Age, worksite location, neuromodulators, and task performance in the ant Pheidole dentata

Social insect workers modify task performance according to age-related schedules of behavioral development, and/or changing colony labor requirements based on flexible responses that may be independent of age. Using known-age minor workers of the ant Pheidole dentata throughout 68 % of their 140-day laboratory lifespan, we asked whether workers found inside or outside the nest differed in task performance and if behaviors were correlated with and/or causally linked to changes in brain serotonin (5HT) and dopamine (DA). Our results suggest that task performance patterns of individually assayed minors collected at these two spatially different worksites were independent of age. Outside-nest minors displayed significantly higher levels of predatory behavior and greater activity than inside-nest minors, but these groups did not differ in brood care or phototaxis. We examined the relationship of 5HT and DA to these behaviors in known-age minors by quantifying individual brain titers. Both monoamines did not increase significantly from 20 to 95 days of age. DA did not appear to directly regulate worksite location, although titers were significantly higher in outside-nest than inside-nest workers. Pharmacological depletion of 5HT did not affect nursing, predation, phototaxis, or activity. Our results suggest that worker task capabilities are independent of age beyond 20 days, and only predatory behavior can be consistently predicted by spatial location. This could reflect worker flexibility or variability in the behavior of individuals collected at each location, which could be influenced by complex interactions between age, worksite location, social interactions, neuromodulators, and other environmental and internal regulators of behavior. Physiological changes associated with worker age are considered to be important regulators of task performance in social insects. The extent to which worker age is correlated with behavior, and the degree to which developmental changes in neuromodulators control worker labor, however, are poorly understood. We found that ant workers are behaviorally flexible in respect to task performance at a given age, but differ in predatory response and activity level based on their worksite location (within or outside of the nest). Dopamine level was higher in outside-nest workers; serotonin did not appear to be causally linked to any behavior we examined. Our findings suggest that worker task performance can be independent of age, and workers maintain task efficacy throughout their lifespan while differing in some aspects of behavioral performance that may change with worksite location. Relationships between age, worksite, and neuromodulator titers appear to be complex.