Behavioral and hormonal responses to urbanization in ants

Urbanization has profound effects on biological communities. Many organisms cannot persist in anthropogenic environments, while others may adapt to urban conditions. Behavioral traits can facilitate this adaptation and predict how species might respond to urbanization. We studied the behavior of the odorous house ant (Tapinoma sessile) which is common in both natural (i.e., forests) and urban areas. Relative to natural environments, colonies in urban areas are typically more aggressive and have many more workers and queens. To examine how this variation may influence other behaviors, we compared the exploratory behavior of T. sessile workers and colonies from natural and urban environments. We found repeatable variation in exploratory behavior, suggesting workers have distinct behavioral types. Additionally, colonies from natural environments had higher exploration and foraging activity relative to urban colonies. Activity also varied among ants with different behavioral roles - workers that were foraging were more exploratory than workers taken from the nest or that were engaged in a defensive role (i.e., recruited to the location of a different colony). Finally, we identified a potential proximate mechanism that might be influencing activity. Treatment with the hormone octopamine led to increased levels of individual exploration and colony-level foraging activity for colonies from both habitat types. However, natural variation in worker octopamine levels did not vary between environments. Together, these results suggest that exploratory behavior may play a role in adaptation to urbanization and that octopamine may be a key driver for exploratory and foraging behavior in odorous house ants.