Queen brood care behavior is plastic and socially regulated in an annually eusocial insect
This study demonstrates that bumble bee queens retain behavioral plasticity in brood care throughout colony development, specifically showing that they can socially regulate incubation and feeding behaviors in response to worker loss, with incubation exhibiting greater flexibility than feeding.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
In the world of insects, the way a mother cares for her young often changes as her family grows. For many species, there is a clear turning point: a mother starts by doing everything herself, but once her children grow up and can help, she steps back to focus on making more babies. This shift is a fundamental part of how social insect colonies, like those of bees and ants, function. Scientists call this "behavioral plasticity," which is simply the ability of an animal to change its actions when its environment changes. In social groups, this means adjusting behavior based on who is around. While we know that insect mothers can switch roles when their helpers first arrive, it has remained a mystery whether this switch is permanent. Once a queen bee stops changing diapers and starts laying eggs, does she lose the ability to go back to caring for her young if the helpers disappear? Or is her new role so fixed that she cannot adapt if the social world around her collapses?
A team of researchers at the University of California, Riverside, decided to find out by watching bumble bee queens in a controlled setting. They focused on the common eastern bumble bee, a species that starts its life alone. A new queen builds a nest, lays eggs, and cares for the first batch of larvae by herself. She feeds them and keeps them warm. Eventually, her first daughters hatch and become workers. These workers take over the heavy lifting of feeding and warming the brood, allowing the queen to dedicate herself almost entirely to laying eggs. The researchers wanted to test if this transition was a one-way street. They wondered if a queen, even in a large, mature colony with dozens of workers, could suddenly remember how to care for her young if all the workers were taken away.
To answer this, the scientists set up an experiment with fifty bumble bee colonies. They raised these colonies in the lab until they reached three different stages of growth: early, middle, and late. The early colonies had about five workers, the middle ones had around fifteen, and the late ones had roughly fifty. At each stage, they split the colonies into two groups. In one group, they left the workers alone. In the other group, they carefully removed every single worker from the nest, leaving the queen completely alone with her brood. They then filmed the queens for two days, watching closely to see how they behaved before and after the workers were gone. The researchers were looking for two specific actions: incubation, which is when the queen sits on the eggs or larvae to keep them warm, and feeding, where she regurgitates food directly into the mouths of the young.
The results showed that the queens were far more flexible than anyone expected. When the workers were removed, the queens stepped up to fill the gap over the course of the following day. In every single colony, regardless of whether it was young or old, the queens increased the amount of time they spent incubating the brood. They sat on the young bees more often and for longer periods to ensure they stayed warm. This happened even in the oldest colonies, where the queens had been laying eggs for weeks and had never needed to provide much care. The study found that the queens did not just sit there; they actively adjusted their behavior to match the new, lonely reality of their nests. However, there was a limit to this flexibility. While the queens became much better at keeping the brood warm, they did not significantly increase how often they fed the larvae. Feeding remained a rare event, occurring just as infrequently as it did when the workers were present. This suggests that while the ability to keep the nest warm is a skill queens can turn on and off, the act of feeding is a different, more rigid behavior.
The researchers also looked at what happened to the queen's ability to lay eggs when the workers vanished. In the oldest colonies, the queens laid significantly fewer eggs after the workers were removed. This indicates a trade-off: when the queen had to work hard to keep the brood warm, she had less energy or time to produce new eggs. It appears that the queen's body is constantly balancing the cost of caring for the young against the cost of making more of them. The study also revealed that queens are not just mindlessly caring for any young they see; they are selective. The queens spent most of their time warming the oldest larvae and pupae, while they almost exclusively fed the youngest larvae. This suggests that even when a queen is doing all the work herself, she is making strategic decisions about which young need her attention most.
Perhaps the most surprising discovery was that this ability to switch roles never disappears. The researchers even looked at fully mature colonies with hundreds of workers, where the queen is expected to do nothing but lay eggs. Even in these massive nests, when workers were removed, the queens were observed incubating the brood again. This proves that the transition from a caretaker to a reproductive specialist is not a permanent loss of ability. The queen retains the capacity to care for her young, even if she rarely uses it. This flexibility might be a crucial survival tool. In the wild, if a colony loses its workers to a predator or a storm, the queen must be able to step in and save the remaining brood, or the entire colony will die.
The study challenges the old idea that once an insect queen specializes in reproduction, she loses her maternal instincts. Instead, it shows that these instincts are always there, waiting to be reactivated if the social environment demands it. The queens did not need to learn how to care for the young again; they simply had to remember how to do it. This finding changes our understanding of how social insects evolve. It suggests that the ability to adapt to changing social conditions is a powerful trait that is kept alive, even as the colony grows and the queen's role becomes more specialized. The queen is not just an egg-laying machine; she is a resilient mother who can shift gears instantly to ensure her family survives, no matter how many helpers she has or how old the colony gets.
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