|Title: ||The chemical crown of social insect life: the origin and evolution of queen pheromones in social wasps|
|Other Titles: ||De chemische kroon van sociale insecten: de oorsprong en evolutie van koninginnenferomonen bij sociale wespen ,,|
|Authors: ||Oi, Cintia Akemi|
|Issue Date: ||10-Oct-2016 |
|Abstract: ||Social insects colonies are known for the incredible level of organization and provide hints about how social organisms and their communication evolved. Although the individuals of the colony cooperate and workers are known for their altruistic behaviour, there is a conflict between queen and workers over male production, since in most species of social Hymenoptera workers retain functional ovaries and are thus capable to lay unfertilized male eggs. In order to solve this potential reproductive conflict, social insects require an effective communication system to keep the harmony. Cuticular hydrocarbons (CHCs) protect insects against desiccation, but have been co-opted in several communicative functions including nestmate recognition, sex pheromones and to signal fertility and dominance status. Queen pheromones are queen-produced chemicals that signal her presence and potentially her fertility, inducing worker sterility and policing behaviour, and are thought to play a key role in the resolution of reproductive conflict.
In this thesis, I focused on the study of queen pheromones in the family of the Vespidae wasps. The aim was to test the hypothesis that a common pheromone signalling pathway underlies reproductive division of labour in different species, by identifying and comparing the active queen pheromones. This was done by measuring differences in CHCs between reproductive and sterile females by gas-chromatography-mass-spectrometry (GC-MS) and conducting worker-reproduction or worker-policing bioassays to test their efficacy.
Firstly, I found that the same signals are used by queens of the common wasp (Vespula vulgaris) to directly signal her presence and to mark and protect her eggs, thus allowing workers to perform policing behaviour, which is an additional mechanism to keep the queen’s reproductive dominance. Furthermore, a blend of CHCs that were very similar to the queen pheromones of V. vulgaris and characteristic of queens of the Saxon wasp (Dolichovespula saxonica) as well, significantly reduced worker ovary development in the latter. However, a similar experiment with another highly eusocial species, the German wasp (Vespula germanica), did not show a similar reduction in ovary development, but a strong significant effect of colony size was observed, which may have clouded the effects of pheromones. This shows that these experiments may have to be repeated, standardizing the colonies to not have such an effect. Next, in the primitively eusocial wasp Polistes satan (Polistinae), chemical cues are used only secondarily to avoid conflict, but other mechanisms such as aggression and visual cues are necessary to establish the reproductive division of labour in the nest. Nonetheless, the differences in CHCs between reproductive females and workers are similar to those found in the highly eusocial vespines, suggesting that the chemical cues were already present in a primitively eusocial ancestor but were not used as signals. Lastly, the CHCs analyses in the solitary wasp Monobia quadridens showed a higher amount of alkenes in reproductive females compared to males which could indicate a potential for sex pheromones.
In conclusion, queen pheromones probably evolved from by-products of ovary development, since I found a large degree of conservation amongst queen-specific compounds: specific linear alkanes and methyl-branched hydrocarbons are characteristic of queens and other dominant females. Future studies should focus on the evolution of queen pheromones in a phylogenetic context, or expression differences in the enzymes and hormones underlying the biosynthesis of these specific hydrocarbons.
|Publication status: ||published|
|KU Leuven publication type: ||TH|
|Appears in Collections:||Ecology, Evolution and Biodiversity Conservation Section|