Ants and mammals use related brain signalling systems that help control caregiving behaviour. Ants also change their social roles as they grow older, making them useful for studying how parenting evolved and how behaviour shifts as their brains age. The findings could eventually offer clues about similar processes in mammals, including humans.
For much of evolutionary history, many animals reproduced and then left their offspring to survive alone. A study published in Nature now offers a possible explanation for how caregiving emerged from those distant, nonparental beginnings.
By studying clonal raider ants, researchers found that evolution may not have created entirely new brain systems for parental behaviour. Instead, it appears to have adapted ancient neural pathways that originally regulated hunger and feeding, giving them a new role in social care.
“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 Behaviour at Rockefeller. “Evolution takes what it has and works with that, sometimes in very surprising ways.”
How Evolution May Have Built Parenting
Parental care appears in many forms across the animal kingdom. Mammals feed their young with milk, birds protect and maintain nests, and ants tend developing larvae. Scientists have long wondered how such complex caregiving behaviours evolved from ancestors that offered minimal care.
One leading idea is that evolution reused biological systems that already existed. Earlier research in mammals suggested that certain neuropeptides, which are small molecules used by the brain to communicate, may have shifted from regulating hunger to encouraging parental behaviour.
Proving that connection has been difficult. Fruit flies and roundworms, two widely used animals in neuroscience research, do not care for their offspring. Mice do provide extensive parental care, and scientists have identified several neuropeptides involved in this behaviour, but the mouse brain is highly complex.
Kronauer’s team found that some of the neuromodulatory mechanisms involved in caregiving overlap in ants and mice. This makes ants a potentially valuable research model. An ant brain contains about 60,000 cells, compared with roughly 100 million in a mouse brain, so scientists may be able to study the underlying circuits in much greater detail and at a faster pace.
Tracking Caregiving One Ant at a Time
The researchers created an automated behavioural system that placed individual ants with individual larvae. This setup allowed the team to monitor hundreds of caregiving interactions.
They then identified and synthesised many of the chemical messengers found in the ant brain. Each molecule was tested to see whether it changed the ants’ caregiving behaviour.
Ant colonies have a strict division of labour that is heavily dependent on age. Younger ants generally remain inside the nest and care for larvae. As they grow older, they are more likely to leave the nest and forage for food.
The researchers wanted to understand how changes in brain chemistry control this transition. They studied where the most promising molecules were produced, how their levels changed over an ant’s lifetime, and what happened when their activity was increased or reduced.
The team also compared ants that had been fed with ants that had been deprived of food. This allowed the scientists to test whether the signals involved in caregiving were still 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 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 Brain Molecules Shape Ant Behavior
The results showed that caregiving in ants remains closely tied to the brain systems that regulate hunger. Two signalling molecules appeared to push behaviour in opposite directions, depending on the ant’s age and internal conditions.
Neuropeptide F (NPF) encouraged ants to care for larvae. Allatostatin A (AstA), in contrast, made ants more likely to leave the larvae and begin foraging.
Young ants naturally had higher levels of NPF and lower levels of AstA in important areas of the brain. Older ants showed the reverse pattern. That shift matched the insects’ normal progression from nursing larvae inside the nest to gathering food outside it.
When researchers altered the activity of either molecule, the ants changed their behaviour. These results demonstrated that the neuropeptides were not merely associated with caregiving but could actively influence whether an ant nurtured larvae or went searching for food.
Hunger Can Push Ants Toward Caregiving
The same molecules also responded to hunger, just as related signals do in mammals. Starved ants developed higher levels of NPF and lower levels of AstA, making them behave more like carers.
After the ants were fed, the chemical balance reversed. They became less focused on tending larvae and more inclined to forage.
“We learnt that parental behaviours build on the neural circuitry for feeding, and that makes some sense,” Kronauer says. “Parental behaviour is largely about feeding — not just yourself, but also your offspring.”
The findings support the idea that parental care evolved by adapting brain systems that were already responsible for finding and consuming food. Rather than inventing caregiving from nothing, evolution may have expanded feeding behaviour so that animals became motivated to provide nourishment to their offspring as well as to themselves.
A Shared Blueprint for Parenting
The researchers now plan to identify the specific neural circuits affected by NPF and AstA. Mapping those pathways could reveal how chemical signals translate into caregiving behaviour.
Mammals appear to use some of the same neuropeptides when caring for their young. Comparing the relevant circuits in ants and mammals may therefore help scientists uncover a shared biological strategy for parenting that crosses widely separated branches of the animal kingdom.
“It amazes me that similar parenting behaviours have evolved so many times in so many distinct animal lineages,” says Kay. “Our paper suggests that the evolutionary routes to these sorts of behaviours are far more constrained than we may have naively imagined. That’s very exciting, as it may eventually lead to a blueprint for how these complex social behaviours evolve.
Ants Could Also Reveal How Brains Age
Clonal raider ants may be useful for more than studying parenting. Their predictable transition from carers to foragers could also help researchers investigate how healthy ageing affects the brain and behaviour.
Much of ageing research focuses on severe disorders that appear late in life. Scientists know far less about the gradual changes that occur in a healthy brain across an individual’s normal lifespan.
Because age-related changes in ant behaviour are essential to the organisation of the colony, ants offer a natural system for studying how brain chemistry reshapes social roles over time. The researchers believe that similar chemical mechanisms may also influence age-related behavioural changes in other animals.
“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,” says Kronauer. In ant colonies, these dynamics are central to the organisation of their society. Our discovery provides a striking demonstration that neuromodulators can produce age-dependent changes in behavioural proclivities in ants, and I suspect that this is also the case in other animals, including humans.
