INHERITANCE OF A POPULATION-SPECIFIC MOLT BY CROSS-BREEDING BLACKCAPS (SYLVIA-ATRICAPILLA) OF DIFFERENT POPULATIONS

A comparative study of migratory blackcaps from Central Europe (S. Germany) and resident conspecifics from the Cape Verde Islands revealed marked differences in annual periodicity. European blackcaps, with one breeding season per year, have a single-peaked annual gonadal cycle whereas the African birds with two breeding seasons per annum have a two-peaked gonadal cycle- The European birds go through a post-juvenile moult (partial moult in first-year birds) or postnuptial moult (complete moult in adults) and, in addition, through a partial winter moult (all age classes) before the next gonadal cycle and breeding season. Their African conspecifics, on the other hand, have only one moult between two gonadal cycles, the summer moult also being the complete one- Here, we demonstrate that the ''additional' winter moult of European blackcaps is heritable and can be transmitted into interpopulational hybrids. When blackcaps from S. Germany and the Cape Verdes were cross-bred, 16 out of 21 hybrids displayed the partial winter moult of their German parents. The fact that not all but only 76 % of the F1 hybrids passed through this moult favours the idea that its incidence is controlled by a polygenic rather than a single locus system. Most likely winter moult in European blackcaps represents a threshold character as several migratory features do.