Urban colonization by wildlife involves a combination of several different mechanisms, including phenotype or genotype sorting, phenotypic plasticity and microevolutionary adaptation. Combination of these processes can produce a rapid phenotypic, but also genetic divergence of urban versus rural populations. Here, we examined the pattern of genetic differentiation between urban and rural populations of a colonial migratory bird, the black‐headed gull Chroicocephalus ridibundus. To this end, we sampled ca 170 individuals from six (two urban and four rural) colonies in northern Poland, and genotyped them at ten microsatellite loci. Our analysis provided evidence for negligible genetic divergence of urban and rural colonies, as assessed with fixation index FST and Nei's unbiased genetic distance D (mean pairwise urban‐rural comparisons: FST = 0.003 ± 0.001 [SE] and D = 0.012 ± 0.006 [SE]). Bayesian clustering methods provided support for homogeneous genetic structure across all urban and rural populations. Also, we found no support for reduced allelic diversity in urban versus rural colonies. These results stand in a stark contrast to the previous findings on the genetic consequences of urbanization in birds. We hypothesize that this pattern could possibly be attributed to the important life‐history characters of the black‐headed gull, including coloniality, migratoriness, and high dispersal propensity. Our study provides a novel insight into the urban landscape genetics, underlining large variation in the mechanisms of urban colonization and its genetic consequences in wild animal populations.

The Major Histocompatibility Complex (MHC) genes code for key immune receptors responsible for recognition of intra- and extra-cellular pathogens (MHC class I and class II, respectively). It was hypothesized that MHC polymorphism can be maintained via fluctuating selection resulting from between-habitat variation in pathogen regimes. We examined associations between MHC class I and class II genes and habitat structure in an apex avian predator, the white-tailed eagle Haliaeetus albicilla. We genotyped MHC class I and class II genes in ca. 150 white-tailed eagle chicks from nearly one hundred nesting territories distributed across three distinct populations in Poland. Habitat structure was quantified at the levels of foraging territories and directly at the nest sites. We found strong support for associations of habitat traits with diversity and allelic composition at the MHC class II. Forest area within territory and forest productivity were identified as the major habitat predictors of MHC class II polymorphism, while other habitat traits (distance to nearest open water, grassland and water area within territory or understory presence) showed fewer associations with class II alleles. In contrast, there was little support for associations between MHC class I genes and habitat structure. All significant associations were apparent at the within- rather than between-population level. Our results suggest that extra-cellular (rather than intra-cellular) pathogens may exert much stronger selective pressure on the white-tailed eagle. Associations of habitat structure with MHC class II may reflect fluctuating (balancing) selection which maintains MHC diversity within populations.

No abstract