Responses to nutritional challenges in ant colonies

In social insects, food collection for the entire colony relies on a minority of its workers. How can the colony choose between resources, determine the task allocation of workers and exhibit a flexible food storage strategy from the foraging decisions taken only by a minority? We addressed this question by posing nutritional challenges to trap-jaw ants, Odontomachus hastatus , and explored their response in terms of survival, foraging behaviour and energy storage. In the first challenge, ants alternated between long periods of confinement to a high-protein diet and short periods of confinement to a high-carbohydrate diet. In the second challenge, ants alternated between long periods of confinement to a high-carbohydrate diet and short periods of confinement to a high-protein diet. In the third challenge, ants were given simultaneously a high protein and high-carbohydrate diet. First, we showed that (1) mortality increased with protein consumption, (2) a brief exposure to a high-carbohydrate diet lessened the negative consequence of high protein consumption and (3) ants given a choice of complementary diets regulated intake and minimized mortality. We also demonstrated that ants used an energy-saving strategy to overcome challenging nutritional environments. In addition we showed that the ants had an extraordinary capacity to regulate the amounts of food entering the nest both at the collective level by allocating more workers to foraging on a high-protein diet and at the individual level by collecting more food on a high-carbohydrate diet. Our study provides new insights into the strategies used by ants facing nutritional challenges and deepens our understanding of the nutritional ecology of ants and, thereby, their vast ecological success.