In order to study the diversity, phylogenetic relationships and distribution of marsh frogs of the Pelophylax ridibundus complex in Kazakhstan and northwest China, we conducted phylogeographic analyses of 125 samples from 53 localities using the mtDNA ND2 and COI genes and the SAI nuclear gene sequences. Phylogenetic inference of mtDNA revealed three main lineages—sister lineages Balkhash and Syrdarya (as the Central Asian P. sp. novum), and the Anatolian P. cf. bedriagae, while from nDNA data, we additionally detected the western form, P. ridibundus. According to mtDNA data, the mean genetic distances between P. sp. novum and two other forms of marsh frogs was more than 5%. Genetic homogeneity within populations of the Syrdarya lineage and P. cf. bedriagae is characterized by low nucleotide diversity and high haplotype diversity. Demographic analyses of the lineages showed past population expansions of the Balkhash and the Syrdarya forms. Divergence from the most recent ancestor had occurred in the Early Pleistocene period (2.46 Mya) for the Balkhash and the Syrdarya lineages, and 1.27 Mya for the P. cf. bedriagae. Our findings provide a first investigation of the lineage diversification and population dynamics of the Central Asian marsh frogs and will be useful for further taxonomic implications and conservational actions.

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According to 2005 data, during the second half of the 20th century, the range of marsh frogs (Pelophylax ridibundus complex) in Kazakhstan almost doubled, which was facilitated by the unintentional introduction of these amphibians in the central and eastern regions of the country against the backdrop of favorable climate change. This paper analyzes the results of the next monitoring of the distribution of the marsh frogs in Kazakhstan in the light of the hypothesis of the ongoing dispersal of amphibians throughout the country. During the revision of literature, museum and archival materials over the past 15 years and the analysis of the authors’ field data for 2021, about 500 amphibian sighting points were collected, which is almost 2 times higher than previously known information. It has been established that the modern range of the complex occupies the territory of all major hydrographic basins of Kazakhstan: The Ural-Emba, Aral-Syrdarya, Nura-Tengiz, Balkhash-Alakol, Tobol-Ishim and Irtysh basins, of which only the last two belong to the area of oceanic runoff, the rest are the drainless inland. A chronological analysis of the data obtained for each basin made it possible to conclude that over the historical period the area of the marsh frogs’ range has changed, but mainly due to periodic reductions or expansions within the drainless inland basins, the level and mineralization of water bodies of which are determined by cyclic climate fluctuations. In a broad sense, it is proposed to talk about the constancy of the autochthonous range of the marsh frogs in the west, south and southeast of Kazakhstan. The phenomenon of “settlement” includes the movements of lake frogs within the Nura-Tengiz and Irtysh basins, where they did not live in the historical past. In geological retrospect, this process probably restores the boundaries of the Neogene distribution of representatives of the P. ridibundus complex. From the point of view of the genetic composition of the complex, one can speak of the dispersal or even expansion of the Anatolian P. cf. bedriagae, which has successfully advanced to all regions of Kazakhstan from the eastern borders of its autochthonous range in the Caspian Plain and the coasts of the Mangyshlak Peninsula.

Pike-perch is an invader for the water basins of Central Kazakhstan. These species have stable self-reproductive populations in the regional waters. Back calculation method was used to investigate pike-perch growth rates in reservoirs of K. Satpayev’s channel. For comparison, the data from the other water bodies (Vyacheslavsky and Sherubay-Nurinsky water reservoirs) were used, as well as literature data. Pike-perch species from the investigated waters don’t show high growth rates. The populations from the reservoirs of K. Satpayev’s channel have quite similar growth rates with populations from the Amur river, from a number of reservoirs in the Volga river basin and from the reservoir in Spain. Sexual differences in growth have not been observed. Evaluating possible influence of various abiotic and biotic factors on the growth rate of pike-perch in the reservoirs of K. Satpayev’s channel was carried out. It has been stated that the availability of trophic resources cannot play a key role in growth dynamics because of their high abundance. Morphology of water bodies also does not play a role, as well as chromaticity, turbidity and other optical water indicators. It can be supposed that the main factor influencing growth of pike perch is the habitat’s temperature. This factor hardly ever approaches optimal values for the species in reservoirs of K. Satpaev’s channel. The possible influence of fishing selectivity on pike-perch growth rates was also evaluated. Currently, there has been imposed a moratorium on pike-perch catch. However, pike-perch is found in by-catches and in catches of amateur fishermen. It should be said that such seizures have an insignificant role in the dynamics of growth rates.