Are there ecological consequences of urban adaptation? A test of eco-evolutionary dynamics in a terrestrial isopod (Oniscus asellus)

Urbanization affects many aspects of the environment with the potential to alter both ecological and evolutionary processes. However, while examples of urban evolution are accumulating, tests of urban eco-evolutionary dynamics are rare. We carried out a reciprocal transplantation experiment using the terrestrial isopod Oniscus asellus to test how adaptation to the urban heat island influenced ecological processes. As isopods are important decomposers, we asked if leaf-litter decomposition differed among reciprocal transplant treatments and used a separate laboratory experiment to isolate the effects of temperature on rates of isopod leaf consumption. We found that leaf-litter decomposition was greater in urban habitats, and that leaf consumption was elevated at higher laboratory temperatures and for rural isopods compared with urbanisopods. Although we found evidence for local adaption to both environments, fitness was lower overall within urban environments. However, urban adaptation did not feedback to influence leaf-decomposition. As fitness was depressed in urban environments, our results suggest that populations could struggle to keep pace with anthropogenic change. Additionally, our results for leaf-litter decomposition indicate that the warmed environment of cities has the potential to alter important ecological processes, but that contemporary urban adaptation does not necessarily cause further urban eco-evolutionary feedbacks.