Data from: Assortative mating frames establishment in a young island bird population

Successful island colonizations are key events to understand range dynamic processes, but studying a young population right after it reaches establishment is a rare opportunity in natural systems. However, the genetic structure of a recently established population may offer unique insights into its colonization history and demographic processes important for a successful colonization. Here, we studied the population genetics of a recently established island population of Eurasian blackbirds (Aves: Turdus merula) located on the island of Heligoland in the German North Sea. Using microsatellites, we genotyped the majority of the island population, including the nestlings, over a four-year period between 2004 and 2007. We also genotyped high numbers of migrants on stopover and mainland individuals, as they are potential founders of the island population. We identified two genetic clusters that comply with the migrating and mainland birds respectively. While most of the island birds belong to the mainland cluster, some breeding individuals and a low fraction of the offspring belong to the genetic cluster found in migrating individuals with almost no admixture between the two, pointing to assortative mating acting on the island population. We did not find any evidence for founder events and detected deviations from Hardy-Weinberg equilibrium that disappeared in cohorts of older age that coincide with a lower number of siblings in older cohorts. The observed genetic patterns unravel a complex colonization history to which migratory and mainland birds have contributed and which is characterized by assortative mating. Further research will be directed towards habitat selection and phenotypic differences as potential drivers of assortative mating in this island population.Blackbird genotypesExcel file of genotype by scored alleles for each individual (n tot = 822). The last seven columns provide data for each microsatellite used with biallelic scores written in a format to be read by / transformed to most population genetics software packages. A value of 999 indicated a missing (i.e. NA) value. The column "pop_name_paper" provides information on the population the individual belongs as named in the paper.genotype_cr_t4.xls