̽��ֱ�� of Cambridge - Marine Biological Laboratory

Ageing cuttlefish can remember the details of last week’s dinner

jg533 — Wed, 18 Aug 2021 07:04:06 +0000

̽��ֱ��results, published today in the journal Proceedings of the Royal Society B, are the first evidence of an animal whose memory of specific events does not deteriorate with age.

Researchers from the ̽��ֱ�� of Cambridge, the Marine Biological Laboratory in Woods Hole, Massachusetts, and the ̽��ֱ�� of Caen, conducted memory tests on 24 common cuttlefish, Sepia officinalis. Half of these were 10-12 months old – not-quite adult, and the other half were in old age at 22-24 months – equivalent to humans in their 90s.

“Cuttlefish can remember what they ate, where and when, and use this to guide their feeding decisions in the future. What’s surprising is that they don’t lose this ability with age, despite showing other signs of ageing like loss of muscle function and appetite,” said Dr Alexandra Schnell in the ̽��ֱ�� of Cambridge’s Department of Psychology, first author of the paper.

As humans age, we gradually lose the ability to remember experiences that happened at particular times and places – for example, what we had for dinner last Tuesday. This is termed ‘episodic memory’, and its decline is thought to be due to deterioration of a part of the brain called the hippocampus.

Cuttlefish do not have a hippocampus, and their brain structure is dramatically different to ours. ̽��ֱ��‘vertical lobe’ of the cuttlefish brain is associated with learning and memory. This does not deteriorate until the last two to three days of the animal’s life, which the researchers say could explain why episodic-like memory is not affected by age in cuttlefish.

To conduct the experiment, the cuttlefish were first trained to approach a specific location in their tank marked with a black and white flag. Then they were trained to learn that two foods they commonly eat were available at specific flag-marked locations and after specific delays. At one spot, the flag was waved and a piece of king prawn, their less preferred food, was provided. Live grass shrimp, which they like more, was provided at a different spot where another flag was also waved - but only every three hours. This was repeated for four weeks.

Then the cuttlefishes’ recall of which food would be available, where, and when was tested. To make sure they hadn’t just learned a pattern, the two feeding locations were unique each day. All the cuttlefish – regardless of age – watched which food first appeared at each flag and used that to work out which feeding spot was best at each subsequent flag-waving. This suggests that episodic-like memory does not decline with age in cuttlefish, unlike in humans.

“ ̽��ֱ��old cuttlefish were just as good as the younger ones in the memory task – in fact, many of the older ones did better in the test phase. We think this ability might help cuttlefish in the wild to remember who they mated with, so they don’t go back to the same partner,” said Schnell.

Cuttlefish only breed at the end of their life. By remembering who they mated with, where, and how long ago, the researchers think this helps the cuttlefish to spread their genes widely by mating with as many partners as possible.

Cuttlefish have short lifespans – most live until around two years old – making them a good subject to test whether memory declines with age. Since it is impossible to test whether animals are consciously remembering things, the authors used the term ‘episodic-like memory’ to refer to the ability of cuttlefish to remember what, where and when specific things happened.

This research was funded by the Royal Society and the Grass Foundation.

Reference
Schnell, AK et al: ‘Episodic-like memory is preserved with age in cuttlefish.’ Proceedings of the Royal Society B, August 2021. DOI: 10.1098/rspb.2021.1052

Cuttlefish can remember what, where, and when specific things happened – right up to their last few days of life, researchers have found.

̽��ֱ��old cuttlefish were just as good as the younger ones in the memory task

Alexandra Schnell

Ageing cuttlefish can remember the details of last week’s dinner

Phuket@photographer.net

Cuttlefish

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Cuttlefish show their intelligence by snubbing sub-standard snacks

jg533 — Wed, 03 Mar 2021 00:00:01 +0000

̽��ֱ��results, published on 3 March in the journal Proceedings of the Royal Society B, provide the first evidence of a link between self-control and intelligence in a non-primate species.

To conduct the experiment, common cuttlefish (Sepia officinalis) in tanks were presented with two foods they commonly eat, each in a separate Perspex chamber. In one chamber was a piece of king prawn, which they could eat immediately. In the other was a live grass shrimp, their preferred food, but they could only have the shrimp if they waited and didn’t eat the prawn.

A range of delays were tested, starting at 10 seconds and increasing by 10 seconds each time. All six cuttlefish in the experiment showed self-control, waiting for the grass shrimp and ignoring the king prawn. Those with the most self-control could wait 130 seconds for the grass shrimp to be released – an ability comparable with large-brained animals like chimpanzees.

“It was quite astonishing that the cuttlefish could wait for over two minutes for a better snack. Why would a fast-growing animal with an average life-span of less than two years be a picky eater?” said Dr Alexandra Schnell in the ̽��ֱ�� of Cambridge’s Department of Psychology, first author of the paper.

̽��ֱ��learning ability of each cuttlefish was then tested in a different task. A dark grey marker and a white marker were placed in random positions in the tank. After learning to associate one colour with a reward, the reward was switched to be associated with the other colour. ̽��ֱ��cuttlefish that were both quicker to learn the association and quicker to realise the switch were the same ones showing more self-control in the first task.

“We found that cuttlefish with better learning performance - an indicator of intelligence - also showed better self-control. This link exists in humans and chimpanzees, but this is the first time it has been shown in a non-primate species,” said Schnell.

̽��ֱ��researchers suggest that self-control in cuttlefish is the by-product of another behaviour: staying camouflaged on the sea bed for long periods of time to avoid predators. These periods are punctuated by brief foraging bouts in the open. Self-control may help the cuttlefish optimise their foraging by only striking prey of better quality.

“ ̽��ֱ��ability to exert self-control is an important element of the ability to plan for the future, which is quite a sophisticated behaviour,” said Professor Nicola Clayton FRS in Cambridge’s Department of Psychology, senior author of the report.

She added: “Self-control requires an understanding that ‘less is sometimes more’ - that avoiding temptation now might lead to a better future outcome. This is a critically important building block for the evolution of complex decision-making.”

̽��ֱ��researchers also noticed that the cuttlefish in the self-control task turned their bodies away from the immediately available food, as if to distract themselves from eating it.

Self-control - the ability to resist temptation in favour of a better but delayed reward – is a vital skill that underpins effective decision-making, goal-directed behaviour and future planning. Amongst animals, apes and their clever feathered cousins the corvids and parrots have relatively high self-control when it comes to eating. Rats, chickens and pigeons find it much more difficult not to eat food immediately.

̽��ֱ��experiments were conducted with collaborators including Professor Roger Hanlon at the Marine Biological Laboratory in Woods Hole, Massachusetts. Their design was inspired by the 1972 Stanford marshmallow test, in which children were offered a choice between one marshmallow immediately, or two if they waited for a period of time.

Two additional cuttlefish were recruited to the study but refused to take part.

This research was funded by the Royal Society.

Reference

Schnell, A.K. et al: ‘Cuttlefish exert self-control in a delay of gratification task.’ Proceedings of the Royal Society B, March 2021. DOI: 10.1098/rspb.2020.3161

A study has found that cuttlefish can pass a fishy version of the ‘marshmallow test’ – and those that can delay gratification the longest are the most intelligent.

It was quite astonishing that the cuttlefish could wait for over two minutes for a better snack. Why would a fast-growing animal with an average life-span of less than two years be a picky eater?

Alex Schnell

Alex Scnhell

Cuttlefish

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Adult skates can spontaneously repair cartilage injuries

jg533 — Tue, 12 May 2020 08:14:11 +0000

Researchers have found that adult skates have the ability to spontaneously repair injured cartilage, using a type of cartilage stem cell. Human cartilage has very limited capacity for repair, and the finding may lead to new stem cell treatments for human cartilage injuries.

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.

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