Context-dependent aggression toward non-nestmates in the ant Diacamma sp. from Japan
Aggression toward competitors is a useful measure of resource ownership and defense in animals, but aggressive behavior is costly. Therefore, it is predicted that animals will display aggression only when the expected benefit to individual fitness exceeds the expected cost. In ants, when conspecific individuals belonging to different colonies encounter each other, fighting occurs, seemingly facultatively. However, the context that influences the expression of ants’ aggressive behavior, especially in the field, is still largely unknown. We investigated the plasticity of aggressiveness toward non-nestmates in Diacamma sp. from Japan. Our field experiment clearly showed that the same foragers that were aggressive toward non-nestmates in the vicinity of their nest changed to be non-aggressive at greater distances from the nest. Furthermore, the size of the colony to which the foragers belonged weakly but significantly affected their aggressiveness: foragers belonging to larger colonies behaved more aggressively toward non-nestmates. We discuss the possible adaptive significance of the observed facultative aggression between conspecific non-nestmates. Digital video images related to the article are available at http://www.momo-p.com/showdetail-e.php?movieid=momo190618ds01a and http://www.momo-p.com/showdetail-e.php?movieid=momo190618ds02a.
KeywordsSocial insect Nestmate discrimination Intraspecific competition Social parasitism Cost and benefit
We thank H. Tatsuta, K. Tsurui, Aey T. Win, Y. Okada, and H. Fujioka for their help and advice with the field experiments and analysis. Kazuki Tsuji is received the fund from the Japan Society for the Promotion of Science (JP) with the Grants numbers KAKENHI 16F16794, KAKANHI 17H01249, KAKANHI 16H04846, KAKANHI 16K14865, KAKANHI 15H02652.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any studies with human participants performed by any of the authors. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All procedures performed in studies involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted.
Supplementary material 1 (MP4 6941 kb) The aggressive behavior of marked worker toward an attached worker
Supplementary material 2 (MP4 5361 kb) The escape behavior of marked worker from an attached worker
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