Differential responses to chemical cues correlate with task performance in ant foragers

Abstract: Division of labor in social insects has been explained by response threshold models which are based on differential responses to task-specific stimuli. In the present study, we argue that other types of stimuli, such as location-related cues, which are correlated with but not directly linked to task performance, may be significant. Using the black garden ant Lasius niger as a model, we focused on three groups of workers that perform extranidal tasks: (1) scouts, which explore new and unmarked areas remote from the nest; (2) patrollers, which are not recruited by other ants, but nonetheless walk outside in the nest vicinity; and (3) recruits, which are temporary foragers whose exit is triggered by recruitment. We used standardized tests to investigate, in a context-independent way, whether differences in task performance by these three groups could be correlated to intrinsic differences in their responsiveness to trail pheromone or to nest-related stimuli such as the presence of nestmates or colony odor. Overall, we found that the task profile of workers was correlated neither with their tendency to explore unmarked areas nor with their social attraction to nestmates. Scouts showed a lower attraction to colony odor and lower scores of trail following than recruits. Conversely, recruits were more attracted to colony chemical cues and showed lower response threshold to trail pheromone. Patrollers displayed behaviors between those of recruits and scouts. Our study thus shows that differences in ant responsiveness to location-related cues and recruitment trails contribute to the regulation of extranidal tasks in ants. Significance statement: Work organization in insect societies has been explained by models of differential response thresholds to stimuli that are directly linked to the performance of specific tasks. However, the task performance of individuals could also depend on their responsiveness to social and location-related cues that are correlated but not directly linked to these tasks. Using standardized context-independent tests, we found that scout ants, which explore unknown areas, display a lower responsiveness to colony area marking and trail pheromone. Conversely, recruits, which forage outside the nest only during food exploitation, are the most attracted to nestmates, colony area marking and trail pheromone. Patrollers display intermediate levels of attraction. Location-related cues could therefore play a role in determining the level of task performance by ants and should be taken into consideration in threshold models of task allocation.SCOPUS: ar.j