How birds colonize cities: genetic evidence from a common waterbird,the Eurasian coot

Much effort has been devoted to identify ecological and life‐history traits which facilitate urban colonization by wild avian species, but surprisingly little is known about the population‐level mechanisms of urbanization processes. In general, two different patterns of urban colonization have been proposed: 1) the model of independent colonization predicts that birds colonize cities independently in different geographical regions; 2) the model of leapfrog colonization assumes a single colonization event, while additional urban populations are established from the initial urban populations. The aim of this paper was to determine the pattern of urban colonization in a common waterbird, the Eurasian coot Fulica atra. For this purpose, we analysed microsatellite variation in three pairs of urban and rural coot populations from central Poland. We found that a newly‐established urban population was genetically more similar to neighbouring rural populations than to long‐established urban populations, as indicated by the analysis of fixation index, genetic distance and Bayesian assignment of individuals to genetic clusters. These results are consistent with the model of independent colonization, where neighbouring rural populations are a source of individuals that colonize new urban areas. However, our analysis also showed significant differentiation between long‐established urban populations and adjacent rural populations, suggesting that genetic connectivity between two types of habitat decreases with increasing time since urbanization. Our study shows high complexity of urbanization processes in wild animal populations, as well as it underpins utility of molecular tools in studying population‐level mechanisms of urbanization.