Macronutrient regulation in the Rasberry crazy ant (Nylanderia sp. nr. pubens)

Authors: Cook, Steven; WYNALDA, RACHEL - Texas A&M University; GOLD, ROGER - Texas A&M University; BEHMER, SPENCER - Texas A&M University

Submitted to: Insectes Sociaux
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2011
Publication Date: 1/1/2012
Citation: Cook, S.C., Wynalda, R., Gold, R.E., Behmer, S.T. 2012. Macronutrient regulation in the Rasberry crazy ant (Nylanderia sp. nr. pubens). Insectes Sociaux. 59(1):93-100.

Interpretive Summary: Animals preform best when they consume enough foods having the correct balance of nutrients. Experiments have shown that animals can actively regulate their intake of these optimal diets through changes in food collection behavior, even when available foods are nutritionally imbalanced. Interestingly, animals that live in groups, such as colonies of ants, that have a broad range of nutrient needs, also show active regulation of nutrient intake, even though only a fraction of the colony members actually collect the food. In a set of two experiments, we used a series of artificial foods having known nutrient content to investigate the preferred and optimal diet for the Rasberry crazy ant (Nylanderia sp. nr. pubens), a newly invasive ant species in parts of Texas. We used worker mortality as a gauge to determine the optimal diet for this species. Experiments revealed that this species prefers carbohydrates, but regulates nutrient intake such that the ratio of protein (p) to carbohydrate (c) content of the diet was approximates 1:2. The value of this ratio is consistent with that observed in other recent ant nutrient regulation studies. Taken together, the results from these combined studies reveal emerging commonalities among ants in similarities in foraging behaviors and nutrient content of preferred diets. Our results will be of particular use when formulating the nutrient content of the attractant for baits used in control of this newly invasive species.

Technical Abstract: Animals grow and optimize performance when they collect foods in amounts and ratios that best meet their species-specific nutritional requirements. For eusocial organisms like ants, where only a small fraction of the colony members collect food, increasing evidence demonstrates that strong macronutrient regulation occurs at the colony-level. Here, we explored regulation of protein and carbohydrate (p:c) intake in the Rasberry crazy ant, Nylanderia sp.nr. puben. We did this using dry artificial foods (14%–42% total macronutrient content) having a range of fixed p:c ratios in a series of choice and no-choice laboratory experiments, and used worker mortality to gauge colony-level costs associated with active nutrient regulation. Choice experiments revealed that colonies preferred carbohydrate-rich foods, and self-selected a diet having a p:c ratio ~1:2. No-choice experiments demonstrated that food p:c ratio only moderately affected worker food collection behavior, likely because colonies regulated the intake of only the non-limiting nutrients. Absolute worker mortality was generally high, but lowest in colonies feeding on the food having a p:c ratio of 1:2 (the p:c ratio ants self-selected in the choice experiment), although mortality was not significantly affected by food p:c ratio. The self-selected p:c ratio in our study is consistent with that observed in other recent ant nutrient regulation studies. Taken together, the results from these combined studies reveal emerging commonalities among ants in the macronutrient regulation strategies, and similarities in foraging behaviors and costs associated with macronutrient regulation. Finally, from a methodological perspective, the high mortality observed in our study, when compared to other recent studies, suggests that ant nutrient regulation studies should be conducted using foods having high moisture and total macronutrient content.