Similar to the way cells in a tissue work together, ant colonies are more like a symphony than a collection of autonomous individuals sharing a living space.
Now, scientists have found a previously unknown social interaction that brings the colony together and connects ants at all stages of development, including adults, larvae, and pupae, a stage in which ants change from larvae to adults during which they can’t move.
The study, which was published in Nature, shows that pupae secrete a fluid that has never been seen before, which both adults and larvae drink right away.
The health of the whole colony seems to depend on the quick intake of this nutrient-rich fluid; the larvae need it to thrive, and if the adults and larvae do not drink it, the pupae die of fungal infections as the fluid accumulates around them.
According to Daniel Kronauer, the Stanley S. and Sydney R. Shuman Associate Professor at Rockefeller University, “the way that ants use this fluid creates a dependency between different developmental stages.”
“It just shows to what extent ant colonies really operate as an integrated unit.”
Ant larvae “milk”
Ants live in bustling colonies, making it challenging for scientists to study the myriad of ant interactions that maintain the colony’s efficiency.
According to Orli Snir, the study’s lead author and a postdoc in Kronauer’s group, “these interactions lie at the very heart of understanding insect societies but, because of the inherent challenges, they haven’t been investigated systematically.”
To confront this issue, Snir chose to reverse-engineer an ant colony in order to establish some of the fundamental social interaction principles.
To do this, she took ants out of the colony at different stages of development and watched how being alone affected them.
She saw fluid surrounding isolated pupae initially. Insects do not often release fluid during the pupal stage, and ants have also never been known to do so. The pupae died as a result of fungal diseases caused by this fluid.
The pupae only reached the maturity when Snir personally withdrew the fluid. It was obvious that the ant colony was preventing pupal fluid from gathering in some way.
Kronauer, Snir, and colleagues used dye tracing studies to determine where the fluid was flowing, and when they found that adults and larvae were drinking it, they started investigating the fluid’s composition and monitoring what happened to ants who did not consume it.
The researchers found that the fluid comes from an insect process called “molting,” in which the insect sheds its old cuticle so it can grow. Ant pupae share the molting fluid with their nestmates, unlike non-social insects who recycle it to save resources.
Researchers discovered that the fluid is rich in nutrients, psychotropic compounds, hormones, and some components contained in the royal jelly that honeybees reserve for queen bee larvae. And although ants of all ages seem to like the fluid, young ant larvae are dependent on it; those deprived of it during their first four days of life fail to thrive, and many perish.
“The first few days after hatching, larvae rely on the fluid almost like a newborn relies on milk,” Kronauer adds. “The adults also drink it voraciously and, although it’s not clear what it does to the adults, we’re confident that it impacts metabolism and physiology.”
Kronauer’s team discovered the same general phenomena in each of the five main ant subfamilies after doing the original research on clonal raider ants, indicating that the approach of co-opting molting fluid into a nourishing signaling fluid is extremely conserved, according to Kronauer.
“It probably evolved once, early in ant evolution, or even preceding ant evolution.”
How this superorganism works
The ant colony is sometimes called a superorganism, which is a single entity made up of many organisms that work together. In fact, ants communicate by exchanging chemical signals in a manner similar to how cells do so in tissue. They include pheromones, which often transmit information in the short term, and social fluids, which may have a long-lasting physiological and behavioral impact. In this light, the finding of pupal social fluid and its function in linking adults, pupae, and larvae provides more context for seeing ant colonies as interdependent superorganisms.
“Pupal social fluid is the driving force behind a central and hitherto overlooked interaction network in ant societies,” Snir adds. “This reveals a new aspect of dependency between larvae and pupae, and pupae and adults.”
The team plans to investigate the implications of this molting fluid on the colony’s functioning in future research. In particular, Kronauer is curious about whether molting fluid influences the caste of ant larvae and if and how it impacts adult behavior.
“This study only provides a glimpse into the intricate interaction networks of insect societies,” Snir adds. “Our long-term goal is to gain a deep understanding of the neural and molecular mechanisms governing social organization, and how these mechanisms evolved.”
Source: 10.1038/s41586-022-05480-9
Image Credit: Getty