Studies on the Genetic Diversity of Wild Populations of Masu Salmon, Oncorhynchus mason mason, by Microsatellite DNA Markers

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1 Studies on the Genetic Diversity of Wild Populations of Masu Salmon, Oncorhynchus mason mason, by Microsatellite DNA Markers Daiki NOGUCHI1,2 and Nobuhiko TANIGUCHI1,2 Abstract: A large number of hatchery masu salmon, Oncorhynchus mason mason, have been released into the rivers in Japan in order to enhance the fisheries resources of this species. Unconscious genetic changes that may occur during artificial seed production should be prevented if we are to perform effective and responsible resource enhancement. In this paper, the genetic variability and population structure of masu salmon were estimated using five microsatellite DNA markers (msdna). Masu salmon showed a high level of genetic variability at the msdna loci. Average allele numbers ranged between and 15.00, average numbers of allele richness between 9.74 and 11.72, and expected heterozygosities between and Genetic differentiation was not observed between different year classes. Meanwhile, genetic differentiation was detected among captured locations, but distinct correlation between genetic distance and geographic distance was not observed. Finally, methods of brood stock management in artificial propagation to prevent genetic change and loss of variation for conservation of genetic diversity in wild populations are discussed. Key words: Oncorhynchus mason; Microsatellite DNA; Genetic variability; Population structure

2 Fig. 1. Sampling locations of the masu salmon, Oncorhynchus masou masou. JZ2001 and JZ2002 (36 45'N 'E), UN (37 56'N 'E), AR (38 09'N 'E), MM (38 14'N 'E), SR (42 52'N 'E), SK (43 51'N 'E), SB (43 40'N 'E), AK (40 03'N 'E), KS (38 51'N 'E).

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4 Table 1. Genetic variability at five microsatellite loci in four river samples of Oncorhynchus masou masou Sampling abbreviations are listed in Fig. 1. N, Sample size; NA, Number of alleles; AR, Allele richness; ho, Observed heterozygosity; he, Expected heterozygosity; Ho, Average of observed heterozygosity; He, Average of expected heterozygosity; P, Probability value estimates regarding deviation from Hardy- Weinberg equilibrium. *Significant departure from Hardy -Weinberg expectations is indicated by asterisk when P < 0.05.

5 Table 2. Pairwise comparison of FST values (lower) and geographical distances (upper) between samples Sampling abbreviations are listed in Fig. 1. *Significant differentiation is indicated by asterisk when P < Fig. 2. Relationship between FST and geographical distance. Solid square: The geographical distances ranged from 0.00 to km, Solid circle: The geographical distances ranged from to km.

6 Fig. 3. Unrooted neighbor-joining dendrogram(a) and UPGMA dendrogram(b), both of them based on Cavalli-Sforza's chord distance, estimated from microsatellite allele frequencies (percentage value refers to the bootstrap consensus value after 1000 replications).

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