Nest demographics and foraging behavior of Apterostigma collare Emery (Hymenoptera, Formicidae) provide evidence of colony independence

Abstract.

Apterostigma collare Emery is a highly derived fungus-growing ant within the Tribe Attini whose small, fungal nests are found in tropical rain forests. This study focuses on determining the colony structure of A. collare, specifically searching for evidence of polydomy or independence. We surveyed and observed nests in the field, and performed foraging bioassays and dissected nests in the laboratory. We determined the size and contents of nests in field populations. Nests found near other nests were not statistically different in size compared to nests found alone. There was also no statistical difference between near and lone nests regarding the presence of a queen in the nest. Most nests contained one queen with brood and workers, regardless of their proximity to other nests. Observations also were made of foraging and trail-marking behaviors. Foraging activity observed in the field revealed that workers left the nest area and followed trails upwards into the canopy, but they did not interact with foragers from other nearby nests. In a laboratory foraging arena, foragers marked a trail to a food source by dragging the gaster. Bioassays showed that A. collare workers preferred their own foraging trails, but not those of other conspecific colonies. All results suggest that each nest represents an independent colony, supporting a previous report that nests found in close proximity do not constitute a polydomous colony.