BIOLOGIYA MORYA, 2017, Vol. 43, No. 4, pp. 284-292

Divergence of the seasonal races of chum salmon, Oncorhynchus keta Walbaum, 1792, in the Amur and Poronai rivers: ecology, genetics, and morphology

© 2017 L. A. Zhivotovsky^{1, 2}, A. E. Lapshina³, P. B. Mikheev⁴, E. V. Podorozhnyuk⁴, O. I. Pasechnik⁴, A. V. Mamaeva⁵, T. A. Rakitskaya^{1, 2}, G. A. Rubtsova^{1, 2}, K. I. Afanasiev^{1, 2}, M. V. Shitova^{1, 2}

¹N.I.Vavilov Institute of General Genetics, Russian Academy of Sciences, Moscow 119991;
²All-Russian Research Institute of Fisheries and Oceanography, Moscow 107140;
³Sakhalin Basin Agency for Fishery and Conservation of Aquatic Biological Resources (Sakhalinrybvod), Yuzhno-Sakhalinsk 693006;
⁴Khabarovsk Branch, Pacific Research Fisheries Center (TINRO Center), Khabarovsk 680000;
⁵Pobedinsky Hatchery, Sakhalin Basin Agency for Fishery and Conservation of Aquatic Biological Resources (Sakhalinrybvod), Rybovodnoe Village, Sakhalin Oblast 694360

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Chum salmon of the Amur River (the mainland part of the Far East) and the Poronai River (Terpenia Bay, Sakhalin Island) are historically related with one another, as the drainage basins of these rivers are the remnants of the formerly single river system, the Paleoamur, which existed when Sakhalin Island was a part of the continent. Both river populations of chum salmon consist of the early-run and late-run ecological forms (seasonal races), also referred to as the summer and autumn races. They are reproductively isolated from each other by spawning at different times and in different types of spawning grounds. To assess the direction, pattern, and degree of divergence between these chum salmon races in the both river fragments occurred since the Paleoamur, it is necessary to compare them with two types of traits: selectively neutral DNA markers, and morphological and physiological traits, variations in which may have an adaptive value. For this, we have studied chum salmon from both rivers in terms of microsatellite DNA markers, body counts and measurements, body weight, and fecundity. In both the Amur River and the Poronai River, the autumn race of chum salmon prevails over the summer one in body length and weight, fecundity, number of pyloric caeca, and some other meristic traits. The intra-basin differences between the races are much more pronounced in the Amur chum salmon. The inter-race differences in microsatellites are also greater in the Amur chum salmon compared to the Poronai chum. Using microsatellites, three levels of differentiation have been revealed: (1) between the basins of the Amur and Poronai rivers, (2) between the races within each of the river basins, (3) and between population samples within each race of each basin. A hypothesis is proposed that the currently existing races of chum salmon in the Amur and Poronai rivers have evolved since the breakup of the Paleoamur, and the intra-basin divergence of the races started in the Amur River earlier than in the Poronai River. An analysis of our own and the published data suggests that adaptation of the seasonal races of chum salmon to the conditions of their spawning grounds is determined by a complex of morphological and physiological traits, including the number of pyloric caeca, which is an adaptive and highly heritable trait associated with the incubation temperature of water.

Key words: Pacific salmon, seasonal races, population, Far East, microsatellite marker, morphological and physiological traits, pyloric caeca, incubation temperature, reproductive isolation, genetic differentiation, adaptation.