Urbanization drives phenotypic differences but not asymmetry in the damselfly Ischnura elegans

Urbanization is a challenging environment and has a profound impact on organisms. Cities may be the source of important phenotypic changes and lead to developmental instability. To explore the effects of urbanization (percentage of impervious surface) on organisms, we collected ~ 800 adult damselflies Ischnura elegans across 22 ponds along an urbanization gradient. These ponds were also characterized by other environmental parameters: percentage of crops and of forested area, pH, salinity and water temperature. Adults were screened for traits related to body size and dispersion (wing morphology). We also investigated fluctuating asymmetry between right and left wings, a measure of developmental instability. We found that along an urbanization gradient, adult size and thorax length decreased, with urban individuals being smaller. The effects of urbanization were also sex-specific for femur length, with a stronger decrease in urban males. Wing shape was affected by urbanization in a sex-specific manner, with more important shape variation observed in females along the urbanization gradient. Urbanization did not increase fluctuating asymmetry, which was rather pond-specific. Our results provide evidence that urbanization shapes adult phenotype and may ultimately influence dispersal ability. Urbanization did not increase developmental instability, suggesting that some organisms may overcome some city stress.