Study explores the basis of social behavior in the insect brain

A team of scientists led by the University of Tokyo has recently proposed a new model for the evolution of higher brain functions and social behavior in the Hymenoptera – a large order of insects comprising over 150,000 of species of sawflies, wasps, bees, and ants. 

The experts compared the Kenyon neuronal cells in the mushroom bodies – parts of the insect brain structuring the processes of sensory integration, memory, and learning – of “primitive” sawflies and more sophisticated honey bees. They discovered that three specialized Kenyon cell subtypes in the brains of honey bees may have evolved from a single, multifunctional Kenyon cell-subtype ancestor. 

Besides helping scientists better understand how insect behavior has evolved, these findings could also shed new light on the evolution of the behavior of more complex organisms, including humans.

“In 2017, we reported that the complexity of Kenyon cell (KC) subtypes in mushroom bodies in insect brains increases with the behavioral diversification in Hymenoptera (a large and varied order of insects),” said senior author Takeo Kubo, a professor of Animal Physiological Chemistry at Tokyo. “In other words, the more KC subtypes an insect has, the more complex its brain and the behaviors it may exhibit. But we didn’t know how these different subtypes evolved. That was the stimulus for this new study.”  

To clarify these issues, the researchers chose two Hymenoptera species that engage in highly different behaviors: the solitary turnip sawfly, which has a single KC subtype, and the sophisticated, social honey bee, which has three KC subtypes. 

The experts used transcriptome analysis to identify the genetic expression profiles of these various KC subtypes to reveal the potential evolutionary pathways between the primitive sawfly brain and the honey bees’ more complex one.

“I was surprised that each of the three KC subtypes in the honey bee showed comparable similarity to the single KC type in the sawfly,” said co-author Hiroki Kohno, an assistant professor of Biological Sciences at Tokyo. “Based on our initial comparative analysis of several genes, we had previously supposed that additional KC subtypes had been added one by one. However, they appear to have been separated from a multifunctional ancestral type, through functional segregation and specialization.” 

As the numbers of KC subtypes increased, each of them seemed to inherit various properties from an ancestral KC, and later on evolved in different ways, leading to their varied current functions. To clarify how ancestral KC functions are present in both sawflies and honey bees, the researchers trained sawflies to perform a common honey bee behavioral test, in which they learn to associate an olfactory stimulus with a reward. 

In honey bees, a gene called CaMKII contributes to long-term memory formation. The experts manipulated this gene in sawfly larvae. When the larvae grew, their long-term memory was impaired, suggesting that this gene plays a similar role in both species. 

However, while CaMKII is expressed across the entire KC subtype in sawflies, in honey bees it is expressed in only one KC subtype, suggesting that its role in long-term memory was transmitted to a specific KC subtype in honey bees.

Although mammalian brains are significantly larger and much more complex than those of insects, better understanding the evolution and diversification of KC subtypes could shed new light on the evolution of social behavior in mammals, including humans. 

“There are many mysteries about the neural basis that controls social behavior, whether in insects, animals, or humans. How it has evolved still remains largely unknown. I believe that this study is a pioneering work in this field,” concluded lead author Takayoshi Kuwabara, a doctoral student at Tokyo.

The study is published in the journal Science Advances.

Why is social behavior important?

Social behavior is important for a variety of reasons, as it plays a crucial role in the functioning, development, and survival of individuals and societies. Here are some key reasons why social behavior is important:

Social bonding and relationships

Social behavior fosters the formation of relationships and connections among individuals, which are essential for emotional well-being, mental health, and overall happiness.

Cooperation and collaboration

Social behavior enables individuals to work together and pool their resources, skills, and knowledge to achieve common goals, solve problems, and overcome challenges.

Communication

Social behavior involves verbal and non-verbal communication, which allows individuals to share ideas, convey emotions, and coordinate actions effectively.

Social learning

Social behavior facilitates learning from others through observation, imitation, and instruction, which can lead to the acquisition of new skills, knowledge, and behaviors.

Culture and tradition

Social behavior plays a role in the transmission and preservation of cultural values, beliefs, practices, and traditions across generations, helping to maintain a sense of identity and continuity within societies.

Social norms and rules

Social behavior helps establish and maintain social norms and rules that govern how individuals should behave in different situations, which can contribute to social order, stability, and cohesion.

Conflict resolution and negotiation

Social behavior allows individuals to resolve disputes, negotiate differences, and reach compromises, which can prevent or reduce the likelihood of conflicts and promote social harmony.

Emotional support and empathy

Social behavior encourages individuals to provide emotional support and empathy to others, which can help alleviate stress, foster resilience, and promote mental health.

Social influence and conformity

Social behavior can lead to social influence and conformity, which may encourage individuals to adopt socially accepted attitudes, values, and behaviors, and discourage deviant or harmful actions.

Evolution and survival 

From an evolutionary perspective, social behavior has been crucial for the survival and reproduction of many species, including humans, by promoting cooperation, resource sharing, and protection from potential threats.

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By Andrei Ionescu, Earth.com Staff Writer

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