Meeting Abstract
Polymorphism in social insect colonies is predicted to increase colony fitness by improving the efficiency of division of labor, although studies of polymorphic species have not always demonstrated this advantage. In our study we assessed the ability of carpenter ants of different body sizes to learn food-related odors, and investigated the link between learning ability and foraging performance. We showed that smaller C. americanus workers are better learners, and hypothesized that they would therefore forage more than larger nestmates. While foraging is not the only outside-nest task ants perform, we used outside-nest activity as a proxy for foraging effort. In lab-reared colony fragments, large workers were overrepresented outside the nest, contrary to our hypothesis. When lab colonies were placed in larger arenas and imaged so worker distance from the nest entrance could be quantified, we found some evidence that minors ranged farther from the nest entrance than majors, although worker distributions were highly variable and this pattern was not evident in most colonies. Preliminary field pitfall trapping confirmed that C. americanus are primarily nocturnal foragers, but the size distribution of the trapped workers included large individuals and was similar to that of our lab-reared colony fragments, demonstrating that larger individuals work outside the nest under natural conditions. Our results suggest that although small workers are more responsive to liquid food and better able to learn associations between odors and food rewards, they are not strongly overrepresented in the outside-nest worker force. Further work involving direct observations of foraging behavior per se will be necessary to determine if smaller C. americanus workers actually preferentially perform this task in nature.
