Data from: Rapid evolution of ant thermal tolerance across an urban-rural temperature cline

Rates of urbanization are accelerating worldwide. The increases in
temperature associated with ‘urban heat island’ effects provide both an
ecological imperative and a unique opportunity to explore the ecological
and evolutionary mechanisms that underlie organismal responses to rapid
environmental change. We used the acorn ant, Temnothorax curvispinosus
(Mayr 1866), 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 experiment, we found gains in the
ability to withstand high temperatures and losses in the ability to
withstand cool temperatures among ants in urban habitats. Owing to the
greater magnitude of phenotypic change in lower compared with upper
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.
While much of the ecological forecasting literature focuses on plastic
responses to environmental change, our study provides evidence of rapid
evolution of thermal tolerances, and suggests the importance of including
evolutionary responses in forecasts of organismal responses to climatic
change.