Four populations of Caucasian brown frogs (Rana macrocnemis) from different elevations and different mountain systems (Great and Minor Caucasus) were studied. In populations from the Minor Caucasus, the percentage of striped frogs increases with elevation, but not in the Great Caucasus. At the same time, age at sexual maturity in Caucasus Minor populations does not differ between forest and subalpine populations. It is suggested that in this region the increasing proportion of genetically striped frogs is the main adaptation preventing a decrease of reproductive potential with elevation. In the brown frogs mctapopulation inhabiting the Great Caucasus, such a mechanism is absent.