Ever wish you could stop that fruit fly on your kitchen counter in its tracks? Scientists at Max Planck Florida Institute for Neuroscience have created flies that halt under red light. In doing so, they discovered the precise neural mechanisms involved in stopping.

Their findings, published in Nature, have implications far beyond controlling fly behavior. They demonstrate how the brain engages different neural mechanisms depending on environmental context.

The power of Drosophila to understand complex behaviors

Halting is a critical action essential for almost all animal behaviors. When foraging, an animal must stop when it detects food to eat; when dirty, it must stop to groom itself. The ability to stop, while seemingly simple, has not been well understood as it involves complex interactions with competing behaviors like walking.

Max Planck Florida scientist Dr. Salil Bidaye is an expert at using the powerful research model Drosophila Melanogaster (aka the fruit fly) to understand how neural circuit activity leads to precise and complex behaviors such as navigating through an environment. Having previously identified neurons critical for forward, backward, and turning locomotion, Dr. Bidaye and his team turned to stopping.

“Purposeful movement through the world relies on halting at the correct time as much as walking. It is central to important behaviors like eating, mating, and avoiding harm. We were interested in understanding how the brain controls halting and where halting signals override signals for walking,” said Bidaye.

Taking advantage of the fruit fly’s power as a research model, including the animal’s simplified nervous system, short lifespan, and large offspring numbers, Bidaye and his team used a genetic screen to identify neurons that initiate stopping. Using optogenetics to activate specific neurons by shining a red light, the researchers turned on small groups of neurons to see which caused freely walking flies to stop.

Two mechanisms for stopping

Three unique neuron types, named Foxglove, Bluebell, and Brake, caused the flies to stop when activated. Through careful and precise analysis, the scientists determined that the flies’ stopping mechanisms differed depending on which neuron was active. Foxglove and Bluebell neurons inhibited forward walking and turning, respectively, while Brake neurons overrode all walking commands and enhanced leg-joint resistance.

“Our research team’s diverse expertise was critical in analyzing precise stopping mechanisms. Each team member contributed to our understanding by approaching the question through different methods, including leg movement analysis, imaging of neural activity, and computational modeling,” said Bidaye.

“Further, large research collaborations spanning multiple labs and countries have recently mapped the connections between all the neurons in the fly brain and nerve cord. These wiring diagrams guided our experiments and understanding of the neural circuitry and mechanisms of halting.”

The research team, consisting of scientists from Max Planck Florida, Florida Atlantic University, University of Cambridge, University of California, Berkeley and the MRC Laboratory of Molecular Biology, combined the data from the wiring diagrams and these multiple approaches to gain a holistic understanding of the behavioral, muscular, and neuronal mechanisms that induced the fly’s halting.

They found that activating these different neurons did not stop the flies in the same way but used unique mechanisms, which they named “Walk-OFF” and “Brake.”

As the name implies, the “Walk-OFF” mechanism works by turning off neurons that drive walking, similar to removing your foot from the gas pedal of a car. This mechanism, used by the Foxglove and Bluebell neurons, relies on the inhibitory neurotransmitter GABA to suppress neurons in the brain that induce walking.

The “Brake” mechanism, on the other hand, employed by the excitatory cholinergic Brake neurons in the nerve cord, actively prevents stepping by increasing the resistance at the leg joints and providing postural stability.

This mechanism is similar to stepping on the brake in your car to actively stop the wheels from turning. And just as you would remove your foot from the gas to step on the brake, the “Brake” mechanism also inhibits walking-promotion neurons in addition to preventing stepping.

Lead researcher on the project, Neha Sapkal, describes the team’s excitement at discovering the “Brake” mechanism. “Whereas the ‘Walk-Off’ mechanism was similar to stopping mechanisms identified in other animal models, the ‘Brake’ mechanism was completely new and caused such robust stopping in the fly. We were immediately interested in understanding how and when the fly would use these different mechanisms.”

Context-specific activation of halt mechanisms

To determine when the fly might use the “Walk-OFF” and “Brake” mechanisms, the team again took multiple approaches, including predictive modeling based on the wiring diagram of the fly nervous system, recording the activity of halting neurons in the fly, and disrupting the mechanisms in different behavioral scenarios.

Their findings suggested that the two mechanisms were used mutually exclusively in different behavioral contexts and were activated by relevant environmental cues. The “Walk-OFF” mechanism is engaged in the context of feeding and activated by sugar-sensing neurons. On the other hand, the “Brake” mechanism is used during grooming and is predicted to be activated by the sensory information coming from the bristles of the fly.

During grooming, the fly must lift several legs and maintain balance. The Brake mechanism provides this stability through the active resistance at joints and increased postural stability of the standing legs. Indeed, when the scientists disrupted the “Brake” mechanism, flies often tipped over during grooming attempts.

“The fly brain has provided insight into how contextual information engages specific mechanisms of behaviors such as stopping.”

Bidaye says, “We hope understanding these mechanisms will allow us to identify similar context-specific processes in other animals. In humans, when we stop and lift our foot to adjust our shoe or remove a stone from our tread, we are likely taking advantage of a stabilizing mechanism similar to the Brake mechanism.

“Understanding context-specific neural circuits and how they work together with other sensory and motor circuits is the key to understanding complex behaviors.”

Dolphins are extremely playful, but little is known about how they—and other marine mammals—communicate during playtime. New research published October 2 in the journal iScience shows that bottlenose dolphins (Tursiops truncates) use the “open mouth” facial expression—analogous to a smile—to communicate during social play.

The dolphins almost always use the facial expression when they are in their playmate’s field of view, and when playmates perceived a “smile,” they responded in kind 33% of the time.

“We’ve uncovered the presence of a distinct facial display, the open mouth, in bottlenose dolphins, and we showed that dolphins are also able to mirror others’ facial expression,” says senior author and evolutionary biologist Elisabetta Palagi of the University of Pisa.

“Open-mouth signals and rapid mimicry appear repeatedly across the mammal family tree, which suggests that visual communication has played a crucial role in shaping complex social interactions, not only in dolphins but in many species over time.”

Dolphin play can include acrobatics, surfing, playing with objects, chasing, and playfighting, and it’s important that these activities aren’t misinterpreted as aggression. Other mammals use facial expressions to communicate playfulness, but whether marine mammals also use facial expressions to signal playtime hasn’t been previously explored.

“The open mouth gesture likely evolved from the biting action, breaking down the biting sequence to leave only the ‘intention to bite’ without contact,” says Palagi. “The relaxed open mouth, seen in social carnivores, monkeys’ play faces, and even human laughter, is a universal sign of playfulness, helping animals—and us—signal fun and avoid conflict.”

To investigate whether dolphins visually communicate playfulness, the researchers recorded captive bottlenose dolphins while they were playing in pairs and while they were playing freely with their human trainers.

They showed that dolphins frequently use the open mouth expression when playing with other dolphins, but they don’t seem to use it when playing with humans or when they’re playing by themselves.

While only one open mouth event was recorded during solitary play, the researchers recorded a total of 1,288 open mouth events during social play sessions, and 92% of these events occurred during dolphin-dolphin play sessions.

Dolphins were also more likely to assume the open mouth expression when their faces were in the field of view of their playmate—89% of recorded open mouth expressions were emitted in this context—and when this “smile” was perceived, the playmate smiled back 33% of the time.

“Some may argue that dolphins are merely mimicking each other’s open mouth expressions by chance, given they’re often involved in the same activity or context, but this doesn’t explain why the probability of mimicking another dolphin’s open mouth within 1 second is 13 times higher when the receiver actually sees the original expression,” says Palagi.

“This rate of mimicry in dolphins is consistent with what’s been observed in certain carnivores, such as meerkats and sun bears.”

The researchers didn’t record the dolphins’ acoustic signals during playtime, and they say that future studies should investigate the possible role of vocalizations and tactile signals during playful interactions.

“Future research should dive into eye-tracking to explore how dolphins see their world and utilize acoustic signals in their multimodal communication during play,” says corresponding author and zoologist Livio Favaro.

“Dolphins have developed one of the most intricate vocal systems in the animal world, but sound can also expose them to predators or eavesdroppers. When dolphins play together, a mix of whistling and visual cues helps them cooperate and achieve goals, a strategy particularly useful during social play when they’re less on guard for predators.”

New research suggests that green turtle hatchlings ‘swim’ to the surface of the sand, rather than ‘dig,’ in the period between hatching and emergence. The findings have important implications for conserving a declining turtle population globally.

In a study published in Proceedings of the Royal Society B: Biological Sciences, scientists from UNSW’s School of Biological, Earth and Environmental Sciences used a small device, known as an accelerometer, to uncover novel findings into the behaviors of hatchlings as they emerge from their nests.

Sea turtle eggs are buried in nests 30–80cm deep. Once hatched, the newborn turtles make their way to the surface of the sand over three to seven days. But because this all happens underground, we have very little understanding of the first few days of a hatchling‘s life.

The results provided through this novel method revealed that buried hatchlings maintained a head-up orientation and unexpectedly, moved vertically through the sand by rocking forwards and backwards rather than tipping side-to-side as expected with digging.

“When I visualize a hatchling that has just come out of its egg, it is completely in the dark in its surroundings. There’s no sign to point which way is up toward the surface—yet, they will orientate themselves and move upwards regardless,” says Mr. Davey Dor, who led the study as part of his Ph.D. “Our initial findings and ‘proof’ of this new methodology opens the door for so many new questions in sea turtle ecology.”

How can you study something underground?

The image of newly hatched baby turtles moving enthusiastically across the sand and into the ocean is somewhat familiar. But what happens before then?

Once they emerge from their eggs, hatchlings move through the sand column and eventually emerge on the surface.

“It was about 64 years ago that the period of turtles hatching from their eggs and coming up to the surface was first observed,” says Mr. Dor. “And since then, people have tried different techniques to observe this phase, such as using a glass viewing pane to watch the hatchlings, or using microphones to listen to their movement.”

Each of these previous techniques has come with limitations which means it has remained difficult to study the first few days of life for turtle hatchlings.

“You just don’t think about how much work it takes for these tiny hatchlings to swim through the sand in the dark, with almost no oxygen,” says Associate Professor Lisa Schwanz. “It happens right under everyone’s feet, but we haven’t had the technology to really understand what is happening during this time.”

So Mr. Dor, A/Prof. Lisa Schwanz and Dr. David Booth, from the University of Queensland, set out to explore new ways to observe and research this obscure, little-known process.

Miniature accelerometer backpacks

Accelerometers, which measure changes in speed or direction, have previously been used to study animal movement, behaviors and physiology.

“The simple principle of the type of accelerometer we used is that it measures acceleration from three different angles,” says Mr. Dor. “So it can measure a change in velocity in a forwards and backwards motion, an up and down motion and a side to side motion.”

But until now, an accelerometer hadn’t been used in this context.

This research took place on Heron Island, a long-term monitoring nesting site for green turtles in the southern Great Barrier Reef, where nesting season typically runs from December to March.

“After locating the nests, we waited for approximately 60 days for the eggs to develop,” says Mr. Dor. “Three days before they hatched, we put a device called a hatch detector next to 10 different nests. This unique instrument measures voltage at the nest site and lets us know when the hatchlings had hatched out of their eggs.”

As soon as the team became aware that the eggs had hatched, they carefully dug down into the nest, selected the hatchling closest to the surface and attached a light-weight, miniature accelerometer onto the baby turtle, before placing it back. “We then gently layered the sand back in the way it was found,” says Mr. Dor.

It was then a waiting game to see when the hatchlings emerged. “We checked the nest site every three hours and when they did finally emerge, we retrieved the accelerometer from the hatchling carrying it.”

The accelerometer provided new data on the direction, speed and time it took for the ten hatchlings to emerge. “We analyzed the data and found that hatchlings show amazingly consistent head-up orientation—despite being in the complete dark, surrounded by sand,” says Mr. Dor.

“We found that their movement and resting periods are generally quite short, that they move as if they were swimming rather than digging, and that as they approach the surface of the sand, they restrict their movement to nighttime,” says Mr. Dor.

Conservation and nest intervention

Sea turtle populations are in decline in many parts of the world, with several species listed as endangered. The nesting phase is a major vulnerability for turtle populations and as a result, conservation management often focuses on nest intervention, including relocation, shading and watering.

Nest relocation has been used widely around the world for many years and the practice is expected to continue as the effects of climate change and rising sea levels are affecting turtle nesting. However, factors such as moisture and temperatures in the nest, which can vary when a nest is moved, can impact important performance traits of hatchlings, including their speed and movement.

“Altering nest characteristics, such as substrate moisture and depth, could have consequences for hatchlings that we currently don’t understand,” says Mr. Dor.

“This means knowledge of hatchling behavior in the sand column—and its links to offspring success—is key to future conservation practices.”

While we know that in the scramble across the sand to the water, hatchlings are at great risk from predators, “it’s also true that some hatchlings don’t even make it to that point,” says A/Prof. Schwanz. “We have so little knowledge of what makes one hatchling successfully emerge while another doesn’t, so it’s really important that we figure out what might contribute to this.”

Opening the door to further research

The latest publication confirms that using accelerometers to monitor hatchlings provides many benefits, including data of movement and behaviors, and crucially, the ability to study turtles when our visibility of them is limited.

These findings have also provided new insights and changed previous assumptions about hatchlings’ earliest days in the sand.

“There are lots of factors that we don’t really understand because we haven’t been able to observe this stage of their lives, but we hope this will change as a result of this new method, particularly in answering questions about best conservation practices,” says Mr. Dor.

The following summer, Mr. Dor returned to Heron Island to put accelerometers on multiple hatchlings in a single nest.

“So, using the next year’s data, we’ll get a sense of how coordinated the nests are, because there is a theory about whether the turtles coordinate their movements, or if they have a division of labor,” says A/Prof. Schwanz.