Metabolic adjustment in urban birds: glycometabolic enzyme activities in urban and rural tree sparrows (passer montanus)

Urbanization is rapidly changing habitats of wild birds around the world. Food availability is one of the important factors leading to phenotypic differences between urban and rural bird populations. Comparing the physiological plasticity responses of urban and rural bird populations to different food conditions can reveal the mechanism of bird adaptation to urban environment. In this study, we hypothesized that the glycogenolysis, glycogenesis and gluconeogenesis of urban birds have been adjusted to cope with food shortage in urban areas. To test this, we designed a food quantity-controlled experiment to compare the effects of different food quantities (daily 1 g, 3 g, 5 g, 7 g per bird) on the activities of glycogen phosphorylase (GP), glycogen synthase (GS) and phosphoenolpyruvate carboxylase (PEPCK) in plasma of Tree sparrows (Passer montanus) from urban and rural areas of Beijing. The activities of GP and PEPCK in plasma of Tree sparrows from both urban and rural areas increased with the food quantity decrease. Only the activity of PEPCK was significantly different between urban and rural sparrows. The PEPCK activities of urban sparrows were significantly higher than those of rural sparrows in 1 and 3 g treatments. These results indicate that Tree sparrows from urban areas have greater gluconeogenesis plasticity than rural sparrows, which supports our hypothesis that gluconeogenesis plasticity of urban birds has been adjusted in response to urban environment.