The Ontogeny of Collective Personality in Western Harvester Ants



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Animal personality, or consistent, individual differences in behavior over time, are ubiquitous across taxa and can emerge both at the individual and group level. Our understanding of the adaptive significance of these traits has progressed considerably over the last 2 decades. However, relatively little is known about the development of personality traits in either solitary or group-living organisms. Considering the effects of ontogeny on personality will provide considerable insight into its functionality and expose the mechanisms responsible for shaping personality. Likewise, studies on the development of personality are important for understanding how variation in personality emerges and is maintained within a population. My dissertation explores the ontogeny of collective personality traits using western harvester ant (Pogonomyrmex occidentalis) colonies. First, I examine how the intensity and among-colony variance in collective personality traits develops as a function of colony size and age over 2 years. Results from both years revealed that as colony size increases, relative among-colony variability in personality decreases significantly. Essentially, there is much more variability in personality among small colonies, relative to their mean behavior, compared to large colonies, which behave more similarly. Next, I focus on determining whether personality-matching habitat choice, behavioral flexibility, or selection is responsible for the spatial clustering of colonies with similar activity levels among colony ‘neighborhoods’. I found that while newly-founded colonies did not match their neighbors, large colonies matched their neighborhood in both years. Similarly, I observed a stronger correlation between colonies and their neighborhoods as focal colony size increased, supporting the behavioral flexibility hypothesis. These results show that the social environment plays a key role in personality development. Finally, I explore the effects early experience on the ontogeny of collective personality traits in a laboratory experiment. I found that early colony experience has little to no effect on the development of personality, at least during the incipient stages of colony life. Regardless of the experimental treatment, the pattern of change was the same, indicating that behavioral development in very small colonies is highly conserved. The work from this dissertation shows that colony size and the social environment are key factors influencing personality development.



animal personality, collective behavior, development, western harvester ants, social environment, experience