Meeting Abstract
Worldwide, the spread of urbanization is accelerating. Increases in temperature associated with urban heat island effects provide an ecological imperative and a unique opportunity to explore the evolutionary mechanisms that underlie organismal responses to rapid environmental change. We used the acorn ant, Temnothorax curvispinosus, to compare shifts in thermal tolerance of ants from rural and urban habitats throughout Cleveland, USA. Urban warming in the region has been ongoing for the past century, which translates to 20 or fewer acorn ant generations. Using a common garden design, we found that upper and lower thermal tolerances assessed with a fast rate of temperature increase (1 °C min-1), were both higher for ants from urban source populations. Owing to the asymmetry in the magnitude of shifts in upper versus lower tolerances, tolerance breadth decreased in urban habitats. Mechanistically, these shifts in thermal tolerance under urbanization reflected both evolutionary change and phenotypic plasticity, as ants from urban areas exhibited higher thermal tolerances compared with ants from rural areas regardless of rearing temperature, and ants reared in the warmer temperature treatment exhibited higher tolerances than ants reared in the cooler temperature treatment. We also found evidence of evolved plasticity as the slope of the response to warmer and colder rearing environments differed significantly among rural and urban populations. Our study provides evidence of rapid evolution of thermal tolerances, and suggests the importance of including evolutionary responses for understanding and forecasting organismal responses to climatic change.
