Jellyfish, with no central brain, shown to learn from past experience

Even without a central brain, jellyfish can learn from past experiences like humans, mice, and flies, scientists report for the first time on September 22 in the journal Current Biology. They trained Caribbean box jellyfish (Tripedalia cystophora) to learn to spot and dodge obstacles. The study challenges previous notions that advanced learning requires a centralized brain and sheds light on the evolutionary roots of learning and memory.

No bigger than a fingernail, these seemingly simple jellies have a complex visual system with 24 eyes embedded in their bell-like body. Living in mangrove swamps, the animal uses its vision to steer through murky waters and swerve around underwater tree roots to snare prey. Scientists demonstrated that the jellies could acquire the ability to avoid obstacles through associative learning, a process through which organisms form mental connections between sensory stimulations and behaviors.

"Learning is the pinnacle performance for nervous systems," says first author Jan Bielecki of Kiel University, Germany. To successfully teach jellyfish a new trick, he says "it's best to leverage its natural behaviors, something that makes sense to the animal, so it reaches its full potential."

The team dressed a round tank with gray and white stripes to simulate the jellyfish's natural habitat, with gray stripes mimicking mangrove roots that would appear distant. They observed the jellyfish in the tank for 7.5 minutes. Initially, the jelly swam close to these seemingly far stripes and bumped into them frequently. But by the end of the experiment, the jelly increased its average distance to the wall by about 50%, quadrupled the number of successful pivots to avoid collision and cut its contact with the wall by half. The findings suggest that jellyfish can learn from experience through visual and mechanical stimuli.

"If you want to understand complex structures, it's always good to start as simple as you can," says senior author Anders Garm of the University of Copenhagen, Denmark. "Looking at these relatively simple nervous systems in jellyfish, we have a much higher chance of understanding all the details and how it comes together to perform behaviors."

The researchers then sought to identify the underlying process of jellyfish's associative learning by isolating the animal's visual sensory centers called rhopalia. Each of these structures houses six eyes and generates pacemaker signals that govern the jellyfish's pulsing motion, which spikes in frequency when the animal swerves from obstacles.

The team showed the stationary rhopalium moving gray bars to mimic the animal's approach to objects. The structure did not respond to light gray bars, interpreting them as distant. However, after the researchers trained the rhopalium with weak electric stimulation when the bars approach, it started generating obstacle-dodging signals in response to the light gray bars. These electric stimulations mimicked the mechanical stimuli of a collision. The findings further showed that combining visual and mechanical stimuli is required for associative learning in jellyfish and that the rhopalium serves as a learning center.

Next, the team plans to dive deeper into the cellular interactions of jellyfish nervous systems to tease apart memory formation. They also plan to further understand how the mechanical sensor in the bell works to paint a complete picture of the animal's associative learning.

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Scientists discover secret of virgin birth, and switch on the ability in female flies

Scientists have pinpointed a genetic cause for virgin birth for the first time, and once switched on the ability is passed down through generations of females.

For the first time, scientists have managed to induce virgin birth in an animal that usually reproduces sexually: the fruit fly Drosophila melanogaster.

Once induced in this fruit fly, this ability is passed on through the generations: the offspring can reproduce either sexually if there are males around, or by virgin birth if there aren't.

For most animals, reproduction is sexual -- it involves a female's egg being fertilised by a male's sperm. Virgin birth, or 'parthenogenesis', is the process by which an egg develops into an embryo without fertilisation by sperm -- a male is not needed.

The offspring of a virgin birth are not exact clones of their mother but are genetically very similar, and are always female.

"We're the first to show that you can engineer virgin births to happen in an animal -- it was very exciting to see a virgin fly produce an embryo able to develop to adulthood, and then repeat the process," said Dr Alexis Sperling, a researcher at the University of Cambridge and first author of the paper.

She added: "In our genetically manipulated flies, the females waited to find a male for half their lives -- about 40 days -- but then gave up and proceeded to have a virgin birth."

In the experiments, only 1-2% of the second generation of female flies with the ability for virgin birth produced offspring, and this occurred only when there were no male flies around. When males were available, the females mated and reproduced in the normal way.

Switching to a virgin birth can be a survival strategy: a one-off generation of virgin births can help to keep the species going.

The study is published today in the journal Current Biology.

To achieve their results, researchers first sequenced the genomes of two strains of another species of fruit fly, called Drosophila mercatorum. One strain needs males to reproduce, the other reproduces only through virgin birth. They identified the genes that were switched on, or switched off, when the flies were reproducing without fathers.

With the candidate genes for virgin birth ability identified in Drosophila mercatorum, the researchers altered what they thought were the corresponding genes in the model fruit fly, Drosophila melanogaster. It worked: Drosophila melanogaster suddenly acquired the ability for virgin birth.

The research involved over 220,000 virgin fruit flies and took six years to complete.

Key to the discovery was the fact that this work was done in Drosophila melanogaster -- the researchers say it would have been incredibly difficult in any other animal. This fly has been the 'model organism' for research in genetics for over 100 years and its genes are very well understood.

Sperling, who carried out this work in the Department of Genetics, has recently moved to Cambridge Crop Science Centre to work on crop pests and hopes to eventually investigate why virgin birth in insects may be becoming more common, particularly in pest species.

"If there's continued selection pressure for virgin births in insect pests, which there seems to be, it will eventually lead to them reproducing only in this way. It could become a real problem for agriculture because females produce only females, so their ability to spread doubles," said Sperling.

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Flies possess more sophisticated cognitive abilities than previously known

As they annoyingly buzz around a batch of bananas in our kitchens, fruit flies appear to have little in common with mammals. But as a model species for science, researchers are discovering increasing similarities between us and the miniscule fruit-loving insects.

In a new study, researchers at the University of California San Diego's Kavli Institute for Brain and Mind (KIBM) have found that fruit flies (Drosophila melanogaster) have more advanced cognitive abilities than previously believed. Using a custom-built immersive virtual reality environment, neurogenetic manipulations and in vivo real-time brain-activity imaging, the scientists present new evidence Feb. 16 in the journal Nature of the remarkable links between the cognitive abilities of flies and mammals.

The multi-tiered approach of their investigations found attention, working memory and conscious awareness-like capabilities in fruit flies, cognitive abilities typically only tested in mammals. The researchers were able to watch the formation, distractibility and eventual fading of a memory trace in their tiny brains.

"Despite a lack of obvious anatomical similarity, this research speaks to our everyday cognitive functioning -- what we pay attention to and how we do it," said study senior author Ralph Greenspan, a professor in the UC San Diego Division of Biological Sciences and associate director of KIBM. "Since all brains evolved from a common ancestor, we can draw correspondences between fly and mammalian brain regions based on molecular characteristics and how we store our memories."

To arrive at the heart of their new findings the researchers created an immersive virtual reality environment to test the fly's behavior via visual stimulation and coupled the displayed imagery with an infra-red laser as an averse heat stimulus. The near 360-degree panoramic arena allowed Drosophila to flap their wings freely while remaining tethered, and with the virtual reality constantly updating based on their wing movement (analyzed in real-time using high-speed machine-vision cameras) it gave the flies the illusion of flying freely in the world. This gave researchers the ability to train and test flies for conditioning tasks by allowing the insect to orient away from an image associated with the negative heat stimulus and towards a second image not associated with heat.

They tested two variants of conditioning, one in which flies were given visual stimulation overlapping in time with the heat (delay conditioning), both ending together, or a second, trace conditioning, by waiting 5 to 20 seconds to deliver the heat after showing and removing the visual stimulation. The intervening time is considered the "trace" interval during which the fly retains a "trace" of the visual stimulus in its brain, a feature indicative of attention, working memory and conscious awareness in mammals.

The researchers also imaged the brain to track calcium activity in real-time using a fluorescent molecule they genetically engineered into their brain cells. This allowed the researchers to record the formation and duration of the fly's living memory since they saw the trace blinking on and off while being held in the fly's short-term (working) memory. They also found that a distraction introduced during training -- a gentle puff of air -- made the visual memory fade more quickly, marking the first time researchers have been able to prove such distractedness in flies and implicating an attentional requirement in memory formation in Drosophila.

"This work demonstrates not only that flies are capable of this higher form of trace conditioning, and that the learning is distractible just like in mammals and humans, but the neural activity underlying these attentional and working memory processes in the fly show remarkable similarity to those in mammals," said Dhruv Grover, a UC San Diego KIBM research faculty member and lead author of the new study. "This work demonstrates that fruit flies could serve as a powerful model for the study of higher cognitive functions. Simply put, the fly continues to amaze in how smart it really is."

The scientists also identified the area of the fly's brain where the memory formed and faded -- an area known as the ellipsoid body of the fly's central complex, a location that corresponds to the cerebral cortex in the human brain.

Further, the research team discovered that the neurochemical dopamine is required for such learning and higher cognitive functions. The data revealed that dopamine reactions increasingly occurred earlier in the learning process, eventually anticipating the coming heat stimulus.

The researchers are now investigating details of how attention is physiologically encoded in the brain. Grover believes the lessons learned from this model system are likely to directly inform our understanding of human cognition strategies and neural disorders that disrupt them, but also contribute to new engineering approaches that lead to performance breakthroughs in artificial intelligence designs.

Read more at Science Daily

Lonely flies, like many humans, eat more and sleep less

COVID-19 lockdowns scrambled sleep schedules and stretched waistlines. One culprit may be social isolation itself. Scientists have found that lone fruit flies quarantined in test tubes sleep too little and eat too much after only about one week of social isolation, according to a new study published in Nature. The findings, which describe how chronic separation from the group leads to changes in gene expression, neural activity, and behavior in flies, provide one of the first robust animal models for studying the body's biological reaction to loneliness.

"Flies are wired to have a specific response to social isolation," says Michael W. Young, the Richard and Jeanne Fisher Professor and head of the Laboratory of Genetics at Rockefeller. "We found that loneliness has pathological consequences, connected to changes in a small group of neurons, and we've begun to understand what those neurons are doing."

The science of loneliness

Drosophila are social creatures. The fruit flies forage and feed in groups, serenade one another through complex mating rituals, tussle in miniature boxing matches. And then they conk out: flies sleep 16 hours each day, split between a languorous midday nap and a full night's rest.

So when Wanhe Li, a research associate in Young's lab, began investigating the biological underpinnings of chronic social isolation, she turned to the gregarious and well-studied fruit fly. "Over and over again, Drosophila have put us on the right track," says Young. "Evolution packed a great deal of complexity into these insects long ago and, when we dig into their systems, we often find the rudiments of something that is also manifest in mammals and humans."

"When we have no roadmap, the fruit fly becomes our roadmap," Li adds.

For the study, Wanhe Li first compared how flies fare under various lockdown conditions. After seven days, flies housed together in groups of varying sizes produced no anomalous behaviors. Even two flies cut off from the crowd were content with one another. But when a single fly was entirely isolated, the lonely insect began eating more and sleeping less.

Further investigation revealed that a group of genes linked to starvation were expressed differently in the brains of lonely flies -- a tempting genetic basis for the observed connection between isolation and overeating.

Li then found that a small group of brain cells known as P2 neurons were involved in the observed changes to sleep and feeding behavior. Shutting down the P2 neurons of chronically-isolated flies suppressed overeating and restored sleep; boosting P2 in flies isolated from the group for only one day caused them to eat and sleep as if they had been alone for a full week.

"We managed to trick the fly into thinking that it had been chronically isolated," says Wanhe Li. "The P2 neurons seem to be linked to the perception of the duration of social isolation, or the intensiveness of loneliness, like a timer counting down how long the fly has been alone."

The Young lab painstakingly confirmed these observations. They engineered insomniac flies, to make sure that lack of sleep alone did not cause overeating (it didn't). They tested group-reared flies to find out whether manipulating P2 neurons would cause overeating and sleep loss in socialized flies (it doesn't). Ultimately, they concluded that only a perfect storm of both P2 neuron activity and social isolation will cause flies to begin to losing sleep and overeating.

Explaining the "Quarantine 15"

Scientists have observed that many social animals -- from fruit flies to humans -- eat more and sleep less when isolated. The reason for this is unclear. One possibility, Young says, is that social isolation signals a degree of uncertainty about the future. Preparation for tough times may include being alert and awake as often as possible and eating whenever food is available.

This study can hardly confirm that humans in COVID-19 lockdowns ate more and slept less due to the same biological mechanisms that keep lonely flies hungry and sleep deprived. But now that Li and Young have identified the neurons and genes responding to chronic isolation in fruit flies, future researchers can search for corresponding connections between loneliness, overeating, and insomnia in laboratory animals and, eventually, humans.

Read more at Science Daily

More filling? Tastes great? How flies, and maybe people, choose their food

Flies have discriminating taste. Like a gourmet perusing a menu, they spend much of their time seeking sweet nutritious calories and avoiding bitter, potentially toxic food. But what happens in their brains when they make these food choices?

Yale researchers discovered an interesting way to find out. They tricked them.

In a study that could also help illuminate how people make food choices, the researchers gave hungry fruit flies the choice between sweet, nutritious food laced with bitter quinine and a less sweet, but not bitter, food containing fewer calories. Then, using neuroimaging, they tracked neural activity in their brains as they made these tough choices.

So which won? Calories or better taste?

"It depends on how hungry they are," said Michael Nitabach, professor of cellular and molecular physiology, genetics, and neuroscience at Yale School of Medicine and senior author of the study. "The hungrier they are, the more likely they will tolerate bitter taste to obtain more calories."

But the real answer to how flies make these decisions is a little more complex, according to the study published July 5 in the journal Nature Communications.

According to the research team, led by Preeti Sareen, associate research scientist at Yale, flies relay sensory information to a portion of their brain called the fan-shaped body, where signals are integrated, triggering what amounts to the insect version of an executive decision. The researchers found that patterns of neuronal activity in the fan-shaped body change adaptively when novel food choices are introduced, which dictates the fly's decision over what food to eat.

But researchers went a step further. And things got even stranger. They found they could change a fly's choice by manipulating neurons in areas of the brain that feed into the fan-shaped body. For example, when they caused a decrease in activity in the neurons involved in metabolism, the found that it made hungry flies choose the lower calorie food.

"It is one big feedback loop, not just top-down decision making," Nitabach said.

And this is where there are connections to food choices of humans, he said. Neural activity in both a fly's brain and a human's brain are regulated by the secretion of neuropeptides and the neurotransmitter dopamine, which in humans helps regulate sensations of reward. Changes in this network may alter how the brain responds to different types of food. In other words, neurochemistry may sometimes dictate food choices we think we are making consciously.

"The study provides a template to understand how it is that things like hunger and internal emotional states influence our behavior," Nitabach said.

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