Chapter 6. Evolution of the Brain and Behavior

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By Cara Giovanetti The human brain's billions of neurons represent a menagerie of cells that are among both the most highly specialized and variable ones in our bodies. Neurons convert electrical signals to chemical signals, and in humans, their lengths can be so tiny as to span just the tip of a sharpened pencil or, in some cases, even stretch the width of a doorway. Their flexible control of movement and decision-making explains why they are so key to survival in the animal kingdom. Most animals depend on their allotment of neurons for survival. It might stand to reason, then, that the common ancestor of all of these animals also moved about the Earth millions of years ago under the guidance of electrochemical signals transmitted and received by networks of neurons. The idea that these pivotal cells evolved multiple times seems implausible because neurons are highly complex cells, and they are also quite similar among animal lineages. But a series of recent evolutionary biology studies are straining the assumption that all animal neurons have a single origin. These findings are the culmination of several years’ worth of research on and debate about early evolutionary animal lineages and the cells and systems present in those species. The first such finding came from studying relationships among early animals, with a focus on two particular types of organisms: sponges (including sea sponges and freshwater varieties) and ctenophores, invertebrates often known as comb jellies, though they are unrelated to jellyfish. For roughly 15 years, evolutionary biologists have been divided over whether ctenophores or sponges were the first animals to branch from all other animals in the evolutionary tree. Hundreds of millions of years ago the common ancestor to all living animals branched into two species. On one side was the common ancestor of all groups of animals except for one. On the other side was that “one”—the “sister group” that was the first to diverge from all other animals. A persistent question has been whether the sister group was the sponges or ctenophores. A compelling paper published last year lends strong support to the hypothesis that ctenophores are, in fact, the long-sought sister group. Ctenophores, the researchers found, branched off before sponges and are therefore the group most distantly related to all other animals. Yet despite the new evidence, what exactly happened in evolutionary history is still unsettled because of the puzzle it poses in explaining the evolution of neurons. © 2023 SCIENTIFIC AMERICAN,

Keyword: Evolution
Link ID: 29081 - Posted: 01.06.2024

Kamal Nahas Peter Hegemann, a biophysicist at Humboldt University, has spent his career exploring interactions between proteins and light. Specifically, he studies how photoreceptors detect and respond to light, focusing largely on rhodopsins, a family of membrane photoreceptors in animals, plants, fungi, protists, and prokaryotes.1 Early in his career, his curiosity led him to an unknown rhodopsin in green algae that later proved to have useful applications in neuroscience research. Hegemann became a pioneer in the field of optogenetics, which revolutionized the ways in which scientists draw causal links between neuronal activity and behavior. In the early 1980s during his graduate studies at the Max Planck Institute of Biochemistry, Hegemann spent his days exploring rhodopsins in bacteria and archaea. However, the field was crowded, and he was eager to study a rhodopsin that scientists knew nothing about. Around this time, Kenneth Foster, a biophysicist at Syracuse University, was investigating whether the green algae Chlamydomonas, a photosynthetic unicellular eukaryote related to plants, used a rhodopsin in its eyespot organelle to detect light and trigger the algae to swim. He struggled to pinpoint the protein itself, so he took a roundabout approach and started interfering with nearby molecules that interact with rhodopsins.2 Rhodopsins require the small molecule retinal to function as a photoreceptor. When Foster depleted Chlamydomonas of its own retinal, the algae were unable to use light to direct movement, a behavior that was restored when he introduced retinal analogues. In 1985, Hegemann joined Foster’s group as a postdoctoral researcher to continue this work. “I wanted to find something new,” Hegemann said. “Therefore, I worked on an exotic organism and an exotic topic.” A year later, Hegemann started his own research group at the Max Planck Institute of Biochemistry where he searched for the green algae’s rhodopsin that Foster proposed should exist. © 1986–2024 The Scientist.

Keyword: Brain imaging; Vision
Link ID: 29077 - Posted: 01.03.2024

By Elise Cutts On a summer night in the Bay of Naples, hordes of worms swam upward from the seagrass toward the water’s surface under the light of a waning moon. Not long before, the creatures began a gruesome sexual metamorphosis: Their digestive systems withered, and their swimming muscles grew, while their bodies filled with eggs or sperm. The finger-length creatures, now little more than muscular bags of sex cells, fluttered to the surface in unison and, over a few hours, circled each other in a frantic nuptial dance. They released countless eggs and sperm into the bay — and then the moonlit waltz ended in the worms’ deaths. The marine bristle worm Platynereis dumerilii gets only one chance to mate, so its final dance had better not be a solo. To ensure that many worms congregate at the same time, the species synchronizes its reproductive timing with the cycles of the moon. How can an undersea worm tell when the moon is at its brightest? Evolution’s answer is a precise celestial clock wound by a molecule that can sense moonbeams and sync the worms’ reproductive lives to lunar phases. No one had ever seen how one of these moonlight molecules worked. Recently, however, in a study published in Nature Communications, researchers in Germany determined the different structures that one such protein in bristle worms takes in darkness and in sunlight. They also uncovered biochemical details that help explain how the protein distinguishes between brighter sunbeams and softer moonglow. It’s the first time that scientists have determined the molecular structure of any protein responsible for syncing a biological clock to the phases of the moon. “I’m not aware of another system that has been looked at with this degree of sophistication,” said the biochemist Brian Crane of Cornell University, who was not involved in the new study. © 2023 An editorially independent publication supported by the Simons Foundation.

Keyword: Biological Rhythms; Evolution
Link ID: 29062 - Posted: 12.22.2023

By Ann Gibbons Louise hadn’t seen her sister or nephew for 26 years. Yet the moment she spotted them on a computer screen, she recognized them, staring hard at their faces. The feat might have been impressive enough for a human, but Louise is a bonobo—one who had spent most of her life at a separate sanctuary from these relatives. The discovery, published today in the Proceedings of the National Academy of Sciences, reveals that our closest primate cousins can remember the faces of friends and family for years, and sometimes even decades. The study, experts say, shows that the capability for long-term social memory is not unique to people, as was long believed. “It’s a remarkable finding,” says Frans de Waal, a primatologist at Emory University who was not involved with the work. “I’m not even sure we humans remember most individuals we haven’t seen for 2 decades.” The research, he says, raises the possibility that other animals can also do this and may remember far more than we give them credit for. Trying to figure out whether nonhuman primates remember a face isn’t simple. You can’t just ask them. So in the new study, comparative psychologist Christopher Krupenye at Johns Hopkins University and colleagues used eye trackers, infrared cameras that noninvasively map a subject’s gaze as they look at images of people or objects. The scientists worked with 26 chimpanzees and bonobos living in three zoos or sanctuaries in Europe and Japan. The team showed the animals photos of the faces of two apes placed side by side on the screen at the same time for 3 seconds. Some images were of complete strangers; some were of close friends, foes, or family members who had once lived in their same social groups, but whom they hadn’t seen in years.

Keyword: Attention; Learning & Memory
Link ID: 29058 - Posted: 12.19.2023

By Carl Zimmer Neanderthals were morning people, a new study suggests. And some humans today who like getting up early might credit genes they inherited from their Neanderthal ancestors. The new study compared DNA in living humans with genetic material retrieved from Neanderthal fossils. It turns out that Neanderthals carried some of the same clock-related genetic variants as do people who report being early risers. Since the 1990s, studies of Neanderthal DNA have exposed our species’ intertwined history. About 700,000 years ago, our lineages split apart, most likely in Africa. While the ancestors of modern humans largely stayed in Africa, the Neanderthal lineage migrated into Eurasia. About 400,000 years ago, the population split in two. The hominins who spread west became Neanderthals. Their cousins to the east evolved into a group known as Denisovans. The two groups lived for hundreds of thousands of years, hunting game and gathering plants, before disappearing from the fossil record about 40,000 years ago. By then, modern humans had expanded out of Africa, sometimes interbreeding with Neanderthals and Denisovans. And today, fragments of their DNA can be found in most living humans. Research carried out over the past few years by John Capra, a geneticist at the University of California, San Francisco, and other scientists suggested that some of those genes passed on a survival advantage. Immune genes inherited from Neanderthals and Denisovans, for example, might have protected them from new pathogens they had not encountered in Africa. Dr. Capra and his colleagues were intrigued to find that some of the genes from Neanderthals and Denisovans that became more common over generations were related to sleep. For their new study, published in the journal Genome Biology and Evolution, they investigated how these genes might have influenced the daily rhythms of the extinct hominins. © 2023 The New York Times Company

Keyword: Biological Rhythms; Evolution
Link ID: 29052 - Posted: 12.16.2023

By Joseph Howlett Garter snakes have something in common with elephants, orcas, and naked mole rats: They form social groups that center around females. The snakes have clear “communities” composed of individuals they prefer hanging out with, and females act as leaders that tie the groups together and guide their members’ movements, according to the most extensive field study of snake sociality ever carried out. “This is an important first step in understanding how a community of snakes is organized in the wild,” says Gordon Burghardt, an ecologist at the University of Tennessee, Knoxville, who was not involved in the research. Other experts agree: “This is a big deal,” says integrative biologist Robert Mason of Oregon State University. “It’s a whole new avenue of research that I don’t think people have really given any thought to.” Ecologists had long assumed snakes are antisocial loners that hang out together only for core functions such as mating and hibernation. However, in 2020, Morgan Skinner, a behavioral ecologist at Wilfrid Laurier University, and collaborators showed in laboratory experiments that captive garter snakes have “friends”—specific snakes whose company they prefer over others. Still, studies of wild snakes were lacking “because they’re so secretive and difficult to find,” Skinner says. Then he learned that the Ontario Ministry of Transportation had funded an unprecedented long-term study of a huge population of Butler’s garter snakes (Thamnophis butleri) in Windsor, Canada. Ecologists began to monitor the flute-size slitherers in 2009 to keep them safe from nearby road construction. They regularly captured snakes in the 250-hectare study area, using identifying markings to track more than 3000 individuals over a 12-year span—about the lifetime of a garter snake. “We were mainly monitoring the population after they were relocated, to make sure they were thriving,” says Megan Hazell, a biologist with the consulting firm WSP, who led the field research as a graduate student at Queen’s University.

Keyword: Evolution; Sexual Behavior
Link ID: 29050 - Posted: 12.16.2023

By Jake Buehler Nesting chinstrap penguins take nodding off to the extreme. The birds briefly dip into a slumber many thousands of times per day, sleeping for only seconds at a time. The penguins’ breeding colonies are noisy and stressful places, and threats from predatory birds and aggressive neighbor penguins are unrelenting. The extremely disjointed sleep schedule may help the penguins to protect their young while still getting enough shut-eye, researchers report in the Dec. 1 Science. The findings add to evidence “that avian sleep can be very different from the sleep of land mammals,” says UCLA neuroscientist Jerome Siegel. Nearly a decade ago, behavioral ecologist Won Young Lee of the Korea Polar Research Institute in Incheon noticed something peculiar about how chinstrap penguins (Pygoscelis antarcticus) nesting on Antarctica’s King George Island were sleeping. They would seemingly doze off for very short periods of time in their cacophonous colonies. Then in 2018, Lee learned about frigate birds’ ability to steal sleep while airborne on days-long flights. Lee teamed up with sleep ecophysiologist Paul-Antoine Libourel of the Lyon Neuroscience Research Center in France and other researchers to investigate the penguins’ sleep. In 2019, the team studied the daily sleep patterns of 14 nesting chinstrap penguins using data loggers mounted on the birds’ backs. The devices had electrodes surgically implanted into the penguins’ brains for measuring brain activity. Other instruments on the data loggers recorded the animals’ movements and location. Nesting penguins had incredibly fragmented sleep patterns, taking over 600 “microsleeps” an hour, each averaging only four seconds, the researchers found. At times, the penguins slept with only half of their brain; the other half stayed awake. All together, the oodles of snoozes added up, providing over 11 hours of sleep for each brain hemisphere across more than 10,000 brief sleeps each day. © Society for Science & the Public 2000–2023.

Keyword: Sleep; Evolution
Link ID: 29028 - Posted: 12.02.2023

By Annie Roth A few years ago, Nicolas Fasel, a biologist at the University of Lausanne in Switzerland, and his colleagues developed a fascination with the penises of serotine bats, a species found in woodlands and the attics of old buildings across Europe and Asia. Serotine bats sport abnormally long penises with wide, heart-shaped heads. When erect, the members are around seven times longer than the female’s vagina, and their bulbous heads are seven times wider than the female’s vaginal opening. “We wondered: How does that work? How can they use that for copulation?” Dr. Fasel recalled. What they discovered has overturned an assumption about mammalian reproduction, namely that procreation must always involve penetration. In a study, published Monday in the journal Current Biology, Dr. Fassel and his colleagues presented evidence that serotine bats mate without penetration, making them the first mammals known to do so. Instead of using their penises to penetrate their partners, the scientists found, the male bats use them to push their partner’s tail membrane out of the way so they can align their openings and engage in contact mating, a behavior similar to one found in birds and known as “cloacal kissing.” To learn how these bats overcome their substantial genital size difference, Dr. Fasel and his colleagues analyzed nearly 100 videos of serotine bats mating. The videos were provided by a bat rehabilitation center in Ukraine and a citizen scientist filming bats in the attic of a church in the Netherlands. The footage revealed a mating strategy unlike any other used by mammals. While the two bats hang upside down, the male climbs on the female’s back and grasps the nape of her neck. Once he has a firm hold, the male will use his erect penis to push the female’s tail membrane to the side and probe between her legs until he has located her vulva. The male then presses the heart-shaped head of his penis to the female’s vulva and holds it there until the deed is done. While this process took less than an hour for most of the couples the researchers observed, one pair went at it for nearly 13 hours. “It’s a really weird reproductive strategy, but bats are weird and have a lot of weird reproductive strategies,” said Patty Brennan, a biologist at Mount Holyoke College in Massachusetts who studies the evolution of genital morphology but was not involved in the study. © 2023 The New York Times Company

Keyword: Sexual Behavior; Evolution
Link ID: 29014 - Posted: 11.22.2023

By Carl Zimmer 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. If a troop of baboons encounters another troop on the savanna, they may keep a respectful distance or they may get into a fight. But human groups often do something else: They cooperate. Tribes of hunter-gatherers regularly come together for communal hunts or to form large-scale alliances. Villages and towns give rise to nations. Networks of trade span the planet. Human cooperation is so striking that anthropologists have long considered it a hallmark of our species. They have speculated that it emerged thanks to the evolution of our powerful brains, which enable us to use language, establish cultural traditions and perform other complex behaviors. But a new study, published in Science on Thursday, throws that uniqueness into doubt. It turns out that two groups of apes in Africa have regularly mingled and cooperated with each other for years. “To have extended, friendly, cooperative relationships between members of other groups who have no kinship ties is really quite extraordinary,” said Joan Silk, a primatologist at Arizona State University who was not involved in the study. The new research comes from long-term observations of bonobos, an ape species that lives in the forests of the Democratic Republic of Congo. A century ago, primatologists thought bonobos were a slender subspecies of chimpanzee. But the two species are genetically distinct and behave in some remarkably different ways. Among chimpanzees, males hold a dominant place in society. They can be extremely violent, even killing babies. In bonobo groups, however, females dominate, and males have never been observed to commit infanticide. Bonobos often defuse conflict with sex, a strategy that primatologists have not observed among chimpanzees. Scientists made most of their early observations of bonobos in zoos. But in recent years they’ve conducted long-term studies of the apes in the wild. © 2023 The New York Times Company

Keyword: Evolution; Aggression
Link ID: 29011 - Posted: 11.18.2023

By Sean Cummings If a bite of dandelion greens or extra-dark chocolate makes you pucker, there’s good reason. Bitterness can indicate the presence of toxins in potential foods, and animals long ago honed the ability to ferret out harsh tastes. But the ability to sense bitterness may be even older than many presumed, a new study finds. It likely first evolved in vertebrates roughly 460 million years ago, when sharks and other cartilaginous fishes separated from bony vertebrates like ourselves, researchers report today in the Proceedings of the National Academy of Sciences. The bitter taste receptor identified in a pair of shark species may mirror a sort of all-purpose bitterness detector that our common ancestor possessed. “Given how quickly taste receptors change, to have this one receptor conserved over 460 million years, that’s pretty astounding,” says Craig Montell, a neurobiologist at the University of California, Santa Barbara who was not involved in the study. “The ability to react to the particular bitter chemicals that activate it must be really important.” Humans and other bony vertebrates experience bitterness thanks to taste 2 receptors, or T2Rs, which are proteins that transmit taste information to the brain. But scientists had never found T2Rs in cartilaginous vertebrates such as sharks and rays. That led many to assume these receptors had evolved after their lineage split from the bony vertebrates. Yet sharks and other cartilaginous fish do have smell receptors closely related to bitter taste receptors. That made Sigrun Korsching, a neurobiologist at the University of Cologne, wonder: Could bitter taste perception be even older than most believed? To find out, she and colleagues examined 17 genomes from various species of sharks, skates, and sawfish. Twelve of these had genes that coded for taste receptors similar to T2Rs, which they dubbed T2R1s. In the lab, the researchers implanted genes for these receptors from two of the species—bamboo sharks and catsharks—into human kidney cells, then exposed them to 94 bitter substances. These included resveratrol, found in foods such as grapes, peanuts, and cranberries, and amarogentin, a compound from the gentian plant considered one of the most astringent tastes in the world.

Keyword: Chemical Senses (Smell & Taste); Evolution
Link ID: 29006 - Posted: 11.15.2023

By Claudia López Lloreda Genetic tweaks in kingfishers might help cushion the blow when the diving birds plunge beak first into the water to catch fish. Analysis of the genetic instruction book of some diving kingfishers identified changes in genes related to brain function as well as retina and blood vessel development, which might protect against damage during dives, researchers report October 24 in Communications Biology. The results suggest the different species of diving kingfishers may have adapted to survive their dives unscathed in some of the same ways, but it’s still unclear how the genetic changes protect the birds. Hitting speeds of up to 40 kilometers per hour, kingfisher dives put huge amounts of potentially damaging pressure on the birds’ heads, beaks and brains. The birds dive repeatedly, smacking their heads into the water in ways that could cause concussions in humans, says Shannon Hackett, an evolutionary biologist and curator at the Field Museum in Chicago. “So there has to be something that protects them from the terrible consequences of repeatedly hitting their heads against a hard substrate.” Hackett first became interested in how the birds protect their brains while she worked with her son’s hockey team and started worrying about the effect of repeated hits on the human brain. Around the same time, evolutionary biologist Chad Eliason joined the museum to study kingfishers and their plunge diving behavior. In the new study, Hackett, Eliason and colleagues analyzed the complete genome of 30 kingfisher species, some that plunge dive and others that don’t, from specimens frozen and stored at the museum. The preserved birds came from all over the world; some of the diving species came from mainland areas and others from islands and had evolved to dive independently rather than from the same plunge-diving ancestor. The team wanted to know if the different diving species had evolved similar genetic changes to arrive at the same behaviors. Many kingfisher species have developed this behavior, but it was unclear whether this was through genetic convergence, similar to how many species of birds have lost their flight or how bats and dolphins independently developed echolocation (SN: 9/6/2013). © Society for Science & the Public 2000–2023.

Keyword: Brain Injury/Concussion; Evolution
Link ID: 28991 - Posted: 11.08.2023

By Darren Incorvaia The idea of a chicken running around with its head cut off, inspired by a real-life story, may make it seem like the bird doesn’t have much going on upstairs. But Sonja Hillemacher, an animal behavior researcher at the University of Bonn in Germany, always knew that chickens were more than mindless sources of wings and nuggets. “They are way smarter than you think,” Ms. Hillemacher said. Now, in a study published in the journal PLOS One on Wednesday, Ms. Hillemacher and her colleagues say they have found evidence that roosters can recognize themselves in mirrors. In addition to shedding new light on chicken intellect, the researchers hope that their experiment can prompt re-evaluations of the smarts of other animals. The mirror test is a common, but contested, test of self-awareness. It was introduced by the psychologist Gordon Gallup in 1970. He housed chimpanzees with mirrors and then marked their faces with red dye. The chimps didn’t seem to notice until they could see their reflections, and then they began inspecting and touching the marked spot on their faces, suggesting that they recognized themselves in the mirror. The mirror test has since been used to assess self-recognition in many other species. But only a few — such as dolphins and elephants — have passed. After being piloted on primates, the mirror test was “somehow sealed in a nearly magical way as sacred,” said Onur Güntürkün, a neuroscientist at Ruhr University Bochum in Germany and an author of the study who worked with Ms. Hillemacher and Inga Tiemann, also at the University of Bonn. But different cognitive processes are active in different situations, and there’s no reason to think that the mirror test is accurate for animals with vastly different sensory abilities and social systems than what chimps have. The roosters failed the classic mirror test. When the team marked them with pink powder, the birds showed no inclination to inspect or touch the smudge in front of the mirror the way that Dr. Gallup’s chimps did. As an alternative, the team tested rooster self-awareness in a more fowl friendly way. © 2023 The New York Times Company

Keyword: Consciousness; Intelligence
Link ID: 28978 - Posted: 10.28.2023

By Christa Lesté-Lasserre A gray cat stares quietly at a nearby orange tabby, squinting her eyes, flattening her ears, and licking her lips. The tabby glares back, wrinkles his nose, and pulls back his whiskers. Cat people know what’s about to go down: a fight. If looks and growls don’t resolve the budding tiff, claws will pop out and fur will fly. Those faces aren’t the only ones cats make at each other, of course—not by a long shot. In a study published this month in Behavioural Processes, researchers tallied 276 different feline facial expressions, used to communicate hostile and friendly intent and everything in between. What’s more, the team found, we humans might be to thank: Our feline friends may have evolved this range of sneers, smiles, and grimaces over the course of their 10,000-year history with us. “Many people still consider cats—erroneously—to be a largely nonsocial species,” says Daniel Mills, a veterinary behaviorist at the University of Lincoln who was not involved in the study. The facial expressions described in the new study suggest otherwise, he notes. “There is clearly a lot going on that we are not aware of.” Cats can be solitary creatures, but they often form friendships with fellow kitties in people’s homes or on the street; feral cats can live in colonies of thousands, sometimes taking over entire islands. Lauren Scott, a medical student and self-described cat person at the University of Kansas, long wondered how all these felines communicated with one another. There has to be love and diplomacy, not just fighting, yet most studies of feline expression have focused on aggression. Fortunately in 2021, Scott was studying at the University of California, Los Angeles (UCLA), just minutes from the CatCafé Lounge. There, human visitors can interact—and even do yoga—with dozens of group-housed, adoptable cats. From August to June, Scott video recorded 194 minutes of cats’ facial expressions, specifically those aimed at other cats, after the café had closed for the day. Then she and evolutionary psychologist Brittany Florkiewicz, also at UCLA at the time but now at Lyon College, coded all their facial muscle movements—excluding any related to breathing, chewing, yawning, and the like.

Keyword: Emotions; Evolution
Link ID: 28977 - Posted: 10.28.2023

By Bruce Bower Female chimps living in an East African forest experience menopause and then survive years, even decades, after becoming biologically unable to reproduce. The apes are the first known examples of wild, nonhuman primates to go through the fertility-squelching hormonal changes and live well beyond their reproductive years. The finding raises new questions about how menopause evolved, UCLA evolutionary anthropologist Brian Wood and colleagues conclude in the Oct. 27 Science. Until now, females who experience menopause and keep living for years have been documented only in humans and five whale species. It’s unclear what evolutionary benefit exists to explain such longevity past the point of being able to give birth and pass on one’s genes. Although evolutionary explanations for menopause remain debatable, the new finding reflects an especially close genetic relationship between humans and chimps, Wood says. “Both [species] are more predisposed to post-reproductive survival than other great apes.” Some evidence suggests that female fertility ends at similar ages in humans and chimps (Pan troglodytes) if our ape relatives live long enough, says anthropologist Kristen Hawkes of the University of Utah in Salt Lake City. But in other studies, female chimps, such as those studied by Jane Goodall at Tanzania’s Gombe National Park starting in 1960, aged quickly and often died in their early 30s, usually while still having menstrual cycles, she says. “What’s surprising [in Wood’s study] is so many females living so long after menopause,” Hawkes says. © Society for Science & the Public 2000–2023.

Keyword: Hormones & Behavior; Evolution
Link ID: 28975 - Posted: 10.28.2023

Christie Wilcox Adult horsehair worms look about how you’d expect given their name: They’re long, noodlelike creatures that resemble wiggling horse hairs. They live and reproduce in water, but their young only develop inside the bodies of other animals—usually terrestrial insects such as praying mantises. Once they’ve finished growing inside their unwitting vessel, the worms must convince their hosts to drown themselves to complete their life cycle. How these parasites manage to lethally manipulate their hosts has long puzzled scientists. Researchers behind a new study published today in Current Biology suggest horsehair worms possess hundreds of genes that allow them to hijack a mantis’ movement—and they may have acquired these genes directly from their ill-fated hosts. “The results are amazing,” says Clément Gilbert, an evolutionary biologist at the University of Paris-Saclay who wasn’t involved in the work. If it turns out to be true that so many of the mantises’ genes jumped over to the parasitic worms—a process known as horizontal gene transfer—then “this is by far the highest number of horizontally transferred genes that have been reported between two species of animals,” he adds. The phenomenon of parasites mind-controlling their hosts to an early grave has always intrigued Tappei Mishina, an evolutionary biologist at Kyushu University and the RIKEN Center for Biosystems Dynamics Research. “For more than 100 years, there have been horrifying observations of terrestrial insects jumping into water right before our eyes all over the world,” he says. He teamed up with ecologist Takuya Sato of the Center for Ecological Research at Kyoto University to investigate the genetic basis of their parasitism. They focused on horsehair or gordian worms, a group of parasitic animals related to nematodes. Many have complex life cycles involving multiple hosts, and the ones that live in freshwater must generally find their way into an insect to finish developing into adults. The genus Mishina, Sato, and their colleagues specialize in, known as Chordodes, infect mantises and can grow to nearly 1 meter long inside the palm-size insects’ abdomens.

Keyword: Genes & Behavior; Evolution
Link ID: 28971 - Posted: 10.25.2023

By Tim Vernimmen For humans, division of labor has become a necessity: No person in the world has all the knowledge and skills to perform all the tasks that are required to keep our highly technological societies afloat. This has made us entirely dependent on each other, leaving us individually vulnerable. We really can’t make it on our own. From archaeological findings, we can reconstruct more or less how this situation evolved. Initially, everyone was doing more or less the same thing. But because food was shared among people living in hunter-gatherer groups, some were able to specialize in tasks other than finding food, such as fashioning tools, treating illnesses or cultivating plants. These skills enriched the group but made the specialists even more dependent on others. This further reinforced cooperation among group members and pushed our species to even higher levels of specialization — and prosperity. “Societies that have highly developed task-sharing and division of labor between group members are conspicuous because of their exceptional ecological success,” says Michael Taborsky, a behavioral biologist at the University of Bern in Switzerland. And he doesn’t just mean us: Extensive division of labor also can be seen among many social insects — ants, wasps, bees and termites — in which individuals in large colonies often specialize in particular tasks, making them impressively effective. “It is no exaggeration,” Taborsky says, “to say that societies” — of both humans and social insects — “predominate life on Earth.” But how did this division of labor evolve? Why does it seem to be rare outside of our species and the social insects? Is it, in fact, as rare as it seems? Taborsky, who has studied cooperation in animals for decades, has become increasingly interested in these questions. In March 2023, he and Barbara Taborsky, his wife and colleague, organized a scientific workshop on the topic in Berlin to which they invited a number of other experts. Over the course of two days, the group discussed how division of labor may have evolved over time, and what mechanisms allow it to develop, over and over again, in every colony of certain species. One of the invited scientists was Jennifer Fewell, a social insect biologist at Arizona State University who coauthored an influential overview of division of labor in the Annual Review of Entomology in 2001 and has studied the subject for decades. In social insect colonies, she says, “there is no central controller telling everybody what to do, but instead, the division of labor emerges from the interaction between individuals.” © 2023 Annual Reviews

Keyword: Chemical Senses (Smell & Taste); Evolution
Link ID: 28944 - Posted: 10.05.2023

By Carl Zimmer In more than 1,500 animal species, from crickets and sea urchins to bottlenose dolphins and bonobos, scientists have observed sexual encounters between members of the same sex. Some researchers have proposed that this behavior has existed since the dawn of the animal kingdom. But the authors of a new study of thousands of mammalian species paint a different picture, arguing that same-sex sexual behavior evolved when mammals started living in social groups. Although the behavior does not produce offspring to carry on the animals’ genes, it could offer other evolutionary advantages, such as smoothing over conflicts, the researchers proposed. “It may contribute to establishing and maintaining positive social relationships,” said José Gómez, an evolutionary biologist at the Experimental Station of Arid Zones in Almería, Spain, and an author of the new study. But Dr. Gómez cautioned that the study, published on Tuesday in the journal Nature Communications, could not shed much light on sexual orientation in humans. “The type of same-sex sexual behavior we have used in our analysis is so different from that observed in humans that our study is unable to provide an explanation for its expression today,” he said. Previous studies of same-sex sexual behavior have typically involved careful observations of a single species, or a small group of them. Dr. Gómez and his colleagues instead looked for the big evolutionary patterns that gave rise to the behavior in some species but not others. The researchers surveyed the 6,649 species of living mammals that arose from reptilelike ancestors starting roughly 250 million years ago. Looking over the scientific literature, they noted which of them had been seen carrying out same-sex sexual behaviors — defined as anything from courtships and mating to forming long-term bonds. The researchers ended up with a list of 261 species, or about 4 percent of all mammalian species, that exhibited these same-sex behaviors. Males and females were about equally likely to be observed carrying out same-sex sexual behavior, the analysis showed. In some species, only one sex did. But in still others — including cheetahs and white-tailed deer — both males and females engaged in same-sex sexual behavior. © 2023 The New York Times Company

Keyword: Sexual Behavior; Evolution
Link ID: 28943 - Posted: 10.05.2023

By Katherine Harmon Courage On the surface, sleep seems obvious, essential. It comes in long, languid, predictable waves, washing over humans and elephants, birds and fish and beetles. It comes bearing restoration, repair, learning. It follows an ancestral rhythm played deep within our cells, cued by the movement of our planet around our star. Perhaps we could believe this nice, simple fantasy, were it not for an irksome little eyeless fish. More than a decade ago, this fish—the Mexican tetra (Astyanax mexicanus)—caught the eye of a graduate student at New York University. It was not new to science—it had been the subject of fascination for aquarists and researchers for decades, who marveled at its ghostly appearance and the splash of skin where its eyes should have been. But other quirks of the fish turned out to be even more mysterious. In Manhattan, the fish were far from their place of origin: a collection of unassuming caves strung through northeastern Mexico. Inside these caves, it is pitch dark, always cool, quiet, and rather boring. A seemingly perfect place to sleep. So Erik Duboué, the curious graduate student, decided to test if these fish showed any unusual sleep habits. One night in 2009, he made a 2 a.m. visit to the lab and noticed something strange about these sightless fish: They seemed wide awake. On further investigation, he found that despite their soporific native environs, they actually hardly sleep at all. In fact, he discovered, they doze just about three and a half hours out of each 24-hour period. And their bouts of sleep seem to come on entirely randomly and only in brief spurts. Curiously, these eyeless cavefish seem to have been flourishing on this quiescence interruptus for hundreds of thousands of years. “What you have is a fish that is completely healthy—it just doesn’t need to sleep,” says Duboué, who is now a molecular geneticist at Florida Atlantic University. Since then, Duboué and others have been studying the strange sleep of these wakeful creatures—prodding them in the lab to rouse them from their occasional slumber and plumbing their DNA. Combined with investigations into other animals, as well as some peculiar experiments that have sent humans to sleep in caves, scientists are uncovering new, closely guarded truths about sleep that have eluded us in our bright, rhythmic world. © 2023 NautilusNext Inc.

Keyword: Sleep; Evolution
Link ID: 28941 - Posted: 10.03.2023

By Veronique Greenwood In the dappled sunlit waters of Caribbean mangrove forests, tiny box jellyfish bob in and out of the shade. Box jellies are distinguished from true jellyfish in part by their complex visual system — the grape-size predators have 24 eyes. But like other jellyfish, they are brainless, controlling their cube-shaped bodies with a distributed network of neurons. That network, it turns out, is more sophisticated than you might assume. On Friday, researchers published a report in the journal Current Biology indicating that the box jellyfish species Tripedalia cystophora have the ability to learn. Because box jellyfish diverged from our part of the animal kingdom long ago, understanding their cognitive abilities could help scientists trace the evolution of learning. The tricky part about studying learning in box jellies was finding an everyday behavior that scientists could train the creatures to perform in the lab. Anders Garm, a biologist at the University of Copenhagen and an author of the new paper, said his team decided to focus on a swift about-face that box jellies execute when they are about to hit a mangrove root. These roots rise through the water like black towers, while the water around them appears pale by comparison. But the contrast between the two can change from day to day, as silt clouds the water and makes it more difficult to tell how far away a root is. How do box jellies tell when they are getting too close? “The hypothesis was, they need to learn this,” Dr. Garm said. “When they come back to these habitats, they have to learn, how is today’s water quality? How is the contrast changing today?” In the lab, researchers produced images of alternating dark and light stripes, representing the mangrove roots and water, and used them to line the insides of buckets about six inches wide. When the stripes were a stark black and white, representing optimum water clarity, box jellies never got close to the bucket walls. With less contrast between the stripes, however, box jellies immediately began to run into them. This was the scientists’ chance to see if they would learn. © 2023 The New York Times Company

Keyword: Learning & Memory; Evolution
Link ID: 28925 - Posted: 09.23.2023

By Till Hein Human couples could learn a lot from seahorses. The marine marvels spend only quality time together. They flirt, swim together, and mate. The rest of time they go their own way, drifting in ocean currents, leisurely eating their fill. But they do look forward to getting together again. Right after sunrise, male and female seahorses approach one another, gently rubbing their noses together and then begin to circle each other. Many of them make seductive clicking noises. The partners gracefully rock back and forth, as though to the beat of underwater music. They dance and cuddle together dreamily, as though they’ve lost track of time. However, love can be dangerous for seahorses. During partner dancing, hormones are released that can make their camouflage fade. This causes changes in color, so their bodies begin to glow, and the contrasts in the patterns of their skin become more pronounced. Researchers hypothesize this is how seahorses signal their willingness to mate. The partner dances also serve as a means of seduction. Before mating, courtship can take many hours. Finally, the female signals that she’s ready. She swims up toward the water surface, pointing her snout toward the sky, and stretches her body out straight as a stick—a pose that is irresistible to the male. The stallion of the sea presses his chin against his chest and makes his prehensile tail open and close like a switchblade. This enables him to pump water into his brood pouch to show his beloved mare of the sea how roomy it is. Soon afterward, the mare and stallion of the sea snuggle up together closely and let themselves drift upward. They press their bodies together so that their snouts and abdomens are touching. On account of the curves in their body posture, the space between them looks like the shape of a heart. Then, something amazing takes place. A tubular rod appears in the middle of the female seahorse’s belly, which looks a little like a penis, the so-called ovipositor. At the climax of the love scene, both partners lift their heads as though in ecstasy, curving their backs, and the female seahorse transfers her eggs into the male’s brood pouch, while her partner fertilizes them with his sperm. © 2023 NautilusNext Inc., All rights reserved.

Keyword: Sexual Behavior; Evolution
Link ID: 28923 - Posted: 09.23.2023