Hydrostatic pressure-induced apoptosis on nauplii of Calanus sinicus |
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Authors: | Tomoko Yoshiki Banri Yamanoha Tomohiko Kikuchi Akio Shimizu and Tatsuki Toda |
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Institution: | (1) Department of Environmental Engineering for Symbiosis, Faculty of Engineering, Soka University, Tangi-cho, Hachioji, Tokyo 192-8577, Japan;(2) Department of Hydrographic Science, Faculty of Education and Human Science, Yokohama National University, Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan |
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Abstract: | The effect of hydrostatic pressure on embryonic development of the calanoid copepod Calanus sinicus was studied. Differences of pressure effect among blastomere stages, 1-cell, 2-cell, 4-cell, 8-cell, 16-cell, blastula and
limb-bud stage, were examined under two pressurizing conditions, abruptly (10 atm/min) and gradually (0.1 atm/min) increasing.
Egg hatching success, deformity frequency and apoptotic cell degradation of hatched nauplii were examined. Egg hatching success
rate was not significantly different between blastomere stages, and also between pressurizing conditions. Deformity frequencies
of hatched nauplii were low in the early 1-cell and 2-cell stages, and high in the later blastula and limb-bud stages, in
both abrupt and gradual pressurizing conditions. On the other hand, in regard to difference in pressurizing conditions, deformity
frequency in gradual pressurizing was significantly higher than that in abrupt pressurizing rate. Gradual pressure increase
seems to be more harmful to C. sinicus eggs than abrupt pressure change. Apoptosis induced in nauplii by hydrostatic pressure was detected for the first time in
marine zooplankton. The embryos of C. sinicus are sensitive to pressure variations, that is, these embryos are supposed to sink to deeper waters, incurring greater risk
of having deformities. In the field, C. sinicus ascend to the surface and spawn at night. By looking from this upward behavior, eggs are spawned at lower pressure and warmer
temperature. Probably, the harmless low pressure and warm temperature lead eggs to hatch early and to recruit successfully. |
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