Mitochondrial DNA variation in the hybridizing fire-bellied toads, Bombinabombina and B-variegata

Using five restriction enzymes, geographical variation of mitochondrial DNA (mtDNA) in Bombina bombina and B. variegata was studied in samples from 20 locations. Each restriction enzyme produced a species-specific fragment pa ttern. B. bombina haplotypes A and B were closely related to each other. In contrast haplotypes A and B of B. variegata formed two distinct lineages. A very distinctive haplotype (C) was found in the Carpathian Mountains, whe reas two other haplotypes, D and E (differing by a single AvaI site), were present in western Europe and the Balkans, respectively. Populations polymo rphic for haplotypes D and E occurred in the central Balkans where the hapl otypes could replace each other clinally. mtDNA sequence divergence between B. bombina and B. variegata was estimated as 6.0-8.1% and 4.7-5.2% between type C and types D/E of B. variegata. The latter divergence is contrary to allozyme and morphological data that place the western and Carpathian B. v . variegata together (Nei's D = 0.07) and separate them from the Balkan sub species B. v. scabra (Nei's D = 0.18). Broad interspecific correlation amon g morphology, allozymes and mtDNA types in European fire-bellied toads argu es that, despite continuous hybridization (interrupted perhaps during Pleis tocene glacial maxima), little or no mtDNA introgression between the specie s has occurred outside the narrow hybrid zones that separate these parapatr ic species.