Intraspecific behavioral variation and the red imported fire ant foraging gene

Background/Question/Methods

Intraspecific behavioral variation has important consequences for ecology and evolution. In social insects, genetic variation in a behavior can allow a colony to exhibit more flexible, rapid responses to environmental changes and promote homeostasis. In addition, genetic variation in traits enables adaptive evolution. Our preliminary behavioral assays demonstrated significant and persistent colony-level variation in foraging behavior of the red imported fire ant (Solenopsis invicta) including variation in discovery and recruitment to resources, resource preferences, and extra-nest activity and exploration. In a number of social insects, variation in foraging behaviors and division of labor has been associated with variation in expression of the foraging gene (for), a gene encoding cGMP-dependent protein kinase (PKG). In this study we address two questions: (1) Does intraspecific variation in expression of the fire ant foraging gene (sifor) exist? (2) Does variation in sifor expression correlate with colony-level variation in foraging behavior? We established single lineage colonies from newly mated foundress queens and reared them in standard environments for nine months. These colonies were divided into standardized experimental colonies and assayed for colony-level variation in foraging-related behaviors. In order to correlate behavior with gene expression, we flash froze foragers and workers from the interior of the nest and used qPCR to quantify sifor expression.

Results/Conclusions

As expected, behavioral assays revealed a significant effect of colony of origin on all foraging-related behaviors. In fact, colony of origin explained about half of all observed variation in every trait measured (extra-nest activity, exploratory activity, recruitment). Because these colonies were reared in standardized environments and varied only in the genetic lineage of the workers, these results provide compelling evidence for the existence of genetic variation in fire ant foraging behavior. In addition, we observed significant colony-level variation in sifor expression, and increased sifor expression correlated with decreased foraging activity for all measured traits. These results demonstrate an important role of sifor expression and the associated cGMP/PKG signaling pathway in fire ant foraging behavior. This intraspecific variation in behavior may provide insight into variation in the ecological effects of fire ants, their success as invaders, and methods necessary for their control.