When supercolonies collide: genetic differentiation and intraspecific aggression across Argentine ant territory boundaries.
Holway, David *,1, Thomas, Melissa1, Payne, Christine2, Suarez, Andrew2, Tsutsui, Neil3, 1 University of California, San Diego, La Jolla, CA2 University of Illinois, Urbana-Champaign, IL3 University of California, Irvine, CA
ABSTRACT- Invasive ants are noteworthy because introduced populations commonly form expansive supercolonies, a phenomenon known as unicoloniality. Because of strong associations between unicoloniality and ecological dominance, it is important to understand what factors maintain this unusual form of colony structure. Such an understanding is hindered by a lack of information concerning how established supercolonies interact at points of contact. Here, we report genetic and behavioral data from naturally occurring territory borders in introduced populations of the Argentine ant, a widespread, abundant and ecologically damaging invader. At multiple transects spanning borders between mutually antagonistic supercolonies, we observed (1) that aggression was always low within supercolonies and high between colonies, and (2) that all boundaries were well delineated and abrupt. Patterns of Fst variation indicated relatively high levels of gene flow within supercolonies, and little to no gene flow between them. Multiple correspondence tests revealed that aggression levels and estimates of genetic differentiation were correlated, but that geographic distance was correlated with neither intraspecific aggression nor genetic differentiation. Although aggression only occurred between ants from different supercolonies, workers from the immediate vicinity of territory boundaries were more aggressive to one another than were workers from nests that were 500 m apart. This latter result suggests that regular experience with aggressive conspecifics can elevate aggression levels. Taken together, our findings support the notion that supercolonies are genetically distinct, differentiated units, even given prolonged and extensive contact.
Key words: invasion, ants, genetics
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