無腸動物Waminoa sp. の人工飼育と産卵法 : 動物-藻類共生研究のモデル系解発に向けて <論文>

Waminoa sp. is an acoelomorph worm that infests corals and harbors two species of dinofl agellates, Amphidinium sp. and Symbiodinium sp.. These symbiotic algae are inherited vertically from parent to offspring during oogenesis. In this study, we established a method for artificial breeding of Waminoa sp., as the first step toward using Waminoa sp. in the study of the mechanism underlying animal–algal symbiosis and the evolution of this symbiosis. We developed a system in which an aquarium circulated approximately 80 L of artifi cial seawater between an upper aquarium and a lower sump, each of which was 45 cm × 30 cm × 35 cm in size and contained 40 L of seawater. Water flowed into the upper aquarium from the sump alternately through a pipe outlet. The upper aquarium contained the hard coral Symphyllia valenciennesii, live rocks, and a layer of fine sand. A 150-W metal halide lamp was suspended over the aquarium to aid photosynthesis. The system was maintained at a salinity of 32–33 ppt and a temperature of 23°C, on a 14-h light (17–50 μmol quanta m-2s-1) : 10-h dark photoperiod. We succeeded in producing almost every stage of the life cycle of Waminoa sp., including the zygote, embryo, larva, juvenile, and adult stages, independent of seasons. In addition, we developed an artificial oviposition procedure that involved isolation from coral in the mature stage. The system developed in this study will serve as a foundation for future studies on acoel–algal symbiosis.