Self-nonself recognition and aggression in Tetramorium alpestre populations

Abstract

Ants are eusocial insects with complex social structures and behavior patterns that vary strongly across species. In the myrmicine mountain ant Tetramorium alpestre, social structure and behavior vary also intraspecifically, as monodomous-monogynous colonies act peacefully in North Tyrol (Austria) but aggressively in South Tyrol (Italy), and polydomous-polygynous colonies act peacefully in Carinthia (Austria). This social and behavioral polymorphism makes T. alpestre an ideal study organism to identify the factors leading to these differences. In this thesis, we investigated the behavior of T. alpestre from the three populations mentioned by performing worker aggression assays between populations, calculated five different behavior indices, and tested if geographic distance, temporal factors, and/or relatedness influenced the observed behavior. To detect if workers are able to discriminate between nestmates and non-nestmates, we performed bioassays using cuticular hydrocarbon (CHC) extracts of workers. To further detect if peaceful workers can discriminate between nestmates and non-nestmates, we calculated the time of workers at different peaceful behavior levels and compared these results between internest and intranest encounters. We revealed that the between-population behavior was aggressive in most cases. The observed behavior was not influenced by geographic distance among colonies, internest relatedness, intranest relatedness, time of the day, nor the number of days after sampling. The only significant influence we found was that colonies of the South Tyrolean population were influenced by the time that had passed since the start of the experiment, leading to more aggression the later the behavior videos were filmed. We hypothesise that increased vibrations while filming the behavior movies may have caused this effect. The bioassay revealed that the South Tyrolean population was able to discriminate between nestmates and non-nestmates, whereas no evidence was found that populations of North Tyrol and Carinthia were able to do so. Among the peaceful internest encounters, only the workers of the North Tyrolean population could be demonstrated to discriminate between self and nonself, as the amount of time spent at the behavior level “being next to each other” differed significantly between internest and intranest encounters. To explain the observed differences in behavior patterns and nestmate discrimination across the different populations, we suggest to further search for differences in the amount and structure of CHCs of the different workers, as CHCs are known to influence nestmate discrimination and thus the behavior between workers of different colonies.by Gerhard P. Aigner, BSc.University of Innsbruck, Masterarbeit, 2019(VLID)368081