̽��ֱ�� of Cambridge - fish

̽��ֱ��world's their fish finger

jg533 — Thu, 12 Mar 2020 14:07:27 +0000

Smothered in ketchup or squished into a sandwich, there’s one tasty convenience food that’s hard to resist. Now two Cambridge researchers believe that a twist on the classic fish finger might help address the challenge of sustainably feeding our global population.

Shoals of sticklebacks differ in their collective personalities

cjb250 — Wed, 07 Feb 2018 01:34:32 +0000

For centuries, scientists and non-scientists alike have been fascinated by the beautiful and often complex collective behaviour of animal groups, such as the highly synchronised movements of flocks of birds and schools of fish. Often, those spectacular collective patterns emerge from individual group members using simple rules in their interactions, without requiring global knowledge of their group.

In recent years it has also become apparent that, across the animal kingdom, individual animals often differ considerably and consistently in their behaviour, with some individuals being bolder, more active, or more social than others.

New research conducted at the ̽��ֱ�� of Cambridge’s Department of Zoology suggests that observations of different groups of schooling fish could provide important insights into how the make-up of groups can drive collective behaviour and performance.

In the study, published today in the journal Proceedings of the Royal Society B, the researchers created random groups of wild-caught stickleback fish and subjected them repeatedly to a range of environments that included open spaces, plant cover, and patches of food.

Dr Jolle Jolles, lead author of the study, now based at the Max Planck Institute for Ornithology, said: “By filming the schooling fish from above and tracking the groups’ movements in detail, we found that the randomly composed shoals showed profound differences in their collective behaviour that persisted across different ecological contexts. Some groups were consistently faster, better coordinated, more cohesive, and showed clearer leadership structure than others.

“That such differences existed among the groups is remarkable as individuals were randomly grouped with others that were of similar age and size and with which they had very limited previous social contact.”

This research shows for the first time that, even among animals where group membership changes frequently over time and individuals are not very strongly related to each other, such as schooling fish or flocking birds, stable differences can emerge in the collective performance of animal groups.

Such behavioural variability among groups may directly affect the survival and reproductive success of the individuals within them and influence how they associate with one another. Ultimately these findings may therefore help understand the selective pressures that have shaped social behaviour.

Dr Andrea Manica, co-author of the paper from the ̽��ֱ�� of Cambridge, added: “Our research reveals that the collective performance of groups is strongly driven by their composition, suggesting that consistent behavioural differences among groups could be a widespread phenomenon in animal societies.”

These research findings provide important new insights that may help explain and predict the performance of social groups, which could be beneficial in building human teams or constructing automated robot swarms.

̽��ֱ��research was supported by the Biotechnology and Biological Sciences Research Council.

Reference
Jolles, JW et al. Repeatable group differences in the collective behaviour of stickleback shoals across ecological contexts. Proceedings of the Royal Society B; 7 Feb 2018; DOI: 10.1098/rspb.2017.2629

Research from the ̽��ֱ�� of Cambridge has revealed that, among schooling fish, groups can have different collective personalities, with some shoals sticking closer together, being better coordinated, and showing clearer leadership than others.

Jolle Jolles

Stickleback

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Licence type:

Attribution

Deeper origin of gill evolution suggests 'active lifestyle' link in early vertebrates

fpjl2 — Thu, 09 Feb 2017 17:02:27 +0000

A new study has revealed that gills originated much deeper in evolutionary history than previously believed. ̽��ֱ��findings support the idea that gills evolved before the last common ancestor of all vertebrates, helping facilitate a "lifestyle transition" from immobile filter-feeder to actively swimming predator.

̽��ֱ��research, published today in the journal Current Biology, shows that gills develop from the same embryonic tissue in both jawed and jawless vertebrates - a lineage that split very early in our ancestral tree.

Jawed vertebrates - such as fish, birds and mammals - make up 99% of all living vertebrates, including us. Jawless vertebrates include the parasitic lamprey and scavenging hagfish: eel-like creatures that diverged from the ancestral line over 400 million years ago.

Previous work in this area involved slicing thin sections of fish embryos to chart organ growth. These "snapshots" of development led scientists to believe that gills were formed from different tissues: the internal 'endoderm' lining in jawless vertebrates, and the 'ectoderm' outer skin in the jawed.

As a result, since the mid-20th century it was thought that the ancient jawed and jawless lines evolved gills separately after they split, an example of 'convergent evolution' - where nature finds the same solution twice (such as the use of echolocation in both bats and whales, for example).

Biologists at the ̽��ֱ�� of Cambridge used fluorescent labelling to stain cell membranes in skate embryos, and tracked them through the dynamic development process. Their experiment has now shown that the gills of jawed vertebrates emerge from the same internal lining cells as their jawless relatives.

̽��ֱ��researchers say this is strong evidence that gills evolved just once, much earlier in evolutionary history - before the jawless divergence - and that the "crown ancestor" of all vertebrates was consequently a more anatomically complex creature.

̽��ֱ��findings pull the invention of gills closer to the "active lifestyle" shift in our early ancestors: the evolution from passive filter feeders to self-propelled ocean swimmers. Scientists say that gill development may have been a catalyst or consequence of this giant physiological leap.

"These findings demonstrate a single origin of gills that likely corresponds with a key stage in vertebrate evolution: when some of our earliest relatives transitioned from filtering particles out of water pumped through static bodies to actively swimming through the oceans," says lead author Dr Andrew Gillis, a Royal Society ̽��ֱ�� Research Fellow in Cambridge's Department of Zoology, and a Whitman Investigator at the Marine Biological Laboratory in Woods Hole, US.

"Gills provided vertebrates with specialist breathing organs in their head, rather than having to respire exclusively through skin all over the body. We can't say whether these early animals became more active and needed to evolve a new respiratory mechanism, or if it was gill evolution that allowed them to move faster.

"However, whether by demand or opportunity, our work suggests that the physiological innovation of gills occurred at the same time as the lifestyle transition from passive to active in some of our earliest ancestors."

While the jawed vertebrate lineage spawned the majority of vertebrate life that exists on Earth today - "evolutionarily speaking, we are all bony fish," says Gillis - lamprey and hagfish are the living remnants of a once extensive assemblage of primitively predatory jawless vertebrates.

"Lamprey are eel-like parasites that use their tooth-like organs and raspy tongue to latch onto fish and suck out the blood, while hagfish scavenge by taking bites out of dead matter," he says.

Gillis and colleagues used embryos of the little skate to track early gill development through cell tracing. ̽��ֱ��skate is a cartilaginous fish - an early-branching lineage of jawed vertebrates that includes the sharks and stingrays.

This made skate an excellent comparison point to try and infer the primitive anatomical and developmental conditions in the last common ancestor of jawed and jawless vertebrates.

̽��ֱ��embryonic work of the Gillis laboratory neatly complements paleontological research from their Cambridge colleague Prof Simon Conway Morris, who has spent much of his career studying fossils of the Cambrian period of rapid evolution - when most major animal groups originated.

In 2014, Conway Morris was part of the team that discovered Metaspriggina: one of the oldest-known vertebrate fossils, perhaps over 500 million years old, which displayed hints of a gill structure, as well as the muscle arrangement of an active swimmer.

"Our embryological research helps us understand exactly how the gill structures in early vertebrates such as Metaspriggina relate to the gills of living forms," says Gillis.

"Embryology can tell us about the evolutionary relationship between anatomical features in living animals, while palaeontology can pinpoint precisely when these features first appear in deep time. I think that this work nicely illustrates how these two areas of research can inform one another."

Fish embryo study indicates that the last common ancestor of vertebrates was a complex animal complete with gills – overturning prior scientific understanding and complementing recent fossil finds. ̽��ֱ��work places gill evolution concurrent with shift to self-propulsion in our earliest ancestors.

Our work suggests that the physiological innovation of gills occurred at the same time as the lifestyle transition from passive to active in some of our earliest ancestors

Andrew Gillis

Left: Early skate embryo labeled with fluorescent dye. Right: Image of a hatchling skate

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Sonic hedgehog gene provides evidence that our limbs may have evolved from sharks’ gills

jeh98 — Tue, 19 Apr 2016 11:07:28 +0000

An idea first proposed 138 years ago that limbs evolved from gills, which has been widely discredited due to lack of supporting fossil evidence, may prove correct after all – and the clue is in a gene named for everyone’s favourite blue hedgehog.

Unlike other fishes, cartilaginous fishes such as sharks, skates and rays have a series of skin flaps that protect their gills. These flaps are supported by arches of cartilage, with finger-like appendages called branchial rays attached.

In 1878, influential German anatomist Karl Gegenbaur presented the theory that paired fins and eventually limbs evolved from a structure resembling the gill arch of cartilaginous fishes. However, nothing in the fossil record has ever been discovered to support this.

Now, researchers have reinvestigated Gegenbaur’s ideas using the latest genetic techniques on embryos of the little skate – a fish from the very group that first inspired the controversial theory over a century ago – and found striking similarities between the genetic mechanism used in the development of its gill arches and those in human limbs.

Scientists say it comes down to a critical gene in limb development called ‘Sonic hedgehog’, named for the videogame character by a research team at Harvard Medical School.

̽��ֱ��new research shows that the functions of the Sonic hedgehog gene in human limb development, dictating the identity of each finger and maintaining growth of the limb skeleton, are mirrored in the development of the branchial rays in skate embryos. ̽��ֱ��findings are published today in the journal Development.

Dr Andrew Gillis, from the ̽��ֱ�� of Cambridge’s Department of Zoology and the Marine Biological Laboratory, who led the research, says that it shows aspects of Gegenbaur’s theory may in fact be correct, and provides greater understanding of the origin of jawed vertebrates – the group of animals that includes humans.

“Gegenbaur looked at the way that these branchial rays connect to the gill arches and noticed that it looks very similar to the way that the fin and limb skeleton articulates with the shoulder,” says Gillis. “ ̽��ֱ��branchial rays extend like a series of fingers down the side of a shark gill arch.”

“ ̽��ֱ��fact that the Sonic hedgehog gene performs the same two functions in the development of gill arches and branchial rays in skate embryos as it does in the development of limbs in mammal embryos may help explain how Gegenbaur arrived at his controversial theory on the origin of fins and limbs.”

In mammal embryos, the Sonic hedgehog gene sets up the axis of the limb in the early stages of development. “In a hand, for instance, Sonic hedgehog tells the limb which side will be the thumb and which side will be the pinky finger,” explains Gillis. In the later stages of development, Sonic hedgehog maintains outgrowth so that the limb grows to its full size.

To test whether the gene functions in the same way in skate embryos, Gillis and his colleagues inhibited Sonic hedgehog at different points during their development.

They found that if Sonic hedgehog was interrupted early in development, the branchial rays formed on the wrong side of the gill arch. If Sonic hedgehog was interrupted later in development, then fewer branchial rays formed but the ones that did grow, grew on the correct side of the gill arch – showing that the gene works in a remarkably similar way here as in the development of limbs.

“Taken to the extreme, these experiments could be interpreted as evidence that limbs share a genetic programme with gill arches because fins and limbs evolved by transformation of a gill arch in an ancestral vertebrate, as proposed by Gegenbaur,” says Gillis. “However, it could also be that these structures evolved separately, but re-used the same pre-existing genetic programme. Without fossil evidence this remains a bit of a mystery – there is a gap in the fossil record between species with no fins and then suddenly species with paired fins – so we can’t really be sure yet how paired appendages evolved.”

“Either way this is a fascinating discovery, because it provides evidence for a fundamental evolutionary link between branchial rays and limbs,” says Gillis. “While palaeontologists look for fossils to try to reconstruct the evolutionary history of anatomy, we are effectively trying to reconstruct the evolutionary history of genetic programmes that control the development of anatomy.”

Paired appendages, such as arms and hands in humans, are one of the key anatomical features that distinguish jawed vertebrates from other groups. “There is a lot of interest in trying to understand the origins of jawed vertebrates, and the origins of novel features like fins and limbs,” says Gillis.

“What we are learning is that many novel features may not have arisen suddenly from scratch, but rather by tweaking and re-using a relatively small number of ancient developmental programmes.”

Gillis and his colleagues are further testing Gegenbaur’s theory by comparing the function of more genes involved the development of skates’ unusual gills and mammalian limbs.

“Previous studies haven’t found compelling developmental genetic similarities between gill arch derivatives and paired appendages – but these studies were done in animals like mice and zebrafish, which don’t have branchial rays,” says Gillis.

“It is useful to study cartilaginous fishes, not only because they were the group that first inspired Gegenbaur’s theory, but also because they have a lot of unique features that other fishes don’t – and we are finding that we can learn a lot about evolution from these unique features.”

“Many researchers look at mutant mice or fruit flies to understand the genetic control of anatomy. Our approach is to study and compare the diverse anatomical forms that can be found in nature, in order to gain insight into the evolution of the vertebrate body.”

This research was funded by the Royal Society, the Isaac Newton Trust and a research award from the Marine Biological Laboratory.

Inset images: Skeletal preparation of an embryonic bamboo shark (Andrew Gillis); A skate embryo that has been stained for expression of the Shh gene - staining can be seen as dark purple strips running down the length of each gill arch (Andrew Gillis); Late stage skate embryo (Andrew Gillis).

Latest analysis shows that human limbs share a genetic programme with the gills of cartilaginous fishes such as sharks and skates, providing evidence to support a century-old theory on the origin of limbs that had been widely discounted.

̽��ֱ��branchial rays extend like a series of fingers down the side of a shark gill arch

Andrew Gillis

Head skeletons of skate and shark showing gill arch appendages in red.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Even without lungs, zebrafish help us study TB

amb206 — Wed, 25 Nov 2015 09:25:17 +0000

Scroll to the end of the article to listen to the podcast.

Professor Lalita Ramakrishnan shares her workspace at the Laboratory of Molecular Biology (LMB) with thousands of tiny stripy fish. Zebrafish have long been a favourite in domestic aquariums: they are strikingly pretty and constantly on the move. ̽��ֱ��zebrafish at the LMB, each one no bigger than your little finger, are helping Ramakrishnan and her colleagues to find novel ways of preventing and treating tuberculosis (TB). We asked her about her work.

Why are zebrafish such good models for scientists?

Around 40 years ago scientists began to realise that zebrafish, as vertebrates, could tell us a lot about human development and human diseases. This discovery represented a real breakthrough in terms of what could be achieved using zebrafish in laboratories.

There are two key reasons why zebrafish, in particular, are so valuable. Firstly, when the new fish hatches as a tiny larva, it is optically transparent for the first two weeks of its development. This transparency means that, using powerful imaging technology, we are able to observe in real time the development of the organism as it grows to maturity. In our laboratory, we exploit the optical transparency to directly look at how the tuberculosis bacteria cause disease.

̽��ֱ��second reason why zebrafish is such a good model is that a single mating can produce hundreds of eggs – and female zebrafish are capable of producing a new batch of eggs each week. So we have access to large numbers of animals for the work. On top of all this, zebrafish are relatively straight-forward to keep and easy to breed.

We can also create zebrafish with different mutations and we can then assess the impact of host genes on the course of disease. This kind of fundamental work enables us to identify, by a process of deduction and elimination, what genes do – which is essential to developing new medical interventions.

But surely zebrafish and humans have little in common – we’re not fish!

Humans and fish are much more alike than people might suppose – even though we diverged from our last common ancestor at least 300 million years ago. Most of the genes found in fish are also found in humans – and most of the genes that cause disease in fish also cause disease in humans. ̽��ֱ��human immune system, which fights off disease, is a lot like the immune system of fish.

My research is focused on tuberculosis in humans – a disease that affects millions of people worldwide. Without treatment, TB can be life threatening. We tend to associate human TB with the lungs, and of course fish don’t have lungs. TB does affect the lungs but it can affect almost all our organs. In humans, some 40% of TB infection is not in the lungs but elsewhere in the body - brain, bone, kidney, intestine, reproductive organs.

Fish are affected by a close relative of the human TB bacterium. If we can work out how TB works in fish, and how to prevent it and treat it in fish, then we’re a step closer to solving a major health problem in humans.

What is the life of a laboratory zebrafish like?

Our fish live in tanks that are kept pristine by a unit that cleans and circulates the water. We grow the food they need in the lab – it’s a kind of brine shrimp. Putting this live food into the tanks allows the fish to hunt for their food, creating a more natural environment for them. Zebrafish are sociable creatures so we keep them in groups. All our fish are on a programme of 16 hours of daylight and eight hours of night. This routine mimics, as much as possible, the natural environment in the regions of the world where they live. We make sure that they are as healthy and stress-free as possible. Happy fish are healthy fish – and the other way round!

You can identify the males from the females by the roundness of the female’s belly. When we want a new batch of eggs, we put a male and a female in a tank overnight, with the two fish separated by a transparent divider. When daylight comes, the two fish become excited and we take out the divider and they mate. When the eggs are laid, they fall through a fine grill that enables us to take them out of the tank.

All these procedures are done as carefully as possible so as not to harm the fish or eggs.

How do you use the zebrafish eggs?

In my laboratory, we’re studying TB so we need to infect some of the fish eggs, one by one, with bacteria so that we can observe what happens. This procedure is carried out under a microscope using a very fine needle that is hollow, enabling tiny amounts of bacteria to be delivered into the egg. Because zebrafish eggs are so tiny, it takes a while to learn how to do this. It requires good hand-eye coordination and a steady hand – but everyone learns to do it with time and practice.

Once the eggs are infected we put them into small dishes where we can observe them. Because the eggs and the larvae are transparent, we can observe the process by which the bacteria enters the cells – and we can watch what happens as the bacteria and immune system face off. By using fluorescence, we can colour the host (the organism affected by the disease) and the bacteria so that it’s easier to track what’s happening on a cellular level. We can, for example, observe how exactly bacteria invade and spread.

How is your work with fish helping to develop better ways of tackling TB?

At the moment, TB in the human population is treated with a long course of strong antibiotics – it often takes as long as six months to get rid of it. Strains of drug-resistant TB have developed, partly because people do not finish the courses of drugs prescribed to them.

̽��ֱ��work that my colleagues and I are doing suggests that there could be another, and perhaps more effective, approach to tackling TB. Rather than only targeting the bacteria, which are so clever in their invasive strategies, it might be better to additionally target the host and help the immune system to fight it off. We might do this by boosting or tweaking the immune system.

We now need to put to the test our ideas for helping the immune system by trying out a list of available drugs – and, in the initial stages of the research, we will be using zebrafish as models.

What’s the future for zebrafish as a model organism in research?

̽��ֱ��world of research using zebrafish is wonderfully collaborative and fast-moving. Our main partner is the Sanger Institute which is just a few miles from the LMB. We collaborate closely with the scientists there on tools and techniques – including producing the mutants in order to identify genetic pathways.

Zebrafish are still relatively new in terms of their contribution to research – but it’s difficult to overstate how important they are. Every research organism has its limitations, of course. However, there’s much, much more we can learn from zebrafish that will benefit humans in the future.

This is the last article in the Cambridge Animal Alphabet series. If you have missed the others, you can catch up on Medium here.

Inset images: A two day old transgenic zebrafish embryo (Wikimedia Commons / IchaJaroslav); Zebrafish embryos (Wikimedia Commons / Adam Amsterdam, Massachusetts Institute of Technology).

̽��ֱ��Cambridge Animal Alphabet series celebrates Cambridge's connections with animals through literature, art, science and society. Here, Z is for Zebrafish as we talk to eminent immunologist Professor Lalita Ramakrishnan about her research into new ways of treating tuberculosis.

If we can work out how TB works in fish, and how to prevent it and treat it in fish, then we’re a step closer to solving a major health problem in humans

Lalita Ramakrishnan

Wikimedia Commons / Pogrebnoj-Alexandroff

Danio rerio (Zebrafish)

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Fish born in larger groups develop more social skills and a different brain structure

fpjl2 — Thu, 07 May 2015 15:13:26 +0000

A new study shows that cichlid fish reared in larger social groups from birth display a greater and more extensive range of social interactions, which continues into the later life of the fish. Researchers say this indicates the fish develop more attuned social behaviour as a result of early environments.

̽��ֱ��researchers also found that those fish raised in a more complex social environment have a different brain structure to those who experienced fewer group members in early life. If fish experienced the complex social environment for 2 month they had a larger hypothalamus: the area that contains most of the brain nodes of the ‘social behaviour network’. They also had a larger ‘optic tectum’, which processes visual stimuli and could be related to the need to process more visual stimuli in larger groups, say researchers.

̽��ֱ��brains of fish with enhanced social skills were not bigger overall than those reared in small groups; however, the ‘architecture’ within the brain was different.

“Our data suggests that, during development, relative brain parts change their size in response to environmental cues without affecting overall brain size: increasing certain parts forces others to decrease concurrently. These ‘plastic’ adjustments of brain architecture were still present long after the early stages of social interaction,” said study author Dr Stefan Fischer, from Cambridge ̽��ֱ��’s Department of Zoology.

“Social animals need to develop social skills, which regulate social interactions, aggression and hierarchy formations within groups. Such skills are difficult and costly to develop, and only beneficial if the early social environment predicts a high number of social interactions continues to be critically important later in life,” he said.

For the study, published this week in the journal ̽��ֱ��American Naturalist, researchers used the Neolamprologus pulcher (N. Pulcher) breed of cichlid, primarily found in Lake Tanganyika - the great African freshwater lake that feeds into the Congo River.

N. Pulcher lives in family groups with up to 25 individuals, with one breeder pair and several helpers participating in territory defence and raising of offspring - known as ‘cooperative breeding’. To test for social skills, the researchers reared juvenile fish over two months with either three or nine adult group members, and observed all social behaviours at key experimental points.

These interactions included ‘lateral display’ - when one fish interrupts another by displaying their body side-on, sometimes as a mating ritual - as well as ramming, tail quivering, and ‘mouth fighting’: a social display in which fish lock mouths to challenge each other over everything from food to mates.

Six month after this test phase, individual fish brains were measured to investigate the long term consequences of early group size on brain morphology, revealing differences in brain architecture.

̽��ֱ��researchers say that one of the effects on social behaviour in larger groups might be the perception of environmental risk. “In the wild, larger social groups of N. Pulcher represent a low-risk environment with enhanced juvenile survival. Being part of a larger, safer group may increase the motivation of juveniles to interact socially with siblings, enhancing the opportunities to acquire social skills,” said Fischer.

As perhaps with any social creature, Fischer points out that higher social competence and the ability to conform to social hierarchies may well stand the cichlids in good stead in later life:

“Group size for these fish stays relatively stable across the years, they have delayed dispersal. Remaining in a larger group means a better chance of survival. Fish reared in large groups showed more submissive and less aggressive behaviour to big fish in the group, social behaviour which greatly enhances the survival chances of smaller fish.”

Fischer added: “In highly social animals, such as cooperative breeders, almost all activities involve social interactions, where individuals need to adequately respond to social partners. In larger groups, these interactions are more common and individuals developing sophisticated social skills during childhood might highly benefit from them later in life.”

New research on a highly social fish shows that those reared in larger social groups from the earliest stage of life develop increased social skills and a brain shape, or ‘neuroplasticity’, which lingers into the later life of the fish.

Fish reared in large groups showed more submissive and less aggressive behaviour to big fish in the group, social behaviour which greatly enhances the survival chances of smaller fish

Stefan Fischer

Dario Josi

Neolamprologus pulcher (N. Pulcher) breed of cichlid fish used in the study

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

New fossil find pinpoints the origin of jaws in vertebrates

sc604 — Wed, 11 Jun 2014 17:00:00 +0000

A key piece in the puzzle of the evolution of vertebrates has been identified, after the discovery of fossilised fish specimens, dating from the Cambrian period (around 505 million years old), in the Canadian Rockies. ̽��ֱ��fish, known as Metaspriggina, shows pairs of exceptionally well-preserved arches near the front of its body. ̽��ֱ��first of these pairs, closest to the head, eventually led to the evolution of jaws in vertebrates, the first time this feature has been seen so early in the fossil record.

Fish fossils from the Cambrian period are very rare and usually poorly preserved. This new discovery shows in unprecedented detail how some of the earliest vertebrates developed – the starting point of a story which led to animals such as later fish species, but also dinosaurs and mammals such as horses and even ourselves. ̽��ֱ��findings are published in the 11 June edition of the journal Nature.

Fossils of Metaspriggina were recovered from several locations including the Burgess Shale site in Canada’s Rocky Mountains, one of the richest Cambrian fossil deposits in the world. These fossils shed new light on the Cambrian ‘explosion’, a period of rapid evolution starting around 540 million years ago, when most major animal phyla originated.

Previously, only two incomplete specimens of Metaspriggina had been identified. During expeditions conducted by the Royal Ontario Museum in 2012, 44 new Burgess Shale fossils were collected near Marble Canyon in Kootenay National Park in British Columbia, which provide the basis for this study. Researchers from the ̽��ֱ�� of Cambridge and the Royal Ontario Museum/ ̽��ֱ�� of Toronto used these fossils, along with several more specimens from the eastern United States, to reclassify Metaspriggina as one of the first vertebrates.

̽��ֱ��fossils, which date from 505 million years ago, also show clearly for the first time how a series of rod-like structures, known as the gill or branchial arches, were arranged in the earliest vertebrates. These arches have long been known to have played a key role in the evolution of vertebrates, including the origin of jaws, and some of the tiny bones in the ear which transmit sound in mammals. Until now, however, a lack of quality fossils has meant that the arrangement of these arches in the first vertebrates had been hypothetical.

Vertebrates first appear in the fossil record slightly earlier than these finds, but pinpointing exactly how they developed is difficult. This is because fossils of such animals are rare, incomplete and open to varying interpretations, as they show soft tissues which are difficult to identify with complete certainty.

̽��ֱ��new fossils of Metaspriggina are remarkably well-preserved. ̽��ֱ��arrangement of the muscles shows these fish were active swimmers, not unlike a trout, and the animals saw the world through a pair of large eyes and sensed their surrounding environment with nasal structures.

“ ̽��ֱ��detail in this Metaspriggina fossil is stunning,” said lead author Professor Simon Conway Morris of Cambridge’s Department of Earth Sciences. “Even the eyes are beautifully preserved and clearly evident.”

But it is the branchial arches which makes this discovery so important. Previously, they were thought to exist as a series of single arches, but Metaspriggina now shows that they in fact existed in pairs. ̽��ֱ��anteriormost pair of arches is also slightly thicker than the remainder, and this subtle distinction may be the very first step in an evolutionary transformation that in due course led to the appearance of the jaw. “Once the jaws have developed, the whole world opens,” said Professor Conway Morris. “Having a hypothetical model swim into the fossil record like this is incredibly gratifying.”

“Obviously jawed fish came later, but this is like a starting post – everything is there and ready to go,” said the paper’s co-author Dr Jean-Bernard Caron, Curator of Invertebrate Palaeontology at the Royal Ontario Museum and and associate professor in the Departments of Earth Sciences and Ecology & Evolutionary Biology at the ̽��ֱ�� of Toronto. “Not only is this a major new discovery, one that will play a key role in understanding our own origins, but Marble Canyon, the new Burgess Shale locality itself has fantastic potential for revealing key insights into the early evolution of many other animal groups during this crucial time in the history of life.”

David Wilks, Member of Canadian Parliament for Kootenay-Columbia, noted, “ ̽��ֱ��Government of Canada is excited about this incredible fossil find. As an international leader in conservation and steward of the Burgess Shale, Parks Canada is pleased to provide its research partners with access to the fossils. Their remarkable discoveries inform the work we do to share this rich natural history through our popular guided hikes, and to protect this important Canadian heritage in a national park and UNESCO World Heritage Site.”

A major fossil discovery in Canada sheds new light on the development of the earliest vertebrates, including the origin of jaws, the first time this feature has been seen so early in the fossil record

Having a hypothetical model swim into the fossil record like this is incredibly gratifying

Simon Conway Morris

Left: Illustration of Metaspriggina swimming. Right: Fossil of Metaspriggina from Marble Canyon – head to the left with two eyes, and branchial arches at the top.

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Yes

Natural barometer in birds evolved from ancient fish sense organ

bjb42 — Tue, 04 Sep 2012 16:10:14 +0000

Latest research shows that the ‘paratympanic organ’ (PTO) - the innate barometer in the middle ear of birds - evolved from a fish sense organ that detects jaw movement.

̽��ֱ��work, published in Nature Communications, sheds new light on the evolutionary trajectory of sensory systems after tetrapods left the oceans and moved onto land.

̽��ֱ��‘spiracular organ’ found in cartilaginous fishes (sharks and rays) and some bony fishes (including gars, sturgeons and lungfishes) is structurally similar to a bird’s PTO and located in the same position within the head, that is, in the wall of the ‘spiracle’ - the first gill slit - from which the middle ear cavity of all land vertebrates evolved.

Both organs contain motion-detecting hair cells, like those in the human inner ear used for hearing and balance. Ear drum movements in birds, and jaw movements in fish, respectively distort the PTO and spiracular organ, triggering the hair cells.

It has been proposed that birds use the PTO to detect air pressure, assisting with rapid changes in altitude. ̽��ֱ��organ is most complex in fast flyers such as swifts.

By combining gene expression with fate-mapping techniques in chicken embryos, scientists have been able to determine that the PTO stems from a unique ‘placode’ whose existence in birds had not previously been suspected. Placodes are specialised patches of thickened embryonic skin from which sense organs develop.

̽��ֱ��research by Dr Paul O’Neill was started in Dr Clare Baker’s lab in the Department of Physiology, Development and Neuroscience at the ̽��ֱ�� of Cambridge and completed in Dr Raj Ladher’s lab at the RIKEN Center for Developmental Biology in Kobe, Japan.

̽��ֱ��avian PTO was first described in 1911 by Giovanni Vitali at the ̽��ֱ�� of Siena. After initial excitement, which led to Vitali being nominated for the 1934 Nobel Prize in Physiology or Medicine, its existence was largely forgotten or ignored.

“ ̽��ֱ��discovery of this placode removes the only obstacle to accepting an evolutionary relationship between the avian PTO and the spiracular organ,” said Baker.

“ ̽��ֱ��PTO is also found in alligators and has been reported in the tuatara - the sole living representative of an ancient reptilian lineage distinct from lizards and snakes. Although its function in these species is unknown, it could relate to jaw movement. It is not clear why the PTO was lost in the other amniote lineages - mammals, turtles, lizards and snakes - but the PTO’s function is likely to have been modified in birds for detecting air pressure during flight.”

“It will be interesting to use modern molecular techniques to determine whether the PTO placode starts to develop in mammals, even if the organ itself is not found.”

̽��ֱ��UK research was funded by the BBSRC and the work in Japan was funded by the Japan Society for the Promotion of Science (JSPS) and RIKEN.

Previous work on sense organ development from Baker’s Cambridge lab, published in Nature Communications and Development, showed that the last common ancestor of all vertebrates with jaws (that is, all living vertebrates except lampreys and hagfishes) had a placode-derived system of electrosensory organs for detecting changes in the local electric field, used for hunting live prey.

New research indicates that a bird’s ability to detect changes in air pressure is the evolutionary remnant of an ancient sense organ found in sharks and sturgeons.

̽��ֱ��PTO’s function is likely to have been modified in birds for detecting air pressure during flight.

Clare Baker

Paul O'Neill

PTO organ with hair cells labelled in green

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