Task partitioning allows for efficient coordination of behavior in social insect colonies. Many task allocation studies focus on social insect species with discrete morphological worker subcastes, such as those possessing major and minor workers with strongly differentiated body plans. Much less is known about task partitioning among size-variable workers lacking discrete morphological subcastes. We investigated task fidelity and its correlation with worker size in Formica species with differing degrees of body size variation. During a mark-recapture study that focused on three worker tasks (honeydew collection, nest building, and protein foraging) across 2 days, 98.6% of 3570 recaptured workers exhibited task fidelity. In species with high levels of worker size variation, worker size is strongly correlated with task performance. This size-task correlation is weaker, but still present, in species with less variably sized workers. Our results suggest that Formica use size-based task partitioning, a form of morphological polyethism. We expect social insects with and without discrete morphological worker subcastes to differ in ontogeny, evolutionary history, and degree of behavioral flexibility. Identifying the scope of variation in task partitioning mechanisms will facilitate comparative studies, thereby elucidating evolutionary histories and outcomes of alternative strategies.

Formica_Task_Data.xlsx

Species, location, behavioral, and morphometric data for all colonies used in this study. Behavioral data: from a mark-recapture experiment focused on task performance and fidelity among Formica workers. Morphometric data: head-width measurements of a subset of Formica workers for which behavioral data was collected.