Allozyme variation of littleneck clam Ruditapes philippinarum and genetic mixture analysis of foreign clams in Ariake Sea and Shiranui Sea off Kyushu Island, Japan

Abstract

Allozyme variation of the littleneck clam Ruditapes philippinarum was evaluated in four samples from Nameishi and Matsuo in the Ariake Sea, Ryugatake and Ushibuka in the Shiranui Sea off Kyushu Island, Japan, and in one sample from Jinzhou, China, in the Bohai Sea. A Ruditapes bruguieri sample imported from the Korean Bay off Nampo, North Korea was also studied. Among the R. philippinarum samples, heterozygosity varied from 0.265 to 0.301 and FIS estimates indicated significant homozygosity excess in 15 of 40 loci analyzed. Deviations from Hardy-Weinberg equilibrium were significant in all samples (P < 0.05). Pairwise FST estimates indicate that genetic differences between the Chinese and Japanese samples were very low, but significantly different from zero. Mixture proportions with 95% confidence intervals of Chinese R. philippinarum in Nameishi and Matsuo were estimated at 0.4098 [0.2512, 0.5705] and 0.4899 [0.3262, 0.6540], respectively. However, genetic invasion of stocked Chinese R. philippinarum into wild populations in the Ariake Sea remains uncertain due to the low precision of the estimates caused by the high similarity of allele frequencies between Jinzhou and the Ariake Sea.

Molecular and morphological evidence of hybridization between native Ruditapes philippinarum and the introduced Ruditapes form in Japan

“…R. bruguieri (DQ184829) included in our R. variegatus cluster was taken from a tide pool with rocks in Yamaguchi prefecture, Japan, suggesting it was R. variegatus. Vargas et al (2008) tentatively treated R. form as R. bruguieri based on shell-based taxonomy and allozyme variation. However, R. form is not R. bruguieri, because R. bruguieri appears restricted to the Indian Ocean, and the shell characteristics looked different from R. form in the photographs (p. 428 in Huber 2010).…”

“…The annealing temperatures were 51°C for all primers. Allozyme genotypes of 627 individuals in the samples analysed for mitochondrial and microsatellite analysis that had no missing data were used for the data analysis from 722 individuals in Vargas et al (2008Vargas et al ( , 2010. The genotypes were encoded by seven loci (IDH*, MDH-1*, MDH-2*, PGM*, 6PGD*, SOD-1* and SOD-2*), excluding the LAP* locus, which departed from Hardy-Weinberg equilibrium (HWE) in all samples.…”

“…The genotypes were encoded by seven loci (IDH*, MDH-1*, MDH-2*, PGM*, 6PGD*, SOD-1* and SOD-2*), excluding the LAP* locus, which departed from Hardy-Weinberg equilibrium (HWE) in all samples. The techniques employed for electrophoretic analyses and staining protocols were described in Vargas et al (2008).…”

“…However, the release statistics do not include the number of clams released in Japan for recreational clam gathering, and the release information for imported clams is unknown. Vargas et al (2008) examined the shell morphology and allozyme variations of R. philippinarum imported from China and the Korean peninsula at the Chiba Prefectural Fisheries Cooperative Association. They found that the imported clam was very similar to R. philippinarum, but significantly genetically different from R. philippinarum samples collected in Japan and China, which authors concluded had been misidentified as R. philippinarum.…”

“…Finally, we examine if the alien R. form is hybridizing with native R. philippinarum, based on genetic and morphometric measurements of clams from the Ariake Sea and Tokyo Bay, Japan, where large numbers of R. form have been released. In addition, the allozyme genotype data from Vargas et al (2008Vargas et al ( , 2010 were reanalysed for the individuals used in this study. This study provides the first evidence for anthropogenic hybridization of R. philippinarum and R. form, based on their population structure in Japan and China.…”