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

Abstract

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 1,300 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.

Distinct colony boundaries and larval discrimination in polygyne red imported fire ants (Solenopsis invicta)

“…Likewise, gene flow was limited, and some workers were unexpectedly aggressive towards each other within the same supercolony in the unicolonial ant F . pressilabris , suggesting that supercolonies do not always function as a single unit (Hakala et al, 2020). This highlights the importance of quantifying colony boundaries using several different methods (Ellis et al, 2017), as genetic relationships do not always reflect the levels of worker and resource sharing.…”

Do polygyne ants cooperate? : Colony boundaries and larval discrimination in multiple-queen colonies of the red imported fire ant (Solenopsis invicta)

“…Similarly, Argentine ants (L. humile ) did not freely exchange workers between all nests within a single supercolony, even though there were no detectable genetic differences between nests (Heller et al, 2008). Likewise, gene flow was limited and some workers were unexpectedly aggressive towards each other within the same supercolony in the unicolonial ant Formica pressilabris , suggesting that supercolonies do not always function as a single unit (Hakala, Ittonen, Seppä, & Helanterä, 2020). This highlights the importance of quantifying colony boundaries using several different methods (Ellis et al, 2017), as genetic relationships do not always imply a free exchange of workers or resources.…”

Genetic divergence and aggressiveness within a supercolony of the invasive ant Linepithema humile

“…We did not record the time engaged on each attack (see Hakala et al 2020) or posterior attacks produced in the same dish -only the first attack was recorded on each pairto avoid considering behaviours conditioned by the first attack or repeated measures (experiences). We did not study other interactions (antennation, touch, trophallaxis, avoidance, gaster elevation) because previous works that considered these ended up merging their score values (Carlin and Hölldobler 1986;Holway et al 1998;Giraud et al 2002;Roulston et al 2003;Vogel et al 2009;Blight et al 2012Blight et al , 2017Hakala et al 2020) or interpreted them as binomial interactions (i.e. aggressive or non-aggressive; see Suarez et al 1999Suarez et al , 2002Tsutsui et al 2000Tsutsui et al , 2003Thomas et al 2005Thomas et al , 2006Thomas et al , 2007Wetterer and Wetterer 2006;Blight et al 2010).…”