Sucrose deprivation compromises aggression and activity in Argentine ants

Behavioral dominance can result in significant resource costs associated with high rates of activity and aggression. Because these traits require metabolic fuels such as carbohydrates, dietary scarcity of carbohydrates may have more of an effect on dominance than scarcities of protein and other nutrients used preferentially for growth. In this study, we conducted a diet-manipulation experiment using lab colonies of Argentine ants (Linepithema humile) to test how diet composition affects aggression and activity, as well as variables that are tied more directly to colony growth (e.g., brood production, worker mortality). Although comparative studies on ants suggest associations between diet and behavioral dominance, the extent to which macronutrient availability affects foraging behavior and competitive performance has received surprisingly little experimental attention. Here, we found that dietary levels of sucrose and prey had interactive effects on brood production and colony growth rate. However, workers became less aggressive and less active only when colonies were deprived of sucrose, and not when they were deprived of prey. Reductions in per-capita worker aggressiveness and activity levels were associated with smaller worker size (dry mass) and lower whole-ant lipid concentrations, suggesting that shifts in worker behavior were related to changes in the nutritional state of individual ants. These data provide the first experimental support for the hypothesis that carbohydrate scarcity impinges upon activity and aggression, and illustrate in principle how colony access to carbohydrate-rich, plant-based resources (e.g., plant exudates, hemipteran honeydew) might influence behavioral investments that contribute to competitive prowess in ant communities.