Structure and dynamics of a hybrid zone in Bombina (Amphibia: Anura: Discoglossidae)

Population structure in the hybrid zone between the fire-bellied tc,ads Bombina bombina and Bombina variegata in the Waldviertel region of Lower Austria was studied using allozyme electrophoresis. The rarity of suitable biotopes in this region causes a fragmented population structure. Most breeding sites are situated in quarries; the persistence of these habitats appears to depend on continuing anthropogenic disturbance at moderate levels. In some populations the alleles of one species are fixed at several diagnostic loci, while other marker loci show high frequencies (up to 38%) of alleles derived from the other species. Patterns of genetic divergence among neighboring populations indicate that gene flow is low or absent. In comparison with other transects across hybrid zones in Bombina, possible causes of selection are discussed and the opportunity for reinforcement is critically examined.