The Transcriptomic Response Along an Urbanization Gradient Is Also Temperature-Dependent in a Freshwater Insect

Urbanization has become one of the leading causes of habitat transformation affecting ecosystem functioning. However, the transcriptomic response to urbanization remains poorly understood. Here, we conducted a transcriptomic analysis along an urbanization gradient under different warming temperatures. We further explored the genes underlying phenotypic variation along an urbanization gradient using weighted gene co-expression network analysis (WGCNA). We collected adult females in eight ponds spanning an urbanization gradient (percentage of impervious surface) in Southern Poland and raised their larvae in growth chambers under three temperature treatments: current 22°C, + 3°C, and + 6°C above current temperature. When larvae reached the prefinal instar, they were phenotyped for traits related to development and size, and collected for a gene expression analysis. We found that 24 genes varied in expression along a continuous urbanization gradient and were related to proteolysis, extracellular organization and perception. In addition, some genes showed a significant interaction urbanization × temperature and were associated with detection of chemical stimulus and perception. The WGCNA revealed two gene modules associated with urbanization and some phenotype traits, especially with development time. Genes associated with phenotypic differentiation along the urbanization gradient were part of many different pathways including signal transmission, cell cycle and DNA repair. In conclusion, we demonstrated that the transcriptomic response along an urbanization gradient was context-dependent, here on temperature, suggesting that some genes responding to urbanization also exhibited thermal plasticity. Our work highlights the importance of urbanization in inducing phenotypic and gene expression changes in organisms.