Allozyme similarity between the pied and collared flycatchers (Aves: Ficedula hypoleuca and F. albicollis)

The genetic differentiation between two closely related Old World flycatchers, Ficedula hypoleuca and F. albicollis, was studied by protein electrophoresis. These species hybridize in areas of geographic overlap and only hybrid males appear to be fertile. A total of 170 F. hypoleuca from four localities, and 63 F. albicollis from three localities were sampled. The proportion of polymorphic loci, among the 35 loci investigated, was 11.4 % for F. hypoleuca and 8.6 % for F. albicollis. The average heterozygosity was 0.9 % and 1.4 %, respectively. No fixed allelic differences could be found between the species, and. among 8 variable loci, only three showed significant allele frequency differences. The relative gene diversity (GST) between the species was 2.4 %; thus most variation (97.6 %) occurred within each species. Nei's genetic distance was 0.0006±0.0003. The low genetic differentiation found between these two flycatchers is discussed in the light of extensive introgression since their speciation.