MCA: Isolating the role of chemical communication in the displacement of native harvester ants by the invasive Argentine ant

Harvester ants in the genus Pogonomyrmex play an important ecological role in ecosystems where they are found. They harvest seeds from a variety of plant species, helping spread those seeds and support a balanced plant community. However, harvester ants have been extirpated from many places where they used to be common. The invasive Argentine ant, now widespread across California and the Southeastern United States, is rapidly displacing harvester ant populations, which may directly affect plant communities and have downstream impacts on the larger ecosystem. Argentine ants are thought to harm harvester ants primarily by raiding their nests and stealing their brood. However, direct behavioral interactions between the Argentine ant and native harvester ants are poorly understood. It remains unclear how such raids impact harvester ant activity and whether harvester ants engage in behaviors that could prevent raids. This project will test the idea that harvester ants are able to detect chemicals produced by the Argentine ants, thereby avoiding encounters with Argentine ants by changing where they look for food or keeping their nest entrances closed at certain times of day. Such behavior might help avert a raid, but it may also reduce the amount of food they are able to gather. Understanding the behavioral interactions between these species could inspire new ideas to protect harvester ants and limit some of the negative impacts of Argentine ant invasion. This award supports NSF priorities because of the potential impact of chemical cues to biotechnology. Interactions between ants are typically mediated by chemicals. This project aims to test the hypothesis that colonies of the harvester ant avoid Argentine ant encounters by altering their activity when they detect chemicals associated with Argentine ants. One reason that behavioral interactions between the species are poorly documented is that in the well-studied coastal regions of California invaded by the Argentine ant, local populations of harvester ants have disappeared or are in decline, making it difficult to observe unstaged interactions. This project will instead focus on ongoing interactions between the species in a dry, inland fragment of native California shrubland where both species have lived side by side for at least a decade. Working with two well-established mentors to develop new skills in chemical ecology and expertise in a new study system, the PI will (1) characterize individual behavioral responses of the harvester ant to cues of Argentine ant presence, (2) determine the role of Argentine ant chemical cues in stimulating those responses, and (3) develop methods to assess colony-level harvester ant responses across an environmental gradient from cool coastal regions to drier inland regions. By investigating how one native ant species thrives locally despite Argentine ant invasion, the proposed research has the potential to illuminate how environmental factors and chemical communication together shape the impacts of biological invasion. Moreover, the PI will learn chemical ecology skills that will open up a fruitful and sustainable avenue for collaborative research on ant communication. This collaborative research program will provide new, formative interdisciplinary research opportunities for undergraduate students pursuing careers in STEM. 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.