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Title: Seasonality directs contrasting food collection behavior and nutrient regulation strategies of ants

item Cook, Steven
item EUBANKS, MICKY - Texas A&M University
item GOLD, ROGER - Texas A&M University
item BEHMER, SPENCER - Texas A&M University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2011
Publication Date: 9/26/2011
Citation: Cook, S.C., Eubanks, M.D., Gold, R.E., Behmer, S.T. 2011. Seasonality directs contrasting food collection behavior and nutrient regulation strategies of ants. PLoS One. 6(9):Article e25407.

Interpretive Summary: Many long-lived animals are observed to modify food collection behaviors that correspond with seasonal shifts in environmental conditions such as photoperiod or temperature. Good examples of such food collection behaviors include hyperphagia among some bears and hoarding by squirrels prior to holing up for much of the winter months. However, for many animals it remains largely unclear whether food collection is directed by either the relative availability of certain foods, by current nutritional demands, or by some other mechanism resulting in an anticipatory behavior. Ant colonies have also been observed to change foraging behavior seasonally (think of Aesop’s old children’s fable, The Ant and the Grasshopper), but the same questions apply to these long-lived superorganisms. To address this issue, we used colonies of fire ants and experimental foods having known protein (p) and carbohydrate (c) content in sets of dietary choice and no-choice lab experiments that controlled for photoperiod, temperature, and food availability and demand, and conducted both in the summer and fall. We showed that food collection behaviors are seasonally distinct and not directed by current food availability and demand, but by a contrasting response of summer and fall foragers to the p:c content of experimental foods. Summer, but not fall colonies, appear able to anticipate seasonal changes, and collected foods based on regulating the intake of both protein and carbohydrate. These contrasting behaviors appear pre-progammed in summer and fall ants, and are likely directed by an endogenous (unconscious) response of ants to a seasonal cue, likely photoperiod. Results from our study should help scientists to better plan, as well as predict and interpret results from both laboratory and field experiments on animal foraging behavior conducted during different seasons.

Technical Abstract: Long-lived animals, including social insects, often display seasonal shifts in foraging behavior. Foraging is ultimately a nutrient consumption exercise, but the effect of seasonality per se on changes in foraging behavior, particularly as it relates to nutrient regulation, is poorly understood. Here, we show that field-collected fire ant colonies, returned to the laboratory and maintained under identical photoperiod, temperature, and humidity regimes, and presented with experimental foods that had different protein (p) to carbohydrate (c) ratios, practice summer- and fall-specific foraging behaviors with respect to protein-carbohydrate regulation. Summer colonies increased the amount of food collected as the p:c ratio of their food became increasingly imbalanced, but fall colonies collected similar amounts of food regardless of the p:c ratio of their food. Choice experiments revealed that feeding was non-random, and that both fall and summer ants preferred carbohydrate-biased food. However, ants rarely ate all the food they collected, and their cached or discarded food always contained little carbohydrate relative to protein. From a nutrient regulation strategy, ants consumed most of the carbohydrate they collected, but regulated protein consumption to a similar level, regardless of season. We suggest that varied seasonal food collection behaviors and nutrient regulation strategies may be an adaptation that allows long-lived animals to meet current and future nutrient demands when nutrient-rich foods are abundant (e.g. spring and summer), and to conserve energy and be metabolically more efficient when nutritionally balanced foods are less abundant.