Colony-level behavioral variation correlates with differences in expression of the foraging gene in red imported fire ants

Among social insects, colony-level variation is likely to be widespread and have significant ecological consequences. Very few studies, however, have documented how genetic factors relate to behavior at the colony level. Differences in expression of the foraging gene have been associated with differences in foraging and activity of a wide variety of organisms. We quantified expression of the red imported fire ant foraging gene (sifor) in workers from 21 colonies collected across the natural range of Texas fire ant populations, but maintained under standardized, environmentally controlled conditions. Colonies varied significantly in their behavior. The most active colonies had up to 10 times more active foragers than the least active colony and more than 16 times as many workers outside the nest. Expression differences among colonies correlated with this colony-level behavioral variation. Colonies with higher sifor expression in foragers had, on average, significantly higher foraging activity, exploratory activity, and recruitment to nectar than colonies with lower expression. Expression of sifor was also strongly correlated with worker task (foraging versus working in the interior of the nest). These results provide insight into the genetic and physiological processes underlying collective differences in social behavior. Quantifying variation in expression of the foraging gene may provide an important tool for understanding and predicting the ecological consequences of colony-level behavioral variation.