Maintenance of gene flow by female-biased dispersal of Black Grouse Tetrao tetrix in northern Sweden

Sex-biased dispersal is a common phenomenon in most birds. In general, males breed at or near their site of birth while most of the females disperse. We investigated the dispersal patterns and genetic structure of lekking Black Grouse Tetrao tetrix based on ten microsatellite loci. Data for 469 individuals from 25 localities spaced from 45 to 558 km apart revealed low levels of genetic differentiation and high connectivity among studied sites due to female-biased dispersal. The spatial distribution of the genetic variation did not follow an isolation by distance pattern neither for females nor for males. STRUCTURE identified three clusters of male individuals but without any geographical pattern. Only one cluster was identified for females. Several tests of sex-biased dispersal were executed. Most of them showed no difference between sexes, but the mean assignment index and FIS showed a statistically significant female-biased dispersal. Therefore, we consider that the northern Swedish Black Grouse population is a panmictic population. The amount of gene flow throughout time has been consistent with dispersal and with no strong effect of forest fragmentation in the region.