Résumé
Population genetics theory predicts a sex-difference in genetic structure in species displaying extensive sex-biaised dispersal. As a result, the use of molecular methods for inferring patterns of sex-biased dispersal in animals has been increasing in recent years. However, the relationship between movements of genes (or genetic dispersal) and movement of individuals between their birth site and the place where they reproduce (ecological dispersal) might not be straightforward. We compared pattern of genetic structure between males and females in two bird species displaying female biased dispersal. As expected, we detected a more marked isolation-by-distance effect in males than in female in the monogamous rock ptarmigan. However, the reverse trend was found in the lekking black grouse even though female-biased dispersal is probably stronger than in rock ptarmigan. We hypothesize that mating behaviour of both, males and females, is responsive for this situation. We conclude that in species displaying complex mating behaviour, a more or less complete uncoupling between genetic and ecological dispersal could occur. If evidence for such a situation could be gathered in other taxa, the importance of inbreeding in promoting the evolution of sex-biased dispersal would be seriously questionable.