Newswise — The distant ancestors of modern horses had hooved toes instead of a single hoof, which vanished over time, according to researchers.
The animals, such as the Eocene Hyracotherium, had feet like those of a modern tapir: four toes in front and three behind, each individually hooved with an underlying foot pad.
In contrast, modern equids such as horses, asses, and zebras, have only a single toe, the left over original third toe on each foot, encased in a thick-walled keratinous hoof, with an underlying triangular frog on the sole that acts as a shock absorber.
An international team of scientists, from the UK, the US, and the Netherlands, analysed hoof prints and foot bones from modern horses and fossil records to discover what happened to the lost digits.
“In later fossil horses there were only three toes front and back. The extra toes, known as side toes, in these horses were smaller and shorter than in a tapir, and likely did not touch the ground under normal circumstances, but they may have provided support in exceptional situations, such as sliding or forceful impact.”
In findings, published today in Royal Society Open Science, they confirm the older notion that these toes really have been completely lost in evolution, not somehow retained within the hoof, as proposed in another recent paper published in the same journal in 2018.
Lead author Professor Alan Vincelette, of St. John’s Seminary, Camarillo, California pointed out: “Although it does seem that remainders of the proximal (upper portions) of the side digits have been retained in modern horses, as the earlier 2018 paper claimed, the distal (lower portions, or toes) have simply been lost.
The 2018 paper proposed that in modern horses these side toes are retained within the hoof of the central toe, in part contributing to the frog – although there are no actual bones within the frog.
This was partially based on an interpretation of the hoof prints of an extinct three-toed horse, Hipparion (not on the direct line to modern horses) from Laetoli in Tanzania 3.7 million years ago, the same site that yielded the famous foot prints of the hominid Australopithecus. These hoof prints apparently lacked a frog, and this added weight to the notion that the side toes of horses like Hipparion now contribute to the frog of modern horses.
While not all hoof prints of modern horses with frogs record its presence, an undoubted frog can be seen in many hoof prints that are known to have been made by three-toed horses. These observations cast doubt on the notion that the frog of modern horse hooves formed out of the side toes of tridactyl equids.
Alan Vincelette added: “The frog of the horse’s hoof evolved independently of the side toes as a unique structure providing shock absorption and traction during locomotion.”
The team also show that the feet of one-toed horses have a different shape from the main toe of the foot of three-toed horses, being round rather than oval, a difference that may be related to differences in weight distribution and/or ecological habitat.
Paper:
‘Hipparion tracks and horses’ toes: the evolution of the equid single hoof’ by Alan Vincelette, Christine Janis et al. in Royal SocietyOpen Science.
Newswise — Leaf arrangements in the earliest plants differ from most modern plants, overturning a long-held theory regarding the origins of a famous mathematical pattern found in nature, research shows.
The findings indicate that the arrangement of leaves into distinctive spirals, that are common in nature today, were not common in the most ancient land plants that first populated the earth’s surface.
Instead, the ancient plants were found to have another type of spiral. This negates a long held theory about the evolution of plant leaf spirals, indicating that they evolved down two separate evolutionary paths.
Whether it is the vast swirl of a hurricane or the intricate spirals of the DNA double-helix, spirals are common in nature and most can be described by the famous mathematical series the Fibonacci sequence.
Named after the Italian mathematician, Leonardo Fibonacci, this sequence forms the basis of many of nature’s most efficient and stunning patterns.
Spirals are common in plants, with Fibonacci spirals making up over 90% of the spirals. Sunflower heads, pinecones, pineapples and succulent houseplants all include these distinctive spirals in their flower petals, leaves or seeds.
Why Fibonacci spirals, also known as nature’s secret code, are so common in plants has perplexed scientists for centuries, but their evolutionary origin has been largely overlooked.
Based on their widespread distribution it has long been assumed that Fibonacci spirals were an ancient feature that evolved in the earliest land plants and became highly conserved in plants.
However, an international team led by the University of Edinburgh has overthrown this theory with the discovery of non-Fibonacci spirals in a 407-million-year old plant fossil.
Using digital reconstruction techniques the researchers produced the first 3D models of leafy shoots in the fossil clubmoss Asteroxylon mackiei – a member of the earliest group of leafy plants.
The exceptionally preserved fossil was found in the famous fossil site the Rhynie chert, a Scottish sedimentary deposit near the Aberdeenshire village of Rhynie.
The site contains evidence of some of the planet’s earliest ecosystems – when land plants first evolved and gradually started to cover the earth’s rocky surface making it habitable.
The findings revealed that leaves and reproductive structures in Asteroxylon mackiei, were most commonly arranged in non-Fibonacci spirals that are rare in plants today.
This transforms scientists understanding of Fibonacci spirals in land plants. It indicates that non-Fibonacci spirals were common in ancient clubmosses and that the evolution of leaf spirals diverged into two separate paths.
The leaves of ancient clubmosses had an entirely distinct evolutionary history to the other major groups of plants today such as ferns, conifers and flowering plants.
The team created the 3D model of Asteroxylon mackiei, which has been extinct for over 400 million years, by working with digital artist Matt Humpage, using digital rendering and 3D printing.
The research, published in the journal Science, was funded by UK Research and Innovation (UKRI), The Royal Society and the German Research Foundation.
The study also involved researchers from, University College Cork, Ireland, University Münster, Germany and Northern Rogue Studios, UK.
Dr Sandy Hetherington, an evolutionary palaeobiologist and the project’s lead at the University of Edinburgh, said:
“Our model of Asteroxylon mackiei lets us examine leaf arrangement in 3D for the first time. The technology to 3D print a 407-million-year old plant fossils and hold it in your hand is really incredible.
“Our findings give a new perspective on the evolution of Fibonacci spirals in plants.”
Holly-Anne Turner, who worked on the project as an undergraduate student at the University of Edinburgh and is first author of the study, said:
“The clubmoss Asteroxylon mackiei is one of the earliest examples of a plant with leaves in the fossil record.
“Using these reconstructions we have been able to track individual spirals of leaves around the stems of these 407 million year old fossil plants. Our analysis of leaf arrangement in Asteroxylon shows that very early clubmosses developed non-Fibonacci spiral patterns.”
Newswise — Researchers have tested one of the ideas put forward to explain how humanity evolved to become smarter, on non-human primates.
The study, led by a team at the University of Portsmouth, found a significant connection between social organisation and cognitive skills in monkeys.
They assessed three species of macaques with different social tolerance levels, from authoritarian to more relaxed societies, in a series of cognitive touchscreen touchscreen tasks to work out how impulsive and reactive they were.
Tonkean macaques, which are known to get along with each other the most with more diverse and complex relationships, demonstrated better overall control of distraction, emotions and actions compared to the less-tolerant long-tailed and rhesus species.
Lead author and PhD researcher, Dr Louise Loyant from the University of Portsmouth’s Centre of Comparative and Evolutionary Psychology (CCEP), said: “This relationship between social tolerance and cognitive abilities could explain why Tonkean macaques are better at managing complex relationships with others.
“This is important, as it improves our understanding of our own social evolution. Macaques live in complex communities, not too dissimilar from our own, and we can learn a lot from them.
“Existing research on human inhibitory control, or self-control, suggests the better a person is at managing their emotions and reactions, the more successful they’re likely to be in life; whether that be in relationships, work, or just generally. Our results support this hypothesis.”
The study, published in Animal Cognition, also highlighted the influence of ecological factors on self-control skills. Different risks and environmental pressures faced by each species might have shaped their behaviours, emotions, and impulsivity levels.
Long-tailed and rhesus macaques living in areas with a greater number of predators, displayed more reactive and cautious behaviours, while Tonkean macaques who face lower predatory risk, exhibited quieter and less reactive behaviours.
The researchers say that both social and ecological factors may jointly influence self-control skills in primates.
Senior co-author, Dr Marine Joly from the CCEP, explained: “A macaque living in a more competitive environment would benefit from learning how to contain inappropriate behaviours, like feeding or mating, if they’re around others higher up in the social pyramid.
“But there’s also the hypothesis that our closest primate species have evolved over time to have increased brain size and higher cognitive performances, including better self-control.
“Our findings support both of these potential explanations, as well as suggest that species living in more complex societies might have better socio-cognitive skills too, including perception, attention, memory and action planning.”
While the study provides valuable insights, the researchers acknowledge some limitations, including the sample size and some prior cognitive testing experiences among the species. They recommend further research involving a larger number of macaques, as well as a closer evaluation of an individual’s reactions and results.
ENDS
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Newswise — Animals can defend themselves against their natural enemies in various ways. Well-defended species often share conspicuous body colors with other well-defended or undefended species, forming mimetic interactions. Bombardier beetles eject toxic chemicals at a temperature of 100°C to repel enemies such as frogs, and many have warning body colors that function to deter enemies. An assassin bug, Sirthenea flavipes, exhibits a conspicuous body color similar to the bombardier beetle Pheropsophus occipitalis jessoensis which coexist with the assassin bug in the same habitat in Japan (Fig. 1). The assassin bug can stab with its proboscis, causing severe pain in humans. Although both insects are well defended, the mimetic interaction between the bombardier beetle and the assassin bug remains unclear.
Japanese entomologists Shinji Sugiura (Kobe University) and Masakazu Hayashi (Hoshizaki Green Foundation) found that the bombardier beetle P. occipitalis jessoensis has a stronger defense against a shared predator compared to the assassin bug S. flavipes. They also showed that both the bombardier beetle and the assassin bug benefit from the mimetic interaction via the shared predator. Their research appears in the 6 June 2023 issue of PeerJ.
In central Japan, the pond frog Pelophylaxnigromaculatus coexists with the bombardier beetle and the assassin bug in the same habitat. The pond frog, which is well known as a predator of various insects, could potentially attack the bombardier beetle and the assassin bug under field conditions. The researchers observed the behavioral response of pond frogs to bombardier beetles and assassin bugs under laboratory conditions (see video). Among the frogs, 100% rejected bombardier beetles and 75% rejected assassin bugs (Fig. 2), suggesting that the bombardier beetle is better defended against frogs than the assassin bug. The researchers also provided a bombardier beetle or an assassin bug to a frog that had encountered the other insect. Frogs that had previously encountered one insect species were less likely to attack the other species (Fig. 3). Specifically, a history of encounter with assassin bugs reduced the rate of attack on bombardier beetles by frogs from 75.0% to 21.7% (Fig. 3). A history of encounter with bombardier beetles reduced the rate of attack on assassin bugs by frogs from 91.3% to 40.0% (Fig. 3). Therefore, the mimetic interaction between the bombardier beetle and the assassin bug may be mutualistic.
Newswise — Researchers have proposed a new model for the evolution of higher brain functions and behaviors in the Hymenoptera order of insects. The team compared the Kenyon cells, a type of neuronal cell, in the mushroom bodies (a part of the insect brain involved in learning, memory and sensory integration) of “primitive” sawflies and sophisticated honey bees. They found that three diverse, specialized Kenyon cell subtypes in honey bee brains appear to have evolved from a single, multifunctional Kenyon cell-subtype ancestor. In the future, this research could help us better understand the evolution of some of our own higher brain functions and behaviors.
Are you “busy as a bee,” a “social butterfly” or a “fly on the wall”? There are many ways we compare our behavior to that of insects, and as it turns out there may be more to it than just fun idioms. Studying insects could help us understand not only how their behavior has evolved, but also the behavior of highly evolved animals, including ourselves. Mammalian brains are big and complex, so it is difficult to identify which behaviors and neural and genetic changes have co-developed over time. By comparison, insect brains are much smaller and simpler, making them useful models for study.
“In 2017, we reported that the complexity of Kenyon cell (KC) subtypes in mushroom bodies in insect brains increases with the behavioral diversification in Hymenoptera (a large and varied order of insects)” explained Professor Takeo Kubo from the Graduate School of Science at the University of Tokyo and co-author of the current study. “In other words, the more KC subtypes an insect has, the more complex its brain and the behaviors it may exhibit. But we didn’t know how these different subtypes evolved. That was the stimulus for this new study.”
The team from the University of Tokyo and Japan’s National Agriculture and Food Research Organization (NARO) chose two Hymenoptera species as representatives for different behaviors: the solitary turnip sawfly (which has a single KC subtype) and the sophisticated, social honey bee (which has three KC subtypes). As the sawfly has a more “primitive” brain, it is thought to contain some ancestral properties of the honey bee brain. To uncover the potential evolutionary pathways between them, the researchers used transcriptome analysis to identify the gene expression profiles (the genetic activity) of the various KC subtypes and speculate their functions.
“I was surprised that each of the three KC subtypes in the honey bee showed comparable similarity to the single KC type in the sawfly,” said Assistant Professor Hiroki Kohno, co-author from the Graduate School of Science. “Based on our initial comparative analysis of several genes, we had previously supposed that additional KC subtypes had been added one by one. However, they appear to have been separated from a multifunctional ancestral type, through functional segregation and specialization.” As the number of KC subtypes increased, each subtype almost equally inherited some distinct properties from an ancestral KC. These then modified in different ways, resulting in their varied present-day functions.
The researchers wanted a specific behavioral example of how ancestral KC functions are present in both the sawfly and the honey bee. So, they trained sawflies to engage in a common honey bee behavior test, where they learn to associate an odor stimulus with a reward. Although challenging at first, the team was eventually able to engage the sawflies in the memory task. The researchers then manipulated a gene called CaMKII in sawfly larvae, which in honey bees is associated with forming long-term memory, a KC function. When the larvae became adults, their long-term memory was impaired, indicating that the gene plays a similar role in both sawflies and honey bees. Although CaMKII was expressed (i.e., was active) across the entire single KC subtype in sawflies, in honey bees, it was preferentially expressed in only one KC subtype. This suggests that the role of CaMKII in long-term memory was passed down to the specific KC subtype in the honey bee.
Despite differences in the size and complexity of insect and mammalian brains, there are commonalities in terms of function and the basic architecture of the nervous system. That is why the model proposed in this study for the evolution and diversification of KC subtypes may help towards better understanding the evolution of our own behavior. Next, the team is interested in studying KC types acquired in parallel with social behaviors, such as the honey bee’s “waggle dance.”
“We would like to clarify whether the model presented here is applicable to the evolution of other behaviors,” said Takayoshi Kuwabara, doctoral student and lead author from the Graduate School of Science. “There are many mysteries about the neural basis that controls social behavior, whether in insects, animals or humans. How it has evolved still remains largely unknown. I believe that this study is a pioneering work in this field.”
—–
Paper Title:
Takayoshi Kuwabara, Hiroki Kohno, Masatsugu Hatakeyama, Takeo Kubo. Evolutionary dynamics of mushroom body Kenyon cell types in hymenopteran brains from multi-functional type to functionally specialized types. Science Advances. DOI: 10.1126/sciadv.add4201
Funding:
This research was supported by Grant-in-Aid for Scientific Research (B) 20H03300 (TKubo) and Grant-in-Aid for JSPS Fellows 21J20847 (TKuwabara).
Newswise — LAWRENCE — Cycads, a group of gymnosperms which can resemble miniature palm trees (like the popular sago palm houseplant) were long thought to be “living fossils,” a group that had evolved minimally since the time of the dinosaurs. Now, a well-preserved 80-million-year-old pollen cone discovered in California has rewritten scientific understanding of the plants.
The findings are detailed in a paper by two University of Kansas paleobotanists just published in the journal New Phytologist.
“Cycads aren’t well-known but make up a significant part of plant diversity, accounting for around 25% of all gymnosperms,” said lead author Andres Elgorriaga, postdoctoral researcher with the KU Department of Ecology & Evolutionary Biology and KU Biodiversity Institute and Natural History Museum. “Cycads are plants that have thick stems and short stature, with thick, palm-like leaves on top. They produce cones like pine cones and are related to other seed-bearing plants that also don’t produce flowers, like Ginkgo and the monkey puzzle tree. But they’re also highly endangered, with the highest level of endangerment among all plant groups. Trafficking of cycads also is a significant issue.”
Despite their importance, a lack of fossil evidence and confusion over the years about how to classify some fossil specimens has led to a murky scientific grasp of the plants’ evolutionary history. One prominent idea was that cycads today are nearly identical to their prehistoric ancestors.
“The prevailing school of thought is that cycads did not change much in deep time,” said co-author Brian Atkinson, assistant professor of ecology & evolutionary biology and curator of paleobotany at the KU Biodiversity Institute and Natural History Museum. “But the fossil record of cycads is poorly understood, and many things that have been called cycads have turned out not to be cycads at all. Here, we have a three-dimensionally preserved cone clearly assignable to cycads because it has internal anatomy and pollen grains typical of this group. However, the external morphology of this pollen cone is different from living cycads today. This finding suggests cycads aren’t really ‘living fossils’ and they probably have a more dynamic evolutionary history than previously thought.”
According to the KU researchers, their analysis of an 80-million-year-old permineralized pollen cone found in the Campanian Holz Shale formation located in Silverado Canyon, California, tells a more accurate cycad natural history — one where the plants diversified during the Cretaceous.
“With this type of discovery, we realize during this time there were cycads that were really different than the ones today in their size, in their number of pollen sacs, in a lot of things,” Elgorriaga said. “Maybe we haven’t found that many cycad fossils as well — or maybe we’re finding them but we’re just not recognizing them because they were so different from how they are today. They aren’t ‘living fossils.’ They were different in the past.”
To perform their analysis, Elgorriaga and Atkinson studied the specimen’s cone’s architecture, anatomical details and vasculature organization using serial sectioning, scanning electron microscopy and 3D reconstruction. They also performed a series of evolutionary analyses to place the fossil within the cycad family tree.
Relying partly on the shapes of the cone’s scales, pollen and pollen sacs, they assigned the ancient plant to Skyttegaardia, a recently described genus based on isolated cone scales found in Denmark and dated to the Early Cretaceous (about 125 million years ago). Further, they erase some initial doubt about the new genus’ placement in the cycad group.
“The 3D reconstruction was striking because it only had two pollen sacs per cone scale, and the form of this cone scale reminded us of a fossil described from Scandinavia called Skyttegaardia,” Atkinson said. “There were many similarities, but the original in Scandinavia was only described in 2021 based on isolated cone scales. They cautiously explored the idea that the fossil belonged to cycad but were uncomfortable with firmly concluding this primarily because it only had two pollen sacs per cone scale — while cycads today have 20 to 700. Most cycad pollen cones are quite large, while this fossil was only half a centimeter in length.”
With the additional information from the new fossil plant, the KU researchers were “quite confident” in their phylogenetic analysis showing Skyttegaardia’s positive relationship with cycads.
The investigators said their description of the primordial plant shows how paleobotany can tell us more about how nature works through deep time.
“This shows us that the information we collect from the fossil record greatly impacts our understanding of evolutionary patterns,” Atkinson said. “Time, just like fossils, can reveal insights that aren’t apparent from studying only living plants or organisms. This case study is an excellent example of how fossils can contribute to our understanding of evolution over extended periods.”
Newswise — Science educators in India are urging the government to restore material on Darwinian evolution which has been removed from science textbooks on the grounds that the study load on schoolchildren needs to be lightened after the COVID-19 pandemic.
The theory of the 19th century English naturalist Charles Darwin, which centres on the concept that species adapt and evolve over time through a process of natural selection, is fundamental to our understanding of the biological world.
The chapter ‘Evolution and Heredity’, taught to grade 11 and 12 students, has been reduced to ‘Heredity’, and a box on Charles Darwin and his work erased.
An open appeal, signed on by hundreds of leading scientists and science educators and released on 22 April, said the “changes introduced as a temporary measure during the Corona pandemic, are being continued even when schooling has gone back to offline mode”.
In a pointed reference to the COVID-19 rationale given by NCERT, the statement stressed the relevance of Darwin’s theory today. “The principles of natural selection help us understand how any pandemic progresses or why certain species go extinct, among many other critical issues,” it said.
T V Venkateshwaran, a scientist at Vigyan Prasar, a Department of Science and Technology body that aims to popularise science, said the deletions were symptomatic of the handling of science education in India.
“Subjects and topics are added or deleted from textbooks with no reference to evidence from educational psychology or science education,” he told SciDev.Net. “So, when there is a hue and cry that textbooks are heavy, especially after COVID, deletions are made randomly.”
Venkateshwaran believes science education should be about communicating key concepts about the world through modern science. “Otherwise, we will be living with 14th century perceptions that can generate friction and lead to violence,” he said.
“The human genome project, for example, has shown that humankind is one — it has pulled the rug on divisive ideas of race and caste. Also, evolution points to the interconnection among all living beings in the world.”
Objections to the theory of evolution by the ruling pro-Hindu Bharatiya Janata Party were first made known in 2018 when Satya Pal Singh, then minister of state in the education ministry, declared in Parliament that “nobody, including our ancestors, in writing or orally, has said they saw an ape turning into a man”.
“Darwin’s theory is scientifically wrong. It needs to change in school and college curricula,” he added.
Singh was then taken on by India’s three main science academies, the Indian Academy of Science, the Indian National Science Academy and the National Academy of Sciences, which issued a joint statement that said: “It would be a retrograde step to remove the teaching of the theory of evolution from school and college curricula or to dilute this by offering non-scientific explanations or myths.
“The theory of evolution by natural selection as propounded by Charles Darwin and developed and extended subsequently has had a major influence on modern biology and medicine, and indeed all of modern science. It is widely supported across the world.”
Opposition in India to Darwinism is similar to Christian orthodoxy’s problem with the idea that humans evolved from ape-like bipeds, rather than the Biblical idea that god created man in his own image, says D. Raghunandan, member of the All India Peoples Science Network and the Delhi Science Forum, a public interest group.
“Historically, there has never been any conflict between Hindu religious orthodoxy and the theory of evolution simply because there has never been an orthodox view of creationism until the votaries of Hindutva, a politicised version of Hinduism, began propagating their own interpretation of Hindu mythology and legends,” said Raghunandan.
According to Raghunandan, Hindu mythology holds that the deity Vishnu descends to Earth as an “avatar” (form) whenever the cosmic order is disturbed. Vishnu first descended as a fish, then as a tortoise, a boar, a half-man-half-lion, a dwarf, as a warrior-god and finally as Krishna, a preceptor.
“While Hindu mythology sees avatars as stages of consciousness, Hindutva jingoists interpret it as a theory of evolution that long preceded Darwin,” Raghunandan explained.
Islamic orthodoxy also frowns on Darwinism and countries that have banned the theory completely include Turkey, Saudi Arabia, Oman, Algeria and Morocco. Lebanon has removed evolution from the curriculum while in Jordan the subject is taught within a religious framework.
This piece was produced by SciDev.Net’s Asia & Pacific desk.
Newswise — Why is it that certain mammals have an exceptional sense of smell, some hibernate, and yet others, including humans, are predisposed to disease? A major international research project, jointly led by Uppsala University, Sweden and the Broad Institute, USA, has surveyed and analysed the genomes of 240 different mammals. The results, now published in 11 articles in the journal Science, show how the genomes of humans and other mammals have developed over the course of evolution. The research shows which regions have important functions in mammals, which genetic changes have led to specific characteristics in different species and which mutations can cause disease.
“In combination, the 11 articles we are now publishing in Science provide an enormous amount of information about the function and development of mammalian genomes,” says Kerstin Lindblad-Toh, Professor of Comparative Genomics at Uppsala University and one of two leaders of the international consortium of researchers. “Moreover, we have produced data that can be used for studies of evolution and medical research for many years to come.”
In a large international project jointly led by Uppsala University and the Broad Institute, more than 30 research teams have together surveyed and analysed the genomes of 240 mammal species. The results, now published in 11 articles in the journal Science, show how the genomes of humans and other mammals have developed in the course of evolution.
The human genome contains approximately 20,000 genes that constitute the code for manufacturing all the proteins in the body. The genome also contains instructions that direct where, when and how much of the proteins are produced. These parts of the genome, which are called regulatory elements, are much more difficult to identify than the parts that give rise to proteins. However, studying a great many mammals’ genomes makes it possible to figure out which parts of the genome are functionally important.
The hypothesis shared by the researchers behind the publications in Science has been that if a position in the genome has been preserved throughout 100 million years of evolution, it likely serves a function in all mammals. For the first time, they have been able to test this hypothesis on a large scale. By making a detailed survey and systematic comparison of the genomes of 240 mammals, the researchers have identified regions of the human genome with previously uncharacterised function. These regions are likely regulatory elements and are significant for the correct functioning of the genome. Mutations in these can play an important role in the origin of diseases or in the distinctive features of mammal species.
The researchers identified more than three million important regulatory elements in the human genome, about half of which were previously unknown. They were also able to ascertain that at least 10 per cent of the genome is functional, ten times as much as the approximately one per cent that codes for proteins.
The 240 different mammals in the study vary widely in their characteristics, such as the acuteness of their sense of smell or the size of their brain. The researchers were able to find regions in the genomes that lead to some species having a superior sense of smell or to certain species hibernating.
“It’s exciting to now have a picture of which mutations have steered the development of specific traits in these widely divergent mammals,” says Matthew Christmas, researcher and co-first author of one of the articles focusing on the function of the genome and how it affects distinctive features in different species.
One of the studies shows that mammals had begun to change and diverge ven before the Earth was hit by the asteroid that killed the dinosaurs, approximately 65 million years ago.
“Our results can also provide important information about whether mammals are at risk of extinction, depending on how much variation they have in their genome. This is information that can lay the foundation for understanding how to manage a species to help it survive,” says Professor Lindblad-Toh.
The new knowledge also helps researchers understand how diseases arise, by linking the positions in the genome conserved by evolution to known conditions. This can be done for all species and will also be usable with reference to human diseases.
“Our analyses of 240 mammals give us a better insight into the regulatory signals in the genome. We calibrated our results on positions that are known to contribute to disease, and then could use these to suggest additional positions which could be prioritised for neurological traits, such as schizophrenia or immune conditions including asthma or eczema,” says Jennifer Meadows, researcher and co-first author of the second article, which focuses on how the project’s data can contribute to knowledge about diseases.
The genome of healthy and sick people is compared to understand which mutations lead to disease. This produces a picture of the region in the genome that may be important, but does not yield an exact knowledge of which mutation causes the disease.
“A large proportion of the mutations that lead to common diseases, like diabetes or obsessive-compulsive disorder, lie outside the genes and have to do with gene regulation. Our studies make it easier to identify the mutations that lead to disease and to understand what goes wrong,” says Lindblad-Toh.
The researchers also studied the cancer medulloblastoma, which is the most common type of malignant brain tumour in children. Although modern treatments have improved the prognosis, not all children can be cured. Moreover, those that survive often experience lifelong side-effects from the aggressive treatment.
“In patients with medulloblastoma, we found many new mutations in evolutionarily conserved positions. We hope that analysis of these mutations will lay the ground for new diagnostics and therapies,” says Karin Forsberg-Nilsson, Professor of Stem Cell Research at Uppsala University, who led the cancer part of the study.
This work was supported in part by the National Institutes of Health (US), the Swedish Research Council (SWE), the Knut and Alice Wallenberg Foundation (SWE), and the National Science Foundation (US).
Newswise — New fossils in amber have revealed that beetles fed on the feathers of dinosaurs about 105 million years ago, showing a symbiotic relationship of one-sided or mutual benefit, according to an article published in Proceedings of the National Academy of Sciences of the United States of America today*.
The main amber fragments studied, from the Spanish locality of San Just (Teruel), contain larval moults of small beetle larvae tightly surrounded by portions of downy feathers. The feathers belonged to an unknown theropod dinosaur, either avian (a term referring to “birds” in wide sense) or non-avian, as both types of theropods lived during the Early Cretaceous and shared often indistinguishable feather types. However, the studied feathers did not belong to modern birds since the group appeared about 30 million years later in the fossil record, during the Late Cretaceous.
When looking at modern ecosystems, we see how ticks infest cattle, frogs capture insects with acrobatic tongues, or some barnacles grow on the skin of whales. These are just a few of the diverse and complex ecological relationships between vertebrates and arthropods, which have coexisted for more than 500 million years. The way that these two groups have interacted throughout deep time is thought to have critically shaped their evolutionary history, leading to coevolution. Nevertheless, evidence of arthropod-vertebrate relationships is extremely rare in the fossil record.
The larval moults preserved in the amber were identified as related to modern skin beetles, or dermestids. Dermestid beetles are infamous pests of stored products or dried museum collections, feeding on organic materials that are hard for other organisms to decay such as natural fibres. However, dermestids also play a key role in the recycling of organic matter in the natural environment, commonly inhabiting nests of birds and mammals, where feathers, hair, or skin accumulate.
“In our samples, some of the feather portions and other remains – including minute fossil faeces, or coprolites – are in intimate contact with the moults attributed to dermestid beetles and show occasional damage and/or signs of decay. This is hard evidence that the fossil beetles almost certainly fed on the feathers and that these were detached from its host,” explains Dr Enrique Peñalver, from the Geological and Mining Institute of Spain of the Spanish National Research Council (CN IGME-CSIC) and lead author of the study.
“The beetle larvae lived −feeding, defecating, moulting− in accumulated feathers on or close to a resin-producing tree, probably in a nest setting. A flow of resin serendipitously captured that association and preserved it for millions of years.”
“Three additional amber pieces each containing an isolated beetle moult of a different maturity stage but assigned to the same species were also studied, allowing a better understanding of these minute insects than what is usually possible in palaeontology,” says Dr David Peris, from the Botanical Institute of Barcelona (CSIC-Barcelona City Council) and co-author of the study. The most impressive, complete specimen was found in the amber deposit of Rábago/El Soplao in the northern Spain, roughly of the same age as San Just.
“It is unclear whether the feathered theropod host also benefitted from the beetle larvae feeding on its detached feathers in this plausible nest setting,” says Dr Ricardo Pérez-de la Fuente, from Oxford University Museum of Natural History and co-lead author of the study. “However, the theropod was most likely unharmed by the activity of the larvae since our data show these did not feed on living plumage and lacked defensive structures which among modern dermestids can irritate the skin of nest hosts, even killing them.”
**
Notes
The international and multidisciplinary team comprised researchers from the Geological and Mining Institute of Spain of the Spanish National Research Council (CN IGME-CSIC), the Botanical Institute of Barcelona (IBB-CSIC), the University of Barcelona and the Institute for Research on Biodiversity (IRBio), the Complutense University of Madrid, the ‘Parque de las Ciencias’ of Andalusia, the Autonomous University of Madrid, and the Royal Academy of Exact, Physical and Natural Sciences (Spain); the American Museum of Natural History and the Natural History Museum of Los Angeles County (United States of America); the Senckenberg Research Institute (Germany); and Oxford University Museum of Natural History (United Kingdom).
Funding bodies: the project CRE, funded by the Spanish AEI/FEDER, UE Grant CGL2017-84419, the project PGC2018-094034-B-C22 (MCIU/AEI/FEDER, UE), the project CGL2014-52163, funded by the Spanish Ministry of Economy, Industry, and Competitiveness, the Secretary of Universities and Research of the Government of Catalonia and European Social Fund (2021FI_B2 00003), and the Consejería de Industria, Turismo, Innovación, Transporte y Comercio of the Gobierno de Cantabria through the public enterprise EL SOPLAO S.L.
About Oxford University Museum of Natural History
Founded in 1860 as the centre for scientific study at the University of Oxford, the Museum of Natural History now holds the University’s internationally significant collections of entomological, geological and zoological specimens. Housed in a stunning Pre-Raphaelite-inspired example of neo-Gothic architecture, the Museum’s growing collections underpin a broad programme of natural environment research, teaching and public engagement.
Newswise — The story of human evolution has long been a tale of a forested Africa that gradually became drier, giving rise to open grasslands and causing our forest-loving ape ancestors to abandon the trees and become bipedal. Even though ecological and fossil evidence suggested this narrative was too simplistic, the theory remains prominent in many evolutionary scenarios.
Two new studies recently published in Scienceledby researchers at the University of Minnesota Twin Cities put this idea to rest. The findings outline paleoecological reconstructions of early ape fossil sites in eastern Africa dated to the Early Miocene — between 23 and 16 million years ago — showing early apes lived in a wide variety of habitats, including open habitats like scrublands and wooded grasslands that existed 10 million years earlier than previously known.
Research findings include:
Some of these habitats included substantial C4 plant biomass, grasses that today characterize tropical savannas, but were thought previously to have become dominant only 10 million years ago.
Modern ape anatomy may have evolved in open woodlands among leaf-eating apes rather than in forest-dwelling fruit-eating apes.
The combination of open habitats with significant C4 biomass in the Early Miocene suggests that traditional scenarios regarding the evolution of animal and plant communities in Africa, including the origin of hominins, need to be reconsidered.
Researchers across nine fossil site complexes — which included 30 experts from African, North American and European institutions — conducted paleontological and geological fieldwork, collecting thousands of fossil plant and animal remains and sampling fossil deposits for multiple lines of evidence to reconstruct the ancient habitats.
“None of us could have reached these conclusions working in isolation at our individual fossil sites,” said Kieran McNulty, a professor of Anthropology in the College of Liberal Arts, lead author and organizer of the decade-long Research on East African Catarrhine and Hominoid Evolution (REACHE) project. “Working in the fossil record is challenging. We discover hints about past life and need to assemble and interpret them across space and time. It’s like a 4D puzzle, where each team member can only see some of the pieces.”
“You go into a project like this not knowing for sure what you will find out, which is exciting. In this case, we realized we were looking at a picture of Early Miocene communities in eastern Africa that is quite different than what we had expected,” said David Fox, a professor in the Earth and Environmental Sciences Department in the College of Science and Engineering. “There was no single ‘ah ha moment’ but over years of field seasons and the steady accumulation of new fossils and new data, we realized that the environments of the earliest apes varied significantly from the traditional picture of forested habitats.”
“The findings have transformed what we thought we knew about early apes, and the origin for where, when and why they navigate through the trees and on the ground in multiple different ways,” said Robin Bernstein, program director for biological anthropology at the National Science Foundation. “For the first time, by combining diverse lines of evidence, this collaborative research team tied specific aspects of early ape anatomy to nuanced environmental changes in their habitat in eastern Africa, now revealed as more open and less forested than previously thought. The effort outlines a new framework for future studies regarding ape evolutionary origins.”
Continued research at these fossil sites will enhance our understanding of these habitats, especially of finer-grained changes in space and time. Likewise, similar collaborations focused on earlier and later time periods are needed to fully understand the interactions between fossil species and their environments.
“This level of cooperation among different teams is unique in paleoanthropology,” said McNulty. “These two studies highlight the importance of extending collaboration and dialog beyond our immediate research partners.”
The research was funded by theNational Science Foundation, Leakey Foundation, McKnight Land-Grant Fellowship, and Leverhulme Trust Fellowship.
Newswise — The Indo-West Pacific is the largest, most biodiverse marine ecosystem on Earth, and many of the species it supports have comparably wide ranges. Writing in “The Origin of Species,” Charles Darwin noted that “… many fish range from the Pacific into the Indian Ocean, and many shells are common to the eastern islands of the Pacific and the eastern shores of Africa, on almost exactly opposite meridians of latitude.”
At first glance, the same pattern appears to be true for crabs. Chlorodielline crabs, common on coral reefs, look so similar that scientists have struggled to distinguish species in the group based solely on appearance. But a new study reveals a surprising exception to the rule of uniformity across the Indo-West Pacific. While chlorodielline crab species with non-overlapping ranges are often nearly identical, those that occupy the same region have a unique feature.
“They all look the same, until you compare their gonopods, which are structurally complex and very species specific,” said lead author and former Florida Museum of Natural History postdoctoral researcher Robert Lasley.
Gonopods are specialized appendages used for reproduction that have evolved multiple times in different arthropod groups, including crustaceans, moths and butterflies, and millipedes. They’re variously used for sperm transfer and clasping, and in crabs, they sometimes come equipped with elaborate frills that give them the appearance of a spatula with a mohawk.
Lasley, who is currently the curator of Crustacea at the University of Guam’s Biorepository, wanted to see if there was any pattern to the seemingly endless, undirected variation in their gonopods. To do that, he needed a close look at species across the Indo-West Pacific and assiduously collected specimens for more than a decade. He participated in numerous marine field forays in the Red Sea, Singapore, Australia, and the Phoenix Islands, hovering inches above their reefscapes in search of crabs hiding among the coral bric-a-brac.
Chlorodielline crabs are especially diverse in what’s known as the coral triangle, where open sea is punctuated by a vast archipelago that stretches from Indonesia to the Solomon Islands. The shallow waters around these islands support roughly 76% of the world’s coral species and more than a quarter of all coral reef fishes. Chlorodielline crabs, most of which grow no larger than a corn kernel, sit near the base of the food chain in these ecosystems.
“They’re among the most abundant coral reef crustaceans, which makes them very important,” Lasley said. “They live in what are essentially apartment buildings made out of dead coral, and there are so many of them that any time you pick up a piece of reef rubble, they spill out.”
Before Lasley could determine why they had such wildly different gonopods, he first had to figure out how chlorodielline species are related to each other, which he accomplished through an analysis of DNA extracted from museum specimens. The authors then added information regarding the range of each species and the shape of their gonopods.
What they found led them to one of marine biology’s most perplexing mysteries. There are a few key ingredients natural selection needs to make new species, but two of the most crucial are genetic variation and isolation. On land, roaming animals become isolated all the time, but in marine environments, this step in the speciation process can be harder to achieve. Many marine invertebrates — including crabs — have a larval stage, in which individuals drift across the world’s oceans in the form of microscopic plankton. With their strong capacity for long-distance dispersal, how do they remain isolated long enough for evolution to generate diversity?
Naturalists like Darwin saw the Indo West Pacific as one vast body of water, uninterrupted by geographic barriers, like ocean rifts or unproductive dead zones, that would otherwise act like a catalyst in the process of speciation.
The results of this study suggest sheer distance and time can also act as barriers. Many chlorodielline crabs have ranges that extend across the entirety of the Indo-West Pacific. The genetic analysis revealed these cryptic species have slowly accumulated differences in their DNA over millions of years.
But it wasn’t until close relatives were reunited after an extended separation that those genetic differences visibly manifested in a single, peculiar way. In almost every case, close relatives with overlapping ranges had uniquely shaped gonopods but otherwise looked exactly the same.
“What we can say is these crabs start genetically diverging in different geographic areas, and then the divergence of gonopods is an important piece of the speciation process that happens at the tail end of things,” he said.
Lasley isn’t sure why these gonopods only begin to change when two species are in close proximity, but he suspects it’s something inherent in the way these crabs reproduce, which he intends to test in future studies. For now, the results indicate that far more variation exists at the heart of Earth’s most species-rich marine ecosystem than previously suspected, and the engine driving its diversity has yet to be entirely discovered.
Additional authors of the study include Nathaniel Evans of the University of the Ryukyus, Gustav Paulay and Francois Michonneau of the Florida Museum of Natural History, Amanda Windsor of the National Museum of Natural History, Irwansyah of Sylah Kuala University, and Peter Ng of the Lee Kong Chian Natural History Museum.
Funding for the study was provided in part by the National Science Foundation (grants DEB 1856245 and GECCO 1457769), the Gordon and Betty Moore Foundation, the Alfred P. Sloan Foundation and the Japan Society for the Promotion of Science (P22078)
Newswise — Cast your mind back to the spring of 2020, when grocery store shelves sat bare of essential items and ingredients. For birds who live in the forests of Central America, replacement of forest land with coffee plantations essentially “clears out the shelves” of their preferred foods, causing them to shift their diets and habitats to survive.
A new study led by researchers at the University of Utah explores a record of birds’ diets preserved in their feathers and radio tracking of their movements to find that birds eat far fewer invertebrates in coffee plantations than in forests, suggesting that the disturbance of their ecosystem significantly impacts the birds’ dietary options.
“Growing human ecological impact on the planet, especially via habitat loss and degradation and climate change, often impacts bird diets negatively as well,” said Çağan H. Şekercioğlu, the study’s lead author and an ecology and ornithology professor in the U’s School of Biological Sciences. “These negative changes, including declines in key dietary resources like insects and other invertebrates can lead to reduced survival, especially of rapidly growing young, often leading to population declines and losses of these undernourished birds.”
All over the world, forests are being reduced from once-verdant havens of life to much smaller remnants, scattered amongst the agricultural land that has replaced them. Only about one percent of bird species prefer the types of habitats dominated by humans and human activity, but the rapid disappearance of natural forest habitat means that about a third of bird species now find themselves working to survive in human-dominated environments.
In Costa Rica, the land around the Las Cruces Biological Station near the Panama border, has gone from fully forested to now 50% coffee plantations, 20% cattle pastures and 10% other human environments—only 20% of the land is still forested. The agricultural areas are drenched in pesticides, fertilizers and fungicides, drastically impacting the communities of invertebrates on which local birds feed.
Those local birds include four species that the researchers focused on in the study: orange-billed nightingale-thrush, silver-throated tanager, white-throated thrush and ochre-bellied flycatcher. All four species can be found in both the forests and the open countryside where they feed on both fruits and invertebrates. But the invertebrates (including insects) are an important part of their diet, since they provide key nutrients including protein and nitrogen.
Şekercioğlu and his colleagues, including researchers from the United States, Costa Rica, and Singapore, wanted to understand how the bird species they studied were obtaining their nutrients between the agricultural and forest environments, specifically during the crucial breeding season when proper nutrition is key to sustaining the species.
To learn more about the birds’ diet, the researchers analyzed isotopes in their feathers. We are what we eat, and the chemical signatures of the foods we eat, in the form of isotope ratios, are incorporated into our tissues.
Isotopes are different versions of the same element that differ only in the amount of neutrons in their nucleus – an infinitesimal difference in mass between a carbon atom with, say, six neutrons and a carbon atom with seven. But biological and physical processes can prefer either light or heavy isotopes, changing the resulting ratio in a way that can be measured and can provide valuable information.
In humans, for example, a record of our diets is preserved in the isotopes in our hair. In a previous study, co-author Thure Cerling, a distinguished professor in the U’s Department of Geology and Geophysics, and colleagues analyzed hair clippings from barbershops and salons around the Salt Lake Valley and learned about the relative ratios of corn-fed meat and plant-based protein in the diets of local residents.
In Costa Rica, the researchers hoped to do the same, but with the stable carbon and nitrogen isotopes in the birds’ feathers. They collected 170 feathers from the four bird species to analyze diet, and tracked 49 birds’ movements using radio tracking to see where they spent their time.
“It’s definitely not the first time feather isotopic analysis has been used to study bird diets,” said co-author Seth Newsome of the University of New Mexico, “but it might be the first time, especially in the tropics, it has been used in conjunction with radio telemetry to examine diet composition and relative use of agricultural versus natural habitats.”
The results showed that the birds’ habitat of choice had a significant effect on their diet. The isotopic data suggested that three of the four species studied ate significantly fewer invertebrates in coffee plantations than in forests. For silver-throated tanagers and the white-throated thrushes, the data suggested that they were eating twice as much invertebrate biomass in forests than in coffee plantations.
“Our results suggest that coffee plantations are deficient in invertebrates preferred by forest generalist birds that forage in both native forest remnants and coffee plantations,” Şekercioğlu said.
The coffee plantations were planted decades ago, and the researchers don’t have the data to know how the birds behaved when the forest was intact. But from what we know about the birds’ behaviors now, we can infer what the results mean for the birds’ lifestyles.
To consume enough invertebrates, Şekercioğlu said, the birds need to forage frequently in the small forest fragments of around 7-12 acres (about the size of the parking lot at the U’s Rice-Eccles Stadium) and narrow corridors of forests alongside rivers, only around 30-60 ft wide.
“We think that the more mobile birds like silver-throated tanager and white-throated thrush move constantly to get enough food, especially protein-rich invertebrates,” Şekercioğlu said, a hypothesis supported by a 2007 radio tracking study. “Less mobile species like orange-billed nightingale thrush that can have lifelong home range sizes as small as an acre (half a hectare) either have to adapt to coffee plantations and eat fewer invertebrates or they disappear.” The orange-billed nightingale thrush isn’t alone—a 2019 study showed that more bird species were in decline in the region than were stable.
So for the birds of Costa Rica, and for birds in other, similar tropical regions, forest reserves can provide critical resources for birds that have shifted their habitats to the remaining forest and travel through coffee plantations to reach other forest fragments.
“These birds’ shifting their feeding to other places may result in new ecological interactions that can themselves have negative consequences,” Şekercioğlu said. “For example, increased competition with birds in these new places or overpredation on a prey species that was formerly not consumed as much.”
If you’re a coffee drinker, you can help by choosing to buy bird-friendly coffee. According to Şekercioğlu, bird-friendly coffee is grown in plantations with more tree cover and forest remnants, which are beneficial for native birds. He recommends buying shade-grown coffee, coffee certified as Bird Friendly by the Smithsonian Migratory Bird Center, or coffee from Ethiopia which, he said, is among the bird-friendliest.
And local governments in tropical regions can help by prioritizing the conservation of intact forest, secondary growth forests and strips of forest alongside rivers to increase the connectivity of forest remnants.
“It is urgent,” Şekercioğlu said, “to prioritize the conservation and regeneration of forest remnants in increasingly human-dominated agricultural areas that continue to replace the world’s most biodiverse tropical forests.”
A new study published in Science Advances has not only revealed that an ALHS in Colias butterflies has an ancient origin, but also determined the mechanisms contributing to its persistence over millions of generations.
Newswise — A new study investigates how an extinct, carnivorous marsupial relative with canines so large they extended across the top of its skull could hunt effectively despite having wide-set eyes, like a cow or a horse. The skulls of carnivores typically have forward-facing eye sockets, or orbits, which helps enable stereoscopic (3D) vision, a useful adaptation for judging the position of prey before pouncing. Scientists from the American Museum of Natural History and the Instituto Argentino de Nivología, Glaciología, y Ciencias Ambientales in Mendoza, Argentina, studied whether the “marsupial sabertooth” Thylacosmilus atrox could see in 3D at all. Their results are published today in the journal Communications Biology.
Popularly known as the “marsupial (or metatherian) sabertooth” because its extraordinarily large upper canines recall those of the more famous placental sabertooth that evolved in North America, Thylacosmilus lived in South America until its extinction about 3 million years ago. It was a member of Sparassodonta, a group of highly carnivorous mammals related to living marsupials. Although sparassodont species differed considerably in size—Thylacosmilus may have weighed as much as 100 kilograms (220 pounds)—the great majority resembled placental carnivores like cats and dogs in having forward-facing eyes and, presumably, full 3D vision. By contrast, the orbits of Thylacosmilus, a supposed hypercarnivore—an animal with a diet estimated to consist of at least 70 percent meat—were positioned like those of an ungulate, with orbits that face mostly laterally. In this situation, the visual fields do not overlap sufficiently for the brain to integrate them in 3D. Why would a hypercarnivore evolve such a peculiar adaptation? A team of researchers from Argentina and the United States set out to look for an explanation.
“You can’t understand cranial organization in Thylacosmilus without first confronting those enormous canines,” said lead author Charlène Gaillard, a Ph.D. student in the Instituto Argentino de Nivología, Glaciología, y Ciencias Ambientales (INAGLIA). “They weren’t just large; they were ever-growing, to such an extent that the roots of the canines continued over the tops of their skulls. This had consequences, one of which was that no room was available for the orbits in the usual carnivore position on the front of the face.”
Gaillard used CT scanning and 3D virtual reconstructions to assess orbital organization in a number of fossil and modern mammals. She was able to determine how the visual system of Thylacosmilus would have compared to those in other carnivores or other mammals in general. Although low orbital convergence occurs in some modern carnivores, Thylacosmilus was extreme in this regard: it had an orbital convergence value as low as 35 degrees, compared to that of a typical predator, like a cat, at around 65 degrees.
However, good stereoscopic vision also relies on the degree of frontation, which is a measure of how the eyeballs are situated within the orbits. “Thylacosmilus was able to compensate for having its eyes on the side of its head by sticking its orbits out somewhat and orienting them almost vertically, to increase visual field overlap as much as possible,” said co-author Analia M. Forasiepi, also in INAGLIA and a researcher in CONICET, the Argentinian science and research agency. “Even though its orbits were not favorably positioned for 3D vision, it could achieve about 70 percent of visual field overlap—evidently, enough to make it a successful active predator.”
“Compensation appears to be the key to understanding how the skull of Thylacosmilus was put together,” said study co-author Ross D. E. MacPhee, a senior curator at the American Museum of Natural History. “In effect, the growth pattern of the canines during early cranial development would have displaced the orbits away from the front of the face, producing the result we see in adult skulls. The odd orientation of the orbits in Thylacosmilus actually represents a morphological compromise between the primary function of the cranium, which is to hold and protect the brain and sense organs, and a collateral function unique to this species, which was to provide enough room for the development of the enormous canines.”
Lateral displacement of the orbits was not the only cranial modification that Thylacosmilus developed to accommodate its canines while retaining other functions. Placing the eyes on the side of the skull brings them close to the temporal chewing muscles, which might result in deformation during eating. To control for this, some mammals, including primates, have developed a bony structure that closes off the eye sockets from the side. Thylacosmilus did the same thing—another example of convergence among unrelated species.
This leaves a final question: What purpose would have been served by developing huge, ever-growing teeth that required re-engineering of the whole skull?
“It might have made predation easier in some unknown way,” said Gaillard, “But, if so, why didn’t any other sparassodont—or for that matter, any other mammalian carnivore—develop the same adaptation convergently? The canines of Thylacosmilus did not wear down, like the incisors of rodents. Instead, they just seem to have continued growing at the root, eventually extending almost to the rear of the skull.”
Forasiepi underlined this point, saying, “To look for clear-cut adaptive explanations in evolutionary biology is fun but largely futile. One thing is clear: Thylacosmilus was not a freak of nature, but in its time and place it managed, apparently quite admirably, to survive as an ambush predator. We may view it as an anomaly because it doesn’t fit within our preconceived categories of what a proper mammalian carnivore should look like, but evolution makes its own rules.”
ABOUT THE AMERICAN MUSEUM OF NATURAL HISTORY (AMNH)
The American Museum of Natural History, founded in 1869, is one of the world’s preeminent scientific, educational, and cultural institutions. The Museum encompasses more than 40 permanent exhibition halls and galleries for temporary exhibitions, the Rose Center for Earth and Space and the Hayden Planetarium, and the Richard Gilder Center for Science, Education, and Innovation, which opens in 2023. The Museum’s scientists draw on a world-class permanent collection of more than 34 million specimens and artifacts, some of which are billions of years old, and on one of the largest natural history libraries in the world. Through its Richard Gilder Graduate School, the Museum grants the Ph.D. degree in Comparative Biology and the Master of Arts in Teaching (MAT) degree, the only such freestanding, degree-granting programs at any museum in the United States. The Museum’s website, digital videos, and apps for mobile devices bring its collections, exhibitions, and educational programs to millions around the world. Visit amnh.org for more information.
Newswise — Annapolis, MD; March 13, 2023—Black widow spiders have earned a fearsome reputation for their venomous bite. But in parts of the southern United States these spiders have much to fear themselves—from spider relatives who really don’t like their company.
In the past couple decades, researchers have noticed black widow spiders commonly being displaced by the brown widow, a fellow species in the same genus, Latrodectus. But new research suggests this isn’t a just simple case of one species winning the competition for food or habitat. Instead, a study shows brown widow spiders have a striking propensity to seek out and kill nearby black widows.
In experiments pairing brown widow spiders in container habitats with related cobweb spider species, the brown widows were 6.6 times more likely to kill southern black widows than other related species. The findings of the study, conducted by researchers at the University of South Florida (USF), are reported in an article to be published March 13 in the Annals of the Entomological Society of America.
“We have established brown widow behavior as being highly aggressive towards the southern black widows, yet much more tolerant of other spiders within the same family,” says Louis Coticchio, who led the study as part of his undergraduate research at USF.
Brown widow spiders (Latrodectus geometricus) are believed to be native to Africa but have been introduced on all continents but Antarctica. Black widow spiders are native to North America and comprise two closely related species, the western black widow (Latrodectus hesperus) and the southern black widow (Latrodectus mactans).
What Drives Brown Widow Spiders’ Displacement of Black Widows?
Coticchio spent the first part of his career as a zookeeper specializing in venomous animals in California and returned to Florida to earn a degree in biology, channeling a passion for spiders into his research projects. In collecting wild spiders in Florida, he says he noticed brown widows displacing black widows but not other related species. This got him wondering.
“I had a sneaking suspicion that Florida in particular provided plenty of food and habitat for both the brown and black widow, and that there was possibly some other area such as behavioral differences that were playing a role,” he says. “My observations in the field showed that brown widows appeared to be much more tolerant of other species outside of their genus, and so if resources were the main factor, then we should have seen the same behavior with other spiders competing for the same resources, but that did not seem to be that case.”
Coticchio partnered with advisor Deby Cassill, Ph.D., associate professor in the Department of Integrative Biology at USF. Along with spider expert Richard Vetter of the University of California, Riverside, they devised a three-part study to explore the potential drivers of brown widows displacing black widows.
One element of their study applied mathematical modeling to the risk factors to survival that brown and black widow spiders face, which showed both species are far more likely to die by predation than by starvation. In other words, “competition for scarce resources is not a significant cause of mortality among spiderlings for either species,” the researchers say.
They also compared rates of growth and fertility between brown and black widows, finding that sub-adult brown widow females were 9.5 percent larger than black widows, and adult female brown widows reached reproductive maturity 16 percent sooner. While adult male brown widows were 25 percent smaller than adult male black widows, they reached reproductive maturity 21 percent sooner. Meanwhile, brown widow females were about twice as fertile as black widows, with brown widows often producing multiple egg sacs at a time versus black widows producing just one.
Placing brown widows in proximity with black widows and other spider species, however, showed the clearest results. Sub-adult brown widow females simply cohabitated with red house spider (Nesticodes rufipes) females in 50 percent of pairings and were killed and consumed by the red house spiders in 40 percent. Brown widows cohabitated with triangulate cobweb spiders (Steatoda triangulosa) in 80 percent of pairings and were killed in just 10 percent. But when sub-adult brown and black widow females were paired, the brown widows killed and consumed the black widows in 80 percent of pairings. In pairings of adults, black widows were killed in 40 percent of trials, while they defensively killed brown widows in 30 percent of trials and cohabitated in the remaining 30 percent.
Throughout the experiments, brown widow spiders regularly ventured into black widow webs, the researchers say. Red house spiders and triangulate cobweb spiders also showed such “bold” behavior, but black widows were never observed as aggressors.
Surprising Behavior and New Questions Raised
“We didn’t expect to find such a dramatic and consistent difference in the personalities of the brown widow and the black widow,” Cassill says. “Brown widows are boldly aggressive and will immediately investigate a neighbor and attack if there is no resistance from the neighbor. For two bold spiders, the initial attack is often resolved by both individuals going to separate corners and eventually being OK with having a nearby neighbor. The black widows are extremely shy, counterattacking only to defend themselves against an aggressive spider.”
The characterization of brown widow spiders as “aggressive,” however, is a relative term, reflecting their stance toward black widow spiders, but not toward humans. While widow spiders are “synanthropic” (i.e., commonly found around human-made structures, such as barns, garages, and sheds), they “are very shy when harassed by humans or larger animals that are not considered prey,” Coticchio says. “They will run or roll up into a ball and play dead when being attacked or harassed by most other animals outside of their prey range.” Brown widow venom causes less severe reactions to humans than black widows, and bites to people are very rare.
Brown widow spiders’ evident aggression toward black widows raises many questions, perhaps first and foremost: Why? What drives such behavior toward a closely related species? The researchers note that invasive species typically outcompete natives through advantages in factors such as fertility, growth, dispersal, or defenses against predators. Direct predation by an invasive species on its native relative, across the animal kingdom, is rare.
“One question I would love to answer is how brown widows interact with other species of spiders, more specifically black widows in Africa, where brown widows are believed to have originated,” Coticchio says. “I would love to see if their behavior and displacement of black widows is something that they have adapted here in North America, or if this behavior is something they exhibit naturally even in areas where they have coevolved with black widows for much longer periods of time.”
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“Predation by the Introduced Brown Widow Spider (Araneae: Theridiidae) May Explain Local Extinctions of Native Black Widows in Urban Habitats” will be published online on March 13, 2023, in the Annals of the Entomological Society of America. Journalists may request advance copies of the article via the contact below or download the published paper after 10 a.m. March 13, 2023, at https://academic.oup.com/aesa/advance-article/doi/10.1093/aesa/saad003/7044733.
ABOUT: ESA is the largest organization in the world serving the professional and scientific needs of entomologists and people in related disciplines. Founded in 1889, ESA today has more than 7,000 members affiliated with educational institutions, health agencies, private industry, and government. Headquartered in Annapolis, Maryland, the Society stands ready as a non-partisan scientific and educational resource for all insect-related topics. For more information, visit www.entsoc.org.
The Annals of the Entomological Society of America publishes cutting-edge entomological research, reviews, collections of articles, and discussions of topics of broad interest and national or international importance. It aims to stimulate interdisciplinary dialogue across the entomological disciplines and advance cooperative interaction among diverse groups of entomologists. For more information, visit https://academic.oup.com/aesa, or visit www.insectscience.org to view the full portfolio of ESA journals and publications.
A new fossil discovery dating from ‘just’ a few million years after the greatest mass extinction provides the earliest evidence of the insect group that includes mosquitoes and flies
The fossil, found in Mallorca, Spain, is an immature insect related to modern window- or wood-gnats
The excellent preservation of the fossil has allowed detailed studies, including determining its breathing system
Newswise — Near the small harbour of Estellencs at the northeast of Mallorca (Balearic Islands, Spain), a pebbly beach can be found at the base of an impressive scarp that threatens rockfall. Remains of plants, crustaceans, insects, and fish have been discovered in the grey-blue rock layers formed from sediments deposited 247 million years ago. Fossils in these rocks are of great interest since they offer a window into the time where the planet was recovering from the greatest mass extinction.
A few years ago, Mallorcan researcher Josep Juárez made a surprising find during a palaeontological survey in the area – a complete insect larva that had left a slight imprint of organic remains on the two sides that were left exposed when the rock split in half. The detailed study of the fossil had to wait, but eventual examination with a powerful microscope revealed that it was a unique discovery. The larva, very well preserved, belongs to a group of insects that we all know, the dipterans — that is, true flies, mosquitoes, midges, and gnats. Although thousands of fossil dipterans have been found across the globe, both in thinly layered rocks and in amber, this specimen, 247 million years old (early Middle Triassic) –older than the earliest dinosaurs– is the oldest dipteran ever found. This record was previously held by fossils found in France, about one or two million years younger than those from Estellencs.
Enrique Peñalver, from the Spanish National Research Council (CSIC) at the Spanish Geological Survey (CN-IGME), and first author of the recently published study on the new fossil, says: “While I was inspecting it under the microscope, I put a drop of alcohol on it to increase the contrast of the structures, and I was able to witness in awe how the fossil had preserved both the external and internal structures of the head, some parts of the digestive system, and, most importantly, the external openings to its respiratory system, or spiracles.”
Rafel Matamales-Andreu, palaeontologist from the Balearic Museum of Natural Sciences (FJBS-MBCN) and another author of the study, has devoted several years to unravel the environment of this region during the Triassic period, and the changes it underwent for millions of years. “If we were able to visit the region at the beginning of the Triassic, we would see large rivers and floodplains under a climate similar to that found in tropical Africa today, alternating dry and rainy seasons,” he points out.
This larva fed on organic matter from the soil ‘just’ a few million years in the aftermath of likely the most dramatic mass extinction in the history of life on Earth, which erased more than 80 per cent of the species and led to the end of the Palaeozoic Era. “We have been able to look at some of the adaptations by the first dipterans to the postapocalyptic environment at the beginning of the Triassic, for instance, a breathing system that is still found in different groups of insects today”, remarks Ricardo Pérez-de la Fuente, from Oxford University Museum of Natural History and also an author of the study.
The authors have described a new genus and species related to modern window- or wood-gnats named Protoanisolarva juarezi, or “Juárez’s ancestral anisopodoid larva”, honouring its discoverer. This precious fossil is currently being conditioned at the Catalan Institute of Palaeontology Miquel Crusafont for its permanent custody in Mallorca.
The international team comprised researchers from the Spanish Geological Survey (CN-IGME) and the Spanish National Research Council (CSIC), Spain, the Balearic Museum of Natural Sciences (FJBS-MBCN), Mallorca, Spain, the National Museum of Natural History of France and the Sorbonne University in Paris, France, and Oxford University Museum of Natural History, United Kingdom.
Funding bodies: Department of Culture, Heritage and Linguistic Policies from the Insular Council of Mallorca, with the project ‘Mallorca before the dinosaurs: study of the continental ecosystems from the Permian and the Triassic, with special emphasis on the vertebrate remains´ (Ref. 15 – 619/2020); Spanish Geological Survey (CN-IGME, Spain), CERCA program (Government of Catalonia, Spain), predoctoral grant FPU17/01922 from the Ministry of Science, Innovation and Universities, Government of Spain.
About Oxford University Museum of Natural History
Founded in 1860 as the centre for scientific study at the University of Oxford, the Museum of Natural History now holds the University’s internationally significant collections of entomological, geological and zoological specimens. Housed in a stunning Pre-Raphaelite-inspired example of neo-Gothic architecture, the Museum’s growing collections underpin a broad programme of natural environment research, teaching and public engagement.
Newswise — Males of a species evolving traits for sexual conflict can cause problems for females, and, ultimately, the whole population.
A new model by Imperial College London and University of Lausanne researchers, published in Proceedings of the National Academy of Sciences, shows how so-called ‘good genes’ can sometimes cause a population to collapse.
Males of any species may compete for females, either by fighting other males for access or impressing females to win their approval. In both cases, males expressing the most competitive traits – such as the best ornaments, like peacock feathers, or the best weapons, like big body size – access more females.
To have the best traits the males must be in good condition, for example to be in better shape or carry less disease. Over time, as better-condition males mate with more females, the prevalence of ‘good genes’ increases throughout the population of the animal, leading to the population as a whole to improve in condition.
However, it can also backfire. Traits than improve a male’s competitive prowess can also damage females. For example, some insect males have evolved penises that tear the females’ insides, and in many species, including mammals, males have evolved to harass females to induce mating. These behaviours reduce female fecundity or may even kill them.
The team’s model tested theories of sexual competition where males harm females, and compared the results with data for various population experiments. Previous experiments have shown conflicting accounts as to whether sexual selection is positive or negative for the population as a whole. The new model provides an explanation for why some experiments show male condition improving, without female fitness or population viability improving alongside.
First author Dr Ewan Flintham, from Imperial College London and the University of Lausanne, said: “Where males evolve selfish traits that help them individually win, they can actually end up causing the population to crash – it’s a form of evolutionary suicide. Even when females evolve to counter male harm and prevent population collapse, the population still decreases significantly, reducing its viability.”
Sexual interactions like these are an important component of understanding population demographics and conservation. For example, where there are more males, sexual competition intensifies, meaning harm towards females is more likely. This is also true in human-managed populations, for example domestic carp, where males and females must be isolated during spawning season.
Dr Flintham completed the research as part of the Centre for Doctoral Training in Quantitative and Modelling Skills in Ecology and Evolution at Imperial. His project supervisor and study co-author Professor Vincent Savolainen, Director of the Georgina Mace Centre for the Living Planet at Imperial, said: “Male harm evolved in nature as something that was supposed to be good, but is detrimental to females and the whole population. Questions like how and why this happens can only be answered with quantitative methods – data and mathematical models – which can be just as important as field studies.”
Newswise — If the emergence of mechanically propelled weapons in prehistory is commonly perceived as one of the hallmarks of the advance of modern human populations into the European continent, the existence of archery has always been more difficult to trace. The recognition of these technologies in the European Upper Paleolithic has been hampered by ballistic overlaps between weapons projected with a thruster or a bow. Archery technologies are essentially based on the use of perishable materials; wood, fibers, leather, resins, and sinew, which are rarely preserved in European Paleolithic sites and make archaeological recognition of these technologies difficult. It is the flint armatures that constitute the main evidence of these weapon technologies. Based on the analysis of these stone armatures, the recognition of archery is now well documented in Africa dating back some 70,000 years. Some flint or deer antler armatures suggest the existence of archery from the early phases of the Upper Paleolithic in Europe more than 35,000 years ago, but the morphology and the hafting modes of these ancient armatures do not allow them to be linked to a distinct mode of propulsion, making the possible existence of archery during the European Paleolithic nearly invisible. The demonstration of Paleolithic archery has been established only on the basis of the discovery of the oldest bows and arrows found in peat bogs of Northern Europe (at the Stellmoor site in Germany, for example) and dated from the 10 to 12 millennium.
The data from Mandrin cave in Mediterranean France, presented in an article published Wednesday, February 22, 2023 in the journal Science Advances, profoundly enriches our knowledge of these technologies in Europe and now allows us to push back the age of archery in Europe by more than… 40 millennia! The study is based on the functional analysis of thousands of flint artifacts from the same archaeological level that revealed in February 2022 the oldest occupation of modern humans on the European continent. This very rich level, attributed to the Neronian culture, testifies to Homo sapiens occupations dating back to the 54th millennium and is interposed between numerous Neanderthal occupations occupying the cave before and after the modern human installations. The excavation of the Neronian settlement phases has revealed no less than 1500 flint points. Their analysis shows that a significant number of them were used as armatures for arrows propelled with a bow. It is the very small size and more precisely the small width of these armatures, of which some 30% weigh hardly more than a few grams, which allows us to exclude any other mode of ballistic propulsion for these very small weapons. If thanks to this study, archery in Europe, and more broadly throughout Eurasia, makes a remarkable leap back in time, it also sheds light on the weaponry of Neanderthal populations. The study shows that Neanderthals, contemporaries of Neronian modern humans, did not develop mechanically propelled weapons (like technologies using bows or thrusters) and continued to use their traditional weapons based on the use of massive spear-shaped points that were thrusted or thrown by hand, and thus requiring close contact with their game. The traditions and technologies mastered by these two populations were thus profoundly distinct, illustrating a remarkable objective technological advantage to modern populations during their expansion into the European continent. However, in their article, the authors place this debate in a much broader context in which technical choices cannot be limited solely to the cognitive capacities of differing human populations, referring us to the weight of traditions within these Neanderthal and modern human populations as well as to ethologies that may have been profoundly divergent between them.
The study, published today, Feb. 9, in the journal Science, presents what are likely to be the oldest examples of a hugely important stone-age innovation known to scientists as the Oldowan toolkit, as well as the oldest evidence of hominins consuming very large animals. Though multiple lines of evidence suggest the artifacts are likely to be about 2.9 million years old, the artifacts can be more conservatively dated to between 2.6 and 3 million years old, said lead study author Thomas Plummer ofQueens College, research associate in the scientific team of the Smithsonian’s Human Origins Program.
Excavations at the site, named Nyayanga and located on the Homa Peninsula in western Kenya, also produced a pair of massive molars belonging to the human species’ close evolutionary relativeParanthropus. The teeth are the oldest fossilized Paranthropus remains yet found, and their presence at a site loaded with stone tools raises intriguing questions about which human ancestor made those tools, said Rick Potts, senior author of the study and the National Museum of Natural History’s Peter Buck Chair of Human Origins.
“The assumption among researchers has long been that only the genus Homo, to which humans belong, was capable of making stone tools,” Potts said. “But finding Paranthropus alongside these stone tools opens up a fascinating whodunnit.”
Whichever hominin lineage was responsible for the tools, they were found more than 800 miles from the previously known oldest examples of Oldowan stone tools—2.6-million-year-old tools unearthed in Ledi-Geraru, Ethiopia. This greatly expands the area associated with Oldowan technology’s earliest origins. Further, the stone tools from the site in Ethiopia could not be tied to any particular function or use, leading to speculation about what the Oldowan toolkit’s earliest uses might have been.
Through analysis of the wear patterns on the stone tools and animal bones discovered at Nyayanga, Kenya, the team behind this latest discovery shows that these stone tools were used by early human ancestors to process a wide range of materials and foods, including plants, meat and even bone marrow.
The Oldowan toolkit includes three types of stone tools: hammerstones, cores and flakes. Hammerstones can be used for hitting other rocks to create tools or for pounding other materials. Cores typically have an angular or oval shape, and when struck at an angle with a hammerstone, the core splits off a piece, or flake, that can be used as a cutting or scraping edge or further refined using a hammerstone.
“With these tools you can crush better than an elephant’s molar can and cut better than a lion’s canine can,” Potts said. “Oldowan technology was like suddenly evolving a brand-new set of teeth outside your body, and it opened up a new variety of foods on the African savannah to our ancestors.”
Potts and Plummer were first drawn to the Homa Peninsula in Kenya by reports of large numbers of fossilized baboon-like monkeys named Theropithecus oswaldi, which are often found alongside evidence of human ancestors. After many visits to the peninsula, a local man named Peter Onyango working with the team suggested they check out fossils and stone tools eroding from a nearby site that was ultimately named Nyayanga after an adjacent beach.
Beginning in 2015, a series of excavations at Nyayanga returned a trove of 330 artifacts, 1,776 animal bones and the two hominin molars identified as belonging to Paranthropus. The artifacts, Plummer said, were clearly part of the stone-age technological breakthrough that was the Oldowan toolkit.
Compared to the only other stone tools known to have preceded them—a set of 3.3-million-year-old artifacts unearthed at a site called Lomekwi 3, just west of Lake Turkana in Kenya—Oldowan tools were a significant upgrade in sophistication. Oldowan tools were systematically produced and often fashioned using what is known as “freehand percussion,” meaning the core was held in one hand and then struck with a hammerstone being wielded by the opposing hand at just the right angle to produce a flake—a technique that requires significant dexterity and skill.
By contrast, most of the artifacts from Lomekwi 3 were created by using large stationary rocks as anvils, with the toolmaker either banging a core against the flat anvil stone to create flakes or by setting the core down on the anvil and striking it with a hammerstone. These more rudimentary modes of fabrication resulted in larger, cruder and more haphazard-looking tools.
Over time, the Oldowan toolkit spread all the way across Africa and even as far as modern-day Georgia and China, and it was not meaningfully replaced or amended until some 1.7 million years ago when the hand-axes of the Acheulean first appeared.
As part of their study, the researchers conducted microscopic analysis of wear patterns on the stone tools to determine how they were used, and they examined any bones seen to exhibit potential cut marks or other kinds of damage that might have come from stone tools.
The site featured at least three individual hippos. Two of these incomplete skeletons included bones that showed signs of butchery. The team found a deep cut mark on one hippo’s rib fragment and a series of four short, parallel cuts on the shin bone of another. Plummer said they also found antelope bones that showed evidence of hominins slicing away flesh with stone flakes or of having been crushed by hammerstones to extract marrow.
The analysis of wear patterns on 30 of the stone tools found at the site showed that they had been used to cut, scrape and pound both animals and plants. Because fire would not be harnessed by hominins for another 2 million years or so, these stone toolmakers would have eaten everything raw, perhaps pounding the meat into something like a hippo tartare to make it easier to chew.
Using a combination of dating techniques, including the rate of decay of radioactive elements, reversals of Earth’s magnetic field and the presence of certain fossil animals whose timing in the fossil record is well established, the research team was able to date the items recovered from Nyayanga to between 2.58 and 3 million years old.
“This is one of the oldest if not the oldest example of Oldowan technology,” Plummer said. “This shows the toolkit was more widely distributed at an earlier date than people realized, and that it was used to process a wide variety of plant and animal tissues. We don’t know for sure what the adaptive significance was but the variety of uses suggests it was important to these hominins.”
The discovery of teeth from the muscular-jawed Paranthropus alongside these stone tools begs the question of whether it might have been that lineage rather than the Homo genus that was the architect of the earliest Oldowan stone tools, or perhaps even that multiple lineages were making these tools at roughly the same time.
The excavations behind this study offer a snapshot of the world humans’ ancestors inhabited and help illustrate the ways that stone technology allowed these early hominins to adapt to different environments and, ultimately, give rise to the human species.
“East Africa wasn’t a stable cradle for our species’ ancestors,” Potts said. “It was more of a boiling cauldron of environmental change, with downpours and droughts and a diverse, ever-changing menu of foods. Oldowan stone tools could have cut and pounded through it all and helped early toolmakers adapt to new places and new opportunities, whether it’s a dead hippo or a starchy root.”
This research was supported by funding from the Smithsonian, the Leakey Foundation, the National Science Foundation, the Wenner-Gren Foundation, the City University of New York, the Donner Foundation and the Peter Buck Fund for Human Origins Research.
Newswise — Scientists from the Institut Pasteur, Université Paris Cité, the CNRS and the Collège de France have used paleogenomics to trace 10,000 years of human immune system evolution. They analyzed the genomes of more than 2,800 individuals who lived in Europe over the past ten millennia. They were able to date the increase in frequency of most of the mutations that are advantageous in defending against pathogens to after the Bronze Age, 4,500 years ago. The scientists also observed that mutations conferring a higher risk of developing inflammatory disorders have become more frequent over the past 10,000 years. These enlightening results on the effects of natural selection on immunity genes were published in the journal Cell Genomics on January 13, 2023.
In the 1950s, the geneticist J.B.S. Haldane attributed the maintenance or persistence of the mutation responsible for anomalies in red blood cells commonly observed in Africa to the protection these anomalies provided against malaria, an endemic infection that claims millions of lives. This theory suggested that pathogens are among the strongest selective pressures faced by humans. Several population genetics studies subsequently confirmed the theory. But major questions remained, especially regarding the specific epochs during which the selective pressures exerted by pathogens on human populations were strongest and their impact on the present-day risk of developing inflammatory or autoimmune disorders.
To address these questions, scientists from the Institut Pasteur, Université Paris Cité, the CNRS and the Collège de France, in collaboration with the Imagine Institute and The Rockefeller University (United States), adopted an approach based on paleogenomics. This discipline, which studies the DNA from fossil remains, has led to major discoveries about the history and evolution of humans and human diseases, as illustrated by the decision to award the 2022 Nobel Prize in Physiology or Medicine to the paleogeneticist Svante Pääbo. In the study led by the Institut Pasteur, published on January 13 in the journal Cell Genomics, the scientists analyzed the variability of the genomes of more than 2,800 individuals who lived in Europe over the past ten millennia – a period covering the Neolithic, the Bronze Age, the Iron Age, the Middle Ages and the present.
By reconstituting the evolution over time of hundreds of thousands of genetic mutations, the scientists initially identified mutations that rapidly increased in frequency in Europe, indicating that they were advantageous. These mutations that evolved under “positive” natural selection are mainly located in 89 genes enriched in functions relating to the innate immune response, including especially the OAS genes – which are responsible for antiviral activity – and the gene responsible for the ABO blood group system. Surprisingly, most of these positive selection events, which demonstrate a genetic adaptation to the pathogenic environment, began recently, from the start of the Bronze Age, around 4,500 years ago. The scientists explain this “acceleration” in adaptation by the growth in the human population during this period and/or by strong selective pressures exerted by pathogens in the Bronze Age, probably linked to the spread of severe infectious diseases such as plague.
At the same time, the scientists also looked at the opposite situation, in other words, mutations whose frequency fell significantly over the past ten millennia. These mutations are probably subject to “negative” selection because they increase the risk of disease. They noted that once again, these selection events mainly began in the Bronze Age. Many of these disadvantageous mutations were also located in genes associated with the innate immune response, such as TYK2, LPB, TLR3 and IL23R, and have been confirmed in experimental research to have a deleterious effect in terms of infectious disease risk. The results emphasize the value of adopting an evolutionary approach in research on genetic susceptibility to infectious diseases.
Finally, the scientists explored the theory that the selection exerted by pathogens in the past gave an advantage to alleles conferring resistance to infectious diseases, but that in turn these alleles have increased the present-day risk of autoimmune or inflammatory disorders. They investigated the few thousand mutations known to increase susceptibility firstly to tuberculosis, hepatitis, HIV or COVID-19, and secondly to rheumatoid arthritis, systemic lupus erythematosus or inflammatory bowel disease. By looking at the evolution of these mutations over time, they observed that those associated with an increased risk of inflammatory disorders – including Crohn’s disease – became more frequent over the past 10,000 years, while the frequency of those associated with a risk of developing infectious diseases decreased. “These results suggest that the risk of inflammatory disorders has increased in Europeans since the Neolithic period because of a positive selection of mutations improving resistance to infectious diseases,” explains Lluis Quintana-Murci, director of the study and Head of the Human Evolutionary Genetics Unit (Institut Pasteur/CNRS Evolutionary Genomics, Modeling and Health Unit/Université Paris Cité).
The results of the study, which harnessed the huge potential of paleogenomics, show that natural selection has targeted human immunity genes over the past ten millennia in Europe, especially since the start of the Bronze Age, and contributed to present-day disparities in terms of the risk of infectious and inflammatory diseases.
As well as the institutions mentioned above, this research was supported by the French Foundation for Medical Research (FRM), the Allianz-Institut de France Foundation and the Fondation de France.
