The Influence of Brood and Juvenile Hormone on Worker Behavior and Associated Gene Expression in the Red Imported Fire Ant, Solenopsis invicta

Abstract

Division of labor is one of the major pillars of eusociality, alongside overlapping generations and cooperative care of young. This phenomenon allows for individuals within a eusocial setting to be specialized for performing and completing a specific or set of specific tasks improving the efficiency of the colony. The degree of specialization of workers and their ability to transition between different roles varies across different social insect species.

First, I evaluated the behavioral and genetic changes that a S. invicta worker would undergo during task transition in the presence of brood and determined how plastic or rigid worker task might be within a colony. Through observation of worker behaviors performed over multiple time-points per day, I showed that worker task reversion and acceleration does occur in this system. Furthermore, the type of brood influenced the rate at which this occurred, with larvae and eggs having the strongest effect of all types.

Next, I wanted to discern the behavioral and genetic effect that the application of a juvenile hormone (JH) analog might have on S. invicta workers. JH is often associated with task in some eusocial insects, thus lending its propensity for functioning similarly in S. invicta. Applications of a JH analog S-hydroprene were given to nurses to observe behavioral changes. S-hydroprene application to nurses caused a shift in behavior from internal, nest-based behaviors to external, foraging-based behaviors.

Finally, I wanted to investigate which potential genes could be used to determine the task workers are performing in S. invicta colonies, as well as identify what other physiological processes might be associated with JH and task transition. I found 816 differentially expressed genes between foragers and nurses and 100 differentially expressed genes between nurses treated with acetone and nurses treated with S-hydroprene. I focused on the differentially expressed genes between foragers and nurses that were associated with different molecular pathways such as energy metabolism, glycolysis, juvenile hormone synthesis and metabolism, and immunity.

Overall, results from this dissertation increase our understanding of the underlying factors which influence worker task in S. invicta and provide further insight into potential avenues of management for this pest species.