How did parental care evolve? A study published in Nature suggests that caregiving may have developed by repurposing ancient brain circuits that originally controlled hunger, feeding, and food-seeking behavior. Research on clonal raider ants reveals how existing neural systems may have been adapted to support parental care and other complex social behaviors.
Scientists studying clonal raider ants found that evolution may not have needed to create entirely new brain systems for parenting. Instead, it appears to have modified older neural pathways that once regulated hunger and feeding, giving them a new role in caring for offspring.
Ants and mammals use related brain-signaling systems to control caregiving behavior. Clonal raider ants are especially useful for studying these mechanisms because they naturally change social roles as they age. Young ants typically care for larvae inside the nest, while older ants leave the nest to search for food. This predictable transition may provide important clues about the evolution of parenting, social behavior, and healthy brain aging.
“Our work is a prime example of how evolution seldom invents things from scratch,” says Daniel Kronauer, head of the Laboratory of Social Evolution and Behavior at Rockefeller University. “Evolution takes what it has and works with that, sometimes in very surprising ways.”
How Evolution May Have Created Parental Care
Parental care takes many forms throughout the animal kingdom. Mammals nourish their young with milk, birds protect and maintain nests, and ants feed and tend developing larvae. Scientists have long sought to understand how such complex caregiving behaviors evolved from ancestral animals that provided little or no care to their offspring.
One leading theory is that evolution repurposes biological systems that are already available. Earlier studies in mammals suggested that certain neuropeptides—small molecules that help nerve cells communicate—may have shifted from controlling hunger and feeding to motivating parental behavior.
These neuropeptides could have helped transform a basic survival response into a social behavior. A brain system that originally encouraged an animal to find food for itself may, over time, have been adapted to encourage adults to provide food and protection for their young.
Testing this theory has been challenging. Fruit flies and roundworms, two common research organisms, do not provide extensive care for their offspring. Mice do show strong parental behavior, and researchers have identified several neuropeptides involved in caregiving, but the mammalian brain is highly complex and difficult to study in detail.
Kronauer’s team discovered that some of the neuromodulatory mechanisms associated with caregiving overlap in ants and mice. This finding makes ants a valuable model for investigating the neural basis of parenting. An ant brain contains approximately 60,000 cells, compared with about 100 million cells in a mouse brain, allowing researchers to examine its underlying circuits more efficiently and with greater precision.
Tracking Ant Caregiving Behavior
To study caregiving, the researchers developed an automated behavioral system that placed individual ants together with individual larvae. The system recorded hundreds of interactions, allowing the scientists to measure how often ants approached, fed, moved, or cared for larvae.
The team then identified and synthesized many of the chemical messengers present in the ant brain. Each molecule was tested to determine whether changing its activity affected the ants’ caregiving behavior.
Clonal raider ant colonies have a clear age-based division of labor. Younger ants usually remain inside the nest, where they feed and care for larvae. As the ants mature, they are more likely to leave the nest and forage for food.
This age-related change allowed the researchers to investigate how brain chemistry influences social roles. They examined where the most promising neuropeptides were produced, how their levels changed during an ant’s life, and how behavior changed when the molecules were activated or suppressed.
The researchers also compared ants that had been fed with ants that had been deprived of food. This experiment helped determine whether the signals involved in caregiving remained connected to the ancient feeding circuits from which they may have evolved.
“We annotated the neuropeptidome of this ant, the complete set of neuropeptides,” says researcher Kay. “There were 70 that we could identify. It took a lot of hard work, but now we have a set of molecules that we can investigate in numerous ways.”
Two Neuropeptides Influence Ant Social Roles
The results showed that caregiving behavior in ants remains closely linked to the brain systems that regulate hunger. Two signaling molecules appeared to influence behavior in opposite ways, depending on an ant’s age and nutritional state.
Neuropeptide F, or NPF, encouraged ants to care for larvae. Allatostatin A, known as AstA, had the opposite effect: it made ants more likely to leave the larvae and begin foraging outside the nest.
Young ants naturally had higher levels of NPF and lower levels of AstA in key regions of the brain. Older ants showed the reverse pattern. This chemical shift corresponded with the ants’ normal progression from caring for larvae inside the nest to gathering food outside it.
When the researchers increased or reduced the activity of either molecule, the ants changed their behavior. The findings indicate that NPF and AstA do more than simply correlate with caregiving. They can actively influence whether an ant tends larvae or searches for food.
Hunger May Encourage Ants to Care for Larvae
The same neuropeptides also responded to hunger, much like related signaling molecules in mammals. Starved ants developed higher levels of NPF and lower levels of AstA, causing them to behave more like nest-based caregivers.
After the ants were fed, the balance shifted in the opposite direction. The ants became less focused on tending larvae and more likely to leave the nest to forage.
“We learned that parental behaviors build on the neural circuitry for feeding, and that makes some sense,” Kronauer says. “Parental behavior is a lot about feeding—not just yourself, but your offspring.”
These results support the idea that parental care evolved by adapting brain systems that originally helped animals find and consume food. Rather than developing caregiving from scratch, evolution may have expanded feeding-related motivation so that animals became driven to nourish their offspring as well as themselves.
A Shared Biological Blueprint for Parenting
The researchers next plan to identify the specific neural circuits affected by NPF and AstA. Mapping these pathways could show how chemical signals in the brain are converted into caregiving behavior and age-related changes in social roles.
Mammals appear to use some of the same neuropeptides while caring for their young. Comparing the relevant neural circuits in ants and mammals may help scientists identify a shared biological strategy for parenting across distantly related animal groups.
“It amazes me that similar parenting behaviors have evolved so many times in so many distinct animal lineages,” says Kay. “Our paper suggests that the evolutionary routes to these sorts of behaviors are far more constrained than we may have naively imagined. That’s very exciting, because it may eventually lead to a blueprint of how these complex social behaviors evolve.”
Clonal Raider Ants May Help Scientists Study Brain Aging
Clonal raider ants could help researchers investigate more than the evolution of parental care. Their predictable shift from caregivers to foragers also creates a useful model for studying how healthy aging affects the brain and behavior.
Much of aging research focuses on severe neurological disorders that develop later in life. Scientists know considerably less about the gradual changes that occur in a healthy brain throughout an individual’s normal lifespan.
Because age-related changes in ant behavior are central to the organization of the colony, these insects offer a natural system for examining how brain chemistry alters social roles over time. The researchers believe comparable mechanisms may influence age-related behavioral changes in other animals, potentially including humans.
“There’s a lot of research and funding invested in studying late-stage neurodegenerative diseases, but we actually know very little about how the brain changes throughout the normal healthspan of an individual,” Kronauer says. “In ant colonies, these dynamics are central to the organization of the society. Our discovery provides a striking demonstration that neuromodulators can produce age-dependent changes in behavioral proclivities in ants, and I suspect that’s the case in other animals as well, including in humans.”
Source: www.sciencedaily.com