Date of Award

Spring 2016

Project Type


Program or Major


Degree Name

Master of Science

First Advisor

Sandra M Rehan

Second Advisor

Donald S Chandler

Third Advisor

Adrienne I Kovach


Sociality as a life history strategy has many overt benefits, but its origin from solitary living is not fully understood. The cooperation necessary for formation of even basic social groups can present natural selection paradoxes that many models are unable to reconcile. Conversely, aggression is a key component to the formation of dominance hierarchies, a very basic form of social group. These hierarchies can give way to reproductive hierarchies, which are in turn the basis for some of the most complex forms of social organization. The focus of this thesis is to use aggression in an incipiently social bee species to characterize behavioral and genetic patterns useful for further study of the mechanisms behind the evolution of sociality.

In agonistic encounters and contests between conspecifics, the outcome can be determined by physiological traits like size, age, or reproductive activity, by prior experience, or by a combination of these factors. Past experience can inform future efforts, resulting in repetition of the same outcome, while physiological traits can create hierarchies of size, age, etc. Repeated pairings of small carpenter bees (Ceratina calcarata) by circle tube forced association revealed cumulative roles for both size and experience in determining contest outcomes. Size predicted initial dominance, while experience determined subsequent outcomes. I posit that these results may hold true for other species at simple stages of social complexity, and may be important for behavioral studies of social evolution.

The brain gene expression corresponding with these behavioral results similarly yielded targets for evolutionary study. Behavioral syndromes resulting from repeated interactions in the first experiment resulted in significant upregulation of genes of memory, learning, axonogenesis, and transcription regulation in dominant individuals. These genes and their behavioral contexts matched those of a variety of taxa, as did a number of gene ontology terms with similar functions. Enrichment of several transcription factor binding motifs also revealed potential behavioral functions for cis-regulatory elements that are conserved across taxa. Overall, the results suggest key roles for genes, ontology terms, and cis-regulatory elements in behavioral response to aggression, in both simple and complex social groups. I propose that these be used as the foci for future experiments in order to determine the relative role of each of these target factors.

Combining behavioral and genetic data with comparisons to a wide range of taxa gives a more detailed look at the factors that may have influenced the evolution of sociality. These behavioral patterns and target genes/regulatory elements may provide valuable insights to further understanding the origins of animal societies.