Thermal tolerance of Lasius americanus across urbanization and geographical gradients

Cities are emerging as a new venue to overcome the challenges of obtaining
data on compensatory responses to climatic warming through phenotypic
plasticity and evolutionary change. In this review, we highlight how
cities can be used to explore physiological trait responses to
experimental warming and also how cities can be used as human-made
space-for-time substitutions. We synthesized the current literature and
found evidence for significant plasticity and evolution in thermal
tolerance trait responses to urban heat islands. For those studies that
reported both plastic and evolved components of thermal tolerance, we
found evidence that both mechanisms contributed to phenotypic shifts in
thermal tolerance, rather than plastic responses precluding or limiting
evolved responses. Interestingly though, for a broader range of studies,
we found that the magnitude of evolved shifts in thermal tolerance was not
significantly different from the magnitude of shift in those studies that
only reported phenotypic results, which could be a product of evolution,
plasticity, or both. Regardless, the magnitude of shifts in urban thermal
tolerance phenotypes was comparable to more traditional space-for-time
substitutions across latitudinal and altitudinal clines in environmental
temperature. We conclude by considering how urban-derived estimates of
plasticity and evolution of thermal tolerance traits can be used to
improve forecasting methods including macrophysiological models and
species distribution modelling approaches. Finally, we consider areas for
further exploration including sub-lethal performance traits and thermal
performance curves, assessing the adaptive nature of trait shifts, and
taking more full advantage of the environmental thermal variation that
cities generate.