著者

YAMZAKI Masatsugu ASAKAWA Susumu MURASE Jun KIMURA Makoto

出版者

一般社団法人日本土壌肥料学会

雑誌

Soil science and plant nutrition (ISSN:00380768)

巻号頁・発行日

vol.58, no.1, pp.11-23, 2012-02-01

参考文献数

40

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Free-living fresh water Platyhelminthes except for the order Tricladida (planaria) are collectively called microturbellaria, most species of which are less than a few millimeters in length. The ecology and the fauna of microturbellarians in rice fields has not been clarified in detail since Okugawa (1932) reported the morphological and ecological characters of all microturbellarian species that had been observed in Japan. This might be because the observation of living microturbellarians is needed for their identification. To survey phylogenetic diversity of microturbellarians in ten Japanese rice paddy fields, after DNA was extracted from all microturbellarian individuals that were collected in each field, the composition of the amplified 18S rRNA gene fragments of each sample was surveyed by clone library analysis. We also collected Stenostomum species in some of the same fields, identified them on the basis of morphological characters, and checked whether the 18S rRNA fragments of these species were contained within those of microturbellarians that were obtained by clone library analysis. Twenty-eight types of 18S rRNA gene fragments of microturbellarians were isolated on the basis of the difference in the sequence, and they were divided into seven families of microturbellarians (Stenostomidae, Catenulidae, Typhloplanidae, Dalyellidae, Gyratricidae, Macrostomidae, and Microstomidae). We identified four Stenostomum species of Stenostomidae (Stenostomum grande Child 1902, Stenostomum simplex Kepner & Carter 1931, Stenostomum tuberculosum Nuttycombe & Waters 1938, Stenostomum saliens Kepner & Carter 1931) that had never been reported in rice fields. The sequences of 18S rRNA gene fragments of Stenostomidae in the floodwater around rice plants showed the highest diversity, and they were closely related to Stenostomum leucops (Duges 1828) O. Schmidt 1848, S. grande, S. simplex, S. tuberculosum, S. saliens, Stenostomum heebuktense Larsson & Willems 2010, and Rhynchoscolex simplex Leidy 1851. 18S rRNA gene fragments of Catenulidae and Typhloplanidae showed high diversity, and those of Microstomidae, Macrostomidae, Gyratricidae, and Dalyellidae were also retrieved. These molecular biological techniques revealed that many unidentified groups of microturbellarians inhabited rice fields.