What Creates a Eusocial Animal?

For animals to take part in behavior that appears altruistic, such a sharing food and rearing another’s young, they must be closely related. For eusocial behavior to succeed, members of the colony must be closely related. There are several ways to make create a closely related colony.

Sterile Workers

Eusocial colonies will often have one dominant fertile female, while the rest of the members of the colony are sterile. This ensures that every new generation shares the queen’s genes, and are closely related like brother and sister. In naked mole rat colonies, females will fight for dominance. Once dominance has been established, the subordinate workers will produce more oxytocin, the hormone linked with maternal care. The elevated rates of oxytocin will help them care for the young, prevent them from killing babies that aren’t their own, and share food. All of these traits promote eusocial living.

In the eusocial wasp, Ropalidia marginata, Chandran et al. (2012), found that the need to display dominance was necessary for female wasps when trying to develop fertile ovaries quickly. When female wasps were subordinate, their ovary development was suppressed, but the dominant female wasp developed her ovaries quickly. Naked mole rats also have their reproduction suppressed due to social interaction. It was also found that female naked mole rats could regain their ability to reproduce if taken away from the queen and colony. This explains one way new colonies can be formed.

The Importance of Relatedness and Reproductive Policing

It is very important for eusocial colonies that members are closely related. Why? See Hamilton's Rule

Sometimes workers in eusocial colonies have the ability to reproduce, and do. They attempt to take advantage of the nurturing environment and pass on genes that are more closely related to themselves. To prevent this, workers will selectively kill all eggs laid by other workers because each individual is more related to eggs laid by the queen than eggs laid by another worker. In the case of Vespula germanica, a eusocial wasp, a relatedness of .25 for worker to queen’s offspring compared to a relatedness of .21 for worker to worker’s offspring was enough for workers to kill non-queen laid eggs.



Sources used for this page in order of section:

Mooney, Skyler J.; Douglas, Natasha R.; Holmes, Melissa M. 2014

Chandran, Swarnalatha; Gadagkar, Raghavendra; Shukla, Shantanu. 2012

“Louisville Zoo Fact Sheet.”

Bonckaert, Wim; Vuerinckx, Kristel; Billen, Johan; et al. 2008