Characteristics of dominance: behaviours and hormones in a facultatively social bee species (Xylocopa virginica)
In facultatively social species such as Xylocopa virginica (eastern carpenter bee), individuals can breed either on their own or in groups, where resources are monopolized by a single dominant female. As such, we would expect that natural selection would act strongly in this species to promote traits that would make females more dominant. This thesis sets out to determine the characteristics that make female X. virginica dominant both through behavioural assays and hormonal manipulation. I paired females with non-nestmates in dyads consisting of two dominants, two subordinates or one of each, during two separate years. I found higher levels of tolerance in dyads without a dominant female in them, but no difference in aggression between dyad types, which would have been expected if dominants tended to be the most aggressive. Behaviours also differed between years with the high population density year having higher levels of aggression and tolerance overall. Clearly many factors contribute to how female X. virginica interact with potential rivals, beyond simply their level of dominance. I also treated females with a Juvenile Hormone (JH) analogue, methoprene, to determine whether it increases ovarian development in this species, as it does in other Hymenoptera. Increased dose of methoprene lead to increased ovarian development in X. virginica, making treated individuals better able to lay eggs and therefore to take advantage of being in a dominant social position. There was no lethal or negative sublethal effects on treated bees meaning that this method could be used in the future for field testing in this species. I suggest that X. virginica dominance is not defined solely by aggression. There are many ways for females to gain a dominant position, and females that are not aggressive enough on their own to fight their way to a dominant position are likely to use other behaviours such as nestmate feeding to gain dominance. The outcomes of this study highlight why dominance and the factors leading to it should be considered closely for the specific species being studied, because aggression is shown to not be the main source of dominance in X. virginica.
Behaviour, Hormone, Dominance, Bee, Aggression
Networked Digital Library of Theses and Dissertations