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The edible frog, Pelophylax esculentus, is a hybrid form that reproduces via clonal propagation of only one of the parental genomes through generations of hybrids while the genome of other parental species is eliminated during gametogenesis. Such reproductive ability requires hybrids to coexist with one of the parental species or rarely both parental species causing the formation of so-called population systems. Population systems and reproductive biology of water frogs from the east of the range remained partially unexplored. In this study, we investigated the distributions, population systems, genetic structure, types of gametes, and morphological variability of water frogs of the genus Pelophylax from the northeastern parts of their ranges (Mari El Republic and adjacent territories, Russia). We examined 1,337 individuals from 68 localities using morphological traits combined with DNA flow cytometry and a multilocus approach (fragments of a nuclear and two mitochondrial genes). We revealed five types of population systems: “pure” populations of the parental P. ridibundus (R) and P. lessonae (L), mixed populations of parental species (R-L) along and with their hybrids (R-E-L), as well as mixed populations of P. lessonae and P. esculentus (L-E). However, the “pure” hybrid (E) and the mixed P. ridibundus and P. esculentus (R-E) population systems were not found. All hybrids studied by DNA flow cytometry were diploid. Analysis of gametogenesis showed that the majority of hybrid males, as well as hybrid females from the L-E system, produced gametes with the P. ridibundus genome. However, in the R-E-L system, hybrid females were usually sterile. The reproduction of hybrids in such systems is primarily based on crosses of P. esculentus males with P. lessonae females. Molecular analysis showed the presence of mitochondrial and nuclear DNA

The article presents the first results of a study of age and growth of the Hyrcanian frog, Rana pseudodalmatina in the Talysh Mountains. The animals were caught in the first Decade of March 2011 in Sym village in Astara District of Azerbaijan. The age was determined by a skeletochronological analysis of clipped phalanges of the third toe of hind limb. Preparations were made and examined with well-visible thick sections of 56 males and 7 females. Males in the sample were 1 – 5 years old and females were 2 – 4 years old. The average age of males was 3.2 years and 3.7 years of females. Most of studied frogs were specimens in the age of three and four years. The most intensive growth of the Hyrcanian frog occurs before reaching sexual maturity. A male at the age of one year had a body length equal to 309.8% of the average length of the metamorphs from the same reservoir, two-year-old males were 328.8 – 341.3%, three-year-olds were 271.7 – 385.9%, four-year-olds were 347.8 – 388.6%, five-year — 369.6 – 421.2%. The relative length of a two-year-old female was 342.4%, three-year-old females — 391.3 – 432.1, four-year-olds — 383.2 – 397.8%.