@article {12708,
	title = {Mitochondrial DNA variation in the hybridizing fire-bellied toads, <i>Bombina bombina </i>and <i>B. variegata</i>},
	journal = {Molecular EcologyMolecular Ecology},
	volume = {9},
	number = {7},
	year = {2000},
	pages = {891-899},
	publisher = {Blackwell Synergy},
	abstract = {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 pattern. 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, whereas two other haplotypes, D and E (differing by a single AvaI site), were present in western Europe and the Balkans, respectively. Populations polymorphic for haplotypes D and E occurred in the central Balkans where the haplotypes 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{\textquoteright}s D = 0.07) and separate them from the Balkan subspecies B. v. scabra (Nei{\textquoteright}s D = 0.18). Broad interspecific correlation among morphology, allozymes and mtDNA types in European fire-bellied toads argues that, despite continuous hybridization (interrupted perhaps during Pleistocene glacial maxima), little or no mtDNA introgression between the species has occurred outside the narrow hybrid zones that separate these parapatric species.},
	keywords = {Amphibia},
	author = {Szymura, J. M. and Uzzell, T. and Spolsky, C.}
}
@article {3418,
	title = {Geologically dated sea barriers calibrate a protein clock for Aegean water frogs.},
	journal = {EvolutionEvolution},
	volume = {50},
	number = {4},
	year = {1996},
	pages = {1676-1687},
	abstract = {Reliable estimates of phylogenetic relationships and divergence times are a crucial requirement for many evolutionary studies, but are usually difficult because fossils are scarce and their interpretation is often uncertain. Frogs are fresh water animals that generally are unable to cross salt water  barriers (their skin is readily permeable to both salt and water). The geologically determined ages of salt water barriers that isolate related frog populations thus provide an independent measure of the minimum date of genetic divergence between pairs of such populations. For the genetically well-studied western Palearctic water frogs (Rana esculenta group), the Aegean region provides an ideal area for determining the relationship between genetic divergence and time of spatial isolation, using  a nested set of geologically determined isolation times (12,000 yr, 200,000 yr, 1.8 Myr, 2-3 Myr, and 5.2 Myr). Using 31 electrophoretic loci for 33 pairs of neighboring frog populations, a linear relationship between geologically determined isolation time and Hillis{\textquoteright} modified Nei genetic distance was found: D*-Nei = (0.04 +- 0.01) + (0.10 +- 0.01) isolation time (Myr) corresponding to an average divergence rate ("molecular clock" pace) of 0.10 D*-Nei/Myr (0.10 D-Nei/Myr). This rate is in the range of previous estimates reported for protein electrophoretic data; the value is conservative because relatively few of the loci used are "fast evolvers" (13\%; sAAT, ALB, EST-5, MPI). Removing these fast evolvers from the analysis  results in 0.08 D*-Nei/Myr (0.08 D-Nei/Myr). The confidence limits for estimation of the ivergence time given the genetic distance are large, but  unusually narrow for this kind of study; they permit us to estimate divergence times during the Pliocene and Miocene. Few previous studies, including sequence analyses, have provided reasonable estimates of divergence  time for the Pliocene. A test using the outgroup taxa Rana perezi and Rana saharica (also isolated for 5.2 Myr by the Strait of Gibraltar) fits the calibration well: observed genetic Nei distance D*-Nei = 0.55, expected D*-Nei = 0.56. The calculated divergence times, based on this absolute molecular clock, suggest a series of speciation events after the Messinian (5.2 Myr), possibly triggered by the rapid ecological changes accompanying the desiccation and refilling of the Mediterranean Basin.},
	keywords = {Amphibia},
	author = {Beerli, P. and Hotz, H. and Uzzell, T.}
}
