Differences in Temperature Dependence of Early Development of Sea Urchins with Different Growing Seasons

¹ Department of Biology, Faculty of Education, Saitama University, 255 Shimo-okubo, Urawa, Saitama 338, Japan

Three species of sea urchin, Hemicentrotus pulcherrimus, Anthocidaris crassispina, and Hemicentrotus depressus, inhabit the tidal areas around the Misaki Marine Biological Station, on the Pacific coast of Japan. These sea urchins have different breeding seasons and hence their embryos show differences in temperature sensitivity. In this study, differences in the temperature dependence of their embryogenesis were examined. It was found that the upper and lower limits of the optimal temperature range for embryogenesis in each animal were species-specifically determined, and that the range of seawater temperature during the breeding season was within this optimal temperature range. A quasi-linear relationship was obtained between temperature and relative developmental velocity, which was defined as the ratio against the maximal velocity attained at the highest temperature within the optimal temperature range. Based on this result, a form of graphical analysis was devised to represent the differences in species-specific developmental temperature sensitivity. The physiological and ecological significance of species-specific temperature sensitivity was also discussed.