| Abstract: | mtDNA of the hybridogenetic hybrid frog Rana esculenta from Switzerland,
Austria, and Poland was compared to mtDNA of the parental species R.
ridibunda and R. lessonae using electrophoretic analysis of restriction
enzyme fragments. Two mtDNA phenotypes, with 3.4% sequence divergence, are
present in R. lessonae: type C is found in Poland, and type D is found in
Switzerland. Rana ridibunda from Poland has either of two mtDNA phenotypes:
type A is the typical ridibunda mtDNA, and type B is a lessonae
mitochondrial genome, introgressed into R. ridibunda, that differs from
type C mtDNA of R. lessonae by only 0.3%. Each of the three lessonae
genomes differs from A, the typical ridibunda mtDNA, by approximately 8%.
All four types of mtDNA (A and B of R. ridibunda, C and D of R. lessonae)
are found in R. esculenta. Of 62 R. esculenta from Poland, 58 had type C,
three had type A, and one had type B mtDNA. All nine R. esculenta from
Switzerland had type D mtDNA. All three R. esculenta from Austria, from a
population in which males of R. esculenta are rare, had ridibunda mtDNA,
two having type B and one having type A. Both field observations and
studies of mating preference indicate that the primary hybridizations that
produce R. esculenta are between R. ridibunda females and R. lessonae
males; thereafter, R. esculenta lineages are usually maintained by matings
of R. esculenta females with R. lessonae males. The presence of ridibunda
mtDNA in the three R. esculenta sampled from Austria, its occasional
presence in R. esculenta populations in Poland, and its absence from R.
esculenta in Switzerland support both the direction of the original
hybridization and the rarity of formation of new R. esculenta lineages. The
preponderance of R. esculenta individuals with lessonae mtDNA in our
samples from central Europe suggests that most lineages have gone through
at least one mating between an R. lessonae female and an R. esculenta male.
This reveals a greater reproductive role for R. esculenta males than their
partial sterility and infrequent matings would suggest.
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