Hybridization between the fire‐bellied toads Bombina bombina and Bombina variegata in the karst regions of Slovakia and Hungary: morphological and allozyme evidence

Geographic variability and genetic interactions in the contact zone between the fire‐bellied toads, Bombina bombina and B. variegata, were studied using analysis of morphological and genetic variation in sixteen samples from the Slovak Karst and Aggtelek Karst regions. Genotype frequencies at four marker loci (Ldh‐1, Mdh‐1, Adk, Hem) demonstrate the existence of a hybrid zone with highly variable population structures. While some samples appear to represent panmictic hybrid populations, other samples are very heterogeneous. Pure individuals of both species occurred together with hybrids at one site. Habitat segregation among genetically differentiated demes probably causes this heterogeneity of population structures. Increased frequencies of the allele Ldh‐1M, which is present in low proportion in B. bombina south of the contact zone, were found in some hybrid populations.