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Tag: Evolution and Darwin

  • How fluctuating oxygen levels may have accelerated animal evolution

    How fluctuating oxygen levels may have accelerated animal evolution

    Newswise — Oxygen levels in the Earth’s atmosphere are likely to have “fluctuated wildly” one billion years ago, creating conditions that could have accelerated the development of early animal life, according to new research.  

    Scientists believe atmospheric oxygen developed in three stages, starting with what is known as the Great Oxidation Event around two billion years ago, when oxygen first appeared in the atmosphere. The third stage, around 400 million years ago, saw atmospheric oxygen rise to levels that exist today.  

     
    What is uncertain is what happened during the second stage, in a time known as the Neoproterozoic Era, which started about one billion years ago and lasted for around 500 million years, during which time early forms of animal life emerged.   

     
    The question scientists have tried to answer is - was there anything extraordinary about the changes to oxygen levels in the Neoproterozoic Era that may have played a pivotal role in the early evolution of animals – did oxygen levels suddenly rise or was there a gradual increase?  

     
    Fossilised traces of early animals - known as Ediacaran biota, multi-celled organisms that required oxygen - have been found in sedimentary rocks that are 541 to 635 million years old.  

      

    To try and answer the question, a research team at the University of Leeds supported by the Universities of Lyon, Exeter and UCL, used measurements of the different forms of carbon, or carbon isotopes, found in limestone rocks taken from shallow seas. Based on the isotope ratios of the different types of carbon found, the researchers were able to calculate photosynthesis levels that existed millions of years ago and infer atmospheric oxygen levels.  

     
    As a result of the calculations, they have been able to produce a record of oxygen levels in the atmosphere over the last 1.5 billion years, which tells us how much oxygen would have been diffusing into the ocean to support early marine life. 

     
    Dr Alex Krause, a biogeochemical modeller who completed his PhD in the School of Earth and Environment at Leeds and was the lead scientist on the project, said the findings give a new perspective on the way oxygen levels were changing on Earth.  

     
    He added: “The early Earth, for the first two billion years of its existence, was anoxic, devoid of atmospheric oxygen. Then oxygen levels started to rise, which is known as the Great Oxidation Event.   

     
    “Up until now, scientists had thought that after the Great Oxidation Event, oxygen levels were either low and then shot up just before we see the first animals evolve, or that oxygen levels were high for many millions of years before the animals came along. 

     
    “But our study shows oxygen levels were far more dynamic. There was an oscillation between high and low levels of oxygen for a long time before early forms of animal life emerged. We are seeing periods where the ocean environment, where early animals lived, would have had abundant oxygen – and then periods where it does not.  

    Dr Benjamin Mills, who leads the Earth Evolution Modelling Group at Leeds and supervised the project, said: “This periodic change in environmental conditions would have produced evolutionary pressures where some life forms may have become extinct and new ones could emerge.”  

     
    Dr Mills said the oxygenated periods expanded what are known as “habitable spaces” – parts of the ocean where oxygen levels would have been high enough to support early animal life forms.  

     
    He said: “It has been proposed in ecological theory that when you have a habitable space that is expanding and contracting, this can support rapid changes to the diversity of biological life.  

     
    “When oxygen levels decline, there is severe environmental pressure on some organisms which could drive extinctions. And when the oxygen-rich waters expand, the new space allows the survivors to rise to ecological dominance.  

     

    “These expanded habitable spaces would have lasted for millions of years, giving plenty of time for ecosystems to develop.”

    END

    University of Leeds

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  • Bumblebees have poor, but useful memories

    Bumblebees have poor, but useful memories

    Newswise — Bumblebees  don’t seem to keep memories for how sweet a flower was, but instead only remember if it was sweeter than another flower, according to researchers at Queen Mary University of London, along with an international team of scientists. 

    In new research in the journal eLife, bumblebees were first trained on two flowers, learning that one flower was sweeter than a second flower. Later, they learned that a third flower was sweeter than a fourth flower. Then bumblebees were given the choice between two of the flowers they hadn’t seen together before, for example the second and third or the first and third.  

    Over a series of experiments, bumblebees’ preferences during the tests indicated that they could only retain very basic ranking memories for the flowers for very long. The bumblebees could only remember that a flower had been better or worse during training phase. Bees couldn’t seem to remember for more than a few minutes how sweet or rewarding the flowers were on their own or even how much sweeter they were compared to other flowers.  

    Previous research shows that we humans actually keep memories for both absolute information (e.g. how sweet something is) and comparisons [Palminteri and Lebreton, 2021]. Starlings, a bird native to Europe, and the only other animal for which this question has been examined, similarly use a combination of absolute and comparative information when remembering options [Pompilio and Kacelnik, 2010].

    Ms Yonghe Zhou, co-lead author on the paper and currently a PhD student at Queen Mary University of London, says: “Our results reveal an intriguing divergent mechanism for how bumblebees retain and use information about options, compared to humans and birds.” 

    Prof Fei Peng, senior author currently at Southern Medical University, China, states “It may be that the different strategies used by bumblebees and humans may have evolved because of their different diets. Maybe because bumblebees evolved to mostly only eat flower nectar, they never needed to remember the details and could survive and thrive simply using simple comparisons.”  

    Ms Yonghe adds: “Despite what may seem to be a poor memory strategy, bumblebees do very well in finding the most profitable flowers. It’s fascinating to consider how different animals, in their own ecological niche, can be similarly successful using such different strategies.” 

     

    Queen Mary University of London

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  • Scientists peel back ancient layers of banana DNA to reveal ‘mystery ancestors’

    Scientists peel back ancient layers of banana DNA to reveal ‘mystery ancestors’

    Newswise — Bananas are thought to have been first domesticated by people 7,000 years ago on the island of New Guinea. But the domestication history of bananas is complicated, while their classification is hotly debated, as boundaries between species and subspecies are often unclear.

    Now, a study in Frontiers in Plant Science shows that this history is even more complex than previously thought. The results confirm that the genome of today’s domesticated varieties contains traces of three extra, as yet unknown, ancestors.

    “Here we show that most of today’s diploid cultivated bananas that descend from the wild banana M. acuminata are hybrids between different subspecies. At least three extra wild ‘mystery ancestors’ must have contributed to this mixed genome thousands of years ago, but haven’t been identified yet,” said Dr Julie Sardos, a scientist at The Alliance of Bioversity International and CIAT in Montpellier, France, and the study’s first author. 

    Complex domestication history

    Domesticated bananas (except for the Fei bananas in the Pacific) are thought to be descended from a cluster of four ancestors  ̶  either subspecies of the wild banana Musa acuminata, or distinct but closely related species. M. acuminata seems to have evolved in the northern borderlands between India and Myanmar, and to have existed across Australasia approximately 10m years before it was first domesticated. A further complication is that domesticated varieties can have two (‘diploid’), three (‘triploid’), or four (‘tetraploid’) copies of every chromosome, and that many are also descended from the wild species M. balbisiana.

    Recent smaller-scale studies suggested that even this already complex scenario might not be the whole story, and that further ancestors related to M. acuminata could have been involved in the domestication. The new results not only confirm that this is indeed the case, they also show for the first time that that these gene pools are common in domesticated banana genomes.

    Banana collecting missions

    The authors sequenced the DNA in 226 extracts leaf extracts from the world’s largest collection of banana samples at The Alliance of Bioversity International and CIAT’s ‘Musa Germplasm Transit Centre’ in Belgium. Among these samples, 68 belonged to nine wild subspecies of M. acuminata, 154 to diploid domesticated varieties descended from M. acuminata, and four more distantly related wild species and hybrids as comparisons. Many had previously been gathered in dedicated ‘banana collecting missions’ to Indonesia, the island of New Guinea, and the autonomous region of Bougainville.

    The researchers first measured the levels of relatedness between cultivars and wild bananas and made ´family trees´ based on the diversity at 39,031 Single Nucleotide Polymorphisms (SNPs). They used a subset of these – evenly spread across the genome, with each pair demarcating a block of approximately 100,000 ‘DNA letters’ – to statistically analyze the ancestry of each block. For the first time they detected traces of three further ancestors in the genome of all domesticated samples, for which no matches are yet known from the wild.

    Mystery ancestors might survive somewhere

    The mystery ancestors might be long since extinct. “But our personal conviction is that they are still living somewhere in the wild, either poorly described by science or not described at all, in which case they are probably threatened,” said Sardos.

    Sardos et al. have a good idea where to look for them: “Our genetic comparisons show that the first of these mystery ancestors must have come from the region between the Gulf of Thailand and west of the South China Sea. The second, from the region between north Borneo and the Philippines. The third, from the island of New Guinea.”

    Could help breed better bananas

    Which useful traits these mystery ancestors might have contributed to domesticated bananas is not yet known. For example, the crucial trait of parthenocarpy, fruit setting without the need for pollination, is thought to have been inherited from M. acuminata, while cooking bananas owe a large chunk of their DNA to the subspecies (or perhaps separate species) M. acuminata banksii.

    Second corresponding author Dr Mathieu Rouard, likewise at Bioversity International, said: “Identifying the ancestors of cultivated bananas is important, as it will help us understand the processes and the paths that shaped the banana diversity observed today, a crucial step to breed bananas of the future.”

    “Breeders need to understand the genetic make-up of today’s domesticated diploid bananas for their crosses between cultivars, and this study is a major first step toward the characterization in great detail of many of these cultivars.”

    Sardos said: “Based on these results, we will work with partners to explore and genotype wild banana diversity in the three geographic regions that our study pinpointed, with the hope to identify these unidentified contributors to cultivated bananas. It will also be important to investigate the different advantages and traits that each of these contributors provided to cultivated bananas.”

    Frontiers

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  • Ancient ‘shark’ from China is humans’ oldest jawed ancestor

    Ancient ‘shark’ from China is humans’ oldest jawed ancestor

    Newswise — Living sharks are often portrayed as the apex predators of the marine realm. Paleontologists have been able to identify fossils of their extinct ancestors that date back hundreds of millions of years to a time known as the Palaeozoic period. These early “sharks,” known as acanthodians, bristled with spines. In contrast to modern sharks, they developed bony “armor” around their paired fins.

    A recent discovery of a new species of acanthodian from China surprised scientists with its antiquity. The find predates by about 15 million years the earliest acanthodian body fossils and is the oldest undisputed jawed fish.

    These findings were published in Nature on Sept. 28.

    Reconstructed from thousands of tiny skeletal fragments, Fanjingshania, named after the famous UNESCO World Heritage Site Fanjingshan, is a bizarre fish with an external bony “armor” and multiple pairs of fin spines that set it apart from living jawed fish, cartilaginous sharks and rays, and bony ray- and lobe-finned fish.

    Examination of Fanjingshania by a team of researchers from the Chinese Academy of Sciences, Qujing Normal University, and the University of Birmingham revealed that the species is anatomically close to groups of extinct spiny “sharks” collectively known as acanthodians. Unlike modern sharks, acanthodians have skin ossifications of the shoulder region that occur primitively in jawed fish.

    The fossil remains of Fanjingshania were recovered from bone bed samples of the Rongxi Formation at a site in Shiqian County of Guizhou Province, South China.

    These findings present tangible evidence of a diversification of major vertebrate groups tens of millions of years before the beginning of the so called “Age of Fishes” some 420 million years ago.

    The researchers identified features that set apart Fanjingshania from any known vertebrate. It has dermal shoulder girdle plates that fuse as a unit to a number of spines—pectoral, prepectoral and prepelvic. Additionally, it was discovered that the ventral and lateral portions of the shoulder plates extend to the posterior edge of the pectoral fin spines. The species has distinct trunk scales with crowns composed of a row of tooth-like elements (odontodes) adorned by discontinuous nodose ridges. Peculiarly, dentine development is recorded in the scales but is missing in other components of the dermal skeleton such as the fin spines.

    “This is the oldest jawed fish with known anatomy,” said Prof. ZHU Min from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences. “The new data allowed us to place Fanjingshania in the phylogenetic tree of early vertebrates and gain much needed information about the evolutionary steps leading to the origin of important vertebrate adaptations such as jaws, sensory systems, and paired appendages.”

    From the outset, it was clear to the scientists that Fanjingshania‘s shoulder girdle, with its array of fin spines, is key to pinpointing the new species’ position in the evolutionary tree of early vertebrates. They found that a group of acanthodians, known as climatiids, possess the full complement of shoulder spines recognized in Fanjingshania. What is more, in contrast to normal dermal plate development, the pectoral ossifications of Fanjingshania and the climatiids are fused to modified trunk scales. This is seen as a specialization from the primitive condition of jawed vertebrates where the bony plates grow from a single ossification center.

    Unexpectedly, the fossil bones of Fanjingshania show evidence of extensive resorption and remodelling that are typically associated with skeletal development in bony fish, including humans.

    “This level of hard tissue modification is unprecedented in chondrichthyans, a group that includes modern cartilaginous fish and their extinct ancestors,” said lead author Dr. Plamen Andreev, a researcher at Qujing Normal University. “It speaks about greater than currently understood developmental plasticity of the mineralized skeleton at the onset of jawed fish diversification.”

    The resorption features of Fanjingshania are most apparent in isolated trunk scales that show evidence of tooth-like shedding of crown elements and removal of dermal bone from the scale base. Thin-sectioned specimens and tomography slices show that this resorptive stage was followed by deposition of replacement crown elements. Surprisingly, the closest examples of this skeletal remodelling are found in the dentition and skin teeth (denticles) of extinct and living bony fish. In Fanjingshania, however, the resorption did not target individual teeth or denticles, as occurred in bony fish, but instead removed an area that included multiple scale denticles. This peculiar replacement mechanism more closely resembles skeletal repair than the typical tooth/denticle substitution of jawed vertebrates.

    A phylogenetic hypothesis for Fanjingshania that uses a numeric matrix derived from observable characters confirmed the researchers’ initial hypothesis that the species represents an early evolutionary branch of primitive chondrichthyans. These results have profound implications for our understanding of when jawed fish originated since they align with morphological clock estimates for the age of the common ancestor of cartilaginous and bony fish, dating it to around 455 million years ago, during a period known as the Ordovician.

    These results tell us that the absence of undisputed remains of jawed fish of Ordovician age might be explained by under sampling of sediment sequences of comparable antiquity. They also point towards a strong preservation bias against teeth, jaws, and articulated vertebrate fossils in strata coeval with Fanjingshania.

    “The new discovery puts into question existing models of vertebrate evolution by significantly condensing the timeframe for the emergence of jawed fish from their closest jawless ancestors. This will have profound impact on how we assess evolutionary rates in early vertebrates and the relationship between morphological and molecular change in these groups,” said Dr. Ivan J. Sansom from the University of Birmingham.

    Chinese Academy of Sciences

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