Ants are extraordinary insects, known for their strength and organization. And scientists recently discovered that they possess an impressively complex communication system.
A study published in the journal Cell explores how certain danger signaling pheromones—the olfactory markers that ants emit to communicate with each other—activate a specific part of the ants’ brain and can change the behavior of an entire nest.
“Humans are not the only animals with complex societies and communication systems,” explains lead author Taylor Hart of Rockefeller University (USA). “Ants have evolved extremely complex olfactory systems compared to other insects, which allows them to communicate using many different types of pheromones that can mean different things.”
The new research suggests that ants have their own type of communication center in the brain, similar to that of humans. This is how they can interpret the alarm pheromones, or “danger signals”, of other ants.
“There seems to be a sensory center in the ant brain where all the panic-inducing alarm pheromones arrive.”
— Daniel Kronauer, corresponding author from the Laboratory of Social Evolution and Behavior at Rockefeller University in the US.
This section of their brain may be more advanced than that of other insects, such as honey bees, which, according to previous work, rely on many different parts of their brain to coordinate in response to a single pheromone.
The researchers used a modified protein called GCaMP to scan the brain activity of clonal ants exposed to danger signals. GCaMP works by binding to calcium ions, which are activated by brain activity, and the resulting fluorescent chemical can be seen through high-resolution, fitted microscopes.
Running the scans, the researchers found that only a small section of the ants’ brains lit up in response to danger signals, but even so, the insects displayed immediate and complex behaviors in response. These behaviors were called “panic responses” because they involved actions such as running away, evacuating the nest, and transporting their young from the nest to a safer location.
Once researchers better understand the neural differences between castes, sexes, and functions, they will be able to learn how different ant brains process the same signals.
“We are studying the division of labor. Why do genetically identical individuals assume different tasks in the colony? How does this division of labor work? concluded Daniel Kronauer, of the Rockefeller University’s Laboratory of Social Evolution and Behavior.
10 thousand
species of ants exist in the world.
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“Ants have different pheromones to transmit messages”
Daniel Kronauer, corresponding author in the Laboratory of Social Evolution and Behavior, Rockefeller University, USA.
“Ants are social par excellence and live in complex societies where communication is paramount. We have known for over 50 years that ants communicate using chemical signals called pheromones. But very little was known about how pheromones are perceived and processed in the ant brain. It seemed like an important question if we wanted to understand how ant societies are organized, so we decided to address it.
Unlike humans, who communicate through spoken language, ants do so through pheromones. Different pheromones are produced in different exocrine glands and are released into the environment depending on the context. For example, when an ant senses danger, it releases alarm pheromones from the mandibular gland in its head. Other ants in the colony smell this signal and are alarmed: they take their immature young and evacuate the nest. Thus, the colony can avoid the attack of a predator, for example. But ants have many other pheromones that carry other messages.”
Interview
Taylor Hart, lead author of the study from Rockefeller University, USA.
Q: How effective is the communication of ants compared to that of humans and other animals?
– Ant communication works very differently from that of humans, but both systems are quite effective and efficient, as both ants and humans live in well-organized societies, often with large populations (some ant species have populations in the millions). One important difference is that human language can be symbolic, in which we use arbitrary sounds that only mean something because we all agree on what they mean. Symbolic language is extremely flexible and allows humans to invent new words for new concepts. Ants don’t have it, pheromones are considered to be essentially connected. The same pheromone always means the same thing to ants: for example, alarm pheromones mean “danger is near”. Trail pheromones usually mean “this way to the food” or “stay on this path.” Queen pheromones mean “there is a queen present.” There is not so much ambiguity in the meaning. In order to communicate new things, ants have to evolve new types of pheromones and pheromone detection systems, which is much slower, as it occurs over evolutionary time.
Q: And your communication center?
– Since ants communicate using pheromones, their communication centers are directly related to smell. Most of the ants’ sense of smell comes from their antennae, where the olfactory sensory neurons are located. These neurons are connected to a part of the brain called the antennal lobe, which processes olfactory stimuli. The antennal lobe is a large part of the ant brain and is made up of hundreds of tiny subcompartments called glomeruli, each with a different sensitivity to odors. Different odors activate different combinations of glomeruli, and this information informs the ant what it is smelling. In our study, we examined for the first time the responses of all glomeruli at the same time. This allowed us to find all the brain subcompartments that responded to certain odors.
Q: Tell us more about your study and your findings.
– To obtain images of the ants’ brain activity, we had to somehow make their neurons visible. To achieve this, we made genetically modified ants, into which a synthetic gene was inserted. To do this, we inject thousands of ant eggs with the synthetic gene and chemicals called transposons that move the DNA. We then breed the genetically modified ants and use them for experiments. Basically, the inserted gene causes a specific type of cell to produce proteins that fluoresce during neuronal activity. We engineered the gene to be expressed in the cells we’re interested in, the olfactory sensory neurons that connect to the antennal lobe of the brain. Next, we make a small opening in the ant’s head and use a laser scanning microscope to scan the brain for fluorescence. We stimulate the ant with odors and record which parts of the brain fluoresce.
For this study, we have focused on alarm pheromones, the chemical signals of danger. We found that, in each ant, a small number of glomeruli respond very strongly to these danger signals (about 1% of all glomeruli). We have found a small, potentially specialized part of the brain that detects and processes these signals. This could mean that the antennal lobe of ants is organized into many different subregions, each with its own specialty, responding to different pheromones. We have to do more experiments to see if this is true. Now we can also see how responses to pheromones differ between different ants. For example, ants divide their work, like humans, and one possible explanation is that different ants are more sensitive and better attuned to different types of pheromones.