Collaborative Research: Integrative Approach to Understanding the Emergence of Alternate Social Phenotypes through Greenbeard Effects in the Fire Ant

Cooperation has been a longstanding evolutionary problem because cooperators suffer an individual fitness loss to provide benefits to other individuals in the group. A notable solution to this problem involves the greenbeard effect, first conceived of by W.D. Hamilton in the early 1960s as a thought experiment to explain the evolution of altruism, and later popularized by R.

Dawkins. The main tenet of the greenbeard effect is that there exists a hypothetical gene, or set of linked genes, that expresses a perceptible trait (e.g., green beard), enables the bearer to recognize this trait in others, and causes the bearer to behave differently towards others depending on whether or not they possess this trait (e.g., individuals with green beard help other “green beard” individuals but not ones without green beard).

In recent years, these “greenbeard” genes have been discovered in diverse organisms. Yet, because most of these are unicellular microbes, such as amoebae, yeast, and bacteria, we still know little if and how the complex, intricately coordinated, consequential behaviors emerge based on the greenbeard status of group members in their environment. The fire ant, Solenopsis invicta, is one of a few social animals in which a greenbeard effect has been documented.

In this project, therefore, we will investigate the relationship between a greenbeard signal and the individual and collective behaviors that it modulates, using the fire ant, as a model system. A diversity of educational and outreach programs is proposed, including participation in the EcoReach program that provides educational materials for K-12 teachers, outreach at the annual Insectival and to a lifelong learning program for adults, as well as research opportunities for graduate students and undergraduates, including some from nearby HBCUs.

Social animals work together to the advantage of their group. This cooperative behavior poses an evolutionary problem, however, because cooperators typically suffer an individual fitness loss to provide benefits to other individuals in the group. Researchers have suggested a potential solution for this problem—cooperation can evolve if a gene expresses a perceptible trait (e.g., green beard), enables the bearer to recognize this trait in others, and causes the bearer to behave differently towards others depending on the possession of this trait.

The main objective of the proposed project is to investigate the relationship between a greenbeard signal and the individual and collective behaviors that it modulates using the red imported fire ant, Solenopsis invicta, as a model system. The fire ant is one of only a few social animals in which a greenbeard effect has been documented and the underlying greenbeard factor, known as the Sb supergene, has been identified.

Using this unique model system, we aim to (1) learn what distinctive cuticular chemicals constitute greenbeard signals in different classes of nestmates, (2) identify contexts in which workers use such signals during one-on-one social interactions, and (3) reveal how colonies composed of workers with a mix of greenbeard genotypes collectively determine the emergent colony organization.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.