It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Friday, July 02, 2021
Astonishing altitude changes in marathon flights of migratory birds
Extreme differences in flight altitude between day and night may have been an undetected pattern amongst migratory birds - until now. The observation was made by researchers at Lund University in Sweden in a study of great snipes, where they also measured a new altitude record for migratory birds, irrespective of the species, reaching 8 700 metres.
Great snipes are shorebirds that breed in Sweden, among other places, and spend the winter in areas near the equator in Africa. Previous studies have shown that great snipes make long marathon flights of up to 6 000 kilometres lasting 60-90 hours when they migrate between breeding sites in Sweden and wintering sites close to the equator.
In a new study published in Current Biology, the international research team describe how the great snipes fly at a higher altitude during the day than at night. The difference can be as much as several thousand metres. The birds regularly flew at an altitude of over 6 000 metres during the day, compared to an average altitude of about 2 000 metres at night. One bird even flew at over 8 000 metres for five hours during the autumn migration to Africa, reaching a maximum altitude of 8 700 metres.
"It is the highest flight altitude that has ever been recorded for a migratory bird", says Åke Lindström at the Department of Biology in Lund who led the study.
Researchers used small data loggers developed at Lund University and attached these to the great snipes in order to follow changes in flight altitude during the long flights. The record height of 8 700 metres is astonishing.
However, the researchers are even more fascinated by the pattern among migratory birds that they may have detected. A recently published study on great reed warblers, which was also led by researchers in Lund, found that on the few occasions during the migration when the small passerines prolonged their otherwise nocturnal flights into the day, they flew at much higher flight altitudes during the day than at night. This occurred when great reed warblers crossed inhospitable terrain such as the Sahara Desert and the Mediterranean Sea.
The considerably larger great snipes do the same. However, not only when they fly over so-called ecological barriers such as deserts and seas, but also when they fly over the tropics and over Europe.
"Other species that that make long migratory flights are also likely to use this day-and-night rhythm. We may well be tracking a general pattern, it will be up to future studies to show this", says Åke Lindström.
If it transpires to be a pattern amongst many migratory birds, it would enhance our understanding of which environmental factors are important for migratory birds. This knowledge may in turn bring us closer to explaining the great variation in the behaviour of these birds. Why do some species migrate at night and others during the day? Why do some birds only fly short distances at a time while others, such as great snipes fly for several days in a row?
As yet, no one knows for certain why great snipes and great reed warblers fly at a higher altitude in the day than at night during migration. The research team mention three explanations as the most probable: birds can navigate more easily via landmarks, they avoid birds of prey, the cold temperature at high altitudes helps prevent overheating during strenuous exercise under the blazing sun.
"Our main line of inquiry is that they fly at a high altitude to cool down, but we must be humble and acknowledge that there may be other or additional explanations", concludes Åke Lindström.
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Why are some fish warm-blooded? Predatory sharks gain speed advantage
IMAGE: A TIGER SHARK (GALEOCERDO CUVIER) SWIMMING AT THE SURFACE WITH A BIOLOGGING PACKAGE ATTACHED TO DORSAL FIN. THIS PACKAGE RECORDS TEMPERATURE, SWIMMING SPEED, DEPTH, BODY MOVEMENT AND VIDEO FOOTAGE. view more
CREDIT: DIEGO CAMEJO (BENEATH THE WAVES).
New research from marine biologists offers answers to a fundamental puzzle that had until now remained unsolved: why are some fish warm-blooded when most are not?
It turns out that while (warm-blooded) fish able to regulate their own body temperatures can swim faster, they do not live in waters spanning a broader range of temperatures.
The research therefore provides some of the first direct evidence as to the evolutionary advantage of being warm-blooded as well as underlining that species in this demographic - such as the infamous white shark and the speedy bluefin tuna - are likely just as vulnerable to changing global ocean temperatures as their cold-blooded relatives.
Lucy Harding, PhD Candidate in Trinity College Dublin's School of Natural Sciences, is the first author of the associated research article, which has just been published in the journal, Functional Ecology. She said:
"Scientists have long known that not all fish are cold-blooded. Some have evolved the ability to warm parts of their bodies so that they can stay warmer than the water around them, but it has remained unclear what advantages this ability provided.
"Some believed being warm-blooded allowed them to swim faster, as warmer muscles tend to be more powerful, while others believed it allowed them to live in a broader range of temperatures and therefore be more resilient to the effects of ocean warming as a result of climate change."
Lucy and her international team of collaborators assessed these two possibilities by collecting data from wild sharks and bony fish, as well as using existing databases.
By attaching biologging devices to the fins of the animals they caught, they were able to collect information such as water temperatures encountered by the fish in their habitats; the speeds at which the fish swam for most of the day; and the depths of water the fish swam in.
The results showed that warm-blooded fishes swim approximately 1.6 times faster than their cold-blooded relatives, but they did not live in broader temperature ranges.
Nick Payne, Assistant Professor in Zoology in Trinity's School of Natural Sciences, said:
"The faster swimming speeds of the warm-blooded fishes likely gives them competitive advantages when it comes to things like predation and migration. With predation in mind, the hunting abilities of the white shark and bluefin tuna help paint a picture of why this ability might offer a competitive advantage.
"Additionally, and contrary to some previous studies and opinions, our work shows these animals do not live in broader temperature ranges, which implies that they may be equally at risk from the negative impacts of ocean warming. Findings like these - while interesting on their own - are very important as they can aid future conservation efforts for these threatened animals."
The research was supported by Science Foundation Ireland.
CAPTION
A white shark (Carcharodon carcharias) swimming at the surface with a biologging package attached to dorsal fin. This package records temperature, swimming speed, depth, body movement and video footage.
CREDIT
Andrew Fox.
Underwater seismometer can hear how fast a glacier moves
IMAGE: KEY ADVANTAGES OF DEPLOYING AN OCEAN-BOTTOM SEISMOMETER NEAR THE CALVING FRONT OF A TIDEWATER GLACIER. SUBGLACIAL AND OCEAN SEISMO-ACOUSTIC SIGNALS CAN BE DETECTED, WHILE THE IMPACT OF SURFACE SEISMIC SOURCES... view more
CREDIT: EVGENY A. PODOLSKIY, YOSHIO MURAI, NAOYA KANNA, SHIN SUGIYAMA. NATURE COMMUNICATIONS. JUNE 24, 2021
Scientists show that an ocean-bottom seismometer deployed close to the calving front of a glacier in Greenland can detect continuous seismic radiation from a glacier sliding, reminiscent of a slow earthquake.
Basal slip of marine-terminating glaciers controls how fast they discharge ice into the ocean. However, to directly observe such basal motion and determine what controls it is challenging: the calving-front environment is one of the most difficult-to-access environments and seismically noisy -- especially on the glacier surface -- due to heavily crevassed ice and harsh weather conditions.
A team of scientists from Hokkaido University, led by Assistant Professor Evgeny A. Podolskiy from the Arctic Research Center, have used ocean-bottom and surface seismometers to detect previously unknown persistent coastal shaking generated by a sliding of a glacier. Their findings were published in the journal Nature Communications.
Sensors to measure glacial motion can potentially be placed on top of, within, or below the glacier; however, each approach has its own drawbacks. For example, the surface of glaciers is 'noisy' due to wind and tide-modulated crevassing, which can overwhelm all other signals; while the interior is quieter, it is the hardest area to access. However, all of these locations are plagued by common issues such as station drift, melt out and level loss, cold temperatures, and potential instrument destruction by iceberg calving.
In the current study, the scientists used an ocean-bottom seismometer (OBS) that was deployed near the calving front of Bowdoin Glacier (Kangerluarsuup Sermia) to listen to icequakes caused by glacial basal motion. By doing so, they insulated the sensor from the near-surface seismic noise, and also circumvented all the issues that accompany the deployment of sensors on the glacier itself and nearby. The data they collected from the OBS was correlated with data from seismic and ice-speed measurements at the ice surface.
CAPTION
Evgeny A. Podolskiy, lead author of the study, assembling the ocean-bottom seismometer in Qaanaaq, northwest Greenland, July 2019 (Photo: I. Asaji).
CREDIT
I. Asaji
The analysis of the data revealed that there is a continuous seismic tremor generated by the glacier. In particular, the broad-band seismic signal (3.5 Hz to 14.0 Hz) detected by the OBS correlated well with the movement of the glacier. The scientists were able to identify signals that were not associated with glacial basal dynamics. Data from the OBS were necessary to establish a correlation between tremors detected by the surface stations and GPS-recorded displacement of the glacier. In the process, they demonstrated that continuous seismic data that was historically considered 'noise' contains signals that can be used to study glacier dynamics.
The scientists also suggested that glacier slip is similar to slow earthquakes. The characteristics of the Bowdoin-Glacier tremor remind those of tectonic tremors in Japan and Canada. Moreover, the presence of the tremor is in line with recent theoretical models and cold-laboratory experiments.
The scientists have presented a novel method to collect continuous glacioseismic information about glacier motion in an extremely noisy and harsh polar environment using ocean-bottom seismology. "Future research in this area could focus on replicating and expanding upon the findings of this study at other glaciers," says Evgeny A. Podolskiy. "The experimental support for the relationship between glacier tremors and tectonic tremors suggests that a long-term multidisciplinary approach would be beneficial in fully understanding this phenomenon."
CAPTION
The ocean-bottom seismometer being deployed by the authors and colleagues, 21 July 2019, Bowdoin Fjord (Photo: I. Asaji).
CREDIT
I. Asaji
Good food in a nice setting: wild bees need diverse agricultural landscapes
Research team investigates influence of different mass-flowering crops on pollinators
IMAGE: SOLITARY WILD BEE ON AN OILSEED RAPE FLOWER view more
CREDIT: N BEYER
Mass-flowering crops such as oilseed rape or faba bean (also known as broad bean) provide valuable sources of food for bees, which, in turn, contribute to the pollination of both the crops and nearby wild plants when they visit. But not every arable crop that produces flowers is visited by the same bees. A team from the University of Göttingen and the Julius Kühn Institute (JKI) in Braunschweig has investigated how the habitat diversity of the agricultural landscape and the cultivation of different mass-flowering crops affect wild bees. The research shows that diverse agricultural landscapes increase the species richness of wild bees. Flowering arable crops with different flower shapes support different wild bee species. The results of the study have been published in Landscape Ecology.
The research team recorded wild bees in flower-rich, semi-natural habitats such as hedgerows and flower strips in a total of 30 different agricultural landscapes, each covering one square kilometre, near Göttingen, Itzehoe and Leipzig. Researchers counted the number of bees along standardised sections and used a hand net to catch them and identify the species. The landscapes used in the study differed in their diversity and in the proportion of land covered by rapeseed and faba beans.
"The shape of the flower is an important criterion for determining which wild bee species will collect nectar from its flowers," says PhD student Felix Kirsch from the University of Göttingen, who conducted the study as part of his Master's thesis. "For example, the shape of the flower must fit the bee's body size and the length of its tongue. Nectar is easily accessible from rapeseed flowers, while the nectar of faba bean is hidden deep inside the flowers."
CAPTION
Long-tongued bumblebee on a faba bean flower
CREDIT
N Beyer
"Our study shows that faba beans promote social wild bees, especially long-tongued bumblebees," explains Dr Doreen Gabriel from the JKI in Braunschweig. A different picture emerged in landscapes with large amounts of oilseed rape: here, the study found that the proportion of solitary wild bees, which often have a smaller body size, was higher. "The cultivation of a certain mass-flowering crop is not sufficient to maintain diverse bee communities, which in turn ensure the pollination success of many flowering arable crops and wild plants," says first author Nicole Beyer, a postdoctoral researcher in the Functional Agrobiodiversity Department at Göttingen University. The head of the department, Professor Catrin Westphal, concludes: "Our results show convincingly that diverse, flowering arable crops and especially diverse semi-natural habitats in the agricultural landscape are necessary to support a broad range of wild bee species."
Original publication: Beyer, N. et al. Identity of mass-flowering crops moderates functional trait composition of pollinator communities. Landscape Ecology 2021. https://doi.org/10.1007/s10980-021-01261-3
Striking a balance: Trade-offs shape flower diversity
An international research team led by a researcher from the University of Tsukuba proposes that catering to different visitors has influenced flower evolution
IMAGE: FLOWER GENERALIZATION HAS OFTEN BEEN VIEWED AS A SUBOPTIMAL SOLUTION TO MANAGING THE NEEDS OF DIFFERENT VISITORS. RESEARCHERS FROM THE UNIVERSITY OF TSUKUBA HAVE DEVELOPED A FRAMEWORK TO EXAMINE FLOWER-ANIMAL... view more
CREDIT: UNIVERSITY OF TSUKUBA
Ibaraki, Japan - Flowers come in a multitude of shapes and colors. Now, an international research team led by a researcher from Japan has proposed the novel hypothesis that trade-offs caused by different visitors may play an important role in shaping this floral diversity.
In a study published last month, the team explored how the close associations between flowers and the animals that visit them influence flower evolution.
Visitors to flowers may be beneficial, like pollinators, or detrimental, like pollen thieves. All of these visitors interact with flowers in different ways and exert different selection pressures on flower traits such as color and scent. For example, a scent that attracts one pollinator may deter other potential pollinators. In this case, the flower would be expected to cater to the best pollinator.
"On the basis of this theory, you'd expect that flowers would mostly be visited by one particular group of pollinators," says lead author of the study, Professor Kazuharu Ohashi. "But flowers often host many different visitors at the same time and flowers appear to meet the needs of multiple visitors. The question we wanted to answer is how this happens in nature."
Balancing the demands of multiple visitors involves trade-offs. For example, diurnal bees and nocturnal moths can both pollinate goat willow but prefer different smells. A floral scent adapted to only one of these animals would mean missed opportunities for pollination by the other. To see how these types of visitor-mediated trade-offs affect the evolution of flowers, the researchers developed a conceptual framework to examine the different types of trade-offs and how flowers might adapt. They then looked at previous studies of flower-animal interactions to see whether the research supported the proposed framework.
What they found was a variety of strategies for mitigating trade-offs. In the case of goat willow, flowers produce different scents during the day and night, and therefore attract both types of pollinator. Another example is floral color change as a strategy to attract both bees and flies. Retaining old flowers could attract opportunistic foragers like flies, while repelling smart foragers like bees. The color change in flowers as they age could reduce this trade-off by allowing bees to select young, rewarding flowers. Many other strategies were noted, all of which involved acquiring novel combinations of traits to attract, or exclude, different visitors.
"Most flowers are ecologically generalized and the assumption to date has been that this is a suboptimal solution," explains Professor Ohashi. "But our findings suggest that interactions with multiple animals can actually be optimized by minimizing trade-offs in various ways, and such evolutionary processes may have enriched the diversity of flowers."
The discrepancy between observed flower visitors and those predicted on the basis of a flower's traits has long been a topic of debate. Taking visitor-mediated trade-offs into account in future studies of flower evolution may help settle that argument.
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The article, "Trade-off mitigation: a conceptual framework for understanding floral adaptation in multispecies interactions," was published in Biological Reviews at DOI:10.1111/brv.12754
New approach can add diversity to crop species without breeding GMOs
Genetic technique edits every chloroplast in a plant, but does not change nuclear DNA of offspring
IMAGE: RESEARCHERS IN JAPAN HAVE DESIGNED A TECHNIQUE THAT CAN MAKE POINT MUTATIONS TO THE DNA OF PLANT CHLOROPLASTS WITHOUT LEAVING ANY OF THE GENETIC ENGINEERING TECHNOLOGY BEHIND TO BE INHERITED... view more
CREDIT: IMAGE BY HIROKO UCHIDA CC BY-SA 4.0, HTTP://UCHIDAHIROKO.COM/WORKS-S.HTML
Breeding better crops through genetic engineering has been possible for decades, but the use of genetically modified plants has been limited by technical challenges and popular controversies. A new approach potentially solves both of those problems by modifying the energy-producing parts of plant cells and then removing the DNA editing tool so it cannot be inherited by future seeds. The technique was recently demonstrated through proof-of-concept experiments published in the journal Nature Plants by geneticists at the University of Tokyo.
"Now we've got a way to modify chloroplast genes specifically and measure their potential to make a good plant," said Associate Professor Shin-ichi Arimura, who leads the group that performed the research.
Chloroplasts, the parts of plant cells that convert carbon dioxide and sunlight into sugar, possess their own circular DNA that is made of the same ATGC-code as the double helix DNA in the nucleus of the cell. However, chloroplast DNA is maintained and inherited completely separately from nuclear DNA. Every cell can contain multiple chloroplasts, each with many identical copies of the chloroplast DNA. The same change must be made in every copy of chloroplast DNA if any genome editing is to have a noticeable effect that can be inherited by the plant's offspring.
In the 1990s, experts invented a technique to insert new DNA fragments into chloroplast genomes, but it also inserts extra genetic tags or markers.
The goal of Arimura and his colleagues is to make uniform, inheritable modifications to only specific parts of chloroplast DNA without leaving genome editing tools behind or permanently altering nuclear DNA. They started with an existing tool known as TALENs. The original TALENs use a large protein that recognizes specific short DNA sequences and cuts that DNA with an enzyme. In recent years, other research groups have improved TALEN technology: the DNA recognition sequences can be customized and the DNA cutting enzyme can be replaced with an enzyme that changes GC pairs in the DNA code into AT pairs.
These GC to AT changes are subtle -- just changing one point of the DNA code to another, rather than inserting or deleting whole genes. However, point mutations can have major effects depending on their location.
Arimura's team combined these TALEN improvements and added an extra "chloroplast-targeting" component, calling their finalized version ptpTALECDs. For every genome edit that researchers wanted to make, they needed to build a matching left and right pair of ptpTALECDs in bacteria. The design process is complicated because the pairs of large TALENs proteins and the chloroplast-targeting signals must be expressed simultaneously as a single unit from the nuclear DNA.
"Building the ptpTALECDs was an extremely laborious process, but we have a very dedicated master's degree student who did almost all the work, Issei Nakazato," said Arimura. Nakazato is the first author of the research publication.
After designing the ptpTALECDs DNA sequence, researchers then inserted it into Arabidopsis thaliana plants, a species of thale cress common in research laboratories. The UTokyo researchers are confident that after building them, the ptpTALECDs could be inserted into many crop species because that part of the process is a straightforward and standard procedure in agriculture and botany labs.
The ptpTALECDs enter the plants' nuclei and then the cells produce ptpTALECDs in the same way they produce any other protein. The chloroplast-targeting sequence ensures that the finished ptpTALECD proteins are shuttled out of the nucleus into the chloroplasts where they then are expected to edit every chloroplast genome they encounter.
This first generation plants are considered genetically modified organisms (GMOs) because their nuclear DNA has been permanently altered to contain the ptpTALECD sequence.
When these genetically modified plants reproduce with themselves through self-fertilization or with nonmodified (wild-type) plants, the next generation of plants inherits nuclear DNA in the normal way, meaning genes are mixed and matched between the ovules and pollen. Some seeds inherit the ptpTALECD sequence and other seeds do not.
However, plants always inherit their chloroplasts whole and intact through their "mothers," the ovules. So regardless of what nuclear DNA the next generation of plants inherits, if their female parent plant had modified chloroplasts, the next generation will always inherit modified chloroplasts.
Researchers then search the offspring to find plants that did not inherit edited nuclear DNA, but did inherit modified chloroplasts. These members of the second generation of plants and any of their future offspring can be considered non-GMO end products because their nuclear DNA contains none of the ptpTALECDs' genetic engineering machinery.
Legal definitions vary, but broadly speaking, countries either assess the end product or the process when deciding to label an organism as a GMO. By end-product definitions used in Japan and the U.S., plants produced with this technique are not GMOs. However, the same plants are GMOs under process based-definitions used in the European Union.
So far, Arimura's team proved their system works by editing three chloroplast genes and observing the expected effects in the offspring plants.
"Chloroplast DNA encodes less than 1% of the total genetic material in a plant, but it has a very important effect on photosynthesis, and therefore the health of the plant. Hopefully, this method will be useful in fundamental research and applied agriculture," said Arimura.
Researchers are optimistic that the fact that none of the genetic engineering tools are inherited by future generations and that the method only makes point mutations will ensure that the method will be used to breed better crops that are accepted by farmers and consumers.
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Research Publication
Issei Nakazato, Miki Okuno, Hiroshi Yamamoto, Yoshiko Tamura, Takehiko Itoh, Toshiharu Shikanai, Hideki Takanashi, Nobuhiro Tsutsumi, Shin-ichi Arimura. 1 July 2021. Targeted base editing in the plastid genome of Arabidopsis thaliana. Nature Plants. DOI: 10.1038/s41477-021-00954-6 https://www.nature.com/articles/s41477-021-00954-6
Associate Professor Shin-ichi Arimura Laboratory of Plant Molecular Genetics, Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657
About the University of Tokyo
The University of Tokyo is Japan's leading university and one of the world's top research universities. The vast research output of some 6,000 researchers is published in the world's top journals across the arts and sciences. Our vibrant student body of around 15,000 undergraduate and 15,000 graduate students includes over 4,000 international students. Find out more at http://www.u-tokyo.ac.jp/en/ or follow us on Twitter at @UTokyo_News_en.
Funders
This research was supported partly from the University of Tokyo GAP fund program and from the Japan Society for the Promotion of Science (Grant Numbers 20H00417, 16H06279, 19H02927 and 19KK0391).
From meadow to plate: The cultured meat that replaces animals with grass
An affordable lab system that uses grass blades to turn cells into cultured meat has been developed at the University of Bath in the UK
IMAGE: ALIGNED MYOTUBES (CYLINDRICAL CELLS FOUND IN MUSCLE FIBER) GROWING ON GRASS. view more
CREDIT: ALLAN SCOTT
An affordable lab system that uses grass blades to turn cells into cultured meat has been developed at the University of Bath in the UK.
Researchers have successfully taken grass from the university's campus and used it to create a scaffold that animal cells can attach to and grow on. The resulting tissue has the potential to be used both as lab-made meat and as human muscle tissue to repair or replace tissue which has been damaged or lost through injury or disease.
The study, by Dr Paul De Bank (Department of Pharmacy & Pharmacology), Professor Marianne Ellis (Department of Chemical Engineering) and Scott Allan (a PhD researcher in the Department of Chemical Engineering), is published in this month's Journal of Biomedical Materials Research - Part A.
The first step in the new bioengineering process involves emptying grass blades of their native cells in a process known as decellularisation. The decellularised blades are then seeded with a set of cells derived from a mouse cell line (these cells would eventually be replaced by bovine stem cells). The introduced cells stick to the scaffold's surface, multiply and form links with neighbouring cells, eventually growing as a cell mass to form new 3D tissue.
There are several challenges researchers must overcome when looking for a suitable scaffold on which to engineer new muscle tissue. First, the scaffold must be one cells can readily attach to the surface. It must then allow these cells to proliferate and align in a way that precisely mimics the fibres of the natural tissue they are replicating (with muscle fibres, for instance, all the cells need to contract and relax in tandem). Second, for scale-up, the scaffold must be cost-effective and straightforward to manufacture. For lab-grown meat, there is a third challenge: the scaffold must be edible to humans, even if not highly digestible (as is the case for grass).
The Bath project shows grass blades fulfil all criteria.
Dr Paul De Bank, who led the research, said: "When we were looking for a scaffold for our cells, we wanted to find something that was both sustainable and edible. I thought along the lines of a decellularised natural material because cellulose (which grass is largely made of) is edible, but also because grass has aligned grooves that I hoped would allow the cells to line up together to make the fibres we needed - and it worked!"
He added: "When we eat beef, we're partly eating the grass the cows have grazed on in their lifetime. What's neat about our study is that it shows that we can directly replace the animals with the grass they eat. Our system needs to be scaled up but I'm hopeful that sooner rather than later, we could have a meat product on the market based on grass."
The adhesion of the animal stem cells to the grass surface was found to be around 35%, which is considered a good result. "Often, decellularised plant scaffolds need to be chemically modified to get cells to grow on them. The great thing we've found with grass is that we get significant adhesion without further processing steps." said Dr De Bank, adding: "We are, however, hoping to find a way to increase this adhesion - we have a new PhD student who will be working on this, exploring ways to optimise cell attachment and growth.
The next big challenge will be scaling up this process to generate sufficient quantities of both cells and scaffold material in order to produce a significant quantity of muscle tissue. If this is successful then - one day - consumers may be able to buy grass-reared meat with a clear conscience, free from the environmental and animal-welfare concerns many are wrestling with today.
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Global climate dynamics drove the decline of mastodonts and elephants, new study suggests
IMAGE: DUSK FALLS ON EAST AFRICA'S TURKANA BASIN 4 MILLION YEARS AGO, WHERE OUR EARLY UPRIGHT-WALKING APE ANCESTORS, AUSTRALOPITHECUS ANAMENSIS (FOREGROUND), SHARED THEIR HABITAT WITH SEVERAL COEXISTING PROBOSCIDEAN SPECIES, AS PART... view more
CREDIT: JULIUS CSOTONYI
Elephants and their forebears were pushed into wipeout by waves of extreme global environmental change, rather than overhunting by early humans, according to new research.
The study, published today in Nature Ecology & Evolution, challenges claims that early human hunters slaughtered prehistoric elephants, mammoths and mastodonts to extinction over millennia. Instead, its findings indicate the extinction of the last mammoths and mastodonts at the end of the last Ice Age marked the end of progressive climate-driven global decline among elephants over millions of years.
Although elephants today are restricted to just three endangered species in the African and Asian tropics, these are survivors of a once far more diverse and widespread group of giant herbivores, known as the proboscideans, which also include the now completely extinct mastodonts, stegodonts and deinotheres. Only 700,000 years ago, England was home to three types of elephants: two giant species of mammoths and the equally prodigious straight-tusked elephant.
An international group of palaeontologists from the universities of Alcalá, Bristol, and Helsinki, piloted the most detailed analysis to date on the rise and fall of elephants and their predecessors, which examined how 185 different species adapted, spanning 60 million years of evolution that began in North Africa. To probe into this rich evolutionary history, the team surveyed museum fossil collections across the globe, from London's Natural History Museum to Moscow's Paleontological Institute. By investigating traits such as body size, skull shape and the chewing surface of their teeth, the team discovered that all proboscideans fell within one of eight sets of adaptive strategies.
"Remarkably for 30 million years, the entire first half of proboscidean evolution, only two of the eight groups evolved," said Dr Zhang Hanwen, study coauthor and Honorary Research Associate at the University of Bristol's School of Earth Sciences.
"Most proboscideans over this time were nondescript herbivores ranging from the size of a pug to that of a boar. A few species got as big as a hippo, yet these lineages were evolutionary dead-ends. They all bore little resemblance to elephants."
The course of proboscidean evolution changed dramatically some 20 million years ago, as the Afro-Arabian plate collided into the Eurasian continent. Arabia provided crucial migration corridor for the diversifying mastodont-grade species to explore new habitats in Eurasia, and then into North America via the Bering Land Bridge.
CAPTION
A scene from northern Italy 2 million years ago - the primitive southern mammoths Mammuthus meridionalis (right-hand side) sharing their watering hole with the mastodont-grade Anancus arvernensis (left-hand side), the last of its kind. Other animals that brought an 'East African air' to Tuscany included rhinos, hippos and zebra-like wild horses.
CREDIT
Tamura Shuhei
"The immediate impact of proboscidean dispersals beyond Africa was quantified for the very first time in our study," said lead author Dr Juan Cantalapiedra, Senior Research Fellow at the University of Alcalá in Spain.
"Those archaic North African species were slow-evolving with little diversification, yet we calculated that once out of Africa proboscideans evolved 25 times faster, giving rise to a myriad of disparate forms, whose specialisations permitted niche partition between several proboscidean species in the same habitats. One case in point being the massive, flattened lower tusks of the 'shovel-tuskers'. Such coexistence of giant herbivores was unlike anything in today's ecosystems."
Dr Zhang added: "The aim of the game in this boom period of proboscidean evolution was 'adapt or die'. Habitat perturbations were relentless, pertained to the ever-changing global climate, continuously promoting new adaptive solutions while proboscideans that didn't keep up were literally, left for dead. The once greatly diverse and widespread mastodonts were eventually reduced to less than a handful of species in the Americas, including the familiar Ice Age American mastodon."
By 3 million years ago the elephants and stegodonts of Africa and eastern Asia seemingly emerged victorious in this unremitting evolutionary ratchet. However, environmental disruption connected to the coming Ice Ages hit them hard, with surviving species forced to adapt to the new, more austere habitats. The most extreme example was the woolly mammoth, with thick, shaggy hair and big tusks for retrieving vegetation covered under thick snow.
The team's analyses identified final proboscidean extinction peaks starting at around 2.4 million years ago, 160,000 and 75,000 years ago for Africa, Eurasia and the Americas, respectively.
"It is important to note that these ages do not demarcate the precise timing of extinctions, but rather indicate the points in time at which proboscideans on the respective continents became subject to higher extinction risk," said Dr Cantalapiedra.
Unexpectedly, the results do not correlate with the expansion of early humans and their enhanced capabilities to hunt down megaherbivores.
"We didn't foresee this result. It appears as if the broad global pattern of proboscidean extinctions in recent geological history could be reproduced without accounting for impacts of early human diasporas. Conservatively, our data refutes some recent claims regarding the role of archaic humans in wiping out prehistoric elephants, ever since big game hunting became a crucial part of our ancestors' subsistence strategy around 1.5 million years ago," said Dr Zhang.
"Although this isn't to say we conclusively disproved any human involvement. In our scenario, modern humans settled on each landmass after proboscidean extinction risk had already escalated. An ingenious, highly adaptable social predator like our species could be the perfect black swan occurrence to deliver the coup de grâce."
CAPTION
Highly complete fossil skull of a typical mid Miocene 'shovel-tusker', Platybelodon grangeri, roamed in large herds across Central Asia 13 million years ago. The specimen is display mounted at the Hezheng Paleozoological Museum, Gansu Province, China.
CREDIT
Zhang Hanwen
Paper
'The rise and fall of proboscidean ecological diversity' by Cantalapiedra, J.L. et al. in Nature Ecology & Evolution.
Notes to editors
Dr Zhang Hanwen (Steven) is available for interview. To schedule this please email hz1646@bristol.ac.uk and Victoria Tagg, Media & PR Manager (Research) at the University of Bristol: victoria.tagg@bristol.ac.uk
Caption: Dusk falls on East Africa's Turkana Basin 4 million years ago, where our early upright-walking ape ancestors, Australopithecus anamensis (foreground), shared their habitat with several coexisting proboscidean species, as part of a spectacular herbivore community containing some progenitors of today's charismatic East African animals. Background (left to right): Anancus ultimus, last of the African mastodonts; Deinotherium bozasi, colossal herbivore as tall as a giraffe; Loxodonta adaurora, gigantic extinct cousin of modern African elephants, alongside the closely-related, smaller L. exoptata. Middle ground (left to right): Eurygnathohippus turkanense, zebra-sized three-hoofed horse; Tragelaphus kyaloae, a forerunner of the nyala and kudu antelopes; Diceros praecox - ancestor of the modern black rhino.
Caption: Highly complete fossil skull of a typical mid Miocene 'shovel-tusker', Platybelodon grangeri, roamed in large herds across Central Asia 13 million years ago. The specimen is display mounted at the Hezheng Paleozoological Museum, Gansu Province, China.
Image Credit: Zhang Hanwen
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Prehistoric Safari : Pliocene Southern Europe by Jagroar on DeviantArt
Caption: A scene from northern Italy 2 million years ago - the primitive southern mammoths Mammuthus meridionalis (right-hand side) sharing their watering hole with the mastodont-grade Anancus arvernensis (left-hand side), the last of its kind. Other animals that brought an 'East African air' to Tuscany included rhinos, hippos and zebra-like wild horses.
Caption: Disparity of proboscidean forms through 60 million years of evolution. Early proboscideans like Moeritherium (far left) were nondescript herbivores typically the size of a pig. But subsequent evolution of this lineage was almost consistently dominated by gigantic species, many considerably larger than today's elephants (e.g. Deinotherium 2nd left; Palaeoloxodon furthest right). A key factor of proboscidean evolutionary innovation lies with disparities in tooth morphology.
