Heat knock-down times of urban and rural Chiasmia clathrata moth larvae and adults

Urbanization and its urban‐heat‐island effect (UHI) have expanding
footprints worldwide. The UHI means that urban habitats experience a
higher mean and more frequent extreme high temperatures than rural
habitats, impacting the ontogeny and resilience of urban biodiversity.
However, many organisms occupy different microhabitats during different
life stages and thus may experience the UHI differently across their
development. While evolutionary changes in heat tolerance in line with the
UHI have been demonstrated, it is unknown whether such evolutionary
responses can vary across development. Here, using common‐garden‐reared
Chiasmia clathrata moths from urban and rural populations from three
European countries, we tested for urban evolution of heat shock tolerance
in two life stages: larvae and adults. Our results indicate widespread
urban evolution of increased heat tolerance in the adult stage only,
suggesting that the UHI may be a stronger selective agent in adults. We
also found that the difference in heat tolerance between urban and rural
populations was similar to the difference between Mid‐ and North‐European
regions, suggesting similarity between adaptation to the UHI and natural,
latitudinal temperature variation. Our observations incentivize further
research to quantify the impact of these UHI adaptations on fitness during
urbanization and climate change, and to check whether life‐stage‐specific
adaptations in heat tolerance are typical of other ectothermic species
that manage to survive in urbanized settings.