Limited dispersal and an unexpected aggression pattern in a native supercolonial ant

Understanding how social groups function requires studies on how
individuals move across the landscape and interact with each other. Ant
supercolonies are extreme cooperative units that may consist of thousands
of interconnected nests, and their individuals cooperate over large
spatial scales. However, the inner structure of suggested supercolonial
(or unicolonial) societies has rarely been extensively studied using both
genetic and behavioral analyses. We describe a dense supercolony-like
aggregation of more than 1300 nests of the ant Formica (Coptoformica)
pressilabris. We performed aggression assays and found that, while
aggression levels were generally low, there was some aggression within the
assumed supercolony. The occurrence of aggression increased with distance
from the focal nest, in accordance with the genetically viscous population
structure we observe by using 10 DNA microsatellite markers. However, the
aggressive interactions do not follow any clear pattern that would allow
specifying colony borders within the area. The genetic data indicate
limited gene flow within and away from the supercolony. Our results show
that a Formica supercolony is not necessarily a single unit but can be a
more fluid mosaic of aggressive and amicable interactions instead,
highlighting the need to study internest interactions in detail when
describing supercolonies.