful breeding season. After Goro gave her the cold shoulder, she spent many weeks playing the field, expressing interest in no fewer than five males. Among these males was Chris, a male ranked 10th in the troop, and Shikao, who holds the rank just below Chris. But the only male the reserve is sure she mated with was Maruo. Maruo, Yakei’s mate. © 2022 The New York Times Company

Related chapters from BN: Chapter 15: Emotions, Aggression, and Stress; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 11: Emotions, Aggression, and Stress
Link ID: 28279 - Posted: 04.13.2022

By Sabrina Imbler The male Bornean rock frog cannot scream over the sound of a waterfall. Instead, he threatens other frogs with his feet. The frog intimidates his male competitors with a can-can-like gesture: kicking his leg up into the air, fully extending his splayed foot, and dragging it down toward the ground. This foot-flagging display may not sound threatening to a human, but its effect has to do with a frog’s visual perception. To a frog, the world contains two kinds of objects: things that are worms, and things that are not worms. If a frog sees a skinny object moving parallel to its long axis — like how a worm travels along the ground — it sees dinner. But if a frog sees a similar shape moving perpendicular its long axis — very unlike a worm — it sees a threat to flee from. Scientists call this latter movement the anti-worm stimulus, and it strikes fear into the hearts of frogs. Frogs likely evolved this visual system to hunt worms and stay safe from larger predators. Now, researchers suggest some male frogs have evolved to take advantage of their froggy brethren’s fears by kicking and lowering their legs in a gesture that looks a lot like an anti-worm signal, as a way to frighten their competition. In a paper published Wednesday in Proceedings of the Royal Society B, researchers reveal that they could amplify the foot-flagging behavior of Bornean rock frogs by giving the frogs a dose of testosterone. The hormone acts on the muscles in the frog’s leg to exaggerate the gesture, meaning the more testosterone coursing through the frog, the bigger the foot-flagging display. This flamboyant foot display, intensified by the sex hormone, suggests the frogs evolved a way to exploit their competitors’ unusual visual system to appear more dangerous to other frogs. © 2021 The New York Times Company

Related chapters from BN: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 28087 - Posted: 11.20.2021