1 0 0 0 OA エダアシクラゲの放卵・放精の光条件
The hydrozoan jellyfish Cladonema pacificum is widely distributed on the coast of Japan. Here we report on light-dark conditions for spawning in medusae of this species. All of the medusae captured at Orinohama (Ishinomaki City, Miyagi Prefecture) and at Matsushima (Higashi-Matsushima City, Miyagi Prefecture) spawnedafter dark in the evening of the capture day and continued to spawn every day by dark stimulation (dark-type medusae). In contrast, most of the medusae captured at Asamushi (Aomori City, Aomori Prefecture) spawned in the next morning, following the switch from dark to light; they spawned every day by light stimulation (lighttypemedusae). Medusae of the next generation that had developed from eggs and sperm from Asamushi lighttype medusae spawned in response to light after dark. On the other hand, zygotes from Orinohama and Matsushima medusae developed into dark-type medusae. In light-type female medusae, a light period of 10 seconds after dark was sufficient to induce normal spawning, whereas a continuous dark period of 3 - 9 hours was required before the light stimulation. In dark-type females, a dark period lasting for 3 - 5 minutes was required for spawning. Interestingly, they also spawned in response to light when the order of light and dark periods was reversed. Our data suggest that there are populations of C. pacificum using different light-dark conditions as the trigger for spawning, and that these characters are caused by genetic factors.