Rebellion in the beehive

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Understanding the evolution of social systems in human and animal societies belongs to the area of interest of economic and sociological sciences, but also ecology and biology. While economists and sociologists focus on the interactions between people, ecologists and biologists are trying to understand the evolution of these complex systems. Such an approach allows for the testing of numerous general issues, including Charles Darwin's theory of evolution. An example is the research on bee colonies conducted at the Jagiellonian University.

Eusocial systems are a form of grouping of animals, characterized by a high degree of socialization, cooperative brood care and a division of labor into reproductive and non-reproductive groups. This means that some of the individuals have limited reproductive capabilities, or are sterile, and cannot transfer their genes further along. Such systems exist in insects of the order Hymenoptera (bees, wasps, and ants) and termites.

Why is it better to take care of one's sister?

In the past, inherited sterility on part of the individuals in eusocial societies was used as an argument against Darwin's theory of evolution. However, the theory proposed in 1964 by William D. Hamilton – called kin selection theory – explains the emergence of both eusocial systems and other types of altruistic behavior through natural selection. Hamilton noticed that individuals can transfer their genes not only through their offspring but also through the offspring of related individuals. As a result, altruistic behavior towards relatives may be promoted in the course of evolution, as the crucial element is the effective dissemination of the individual's genes, regardless of whether it is the individual itself that reproduces or its relative, as a result of altruistic behavior.

In eusocial systems, among insects of the order Hymenoptera (bees, wasps and ants), a characteristic sex determination occurs: males develop from unfertilized eggs while females develop from fertilized ones. As a result, the relatedness between sisters originating from a singlymated mother (75% relatedness) is higher than between mother and daughter (50% relatedness). This means that individuals who invested in raising their sisters transferred 75% of their genes, i.e., more than they would transfer if they only cared about their own offspring, enabling them to transfer only 50% of their genes. As a result, altruistic behavior towards sisters became more common than in other groups of animals. In spite of numerous studies confirming the assumptions of Hamilton's theory, the evolution of eusocial systems in the course of kin selection still remains a subject of discussion, and further research on the topic is met with wide interest.

Experimental apiary of the Department of Environmental Sciences
located in the Campus of the 600th Anniversary of the JU Revival

Swarming and rebels workers

The honeybee (Apis mellifera L.) is the best-known eusocial insect due to its large economic significance in pollinating crops and the production of honey. The bee family is also often used to illustrate an example of a perfect society, in which the workers give up their own reproduction in order to take care of the mother and her offspring. Research published in 2012 by scientists from the Department of Environmental Sciences that presents "rebel" workers in honeybees (M. Woyciechowski, K. Kuszewska, Swarming generates rebel workers in honeybee, Curr. Biol. 22. 707-711, 2012) is one of the studies that shows that the relations between individuals within a bee colony are not that perfect and that conflicts and tensions between family members exist.

Rebels are workers raised immediately after swarming, which is the only way of honeybee colony multiplication. During this time, the queen bee leaves the home nest with some of the workers (the swarm) and starts looking for a new nest site. The other workers remain in the nest, abandoned by the mother- queen, where they care for the developing future sister-queens and eggs, larvae and pupae of workers. It is these eggs and larvae, which are temporarily deprived of an adult mother-queen, that develop into rebel workers whose ovaries are better developed than in normal workers. In the future, this will allow them to reproduce, i.e., to lay unfertilized eggs from which only males (drones) will hatch. However, rebels have poorly developed organs for the production of food for queen and larvae; thus, they cannot engage themselves strongly enough to raise subsequent generations of bees. In other words, they are egoistic workers who object to the generally accepted rules of bee family functionality and instead of working for the "new mother and her offspring," try to raise their own offspring.

Conflicting interests

The most interesting part of this story is the answer to the question: "Why do the larvae of workers develop into more egoistic individuals after the swarm leaves? What are the consequences of this process?" There are two explanations of this issue. The first proximate explanation refers to a signal that acts upon larvae and is the direct cause of the development of rebels. The absence of an adult queen in the nest after the swarm has left may be considered a factor that is sensed by larvae and causes them to develop into rebel workers.

On the other hand, the second explanation of the occurrence of such an egoistic strategy of workers is connected with evolutionary factors. It is based on kin selection theory, which also explains the conflicts occurring in eusocial systems. Before the mother-queens leave, workers raise their brothers and sisters, while they will have to raise the offspring of the new sister-queen after the swarm leaves. Thus, future workers will have to raise their nieces and nephews to whom they are only half as related as they were to their brothers and sisters, which means that they will transfer fewer of their own genes to the next generation. It is precisely this decrease in relatedness within the colony that causes the evolution of rebellious strategy of workers, who have already prepared for rebellion in adult life as larvae. However, this is not the longterm state of a bee colony, as the rebels – like other workers – live for approximately one month, while the generation of workers raised from eggs lain by the new sisterqueen develops into regular workers (who also live for approximately a month), who take care of the queen and her offspring.

Each discovery generates other questions and problems. This is also true in the case of rebel workers. "Current research focuses on understanding the biology of rebels and their influence on the family in which they exist. Issues related to metabolism, lifespan and immunological response of rebels will be analyzed," concluded Karolina Kuszewska from the Department of Environmental Sciences of the Jagiellonian University. So far, we still do not know how the larvae "find out" about the temporary absence of a queen in the nest. Thus, further research on rebel bees will be a fascinating adventure, allowing for not only better understanding of the biology of honeybees, but also the improvement of our perception of the evolution of complex social systems.

Research team: Professor Michał Woyciechowski, Hajnalka Szentgyörgyi, PhD, Karolina Kuszewska, PhD, Justyna Kierat, MSc, Jędrzej Pitorak