Coastal fisheries show surprising resilience to marine heat waves

Rutgers-led study finds that in the years following marine heat waves, effects on fish communities were often minimal

Peer-Reviewed Publication

RUTGERS UNIVERSITY

Rutgers-led research found that marine heat waves – prolonged periods of unusually warm ocean temperatures – haven’t had a lasting effect on the fish communities that feed most of the world.

The finding is in stark contrast to the devastating effects seen on other marine ecosystems cataloged by scientists after similar periods of warming, including widespread coral bleaching and harmful algal blooms.

“There is an emerging sense that the oceans do have some resilience, and while they are changing in response to climate change, we don’t see evidence that marine heat waves are wiping out fisheries,” said Alexa Fredston, the lead author of the study who conducted the research as a postdoctoral associate in the Global Change Research Group, part of the Department of Ecology, Evolution and Natural Resources in the Rutgers School of Environmental and Biological Sciences (SEBS.)

The study, published in Nature, assessed effects on commercially important fish such as flounder, pollock and rockfish based on data extracted from long-running scientific trawl surveys – conducted by towing a net along the seafloor – of continental shelf ecosystems in North America and Europe between 1993 and 2019. The analysis included 248 marine heat waves with extreme sea bottom temperatures during this period. The researchers were surprised to find that marine heat waves in general don’t show major adverse effects on regional fish communities.

Although declines in biomass did occur after some marine heat waves, the researchers said these cases were the exception, not the rule. Overall, they found that the effects of marine heat waves aren’t distinguishable from the natural variability in these ecosystems.

“The oceans are highly variable, and fish populations vary quite a lot,” said Fredston, now an assistant professor of ocean sciences at University of California, Santa Cruz. “Marine heat waves can drive local change, but there have been hundreds of marine heat waves with no lasting impacts.”

In addition to assessing the impact on the total quantity of organisms in a given area, known as biomass, the researchers examined whether marine heat waves were causing changes in the variety of fish species composing fish communities. For example, evidence might show the loss of species associated with cold water and an increase in species associated with warm water, a phenomenon known as tropicalization.

The findings suggest fish may be able to find safe havens by moving to areas with cooler water during marine heat waves, which the researchers defined as periods of more than five days with extreme sea bottom temperatures for that region and season.

The data included some notable examples of marine heat waves that did have profound impacts, such as the 2014-2016 marine heat wave in the Northeast Pacific known as “the Blob,” one of the largest on record.

While “the Blob” led to a 22 percent loss of biomass in the Gulf of Alaska, a 2012 marine heat wave in the Northwest Atlantic led to a 70 percent biomass gain. The authors also noted that these weren’t large changes compared to natural variability in biomass, and similar effects weren’t seen after most other marine heat waves.

“We found that these negative impacts are unpredictable and that other heat waves had no strong impacts,” said Malin Pinsky, an associate professor in the Department of Ecology, Evolution and Natural Resources and director of the Global Change Research Group at SEBS and a co-author of the study. “This means that each heat wave that hits is like rolling the dice: Will it be a bad one or not? We don't know until it happens.”

Other Rutgers researchers who participated in the study include Zoë Kitchel, a doctoral student, and Aurore Maureaud, a postdoctoral associate, both with the Department of Ecology, Evolution and Natural Resources at SEBS.

Researchers from other institutions participated in the study, including the University of British Columbia, the University of Bern in Switzerland, the National Oceanic and Atmospheric Administration, the French Research Institute for Exploitation of the Sea, the University of Montpellier in France, the University of Tromsø in Norway and Fisheries and Oceans Canada.

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JOURNAL

Nature

DOI

10.1038/s41586-023-06449-y 

METHOD OF RESEARCH

Observational study

SUBJECT OF RESEARCH

Animals

ARTICLE TITLE

Marine heatwaves are not a dominant driver of change in demersal fishes

 

Using evidence from last Ice Age, scientists predict effects of rising seas on coastal habitats

Extent of future warming will dictate impacts, according to research

Peer-Reviewed Publication

RUTGERS UNIVERSITY

The rapid sea level rise and resulting retreat of coastal habitat seen at the end of the last Ice Age could repeat itself if global average temperatures rise beyond certain levels, according to an analysis by an international team of scientists from more than a dozen institutions, including Rutgers.

In a study published in Nature, scientists reported how ancient coastal habitats adapted as the last glacial period ended more than 10,000 years ago and projected how they are likely to change with this century’s predicted sea level rise. They conducted their analysis by examining the ocean sediments of ancient shorelines from a time when oceans rose rapidly, mainly because of melting ice sheets in the Northern Hemisphere. This examination allowed them to infer how ancient coastal habitats changed and formed the basis of improved predictions about the present.

“Every ton of carbon dioxide humankind emits turns up the global thermostat, which in turn increases the pace of global sea level rise,” said Robert Kopp, a Distinguished Professor in the Department of Earth and Planetary Sciences in the Rutgers School of Arts and Sciences and an author of the study. “The faster the oceans rise, the greater the threat to tidal marshes, mangroves and coral reefs around the world. For example, in our analysis, most tidal marshes are likely to be able to keep up with sea level rise under 1.5 degrees Celsius [2.7 degrees Fahrenheit] of warming, but two-thirds are unlikely to be able to keep up with 2 degrees Celsius [3.6 degrees Fahrenheit] of warming."

The temperature ranges mentioned in the study are significant because they relate directly to the Paris Agreement, an international treaty on climate change adopted in 2015, said Kopp, who is also the director of the Megalopolitan Coastal Transformation Hub and co-director of the University Office of Climate Action. The goal of the Paris treaty is to substantially reduce carbon emissions worldwide to limit the global temperature increase in this century to 2 degrees Celsius above preindustrial levels while pursuing efforts to limit the increase even further to 1.5 degrees Celsius.

The study predicted higher global temperatures will provoke sea level rises that will lead to instability and profound changes to coastal ecosystems, including tidal marshes, mangrove forests, coral reefs and coral islands.

Tidal marshes – low-lying areas flooded and drained by tidal salt water – protect many of the world’s coastlines. They sequester pollutants, absorb carbon dioxide and protect nearby communities from storm surge and flooding. They are common along the Atlantic shores of North America. Large expanses of tidal marshes line New Jersey’s coast.

“This new paper provides evidence from geological history that, without mitigation and under current projections, tidal marshes will not have the capacity to adjust,” said Judith Weis, a Professor Emerita of Biological Sciences at Rutgers–Newark who isn’t an author of the study but is an expert on tidal marshes. “For many tidal marshes in New Jersey, this is not a prediction but a description of the present situation, in which sea level is rising faster than the marshes can increase their elevation. This makes it even more vital to reduce climate change as rapidly as possible.”

Tidal marshes and mangrove forests adapt to rising seas by accumulating sediment and moving slowly inland.

“Mangroves and tidal marshes act as a buffer between the ocean and the land – they absorb the impact of wave action, prevent erosion and are crucial for biodiversity of fisheries and coastal plants,” said Neil Saintilan, the paper’s lead author and a professor at Macquarie University in Sydney, Australia. “When the plants become water-logged due to higher sea levels, they start to flounder.”

Under worst-case scenarios, these coastal habitats, buffeted by rising sea levels, will shrink and, in some cases, wash away, as they have in the distant past, according to the study.

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JOURNAL

Nature

DOI

10.1038/s41586-023-06448-z 

METHOD OF RESEARCH

Observational study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Widespread retreat of coastal habitat likely at warming levels above 1.5C

 

Arctic soil methane consumption may be larger than previously thought and increases in a drier climate

Peer-Reviewed Publication

UNIVERSITY OF EASTERN FINLAND

 

IMAGE: AUTOMATED CHAMBER MEASUREMENT SET-UP AT TRAIL VALLEY CREEK, WESTERN CANADIAN ARCTIC. view more 

CREDIT: CAROLINA VOIGT.

Arctic wetlands are known emitters of the strong greenhouse gas methane (CH4). Well-drained soils on the other hand remove methane from the atmosphere. In the Arctic and boreal biomes, well drained upland soils with a high potential for atmospheric methane consumption cover more than 80% of the land area. Despite the large upland coverage and their potential importance for methane uptake, the underlying mechanisms, environmental controls and even the magnitude of Arctic soil methane uptake are poorly understood.

A recent study led by researchers from the University of Eastern Finland and the University of Montreal finds that Arctic soil methane uptake may be larger than previously thought, and that methane uptake increases under dry conditions and with availability of labile carbon substrates. The article was published in Nature Climate Change – one of the top-level journals in natural sciences.

The study was primarily conducted at Trail Valley Creek, a tundra site in the Western Canadian Arctic. The authors used a unique experimental set-up consisting of 18 automated chambers for continuous measurements of methane fluxes. No other automated chamber system exists this far North in the Canadian Arctic, and only few exist above the Arctic circle globally, most of which are installed at methane-emitting sites.

The high-resolution measurements of methane uptake (more than 40 000 flux measurements) revealed previously unknown diel and seasonal dynamics in methane uptake: while methane uptake in early and peak summer was largest during the afternoons, coinciding with maximum soil temperature, methane uptake during late summer peaked during the night. Underlying biogeochemical mechanisms are complex, but the study shows that the strongest methane uptake coincided with peaks of ecosystem carbon dioxide (CO2) respiration. Complementing flux measurements at Trail Valley Creek with measurements at other sites spread across the Arctic in Canada and Finland showed that the availability of labile carbon substrates and nutrients may promote methane consumption in Arctic soils.  

On a larger scale, these findings are highly relevant for estimating the current Arctic methane budget, and for predicting the future response of Arctic soil methane uptake to a changing climate. According to the study, high-latitude warming itself, occurring up to four times faster in the Arctic than the rest of the world, will promote atmospheric methane uptake to a lesser extent than the associated large-scale drying.

The study was carried out by an international team of researchers from Canada and Finland, and collaborators from the United States and Germany. The main funding sources for the study were the Academy of Finland, the Canada Foundation for Innovation project Changing Arctic Network, ArcticNet, and the Canada Research Chair and NSERC Discovery Grants programs. Field work was supported by Metsähallitus and the Aurora Research Institute.

CAPTION

Conditions during field work at Trail Valley Creek research camp, Western Canadian Arctic. Photo taken during June, 2021.

Upland tundra landscape during autumn near Inuvik, Western Canadian Arctic.

Upland tundra landscape near Inuvik, Western Canadian Arctic.

CREDIT

Carolina Voigt.

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JOURNAL

Nature Climate Change

DOI

10.1038/s41558-023-01785-3 

ARTICLE TITLE

Arctic soil methane sink increases with drier conditions and higher ecosystem respiration.

 

Evolving chemical system changes its environment

Synthetic replicators show first signs of Darwinian evolution

Peer-Reviewed Publication

UNIVERSITY OF GRONINGEN

 

IMAGE: A POPULATION OF THE TWO MUTANTS CAN UNDERGO DARWINIAN EVOLUTION THROUGH MUTATION AND SELECTION, ADAPTING TO A CHANGE IN THE ENVIRONMENT CAUSED BY THE REPLICATORS THEMSELVES. THE TWO REPLICATOR MUTANTS, A SIX-RING AND A THREE-RING, COMPETE FOR A COMMON BUILDING BLOCK. BOTH REPLICATORS CAN PRODUCE SINGLET OXYGEN WHEN IRRADIATED WITH LIGHT, CAUSING A CHANGE IN THE OXIDATION STATE OF THEIR ENVIRONMENT. AT A HIGH OXIDATION STATE, THE HEXAMER CAN NO LONGER REPLICATE EFFICIENTLY, WHILE TRIMER REPLICATION STALLS AT A LOW OXIDATION STATE. THESE EFFECTS RESULT IN THE ADAPTATION OF THE REPLICATOR POPULATION TO A CHANGE IN OXIDATION LEVEL, WHICH, IN TURN, DEPENDS ON THE LIGHT INTENSITY. THIS BEHAVIOUR SHOWS THAT NATURAL SELECTION CAN ALSO ACT OUTSIDE BIOLOGY ON SYSTEMS OF MAN-MADE MOLECULES. view more 

CREDIT: OTTO LAB, UNIVERSITY OF GRONINGEN

A chemical system of synthetic replicators showing the first signs of Darwinian evolution: two different replicators compete for a common building block, and which one wins depends on the environment. As the replicators can also change their environment, ecological-evolutionary dynamics ensue. This finding shows that Darwinian principles extend beyond biology to synthetic systems. These results, which may be used to develop new catalysts, were published by chemists from the University of Groningen (the Netherlands) in the journal Nature Chemistry on 31 August.

What is life? This question has puzzled scientists for ages. Sijbren Otto, Professor of Systems Chemistry at the University of Groningen, addresses the question by attempting to synthesize a simple form of life from scratch. He has experimented extensively with a system of monomers, that react with each other to produce rings. These, in turn, assemble into fibres. In this process, the rings are replicated and the fibres grow and divide. Previous work showed that the fibres can also perform catalysis under the influence of light, accelerating the formation of the molecules they grow from: a primitive form of metabolism.

Adapting

In their recent study, Otto and his team focused on another key aspect of life: Darwinian evolution. They studied fibres made from self-replicating rings of two different sizes: 3-rings and 6-rings. ‘All rings assemble from the same monomer, for which they compete’, explains Otto. ‘We then placed these systems in a flow cell while adding a solution of monomers at a constant rate. At the same time, we were removing an equal amount of fluid from the cell.’ The scientists then watched the fibres reproduce and evolve by changing their ring size.

Replicators will only survive if they can replicate faster than the rate at which they are removed by the outflow. In this system, the two replicators exhibited different growth rates in different environments: the 3-rings grew fastest if they were in a highly oxidized environment, while the 6-rings won the competition if the environment was less oxidizing. Otto: ‘We saw that the replicators could mutate into a different ring size when the oxidation state of the environment was changed. Thus, these replicators appear to be capable of adapting to a changing environment.’

Dynamics

The researchers further developed this system by giving the replicators the ability to alter the oxidation state of their environment by themselves in response to light. Weak light conditions caused only little oxidation, allowing the 6-ring replicators to dominate. However, under strong light, the 6-ring replicators increased the oxidation level, thereby poisoning its own environment. This reduced the ability of this replicator to grow, and the mutant 3-ring fibres now took over.

‘Our system is very simple, yet it shows some of the dynamics normally only seen in living systems’, says Otto. ‘We showed how a kind of natural selection determines which type of replicator dominates, and also that these replicators can change their own environment, which, in turn, influences replicator evolution. Such eco-evolutionary dynamics are well known in biology, and it is now clear that they also extend to (our) synthetic system.’ But Otto does not yet call the system alive, as this would require additional features, such as the compartmentalization of the replicators in a cell-like structure.

Biology

‘However, it is interesting that Darwinian principles, which are the cornerstone of biology, can also be introduced into our synthetic system. We have replication, a metabolism, and now also a limited kind of Darwinian evolution’, concludes Otto. ‘This is still very rudimentary, but we are keen to see if we can push our systems to become ever more life-like.’ Apart from uncovering how chemical systems can transition into living ones, such systems could also harness the inventive power of Darwinian evolution to develop novel catalysts or materials, for example.

Reference: Kai Liu, Alex Blokhuis, Chris van Ewijk, Armin Kiani, Juntian Wu, Wouter H. Roos and Sijbren Otto: Light-driven eco-evolutionary dynamics in a synthetic replicator system. Nature Chemistry, 31 August 2023

A system of two self-replicating molecules can change the oxidation state of their environment in response to light and depending on light intensity. Intense light leads to a high oxidation state which causes an adaptation of the replicator distribution to favor the 3-ring replicator by mutation and selection. A similar adaptation occurs at a lower light intensity, now favouring the competing 6-ring replicator.

CREDIT

Otto Lab, University of Groningen

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JOURNAL

Nature Chemistry

DOI

10.1038/s41557-023-01301-2 

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Light-driven eco-evolutionary dynamics in a synthetic replicator system

Single-dose psilocybin treatment for major depressive disorder

JAMA

Peer-Reviewed Publication

JAMA NETWORK

About The Study: In a randomized clinical trial with 104 participants, psilocybin treatment was associated with a clinically significant sustained reduction in depressive symptoms and functional disability, without serious adverse events. These findings add to increasing evidence that psilocybin—when administered with psychological support—may hold promise as a novel intervention for major depressive disorder.

Authors: Charles L. Raison, M.D., of Usona Institute in Fitchburg, Wisconsin, is the corresponding author.

link https://media.jamanetwork.com/

(doi:10.1001/jama.2023.14530)

Editor’s Note: Please see the article for additional information, including other authors, author contributions and affiliations, conflict of interest and financial disclosures, and funding and support.

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Embed this link to provide your readers free access to the full-text article 

 https://jamanetwork.com/journals/jama/fullarticle/10.1001/jama.2023.14530?guestAccessKey=7ff7bcd4-634a-4faa-ae0f-3ed11e9ef407&utm_source=For_The_Media&utm_medium=referral&utm_campaign=ftm_links&utm_content=tfl&utm_term=083123

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JOURNAL

JAMA

A new breakthrough in obesity research allows you to lose fat while eating all you want

Researchers discover that astrocytes control a cluster of neurons in the brain that regulates energy expenditure

Peer-Reviewed Publication

INSTITUTE FOR BASIC SCIENCE

 

IMAGE: LEFT) REACTIVE ASTROCYTES EXPRESS A HIGH LEVEL OF MAOB AND RELEASE A HIGH LEVEL OF GABA, WHICH RESULTS IN THE INHIBITION OF GABRA5 NEURONS. THIS RESULTS IN DECREASED THERMOGENESIS IN BROWN FAT TISSUES, AND AN INCREASE IN WHITE FAT STORAGE. RIGHT) WHEN THE GABRA5 NEURON ACTIVITY IS RESTORED, BROWN FAT THERMOGENESIS IS INCREASED AND WHITE FAT STORAGE IS DECREASED. IN BOTH CASES, MICE ARE FED A HIGH-FAT DIET. view more 

CREDIT: INSTITUTE FOR BASIC SCIENCE

This is a significant development that brings hope to the one billion individuals with obesity worldwide. Researchers led by Director C. Justin LEE from the Center for Cognition and Sociality (CCS) within the Institute for Basic Science (IBS) have discovered new insights into the regulation of fat metabolism. The focus of their study lies within the star-shaped non-neuronal cells in the brain, known as 'astrocytes'. Furthermore, the group announced successful animal experiments using the newly developed drug 'KDS2010', which allowed the mice to successfully achieve weight loss without resorting to dietary restrictions.

The complex balance between food intake and energy expenditure is overseen by the hypothalamus in the brain. While it has been known that the neurons in the lateral hypothalamus are connected to fat tissue and are involved in fat metabolism, their exact role in fat metabolism regulation has remained a mystery. The researchers discovered a cluster of neurons in the hypothalamus that specifically express the receptor for the inhibitory neurotransmitter 'GABA (Gamma-Aminobutyric Acid)'. This cluster has been found to be associated with the α5 subunit of the GABAA receptor and was hence named the GABRA5 cluster.

In a diet-induced obese mouse model, the researchers observed significant slowing in the pacemaker firing of the GABRA5 neurons. Researchers continued with the study by attempting to inhibit the activity of these GABRA5 neurons using chemogenetic methods. This in turn caused a reduction in heat production (energy consumption) in the brown fat tissue, leading to fat accumulation and weight gain. On the other hand, when the GABRA5 neurons in the hypothalamus were activated, the mice were able to achieve a successful weight reduction. This suggests that the GABRA5 neurons may act as a switch for weight regulation.

In a new surprising and unexpected turn of events, the research team discovered that the astrocytes in the lateral hypothalamus regulate the activity of the GABRA5 neurons. The numbers and sizes of the reactive astrocytes are increased, and they begin to overexpress the MAO-B enzyme (Monoamine Oxidase B). This enzyme plays a crucial role in the metabolism of neurotransmitters in the nervous system and is more predominantly expressed in reactive astrocytes. This ends up in the production of a large amount of tonic GABA (Gamma-Aminobutyric Acid), which inhibits the surrounding GABRA5 neurons.

It was also discovered that suppressing the expression of the MAO-B gene in reactive astrocytes can decrease GABA secretion, thereby reversing the undesirable inhibition of the GABRA5 neurons. Using this approach the researchers were able to increase the heat production in the fat tissue of the obese mice, which allowed them to achieve weight loss even while consuming a high-calorie diet. This experimentally proves that the MAO-B enzyme in reactive astrocytes can be an effective target for obesity treatment without compromising appetite.

Furthermore, a selective and reversible MAO-B inhibitor, 'KDS2010', which was transferred to a biotech company Neurobiogen in 2019 and is currently undergoing Phase 1 clinical trials, was tested on an obese mouse model. The new drugs yielded remarkable results, demonstrating a substantial reduction in fat accumulation and weight without any impacts on the amount of food intake.

Postdoctoral researcher SA Moonsun said, “Previous obesity treatments targeting the hypothalamus mainly focused on neuronal mechanisms related to appetite regulation.” She added, “To overcome this, we focused on the non-neuronal 'astrocytes' and identified that reactive astrocytes are the cause of obesity.”

Center Director C. Justin LEE also said, “Given that obesity has been designated by the World Health Organization (WHO) as the '21st-century emerging infectious disease,’ we look to KDS2010 as a potential next-generation obesity treatment that can effectively combat obesity without suppressing appetite.”

The research results were in 'Nature Metabolism', a globally renowned academic journal in the field of metabolism with an Impact Factor of 20.8.

GABAergic GABRA5LHA shows decreased activity under a high-fat diet. Through immunostaining in the lateral hypothalamus, GABRA5 neurons were specifically labeled with green fluorescence, allowing us to observe that GABRA5 neurons co-express both GABA and GABRA5.

Astrocytes in LHA show hypertrophy in response to a high-fat diet. After consumption of a high-fat diet, molecular markers of astrocytes increase. Following the intake of a high-fat diet, the number and volume of astrocytes increase, leading to reactive astrogliosis. Subsequently, the expression of MAOB and GABA levels in astrocytes increases.

Reducing GABA production via MAOB reduces obesity. Mice were divided into two dietary groups: a regular diet and a high-fat diet. Each of these groups was further divided into two subgroups, one receiving distilled water and the other receiving KDS2010, resulting in a total of four groups. In both the regular diet and high-fat diet mice, a reduction in body weight was observed in the KDS2010-administered group. There was no change in dietary intake due to KDS2010 administration, but there was a reduction in fat after administration.

CREDIT

Institute for Basic Science

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JOURNAL

Nature Metabolism

DOI

10.1038/s42255-023-00877-w 

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Animals

ARTICLE TITLE

Hypothalamic GABRA5-positive Neurons Control Obesity via Astrocytic GABA

 

Control of behavioral decisions is similar in insects and mammals

Peer-Reviewed Publication

UNIVERSITY OF COLOGNE

 

IMAGE: LIGHT MICROSCOPE FLUORESCENCE IMAGE OF A WHOLE-BODY STAIN OF THE COCKROACH BRAIN, SHOWING PARTS OF THE MUSHROOM BODY (GREEN) AT THE TOP AND PARTS OF THE SENSORY PATHWAY FOR THE PERCEPTION OF SCENTS (ANTENNAL LOBES, MAGENTA) AT THE BOTTOM. view more 

CREDIT: CLAUDIA GROH

The mushroom body – the learning and memory region in the brains of arthropods – is responsible for the ability of insects to make abstract behavioural decisions, which are then carried out by downstream motor networks. That is the result of a study conducted by Professor Dr Martin Paul Nawrot and Dr Cansu Arican from the ‘Computational Systems Neuroscience’ working group at the University of Cologne’s Institute of Zoology. The research was reported in Current Biology under the title ‘The mushroom body output encodes behavioural decision during sensory-motor transformation’.

For a long time, the prevailing view among researchers had been that insects react in a robotic manner according to simple stimulus-response patterns, but this assumption has changed greatly over the past two decades: “Insects have simple cognitive skills such as memory formation and recall as well as experience-dependent decision making. Despite their comparatively small brains, they exhibit complex behavioural patterns,” said Professor Nawrot.

In invertebrate insects and mammals – and thus also humans – the necessary processes of the nervous system follow similar basic principles in many respects. This includes a rapid sensory processing of environmental conditions and their evaluation, a comparison with acquired experience (and accordingly a reliable decision between possible options of behaviour) and ultimately the physical execution of a behavioural sequence.

15 years of research on a brain circuit

An important processing region in the central brain of the insect, known as mushroom body due to its anatomical shape, is crucial for the formation of memory. In the last 15 years, various research endeavours have shown that memory information is encoded by the valence of a sensory stimulus at the output of the mushroom body. Within the framework of the research group FOR 2705 ‘Dissection of a Brain Circuit: Structure, Plasticity and Behavioral Function of the Drosophila Mushroom Body’, which has been funded by the German Research Foundation since 2018, the Cologne team led by Professor Nawrot is also contributing to this research field. Insects determine whether a certain stimulus has previously been memorized as positive (for example, a scent that promises food) or as negative (for example, a scent of pathogenic substances such as harmful bacteria in the food). Recent studies have also shown that the output neurons of the mushroom body also evaluate sensory stimuli that are relevant for innate behaviour, i.e. behaviour not based on experience.

Description of a new function of the mushroom body

In this latest study, lead author Dr Cansu Arican describes how she measured the activity of the output neurons of the mushroom body in the American cockroach (Periplaneta americana) in her experiments, at the same time filming the feeding behaviour of the animals. This large insect species was chosen because it has a much larger brain than the fruit fly Drosophila, which often serves as a model organism in basic research. This allowed for the electronic measurement of neuronal signals, making it possible to simultaneously measure and interpret both the stimulus activity with different food odours and the neuronal responses in the mushroom body – and ultimately the animal’s feeding behaviour – as a possible behavioural response to the stimulus with high temporal precision.

The research team observed that the mushroom body output neurons not only encode the valence of a particular odour, for example the odour of food compared to a neutral odour, they also form a decision on the execution of the respective feeding behaviour based on this information. They make the behavioural decision not only on the basis of the information of this valence; the current state of the animal is also important, for example whether it is hungry or not at that moment. In the respective trial and on the basis of the neural response pattern, it was thus possible to accurately predict whether the animal would show the feeding behaviour only about a tenth of a millisecond later.

Similar to the motor areas of the cerebral cortex in the human brain, the mushroom body thus makes a first behavioural decision and sends an abstract motor command to the downstream motor network – in the case of humans, this is the spinal cord – which then executes the behaviour by activating the relevant muscles. “This result contests the prevailing view of the mushroom body, which can now be seen as a centre for memory formation and behavioural decision-making. This is important because research on insect brains is also relevant for understanding the function of more complex brains,” Dr Cansu Arican summed up the results.

The study was supported by funding from the German Research Foundation and the "iBehave" network.

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JOURNAL

Current Biology

DOI

10.12751/g-node.13f8wi/ 

ARTICLE TITLE

The mushroom body output encodes behavioral decision during sensory-motor transformation