TRAMPUS, Franc I.: The Effect of Unrelated Workers on Colony Perfomance in a Brood Raiding Leptothoracine ant

Intraspecific brood raiding is a common behaviour in many species of ants. This is presumably the result of territorial conflict which may ultimately result in the eviction of a small colony by a numerically larger neighbor that then takes possession of any brood remaining in the captured nest. Instead of being discarded or consumed, captured brood are allowed to eclose within the nest of the victorious colony and are incorporated into the workforce. Consequently, colonies can contain a subset of workers that are unrelated to the queen(s) or the rest of the workers in the nest. Several species of Leptothorax ants have been shown to raid smaller conspecific nests in the laboratory, and adopt the workers that develop from captured brood. I constructed experimental nests of Leptothorax longispinosus containing a queen and equal numbers of worker pupae from one, two or four different colonies to generate nests with decreasing mean relatedness but increasing variability. I measured activity level, task allocation, spacial organization of the workers within the nest and recruitment sucess. Results indicate that workers in colonies derived from a single nest are more active, forage more and have lower mortality than workers in colonies that contain unrelated workers. These results suggest that increasing colony size through brood raiding may reduce average worker productivity.