Contact between supercolonies elevates aggression in Argentine ants |
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Authors: | M L Thomas C M Payne-Makrisâ A V Suarez N D Tsutsui D A Holway |
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Institution: | (1) Division of Biological Sciences, University of California – San Diego, 9500 Gilman Drive, La Jolla, California, USA;(2) Department of Entomology and Department of Animal Biology, University of Illinois, Urbana, Illinois, USA;(3) Department of Ecology and Evolutionary Biology, University of California – Irvine, 321 Steinhaus Hall, Irvine, California, USA;(4) Centre for Evolutionary Biology, School of Animal Biology, The University of Western Australia, Perth, Australia |
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Abstract: | Complex recognition systems underlie the social organization of many organisms. In social insects the acceptance of other
individuals as nestmates can involve a variety of different cues, but the relative importance of these cues can change in
relation to the fitness costs of accepting or rejecting other individuals. In this study we investigate the mechanisms that
underlie recognition behaviour in Argentine ants (Linepithema humile). Introduced populations of Argentine ants are characterized by a social structure known as unicoloniality where intraspecific
aggression is absent over large distances resulting in the formation of expansive supercolonies. Recent research has identified
sites where multiple, mutually aggressive supercolonies co-occur allowing an examination of Argentine ant behaviour at territorial
boundaries. We found that workers from different supercolonies always interact aggressively with one another, but that neighbours
from different colonies (i.e., workers from nests located in the immediate vicinity of territory borders) consistently exhibited
higher levels of aggression compared to those displayed by non-neighbours from different colonies (i.e., workers from nests
located far enough away from a territory border so that interactions are unlikely). This difference in the level of aggression
displayed between neighbours and between non-neighbours from different supercolonies cannot be explained by differences in
relatedness or genetic similarity. Instead our findings suggest that direct contact between mutually antagonistic colonies
is sufficient to elevate aggression. A laboratory experiment in which we manipulated the extent to which colonies with no
prior history of contact could interact with one another, revealed that aggression increased after colonies were permitted
to interact, but dropped after connections between colonies were severed. Moreover, the mere presence of an aggressive supercolony
was sufficient to elicit elevated aggression. Overall these patterns are opposite to the “dear enemy” phenomenon and could
be the result of the intense territorial aggression exhibited by established supercolonies of this species.
Received 8 January 2007; revised 27 March 2007; accepted 28 March 2007. |
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Keywords: | Nestmate recognition dear enemy territory border context-dependent genetic relatedness |
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