New research sheds light on an old fossil solving an evolutionary mystery

A research paper published in Royal Society's Biology Letters on January 10 has revealed that picrodontids -- an extinct family of placental mammals that lived several million years after the extinction of the dinosaurs -- are not primates as previously believed.

The paper -- co-authored by Jordan Crowell, an Anthropology Ph.D. candidate at the CUNY Graduate Center; Stephen Chester, an Associate Professor of Anthropology at Brooklyn College and the Graduate Center; and John Wible, Curator of Mammals at the Carnegie Museum of Natural History -- is significant in that it settled a paleontological debate that has been brewing for over 100 years while helping to paint a more clear picture of primate evolution.

For the last 50 years, paleontologists have believed picrodontids, which were no larger than a mouse and likely ate foods such as fruit, nectar, and pollen, were primates, based on features of their teeth that they share with living primates.

But by using modern CT scan technology to analyze the only known preserved picrodontid skull in Brooklyn College's Mammalian Evolutionary Morphology Laboratory, Crowell, the lead author on the paper, worked with Chester, the paper's senior author, and Wible to determine they are not closely related to primates at all.

"While picrodontids share features of their teeth with living primates, the bones of the skull, specifically the bone that surrounds the ear, are unlike that of any living primate or close fossil relatives of primates," Crowell said.

"This suggests picrodontids and primates independently evolved similarities of their teeth likely for similar diets. This study also highlights the importance of revisiting old specimens with updated techniques to examine them."

Chester, who serves as Crowell's Ph.D. adviser, has both a professional and personal interest in this research.

It was Chester's colleague and "academic grandfather," Professor Emeritus Frederick Szalay from CUNY's Hunter College and the Graduate Center, who in 1968 first convincingly classified picrodontids as primates based on evidence from fossilized teeth.

Szalay studied the teeth of the only known picrodontid skull, Zanycteris paleocenus, for his research -- the same skull this team examined with the new technology that led to their discovery.

"The Zanycteris cranium was prepared and partially submerged in plaster around 1917, so researchers studying this important specimen at the American Museum of Natural History were not aware of how much cranial anatomy was hidden over the last 100 years" Chester said.

"Micro-CT scanning has revolutionized the field of paleontology and allows researchers to discover so much more about previously studied fossils housed in natural history museum collections."

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Early primates likely lived in pairs

Primates -- and this includes humans -- are thought of as highly social animals. Many species of monkeys and apes live in groups. Lemurs and other Strepsirrhines, often colloquially referred to as "wet-nosed" primates, in contrast, have long been believed to be solitary creatures, and it has often been suggested that other forms of social organization evolved later. Previous studies have therefore attempted to explain how and when pair-living evolved in primates.

More recent research, however, indicates that many nocturnal Strepsirrhines, which are more challenging to investigate, are not in fact solitary but live in pairs of males and females.

But what does this mean for the social organization forms of the ancestors of all primates?

And why do some species of monkey live in groups, while others are pair-living or solitary?

Different forms of social organization

Researchers at the Universities of Zurich and Strasbourg have now examined these questions.

For their study, Charlotte Olivier from the Hubert Curien Pluridisciplinary Institute collected detailed information on the composition of social units in primate populations in the wild.

Over several years, the researchers built a detailed database, which covered almost 500 populations from over 200 primate species, from primary field studies.

More than half of the primate species recorded in the database exhibited more than one form of social organization.

"The most common social organization were groups in which multiple females and multiple males lived together, for example chimpanzees or macaques, followed by groups with only one male and multiple females -- such as in gorillas or langurs," says last author Adrian Jaeggi from the University of Zurich.

"But one-quarter of all species lived in pairs."

Smaller ancestors coupled up

Taking into account several socioecological and life history variables such as body size, diet or habitat, the researchers calculated the probability of different forms of social organization, including for our ancestors who lived some 70 million years ago.

The calculations were based on complex statistical models developed by Jordan Martin at UZH's Institute of Evolutionary Medicine.

To reconstruct the ancestral state of primates, the researchers relied on fossils, which showed that ancestral primates were relatively small-bodied and arboreal -- factors that strongly correlate with pair-living.

"Our model shows that the ancestral social organization of primates was variable and that pair-living was by far the most likely form," says Martin.

Only about 15 percent of our ancestors were solitary, he adds.

"Living in larger groups therefore only evolved later in the history of primates."

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Can we decode the language of our primate cousins?

Are we able to differentiate between the vocal emissions of certain primates? A team from the University of Geneva (UNIGE) asked volunteers to categorise the vocalisations of three species of great apes (Hominidae) and humans. During each exposure to these ''onomatopoeia'', brain activity was measured. Unlike previous studies, the scientists reveal that phylogenetic proximity -- or kinship -- is not the only factor influencing our ability to identify these sounds. Acoustic proximity -- the type of frequencies emitted -- is also a determining factor. These results show how the human brain has evolved to process the vocal emissions of some of our closest cousins more efficiently. Find out more in the journal Cerebral Cortex Communications.

Our ability to process verbal language is not based solely on semantics, i.e. the meaning and combination of linguistic units.

Other parameters come into play, such as prosody, which includes pauses, accentuation and intonation.

Affective bursts -- ''Aaaah!'' or ''Oh!'' for example -- are also part of this, and we share these with our primate cousins.

They contribute to the meaning and understanding of our vocal communications.

When such a vocal message is emitted, these sounds are processed by the frontal and orbitofrontal regions of our brain.

The function of these two areas is, among other things, to integrate sensory and contextual information leading to a decision.

Are they activated in the same way when we are exposed to the emotional vocalisations of our close cousins the chimpanzees, macaques and bonobos?

Are we able to differentiate between them?

MRI scans with headphones on

A UNIGE team sought to find out by exposing a group of 25 volunteers to various human and simian vocalisations.

''The participants were placed in an MRI scanner and were given headphones.

After a short period of familiarisation with the different types of vocalisations, each participant had to categorise them, i.e. identify to which species they belonged,'' explains Leonardo Ceravolo, senior lecturer at the UNIGE's Faculty of Psychology and Educational Sciences, and first author of the study.

These vocalisations were of the affiliative type, i.e. linked to a positive interaction, or of the agonistic type, i.e. linked to a threat or distress.

The human vocalisations came from databases recorded by actors.

The simian ones came from field recordings made as part of previous research.

This study is the first of its kind to include bonobo vocalisations.

Bonobos, not so close cousins

The results show that for macaque and chimpanzee vocalisations, the frontal and orbitofrontal regions of the participants were activated in a similar way to human vocalisations.

The participants were able to differentiate between them easily.

On the other hand, when confronted with the ''sounds'' of bonobos, also close cousins of humans, the involved cerebral areas were much less activated, and categorisation was at chance level.

''It was thought that kinship between species -- the 'phylogenetic distance' -- was the main parameter for having the ability, or not, to recognise these different vocalisations.

We thought that the closer we were genetically, the more important this ability was,'' explains Didier Grandjean, full professor at the Swiss Center for Affective Sciences and at the UNIGE's Faculty of Psychology and Educational Sciences, who led the study.

''Our results show that a second parameter comes into play: acoustic distance.

The further the dynamics of the acoustic parameters, such as the frequencies used, are from those of humans, the less certain frontal regions are activated.

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Fossils tell tale of last primate to inhabit North America before humans

The story of Ekgmowechashala, the final primate to inhabit North America before Homo sapiens or Clovis people, reads like a spaghetti western: A grizzled and mysterious loner, against the odds, ekes out an existence on the American Plains.

Except this tale unfolded about 30 million years ago, just after the Eocene-Oligocene transition during which North America saw great cooling and drying, making the continent less hospitable to warmth-loving primates.

Today, paleontologists from the University of Kansas and the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing have published evidence in the Journal of Human Evolution shedding light on the long-standing saga of Ekgmowechashala, based on fossil teeth and jaws found in both Nebraska and China.

To do so, the researchers first had to reconstruct its family tree, a job helped by the discovery of an even more ancient Chinese "sister taxon" of Ekgmowechashala the team has named Palaeohodites (or "ancient wanderer"). The Chinese fossil discovery resolves the mystery of Ekgmowechashala's presence in North America, showing it was an immigrant rather than the product of local evolution.

"This project focuses on a very distinctive fossil primate known to paleontologists since the 1960s," said lead author Kathleen Rust, a doctoral candidate in paleontology at KU's Biodiversity Institute and Natural History Museum. "Due to its unique morphology and its representation only by dental remains, its place on the mammalian evolutionary tree has been a subject of contention and debate. There's been a prevailing consensus leaning towards its classification as a primate. But the timing and appearance of this primate in the North American fossil record are quite unusual. It appears suddenly in the fossil record of the Great Plains more than 4 million years after the extinction of all other North American primates, which occurred around 34 million years ago."

In the 1990s, Rust's doctoral adviser and co-author Chris Beard, KU Foundation Distinguished Professor and senior curator of vertebrate paleontology, collected fossils from the Nadu Formation in the Baise Basin in Guangxi, China, that closely resembled the Ekgmowechashala material known from North America. By that time, Ekgmowechashala was notoriously enigmatic among North American paleontologists.

"When we were working there, we had absolutely no idea that we would find an animal that was closely related to this bizarre primate from North America, but literally as soon as I picked up the jaw and saw it, I thought, 'Wow, this is it,'" Beard said. "It's not like it took a long time, and we had to undertake all kinds of detailed analysis -- we knew what it was. Here in KU's collection, we have some critical fossils, including what is still by far the best upper molar of Ekgmowechashala known from North America. That upper molar is so distinctive and looks quite similar to the one from China that we found that it kind of seals the deal."

Beard left it to Rust to conduct the morphological analysis that tied Ekgmowechashala and its cousin Palaeohodites from China in a phylogenetic tree to establish their evolutionary relationships.

In the course of the work, Rust was able to draw conclusions about how Ekgmowechashala came to be discovered in Nebraska, millions of years after its fellow primates died out in the continent's fossil record.

"We collected a substantial amount of morphological data to create an evolutionary tree using a phylogenetic reconstruction software and algorithm," Rust said. "This evolutionary tree suggests a close evolutionary relationship between North American Ekgmowechashala and Palaeohodites from China, which Chris and his colleagues discovered in the 1990s. The results from our analysis unequivocally supports this hypothesis."

The KU researchers said their discovery is not only exciting in terms of discovering a new primate species from late Eocene China -- but also in settling the origin story of Ekgmowechashala. Based on their investigation, Ekgmowechashala did not descend from an older North American primate that somehow survived the cooler and drier conditions that caused other North American primates to go extinct. Rather, its ancestors crossed over the Beringian region millions of years later, anticipating the route followed by the first Native Americans much later in time.

"Our analysis dispels the idea that Ekgmowechashala is a relic or survivor of earlier primates in North America," Rust said. "Instead, it was an immigrant species that evolved in Asia and migrated to North America during a surprisingly cool period, most likely via Beringia."

Species like Ekgmowechashala that show up suddenly in the fossil record long after their relatives have died off are referred to as "Lazarus taxa" after the biblical figure who was raised from the dead.

"The 'Lazarus effect' in paleontology is when we find evidence in the fossil record of animals apparently going extinct -- only to reappear after a long hiatus, seemingly out of nowhere," Beard said. "This is the grand pattern of evolution that we see in the fossil record of North American primates. The first primates came to North America about 56 million years ago at the beginning of the Eocene, and they flourished on this continent for more than 20 million years. But they went extinct when climate became cooler and drier near the Eocene-Oligocene boundary, about 34 million years ago. Several million years later Ekgmowechashala shows up like a drifting gunslinger in a Western movie, only to be a flash in the pan as far as the long trajectory of evolution is concerned. After Ekgmowechashala is gone for more than 25 million years, Clovis people come to North America, marking the third chapter of primates on this continent. Like Ekgmowechashala, humans in North America are a prime example of the Lazarus effect."

Rust and Beard were joined in the work by co-authors Xijun Ni of the Chinese Academy of Sciences, Beijing, and Kristen Tietjen, scientific illustrator with the KU Biodiversity Institute and Natural History Museum.

According to Rust, the tale of Ekgmowechashala is worth people's attention because it happened in an era of profound environmental and climatic changes, much like our own that's driven by human activity.

"It's crucial to comprehend how past biota reacted to such shifts," she said. "In such situations, organisms typically either adapt by retreating to more hospitable regions with available resources or face extinction. Around 34 million years ago, all of the primates in North America couldn't adapt and survive. North America lacked the necessary conditions for survival. This underscores the significance of accessible resources for our non-human primate relatives during times of drastic climatic change."

The study is also a part of a larger story that represents the earliest chapters of our own evolutionary journey that ultimately led to our own species, Rust said.

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New secrets about cat evolution revealed

Researchers at the Texas A&M School of Veterinary Medicine & Biomedical Sciences (VMBS) and an interdisciplinary team of collaborators have uncovered new information about the history of cat evolution explaining how cats -- including well-known species like lions, tigers, and domestic cats -- evolved into different species and shedding light on how different genetic changes in cats relate to survival abilities like the ability to smell prey.

By comparing genomes of several cat species, the project, published today in Nature Genetics, has helped researchers understand why cat genomes tend to have fewer complex genetic variations (such as rearrangements of DNA segments) than other mammal groups, like primates. It also revealed new insights into which parts of cat DNA are most likely to evolve rapidly and how they play a role in species differentiation.

"Our goal was to better understand how cats evolved and the genetic basis of the trait differences between cat species," said Dr. Bill Murphy, a VMBS professor of veterinary integrative biosciences who specializes in cat evolution. "We wanted to take advantage of some new technologies that allow us to create more complete cat genomic maps.

"Our findings will open doors for people studying feline diseases, behavior, and conservation," he said. "They'll be working with a more complete understanding of the genetic differences that make each type of cat unique."

Variations On A Theme

Among the things the scientists were trying to better understand is why feline chromosomes -- cellular structures containing the genetic information for traits like fur color, size, and sensory abilities -- are more stable than in other mammal groups.

"We've known for a while now that cat chromosomes across species are very similar to each other," Murphy said. "For example, the chromosomes of lions and domestic cats hardly differ at all. There appear to be far fewer duplications, rearrangements, and other types of variation than what are commonly found in great apes."

In the primate order, this kind of genetic variation has led to the evolution of different species -- including humans and great apes.

"The great ape genomes tend to break and rearrange, and even human genomes have very unstable regions," Murphy said. "These variations may predispose certain individuals to have genetic conditions, like autism and other neurological disorders."

The key to this variation between cats and apes, as Murphy found out, appears to be the frequency of something called segmental duplications -- segments of DNA that are highly similar copies of other DNA segments found elsewhere in the genome.

"Primate genome researchers have been able to link these segmental duplications to chromosome rearrangements," he said. The more segmental duplications you have in your DNA, the more likely the chromosomes are to rearrange, etc.

"What we discovered by comparing a large number of cat species genomes is that cats have just a fraction of the segmental duplications found in other mammal groups -- primates actually have seven times more of these duplications than cats. That's a big difference, and now we believe we understand why cat genomes are more stable," he said.

A Needle In A (Double) Helix

While cats may not have as many large genetic rearrangements in their DNA, they still have plenty of differences. Through their research, Murphy and his colleagues now better understand which parts of cat DNA cause those variations, especially the variations that define speciation, or the differences between species.

"It turns out that there's a large region on the center of the X chromosome where most of the genetic rearrangements are happening," Murphy said. "In fact, there's one specific repetitive element within this region called DXZ4 that evidence tells us is largely responsible for the genetic isolation of at least two cat species, the domestic and jungle cat."

DXZ4 is what Murphy calls a satellite repeat -- it's not a typical gene that codes for a physical trait like fur color, but, rather, it aids in the three-dimensional structure of the X chromosome and likely played an important role in cat speciation.

"We still don't know the precise mechanism, but by comparing all these cat genomes, we can better measure the rate at which DXZ4 evolved in one species compared to all the others. What we learned is that DXZ4 is one of the most rapidly evolving parts of the cat genome; it's evolving faster than 99.5% of the rest of the genome," he explained.

"Because of the rate at which it mutates, we were able to demonstrate why DXZ4 is probably linked to speciation," Murphy said.

Sniffing Out Elusive Genes

Using new, highly detailed genome sequences, the team also uncovered clearer links between the number of olfactory genes, which govern scent detection in cats and variation in social behavior and how they relate to their surroundings.

"Since cats are predators who rely heavily on smell to detect their prey, their sense of smell is a pretty important part of who they are," he said. "Cats are a very diverse family, and we've always wanted to understand how genetic variation plays a role in different cat species' ability to smell in their different environments.

"Lions and tigers have a pretty big difference between certain odorant genes involved in detecting pheromones, which are chemicals that different animals release into the environment to communicate information about identity, territory, or danger," Murphy said.

"We think the large difference has to do with lions being very social animals living in family groups and tigers living a solitary lifestyle. Lions may have a reduced reliance on pheromones and other odorants because they're constantly around other lions, reflected in the fewer genes of this type in their genomes," he said.

Tigers, on the other hand, need to be able to smell prey across very large territories as well as find mates.

"Tigers, in general, have large olfactory and pheromone receptor repertoires," Murphy said. "We think this is directly tied to the size of their territories and the variety of environments in which they live."

Domestic cats, on the other hand, appear to have lost a wide range of olfactory genes.

"If they don't have to travel as far to find what they need because they're living with people, it makes sense that natural selection wouldn't preserve those genes," he said.

Murphy shared that his favorite example from the project is the odorant receptors from the fishing cat, an aquatically adapted wild cat species living in Southeast Asia.

"We were able to show that fishing cats have retained many genes for detecting waterborne odorants, which is a pretty rare trait in terrestrial vertebrates," he said. "All of the other cat species have lost these specific genes over time, but fishing cats still have them."

This new information about olfactory genes in cats was made possible through a new approach to genome sequencing called trio binning, which allows researchers to sequence the most difficult regions of a genome.

This new technology also makes separating maternal and paternal DNA much easier.

"With trio binning, you can now take DNA from an F1 hybrid -- an animal whose DNA is split 50-50 between parents of different species -- and cleanly separate the maternal and paternal DNA, giving you two complete sets of DNA, one for each parent species," Murphy said. "The process is much simpler, and the results are more complete."

Filling In The Blanks

One of the most important conclusions from the project is that cat species may be similar in many ways, but their differences matter.

"These differences are showing us how these animals are perfectly suited for their natural environments," Murphy said. "They're not interchangeable, and that's valuable information for conservationists and others working to preserve or restore species in their natural habitats.

"For example, you can't assume that tigers from Sumatra and Siberia are the same," he said. "Their environments are wildly different, and those tiger populations have likely developed specialized genetic adaptations to help them survive in these very different places."

It's also important for scientists to realize that the sections of genomes that are the most difficult to assemble may just be the key to understanding crucial bodily systems like immunity and reproduction.

"Olfactory genes aren't the only ones that have been challenging to sequence and study. Scientists have also struggled to sequence immune and reproductive genes, so previous studies are missing this kind of information. Imagine trying to study a genetic condition in cats, humans, or any species, for that matter, without having all the pieces; this is why assembling complete genomes matters," Murphy said.

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Scientists unveil detailed cell maps of the human brain and the nonhuman primate brain

A group of international scientists have mapped the genetic, cellular, and structural makeup of the human brain and the nonhuman primate brain. This understanding of brain structure, achieved by funding through the National Institutes of Health's Brain Research Through Advancing Innovative Neurotechnologies® Initiative, or The BRAIN Initiative®, allows for a deeper knowledge of the cellular basis of brain function and dysfunction, helping pave the way for a new generation of precision therapeutics for people with mental disorders and other disorders of the brain. The findings appear in a compendium of 24 papers across Science, Science Advances, and Science Translational Medicine.

"Mapping the brain's cellular landscape is a critical step toward understanding how this vital organ works in health and disease," said Joshua A. Gordon, M.D., Ph.D., director of the National Institute of Mental Health. "These new detailed cell atlases of the human brain and the nonhuman primate brain offer a foundation for designing new therapies that can target the specific brain cells and circuits involved in brain disorders."

The 24 papers in this latest BRAIN Initiative Cell Census Network (BICCN) collection detail the exceptionally complex diversity of cells in the human brain and the nonhuman primate brain. The studies identify similarities and differences in how cells are organized and how genes are regulated in the human brain and the nonhuman primate brain. For example:

• Three papers in the collection present the first atlas of cells in the adult human brain, mapping the transcriptional and epigenomic landscape of the brain. The transcriptome is the complete set of gene readouts in a cell, which contains instructions for making proteins and other cellular products. The epigenome refers to chemical modifications to a cell's DNA and chromosomes that alter the way the cell's genetic information is expressed.
• In another paper, a comparison of the cellular and molecular properties of the human brain and several nonhuman primate brains (chimpanzee, gorilla, macaque, and marmoset brains) revealed clear similarities in the types, proportions, and spatial organization of cells in the cerebral cortex of humans and nonhuman primates. Examination of the genetic expression of cortical cells across species suggests that relatively small changes in gene expression in the human lineage led to changes in neuronal wiring and synaptic function that likely allowed for greater brain plasticity in humans, supporting the human brain's ability to adapt, learn, and change.
• A study exploring how cells vary in different brain regions in marmosets found a link between the properties of cells in the adult brain and the properties of those cells during development. The link suggests that developmental programming is embedded in cells when they are formed and maintained into adulthood and that some observable cellular properties in an adult may have their origins very early in life. This finding could lead to new insights into brain development and function across the lifespan.
• An exploration of the anatomy and physiology of neurons in the outermost layer of the neocortex -- part of the brain involved in higher-order functions such as cognition, motor commands, and language -- revealed differences in the human brain and the mouse brain that suggest this region may be an evolutionary hotspot, with changes in humans reflecting the higher demands of regulating humans' more complex brain circuits.

The core aim of the BICCN, a groundbreaking effort to understand the brain's cellular makeup, is to develop a comprehensive inventory of the cells in the brain -- where they are, how they develop, how they work together, and how they regulate their activity -- to better understand how brain disorders develop, progress, and are best treated.

"This suite of studies represents a landmark achievement in illuminating the complexity of the human brain at the cellular level," said John Ngai, Ph.D., director of the NIH BRAIN Initiative. "The scientific collaborations forged through BICCN are propelling the field forward at an exponential pace; the progress -- and possibilities -- have been simply breathtaking."

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Size does matter: Group size and mating preferences drive deeper male voices

Deeper male voices in primates, including humans, offer more than sex appeal -- they may have evolved as another way for males to drive off competitors in large groups that favored polygyny, or mating systems where a male has multiple mates, according to researchers. The research is the most comprehensive investigation of differences in vocal pitch between sexes to date and has the potential to help to shed light on social behavior in humans and their closest living relatives.

The average speaking pitch of an adult male human is about half the average pitch, an octave lower, than that of an adult female human, said David Puts, professor of anthropology at Penn State and study co-author.

"It's a sex difference that emerges at sexual maturity across species and it probably influences mating success through attracting mates or by intimidating competitors," he said. "I thought it has to be a trait that's been subjected to sexual selection, in which mating opportunities influence which traits are passed down to offspring. Humans and many other primates are highly communicative, especially through vocal communication. So it seems like a really relevant trait for thinking about social behavior in humans and primates in general."

The researchers used specialized computer software to visualize vocalizations and measure voice pitch in recordings from 37 anthropoid primate species, or those most closely related to humans, including gorillas, chimpanzees and recordings of 60 humans evenly divided by sex. Samples for each species included at least two male and two female vocal recordings, for a total of 1,914 vocalizations. The team then calculated average male and female vocal fundamental frequency for each species to see how pronounced the difference was between sexes.

The scientists collected additional information for each species to help identify correlations between male versus female voice pitch and factors that could have contributed to the trait's evolution. Additional variables included body size and body mass differences between males and females, habitat type, adult sex ratios, mating competition intensity and testes size. They also categorized each species by mating system -- monogamous, in which males and females have one mate at a time; polygynandrous, in which males and females have multiple mating partners; and polygynous, in which some males have several mates.

The researchers used these data to test five hypotheses simultaneously to identify which factors may have played the strongest roles in driving sex differences in vocal pitch. The hypotheses were: intensity of mating competition, large group size, multilevel social organization, trade-off against the intensity of sperm competition, and poor acoustic habitats. Previous research has looked at one or two of these hypotheses at a time. The current study is the first to test multiple hypotheses simultaneously for vocal pitch differences using a robust dataset, ensuring data consistency and garnering convincing results, according to Puts.

The team found that fundamental frequency differences by sex increased in larger groups and those with polygynous mating systems, especially in groups with a higher female-to-male ratio. They reported their findings today (July 10) in Nature Communications.

"Our findings highlight the important role of sexual selection and offer possible evolutionary explanations for why males and females differ in voice pitch across primates," said Toe Aung, first author and assistant professor of psychology and counseling at Immaculata University, who worked on the study as part of his doctoral dissertation at Penn State. "This research also provides insight into sex differences in voice pitch in our common ancestors who lived millions of years ago."

Deeper male voices may act as an additional way to fend off mating competitors without having to engage in costly fighting by making males sound bigger, in addition to other physical traits like height and muscle size, according to the researchers. In adult humans, for instance, males vocalize at an average of 120 hertz whereas females vocalize at an average of about 220 hertz, putting humans right in the middle of polygynous societies, the researchers reported.

"Although social monogamy is really common in humans, mating and reproduction in our ancestors was substantially polygynous," Puts said. "Our findings help us to understand why male and female voices of our species differ so drastically. It may be a product of our evolutionary history, particularly our history of living in large groups in which some males reproduced with multiple females."

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Genomes of 233 primate species sequenced

Researchers from 24 countries have analyzed the genomes of 809 individuals from 233 primate species, generating the most complete catalog of genomic information about our closest relatives to date. The project, which consists of a series of studies in which researchers from the German Primate Center -- Leibniz Institute for Primate Research (DPZ) were also involved, provides new insights into the evolution of primates, including humans, and their diversity. In baboons, for example, hybridization and gene flow between different species occurred in the past and is still ongoing in several regions of their range. This makes baboons a good model for the evolution of early human lineages within and outside Africa. In addition, using a specially designed AI algorithm, the genomic data enable new insights into the genetic causes of human diseases (Science, Special Issue).

Primates show great genetic diversity that varies between species and geographic regions. "Studying this diversity is crucial also for understanding human evolution, the causes of human diseases, and for preserving our closest relatives," says Christian Roos, a scientist in the Primate Genetics Laboratory at the German Primate Center and one of the authors. Led by researchers from Universitat Pompeu Fabra, Spain, Baylor College of Medicine, USA, and Illumina Inc, USA, the genomes of 809 individuals from 233 primate species have been sequenced. This covers nearly half of the extant primate species and increases the number of available primate genomes fourfold.

New insights into primate evolution and the uniqueness of humans

The comparative analyses provide fundamental information on the genetic diversity and evolutionary history of primates and important insights into what distinguishes humans from other primates. The genomic data have halved the number of genomic variants thought to occur exclusively in humans. "This makes it easier to look for mutations that we do not share with other primates and that could therefore be the basis for the traits that make us human," says Dietmar Zinner, a scientist in the Cognitive Ethology Laboratory at the German Primate Center and also one of the authors. One of the studies looks more closely at baboon evolution and finds that there have been several, previously unknown episodes of hybridization and gene flow between baboon species. "We found that baboons from western Tanzania are the first nonhuman primates to have received input from three genetic lineages," said Liye Zhang, a doctoral student at the German Primate Center and one of the lead authors of the baboon study. "These results suggest that the genetic structure of the baboon population and its history of genetic exchange between species is more complex than previously thought and show that baboons make a good model for similar processes in the evolution of early human lineages in and outside Africa," says Dietmar Zinner.

Species conservation with the help of genome data

High genetic diversity enables species to better adapt to changing environmental conditions and pathogens. Especially in small populations, there is a risk of inbreeding and thus a reduction in genetic diversity. Already, 63 percent of all primate species are threatened with extinction, and the analysis of genetic diversity provides information which species most urgently need to be protected, at least from a genetic point of view. "We found particularly low genetic diversity in the golden snub-nosed monkey of China and the aye-aye in Madagascar," says Christian Roos.

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Information 'deleted' from the human genome may be what made us human

What the human genome is lacking compared with the genomes of other primates might have been as crucial to the development of humankind as what has been added during our evolutionary history, according to a new study led by researchers at Yale and the Broad Institute of MIT and Harvard.

The new findings, published April 28 in the journal Science, fill an important gap in what is known about historical changes to the human genome. While a revolution in the capacity to collect data from genomes of different species has allowed scientists to identify additions that are specific to the human genome -- such as a gene that was critical for humans to develop the ability to speak -- less attention has been paid to what's missing in the human genome.

For the new study researchers used an even deeper genomic dive into primate DNA to show that the loss of about 10,000 bits of genetic information -- most as small as a few base pairs of DNA -- over the course of our evolutionary history differentiate humans from chimpanzees, our closest primate relative. Some of those "deleted" pieces of genetic information are closely related to genes involved in neuronal and cognitive functions, including one associated with the formation of cells in the developing brain.

These 10,000 missing pieces of DNA -- which are present in the genomes of other mammals -- are common to all humans, the Yale team found.

The fact that these genetic deletions became conserved in all humans, the authors say, attests to their evolutionary importance, suggesting that they conferred some biological advantage.

"Often we think new biological functions must require new pieces of DNA, but this work shows us that deleting genetic code can result in profound consequences for traits make us unique as a species," said Steven Reilly, an assistant professor of genetics at Yale School of Medicine and senior author of the paper.

The paper was one of several published in Science from the Zoonomia Project, an international research collaboration that is cataloging the diversity in mammalian genomes by comparing DNA sequences from 240 species of mammals that exist today.

In their study, the Yale team found that some genetic sequences found in the genomes of most other mammal species, from mice to whales, vanished in humans. But rather than disrupt human biology, they say, some of these deletions created new genetic encodings that eliminated elements that would normally turn genes off.

The deletion of this genetic information, Reilly said, had an effect that was the equivalent of removing three characters -- "n't" -- from the word "isn't" to create a new word, "is."

"[Such deletions] can tweak the meaning of the instructions of how to make a human slightly, helping explain our bigger brains and complex cognition," he said.

The researchers used a technology called Massively Parallel Reporter Assays (MPRA), which can simultaneously screen and measure the function of thousands of genetic changes among species.

Read more at Science Daily

1,700-year-old spider monkey remains discovered in Teotihuacán, Mexico

The complete skeletal remains of a spider monkey -- seen as an exotic curiosity in pre-Hispanic Mexico -- grants researchers new evidence regarding social-political ties between two ancient powerhouses: Teotihuacán and Maya Indigenous rulers.

The discovery was made by Nawa Sugiyama, a UC Riverside anthropological archaeologist, and a team of archaeologists and anthropologists who since 2015 have been excavating at Plaza of Columns Complex, in Teotihuacán, Mexico. The remains of other animals were also discovered, as well as thousands of Maya-style mural fragments and over 14,000 ceramic sherds from a grand feast. These pieces are more than 1,700 years old.

The spider monkey is the earliest evidence of primate captivity, translocation, and gift diplomacy between Teotihuacán and the Maya. Details of the discovery will be published in the journal PNAS. This finding allows researchers to piece evidence of high diplomacy interactions and debunks previous beliefs that Maya presence in Teotihuacán was restricted to migrant communities, said Sugiyama, who led the research.

"Teotihuacán attracted people from all over, it was a place where people came to exchange goods, property, and ideas. It was a place of innovation," said Sugiyama, who is collaborating with other researchers, including Professor Saburo Sugiyama, co-director of the project and a professor at Arizona State University, and Courtney A. Hofman, a molecular anthropologist with the University of Oklahoma. "Finding the spider monkey has allowed us to discover reassigned connections between Teotihuacán and Maya leaders. The spider monkey brought to life this dynamic space, depicted in the mural art. It's exciting to reconstruct this live history."

Researchers applied a multimethod archaeometric (zooarchaeology, isotopes, ancient DNA, paleobotany, and radiocarbon dating) approach to detail the life of this female spider monkey. The animal was likely between 5 and 8 years old at the time of death.

Its skeletal remains were found alongside a golden eagle and several rattlesnakes, surrounded by unique artifacts, such as fine greenstone figurines made of jade from the Motagua Valley in Guatemala, copious shell/snail artifacts, and lavish obsidian goods such as blades and projectiles points. This is consistent with evidence of live sacrifice of symbolically potent animals participating in state rituals observed in Moon and Sun Pyramid dedicatory caches, researchers stated in the paper.

Results from the examination of two teeth, the upper and lower canines, indicate the spider monkey in Teotihuacán ate maize and chili peppers, among other food items. The bone chemistry, which offers insight to the diet and environmental information, indicates at least two years of captivity. Prior to arriving in Teotihuacán, it lived in a humid environment, eating primarily plants and roots.

The research is primarily funded by grants awarded to Sugiyama from the National Science Foundation and National Endowment for the Humanities. Teotihuacán is a pre-Hispanic city recognized as an UNESCO World Heritage site and receives more than three million visitors annually.

In addition to studying ancient rituals and uncovering pieces of history, the finding allows for a reconstruction of greater narratives, of understanding how these powerful, advanced societies dealt with social and political stressors that very much reflect today's world, Sugiyama said.

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Differences between brains of primates are small but significant, study shows

While the physical differences between humans and non-human primates are quite distinct, a new study reveals their brains may be remarkably similar. And yet, the smallest changes may make big differences in developmental and psychiatric disorders.

Understanding the molecular differences that make the human brain distinct can help researchers study disruptions in its development. A new study, published recently in the journal Science by a team including University of Wisconsin-Madison neuroscience professor Andre Sousa, investigates the differences and similarities of cells in the prefrontal cortex -- the frontmost region of the brain, an area that plays a central role in higher cognitive functions -- between humans and non-human primates such as chimpanzees, Rhesus macaques and marmosets.

The cellular differences between these species may illuminate steps in their evolution and how those differences can be implicated in disorders, such as autism and intellectual disabilities, seen in humans. Sousa, who studies the developmental biology of the brain at UW-Madison's Waisman Center, decided to start by studying and categorizing the cells in the prefrontal cortex in partnership with the Yale University lab where he worked as a postdoctoral researcher.

"We are profiling the dorsolateral prefrontal cortex because it is particularly interesting. This cortical area only exists in primates. It doesn't exist in other species," Sousa says. "It has been associated with several relevant functions in terms of high cognition, like working memory. It has also been implicated in several neuropsychiatric disorders. So, we decided to do this study to understand what is unique about humans in this brain region."

Sousa and his lab collected genetic information from more than 600,000 prefrontal cortex cells from tissue samples from humans, chimpanzees, macaques and marmosets. They analyzed that data to categorize the cells into types and determine the differences in similar cells across species. Unsurprisingly, the vast majority of the cells were fairly comparable.

"Most of the cells are actually very similar because these species are relatively close evolutionarily," Sousa says.

Sousa and his collaborators found five cell types in the prefrontal cortex that were not present in all four of the species. They also found differences in the abundancies of certain cell types as well as diversity among similar cell populations across species. When comparing a chimpanzee to a human the differences seem huge -- from their physical appearances down to the capabilities of their brains. But at the cellular and genetic level, at least in the prefrontal cortex, the similarities are many and the dissimilarities sparing.

"Our lab really wants to know what is unique about the human brain. Obviously from this study and our previous work, most of it is actually the same, at least among primates," Sousa says.

The slight differences the researchers found may be the beginning of determining some of those unique factors, and that information could lead to revelations about development and developmental disorders at a molecular level.

"We want to know what happened after the evolutionary split between humans and other primates," Sousa says. "The idea is you have a mutation in a gene or in several genes and those genes now have slightly different functions. But if these genes are relevant for brain development, for example, how many of a certain cell is produced, or how cells are connecting to other cells, how is it affecting the neuronal circuitry and their physiological properties? We want to understand how these differences lead to differences in the brain and then lead to differences we can observe in adults."

The study's observations were made in the brains of adults, after much of the development is complete. This means that the differences may be occurring during the brain's development. So, the researchers' next step is to study samples from developing brains and extend their area of investigation past the prefrontal cortex to potentially find where and when these differences originate. The hope is that this information will lead to a more robust foundation to lay developmental disorder research on top of.

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What makes the human brain different? Study reveals clues

What makes the human brain distinct from that of all other animals -- including even our closest primate relatives? In an analysis of cell types in the prefrontal cortex of four primate species, Yale researchers identified species-specific -- particularly human-specific -- features, they report Aug. 25 in the journal Science.

And they found that what makes us human may also makes us susceptible to neuropsychiatric diseases.

For the study, the researchers looked specifically at the dorsolateral prefrontal cortex (dlPFC), a brain region that is unique to primates and essential for higher-order cognition. Using a single cell RNA-sequencing technique, they profiled expression levels of genes in hundreds of thousands of cells collected from the dlPFC of adult humans, chimpanzees, macaque, and marmoset monkeys.

"Today, we view the dorsolateral prefrontal cortex as the core component of human identity, but still we don't know what makes this unique in humans and distinguishes us from other primate species." said Nenad Sestan, the Harvey and Kate Cushing Professor of Neuroscience at Yale, professor of comparative medicine, of genetics. and of psychiatry, and the lead senior author of the paper. "Now we have more clues."

To answer this, the researchers first asked whether there are there any cell types uniquely present in humans or other analyzed non-human primate species. After grouping cells with similar expression profiles they revealed 109 shared primate cell types but also five that were not common to all species. These included a type of microglia, or brain-specific immune cell, that was present only in humans and a second type shared by only humans and chimpanzees.

The human-specific microglia type exists throughout development and adulthood, the researchers found, suggesting the cells play a role in maintenance of the brain upkeep rather than combatting disease.

"We humans live in a very different environment with a unique lifestyle compared to other primate species; and glia cells, including microglia, are very sensitive to these differences," Sestan said. "The type of microglia found in the human brain might represent an immune response to the environment."

An analysis of gene expression in the microglia revealed another human-specific surprise -- the presence of the gene FOXP2. This discovery raised great interest because variants of FOXP2 have been linked to verbal dyspraxia, a condition in which patients have difficulty producing language or speech. Other studies have also shown that FOXP2 is associated with other neuropsychiatric diseases, such as autism, schizophrenia, and epilepsy.

Sestan and colleagues found that this gene exhibits primate-specific expression in a subset of excitatory neurons and human-specific expression in microglia.

"FOXP2 has intrigued many scientists for decades, but still we had no idea of what makes it unique in humans versus other primate species," said Shaojie Ma, a postdoctoral associate in Sestan's lab and co-lead author. We are extremely excited about the FOXP2 findings because they open new directions in the study of language and diseases."

Read more at Science Daily

How anesthetics affect brain functions

Modern anesthesia is one of the most important medical achievements. Whereas before, patients had to suffer hellish agonies during every operation, today anesthesia enables completely painless procedures. One feels nothing and can remember nothing afterwards. It is already known from electroencephalography (EEG) studies on patients that during anesthesia the brain is put into a deep sleep-like state in which periods of rhythmic electrical activity alternate with periods of complete inactivity. This state is called burst-suppression. Until now, it was unclear where exactly this state happens in the brain and which brain areas are involved.

However, this question is important to better understand the phenomenon and thus how the brain functions under anesthesia. Researchers from the Functional Imaging Unit at the German Primate Center (DPZ) -- Leibniz Institute for Primate Research in Göttingen have used functional magnetic resonance imaging (fMRI) to study the precise spatial distribution of synchronously working brain regions in anesthetized humans, long-tailed macaques, common marmosets and rats. They were able to show for the first time that the areas where burst-suppression is evident differ significantly in primates and rodents. While in rats large parts of the cerebral cortex synchronously show the burst-suppression pattern, in primates individual sensory regions, such as the visual cortex, are excluded from it.

"Our brain can be thought of as a full soccer stadium when we are awake," explains Nikoloz Sirmpilatze, a scientist in the Functional Imaging Unit and lead author of the study. "Our active neurons are like tens of thousands of spectators all talking at once. Under anesthesia, however, neuronal activity is synchronized. You can measure this activity using EEG as uniform waves, as if all the spectators in the stadium were singing the same song. In deep anesthesia, this song is repeatedly interrupted by periods of silence. This is called burst-suppression. The deeper the anesthesia, the shorter the phases of uniform activity, the bursts, and the longer the periodically recurring inactive phases, the so-called suppressions."

The phenomenon is caused by many different anesthetics, some of which vary in their mechanisms of action. And burst-suppression is also detectable in coma patients. However, it is not known whether this condition is a protective reaction of the brain or a sign of impaired functioning. It has also been unclear where in the brain burst-suppression occurs and which brain areas are involved, as localization by EEG alone is not possible.

To answer this question, Nikoloz Sirmpilatze and the researcher team used the imaging technique of fMRI. The method makes blood flow changes in the brain visible. The increased activity of neurons in a particular area of the brain leads to an increase in metabolism, followed by an increased blood and oxygen supply at this location, which is ultimately visible in the fMRI image.

In the first part of the study, the researchers established a system to evaluate fMRI data in humans, monkeys and rodents in a standardized manner using the same method. To do this, they used simultaneously-measured EEG and fMRI data from anesthetized patients that had been generated in a previously conducted study at the Technical University of Munich. "We first looked to see whether the burst-suppression detected in the EEG was also visible in the fMRI data and whether it showed a certain pattern," says Nikoloz Sirmpilatze. "Based on that, we developed a new algorithm that allowed detecting burst-suppression events in the experimental animals using fMRI, without additional EEG measurement."

The researchers then performed fMRI measurements in anesthetized long-tailed macaques, common marmosets and rats. In all animals, they were able to detect and precisely localize burst-suppression as a function of anesthetic concentration. The spatial distribution of burst-suppression showed that in both humans and monkey species, certain sensory areas, such as the visual cortex, were excluded from it. In contrast, in the rats, the entire cerebral cortex was affected by burst-suppression.

"At the moment, we can only speculate about the reasons," says Nikoloz Sirmpilatze, who was awarded the German Primate Center's 2021 PhD Thesis Award for his work. "Primates orient themselves mainly through their sense of sight. Therefore, the visual cortex is a highly specialized region that differs from other brain areas by special cell types and structures. In rats, this is not the case. In future studies, we will investigate what exactly happens in these regions during anesthesia to ultimately understand why burst-suppression is not detectable there with fMRI."

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Ecotourism is having a negative effect on primate's behavior

New research shows that the increase in primate ecotourism is having a negative effect on monkey's behaviour.

The study, led by the University of Portsmouth, found that this fast-growing tourism sector where tourists can conveniently reach primates via motor boats is causing stress-related behaviours in monkeys.

The research looked at the impact of a single engine motor boat approaching a community of proboscis monkeys, an endangered species living in a remote riparian area (strips of vegetation that border rivers, streams and lakes) in Sabah, Malaysia. Proboscis monkeys are unusual looking with their very long noses, which adds to making them appealing to tourists.

Many of these boats, carrying multiple tourists, approach the primates quickly and loudly, often reaching the river banks just a few metres away from the wildlife.

The researchers found that frequent visits by such groups, which often involve an unusually high level of noise, caused stress-related behaviours in the primates such as self-scratching, an increased vigilant state, increased levels of aggression and reduced feeding.

Lead author of the study, Dr Marina Davila-Ross, Reader in Comparative Psychology at the University of Portsmouth, said: "Our evidence shows that even a single motor boat moving slowly, with humans behaving calmly, can negatively affect the primate's behaviour and induce stress -- an impact that is likely to be larger with tourist boats.

"The riparian area is an important habitat that has become increasingly popular to primate ecotourism, because it enables tourists to conveniently reach primates via motor boats."

The researchers conducted the experiment by approaching the monkeys in a motor boat with different speeds and travel distances -- fast-close (approaching the monkeys for 10 seconds when 40 metres away at a speed of 14.4 km/hr), slow-close (approaching the monkey for 40 seconds when 40 metres away at a speed of 3.6 km/hr), and slow-far conditions (approaching the monkeys for 20 seconds when 100 metres away, at a speed of 3.6 km/hr). For each condition, they compared stress-related behaviours before the boat approached with after the boat started its approach.

The results showed that the monkeys displayed stress-related behaviours for longer in the fast-close and slow-close conditions and also reduced feeding as a result of the boat approaching in the fast-close condition. They also found that male proboscis monkeys displayed more vigilant behaviour than females.

Once the boat started to approach, the proboscis monkeys gazed at the boat for longer than before the boat approached, showed repeated scratching, and often moved quickly backwards to hide in the trees. This could potentially cause the monkeys to leave their safe sleeping sites and to retreat deep into the forest as it gets dark, where they could face a higher risk of predation.

Dr Davila-Ross said: "Collectively, our findings suggest that the approach of a single motor boat induces stress in proboscis monkeys when approaching them as closely as 60 metres from the other side of the river, regardless of the speed of approach. The findings match those obtained in studies on sea mammals and birds, suggesting that stress is a universal response across animals when a boat approaches -- a large, loud, and artificial object moving toward them is likely to be threatening."

The researchers propose that guidelines for primate tourism in the riparian areas, which are largely unregulated, should include an approach speed of no more than 4 km/hr within 100 metres of the proboscis monkeys. They suggest it is also important to keep a distance, preferably no closer than 60 metres away, from the monkeys.

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Human fetuses evolved to slow shoulder growth for easier delivery

Why do human mothers have a much harder time giving birth compared to our evolutionary cousins, the chimpanzees and macaques?

The differences are a big head and wide shoulders. But it has made all the difference for safer births.

"The question is actually two-fold, " says study author Naoki Morimoto of Kyoto University. "What also makes childbirth difficult for women is the relatively narrow pelvis."

Morimoto's team discovered two central aspects of the female human skeletal anatomy that deserve attention when discussing the evolution of childbirth.

The first comes with its own set of points: initially, the growth of human shoulders slows down just before birth and speeds up thereafter; next, this phenomenon alleviates the problem of shoulder dystocia, where the shoulders interfere with safe passage of the fetus through the birth canal.

"It is important to note that the second point reconciles the incompatibility of wide shoulders with the narrow birth canal. The shoulders show an 'intelligent' modification in fetal development," notes lead author PhD candidate Mikaze Kawada.

What makes a human skeletal makeup 'human' in terms of the head and shoulders is size proportionality to the pelvis. Our largely developed brains have resulted in large heads, and our wide shoulders explain bipedal stability and an ability to throw objects far.

On the other hand, the need to make walking more efficient reduced the size of the pelvis as our ancestors treaded farther and more frequently.

Morimoto and his team used computed tomography to obtain cross-sectional representations of the clavicle in humans, chimpanzees, and Japanese macaques from fetal to adult samples.

The team then looked at different shoulder-width to birth-risk correlations between humans and the two other primates. Chimpanzees have proportionally large shoulders and yet, like macaques, fewer shoulder-related birth complications. Since chimpanzees move about less frequently on two feet, their pelvis -- and therefore their birth canal -- is larger than that of their human counterparts.

"We surmise that the wide shoulders, relative to the pelvis of our ancestors, emerged simultaneously with the narrower pelvis as we became fully bipedal," says Morimoto, "but before the brain evolved to today's size."

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Tooth cavities provide unique ecological insight into living primates and fossil humans

Tooth decay is a common and unfortunate problem for many of us, but two University of Otago studies show it is also an issue for other primates, as well as our fossil relatives and ancestors.

Dr Ian Towle, the former Sir Thomas Sidey Postdoctoral Fellow in Otago's Faculty of Dentistry, says cavities are often considered to be a modern disease unique to humans, related to a diet rich in processed sugary foods. However, he says there is growing evidence tooth decay also occurs to a certain extent in other animal groups.

"Our new research shows caries also occurs in wild primates in low frequencies, although this is highly variable among groups and the teeth affected also vary," he says.

"This research helps us understand changes in diet and behaviour in human evolution; it also provides insight into particular behaviours in our living primate relatives."

For the research, published in the American Journal of Primatology and South African Journal of Science, Dr Towle and colleagues analysed more than 8000 extant primate and fossil human teeth and assessed variation in tooth decay patterns in relation to diet and behaviour.

They found 3.3 per cent of teeth in living primates had caries, which is similar to the incidence in fossil humans (ranging from 1 to 4 per cent of teeth in different species). However, all caries in the fossil humans samples studied were on back teeth, whereas the vast majority in living primates were on the front teeth.

"The fascinating feeding behaviours of animals such as chimpanzees, using their large front teeth to help suck sugary liquid out of figs, contributes to creating caries patterns rarely seen in humans.

"Indeed, in humans our back teeth are mostly affected by dental decay, whereas in other primates it's typically the front teeth," Dr Towle says.

Another interesting aspect of this research was that female chimpanzees had more caries than males (9.3 per cent compared to 1.8 per cent), with similar sex differences often evident in humans.

The work also revealed how similar decay patterns between captive primates and humans are, highlighting how primates often don't undertake specific natural behaviours in captivity.

"Caries occurred throughout human evolution and that doesn't seem to change much for millions of years, with less than 5 per cent of teeth affected. However, with the onset of agriculture, this increased rapidly to more than 20 per cent of teeth having cavities in some samples."

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What big teeth you have: Tooth root surface area can determine primate size

An often overlooked feature could give scientists new insight into the lives of ancient primate species. Researchers from North Carolina State University have developed formulas that can calculate the body size of a primate based on the root size of its teeth. The formulas could allow researchers to make use of partial and incomplete fossils in order to learn how ancient primates -- including human ancestors -- interacted with their environment.

Ashley Deutsch, NC State graduate student and first author of a paper describing the research, wanted to know if it was possible to determine what a primate's diet was without having the actual tooth crowns at hand -- by looking instead at the roots.

What we commonly think of when we think of teeth isn't the whole story -- the part that does the chewing is merely the crown. The part that keeps the tooth anchored in the jaw is the root.

"The tooth root transmits the force of the jaws into the food," says Adam Hartstone-Rose, professor of biological sciences at NC State and paper coauthor. "You can think of the root as the handle of a hammer -- the handle size is related to the amount of force you can put into the hammer. So if a hammer has a small handle, it will have a small head to hammer small things. In the same way, a big tooth root can transmit more force to the tooth's crown to crush more obdurate foods."

Deutsch and the research team initially set out to determine whether tooth roots could indicate the shape of the tooth's crown, thus telling them what particular primates preferred to eat. Using computer tomography, Deutsch analyzed and calculated the tooth root surface area -- or area of contact where the root fits into the jaw -- of 70 primates from 75 species, ranging in size from tiny mouse lemurs to great apes.

"It was a bit like trying to figure out if you have an axe or hammer based on the shape of the handle," Deutsch says.

Ultimately, she found that the tooth roots only related to diet in a few lineages (for example, lemurs); however, she was able to determine how big the primates were across all lineages.

Deutsch developed a series of formulas based on the relationship between the tooth root surface of a molar or premolar -- the teeth located between canines and molars -- and primate body mass. The formulas can be used to estimate body mass of primates with more or less specificity, depending upon whether their class is known. The formulas can also explain up to 96% of variation in body mass within the examined primate sample.

But perhaps the most useful application of the equation will be with fossils that are currently of little use to anthropologists and paleontologists.

"As long as the fossil has a bit of root you can use the formulas even if the tooth crowns are missing," Deutsch says. "Fossils are often maddeningly incomplete, but now those incomplete pieces can be useful, and they could answer questions about our own lineage, like how big our ancient ancestors were."

Deutsch hopes to continue refining the existing equations and expand the work beyond primates to other mammals, including carnivores.

"Ashley has looked at something that is often preserved but also generally ignored by science and found it might hold answers to one of the most important ecological questions," Hartstone-Rose says. "Just knowing how big an animal is tells you a lot about how it interacted with the environment. And that could give us a lot of insight into our own ancient history."

Read more at Science Daily

That primate’s got rhythm!

Songbirds share the human sense of rhythm, but it is a rare trait in non-human mammals. An international research team led by senior investigators Marco Gamba from the University of Turin and MPI’s Andrea Ravignani set out to look for musical abilities in primates. “There is longstanding interest in understanding how human musicality evolved, but musicality is not restricted to humans”, says Ravignani. “Looking for musical features in other species allows us to build an ‘evolutionary tree’ of musical traits, and understand how rhythm capacities originated and evolved in humans.”

To find out whether non-human mammals have a sense of rhythm, the team decided to study one of the few ‘singing’ primates, the critically endangered lemur Indri indri. The researchers wanted to know whether indri songs have categorical rhythm, a ‘rhythmic universal’ found across human musical cultures. Rhythm is categorical when intervals between sounds have exactly the same duration (1:1 rhythm) or doubled duration (1:2 rhythm). This type of rhythm makes a song easily recognisable, even if it is sung at different speeds. Would indri songs show this “uniquely human” rhythm?

Ritardando in the rainforest

Over a period of twelve years, the researchers from Turin visited the rainforest of Madagascar to collaborate with a local primate study group. The investigators recorded songs from twenty indri groups (39 animals), living in their natural habitat. Members of an indri family group tend to sing together, in harmonised duets and choruses. The team found that indri songs had the classic rhythmic categories (both 1:1 and 1:2), as well as the typical ‘ritardando’ or slowing down found in several musical traditions. Male and female songs had a different tempo but showed the same rhythm.

According to first author Chiara de Gregorio and her colleagues, this is the first evidence of a ‘rhythmic universal’ in a non-human mammal. But why should another primate produce categorical ‘music-like’ rhythms? The ability may have evolved independently among ‘singing’ species, as the last common ancestor between humans and indri lived 77.5 million years ago. Rhythm may make it easier to produce and process songs, or even to learn them.

Endangered species

“Categorical rhythms are just one of the six universals that have been identified so far”, explains Ravignani. “We would like to look for evidence of others, including an underlying ‘repetitive’ beat and a hierarchical organisation of beats—in indri and other species.” The authors encourage other researchers to gather data on indri and other endangered species, “before it is too late to witness their breath-taking singing displays.”

From Science Daily

Primates’ ancestors may have left trees to survive asteroid

When an asteroid struck 66 million years ago and wiped out dinosaurs not related to birds and three-quarters of life on Earth, early ancestors of primates and marsupials were among the only tree-dwelling (arboreal) mammals that survived, according to a new study.

Arboreal species were especially at risk of extinction due to global deforestation caused by wildfires from the asteroid's impact.

In the study, computer models, fossil records and information from living mammals revealed that most of the surviving mammals did not rely on trees, though the few arboreal mammals that lived on -- including human ancestors -- may have been versatile enough to adapt to the loss of trees.

The study points to the influence of this extinction event, known as the Cretaceous-Paleogene (K-Pg) boundary, on shaping the early evolution and diversification of mammals.

"One possible explanation for how primates survived across the K-Pg boundary, in spite of being arboreal, might be due to some behavioral flexibility, which may have been a critical factor that let them survive," said Jonathan Hughes, the paper's co-first author and a doctoral student in the lab of Jeremy Searle, professor of ecology and evolutionary biology in the College of Agriculture and Life Sciences. Co-first author Jacob Berv, Ph.D. '19, is currently a Life Sciences Fellow at the University of Michigan.

The study, "Ecological Selectivity and the Evolution of Mammalian Substrate Preference Across the K-Pg Boundary," published October 11 in the journal Ecology and Evolution.

The earliest mammals appeared roughly 300 million years ago and may have diversified in tandem with an expansion of flowering plants about 20 million years prior to the K-Pg event. When the asteroid struck, many of these mammal lineages died off, Hughes said.

"At the same time, the mammals that did survive diversified into all the new ecological niches that opened up when dinosaurs and other species became extinct," Hughes said.

In the study, the researchers used published phylogenies (branching, tree-like diagrams that show evolutionary relatedness among groups of organisms) for mammals. They then classified each living mammal on those phylogenies into three categories -- arboreal, semi-arboreal and non-arboreal -- based on their preferred habitats. They also designed computer models that reconstructed the evolutionary history of mammals.

Mammal fossils from around the K-Pg are very rare and are difficult to use to interpret an animal's habitat preference. The researchers compared information known from living mammals against available fossils to help provide additional context for their results.

Generally, the models showed that surviving species were predominantly non-arboreal through the K-Pg event, with two possible exceptions: ancestors of primates and marsupials. Primate ancestors and their closest relatives were found to be arboreal right before the K-Pg event in every model. Marsupial ancestors were found to be arboreal in half of the model reconstructions.

The researchers also examined how mammals as a group may have been changing over time.

"We were able to see that leading up to the K-Pg event, around that time frame, there was a big spike in transitions from arboreal and semi-arboreal to non-arboreal, so it's not just that we are seeing mostly non-arboreal [species], but things were rapidly transitioning away from arboreality," Hughes said.

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T cell response not critical for immune memory to SARS-CoV-2 or recovery from COVID-19, study finds

New research conducted in monkeys reveals that T cells are not critical for the recovery of primates from acute COVID-19 infections. T cell depletion does not induce severe disease, and T cells do not account for the natural resistance of rhesus macaques to severe COVID-19. Furthermore, strongly T cell-depleted macaques still develop potent memory responses to a second infection.

The findings, published in the mBio, an open-access journal of the American Society for Microbiology, have implications for the development of second-generation vaccines and therapeutics.

"We started this study early in the pandemic, trying to figure out how to make a good model to study the disease in humans using animals. The monkeys turned out to be more resistant to the disease than we expected, so we wanted to try to figure out why that was and try to gain some insights into the disease in humans as well," said lead study author Kim Hasenkrug, PhD, senior investigator in the Laboratory of Persistent Viral Diseases, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, in Hamilton, Montana. "We now know that the antibody response is the most critical response for protection by vaccination, not the T cell response."

In the new study, the researchers used classic reagents known to deplete CD4+ and CD8+ T cells in rhesus macaques. While CD8+ T cells directly attack infected cells and kill them, CD4+ T cells are helper T cells that trigger the immune response by recognizing pathogens and secreting cytokines, small proteins, that signal other immune cells to act, including CD8+ T cells and antibody-producing B cells.

One week after depleting the macaques of CD4+ T cells, CD8+ T cells, or both at the same time, the researchers infected the animals with SARS-CoV-2. "We depleted, we infected them and then we continued the depletions during the first week of infection to make sure the animals were well depleted. Then we studied their blood to see how they were responding in terms of their T cells and B cells," said Hasenkrug. For six weeks, the researchers studied nasal swabs and bronchoalveolar lavages to measure virus in the nose, mouth and lungs, and rectal swabs to see if the gut was shedding virus. After six weeks, the researchers re-challenged the monkeys with SARS-CoV-2 and they repeated their collection of virus and blood samples, which allowed the researchers to evaluate immune memory responses. "If there is a memory response, you get a much quicker immune response and control of the virus. That is how vaccinations work. Once your body has seen a viral pathogen, the next time it sees it, you can get a much faster and stronger immune response," said Dr. Hasenkrug.

The researchers found that the monkeys were able to mount a good memory response against the virus regardless of T cell depletion. "We found we got really good memory responses regardless of whether we depleted T cells or not. Basically, we found very strong virus neutralizing antibodies, and they are the most important antibodies in controlling the infection. That was unexpected by most immunologists, virologists and vaccinologists," said Hasenkrug.

"The other thing that happens during a memory response is that antibodies mature, becoming, stronger and more potent at binding the viral pathogen. We saw indications of this through what's called "class switching,," said Hasenkrug.

"Class switching" was also unexpected in these monkeys with depleted T cells. "We don't have a firm explanation as to why that happened, but we think it involves some sort of compensatory response, which you can see in our study. For example, when we depleted CD8+ T cells, we saw stronger CD4+ T cell or B cells responses in some animals. When the animals are missing something, they will try to make up for it by making more of something else."

Hasenkrug doesn't know why the T cells didn't turn out to be more important, but it is probably a good thing that they are not required, because then, people who fail to mount sufficient T cell responses still have opportunities to recover.

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