GENETIC POLLUTION AND DISTURBANCE OF SYMBIOTIC SYSTEM OF THE FRESHWATER SHRIMP, NEOCARIDINA DENTICULATA DENTUCULATA, BY THE INVASION OF CLOSELY RELATED ALIEN SPECIES

近年来，日本怀疑从中国进口的未分类清虾作为饵料进入日本。为了阐明这一怀疑，在日本和中国收集并分析了虾及其共生体。通过对Neocaridina spp. mtDNA部分CO 1和16SrRNA基因的测序，发现了Neocaridina spp.两个主要的单倍型分支。进化枝I由仅在日本检测到的单倍型组成，而进化枝II由两国观察到的单倍型组成。进化支II包括日本和中国具有相同或很少核苷酸差异的单倍型。这表明I枝和II枝分别属于日本本土谱系（即N.denticulata denticulata）和来自中国的外来谱系。这些事实表明，新蝇属从中国入侵日本确实发生过。在日本的4个地方，这两个支系被观察到是对称的，这意味着遗传污染是通过本地种群和外来种群之间的杂交或渐渗而产生的。结合对虾进出口商的听觉调查，认为外来的新虾属（Neocaridina）可能是从中国北部和中部引进的，而共生的branchiobdellid纲（H. truncatus）最近在日本中部记录到的是来自中国中部。

Recent invasion of taxonomically unsettled atyid shrimp Neocaridina spp. from China into Japan has been suspected through the import as fishing bait. To elucidate this suspicion, the shrimps and their symbionts were collected and analyzed both from Japan and China. Two major haplotype clades were found for Neocaridina spp., based on the sequenced partial CO I and 16SrRNA genes of the mtDNA. Clade I was composed of the haplotypes detected only from Japan, while Clade II was composed of those observed from both countries. Clade II included the haplotypes with identical or few nucleotide differences between Japan and China. This indicates that Clades I and II are assigned to the indigenous lineage in Japan (i.e., N.denticulata denticulata) and the exotic ones from China, respectively. These facts suggest that invasion of Neocaridina spp. from China into Japan has really occurred. In four localities of Japan, the two clades were observed sympatrically, implying the genetic pollution through hybridization or introgression between indigenous and exotic populations. Together with the hearing investigation from exporters and importers of the shrimps, exotic Neocaridina spp. were supposed to have been introduced from the northern and middle part of China, and the symbiotic branchiobdellidan, H. truncatus, recently recorded in central Japan from the middle part of China.