Study On Embryonic Development Of Centropages Tenuiremis

Marine copepods are important links in the process of energy transformation, material circulation and biogeochemical cycle in marine ecosystem. Embryogenesis is a key phase of the process of biological ontogeny, and it directly affects the hatching success, larval development, and then the population and resource recruitment. The planktonic calanoid copepod Centropages tenuiremis is one of the dominant copepod species in Xiamen waters in winter-spring. Embryonic morphology, respiration rates and ecdysteroids levels in both subitaneous and diapause eggs of C. tenuiremis were all investigated in this study to understand the noticeable period in its life history and to discuss its physiological mechanism of diapause preliminarily. The main results were as follows:1. The morphology of embryonic development. Subitaneous eggs of C. tenuiremis were stained with fluorescent nucleic acid stains DAPI and then observed with confocal laser microscopy. We presented different developmental stages at20℃: cleavage stage (including2-cell,4-cell,8-cell,16-cell,32-cell,64-cell and128-cell), blastula stage, gastrula stage and limb-bud stage, which lasted10.3h,1.6h,11.3h and4.8h respectively. The observation showed the completely radial cleavage mode of C. tenuiremis, and median hatching time was28.0h. Subitaneous eggs had a thin, smooth shell while the diapauses eggs were thicker and with "spine" on it, which lengthened up to10-15μm after being laid for0.5h. DAPI penetrated the chorion after treatment of chitinase enzyme so that the diapause was presented after being laid for20h, at blastula stage.2. The respiration rate of embryo. The respiration rates in both subitaneous and diapause eggs were measured using Oxygraph Liquid-Phase Oxygen Measurement System. Respiration rates of subitaneous eggs increased steadily with development and reached maximum of7.32ng O2embryo-1h-118h after deposition, and the average respiration rate was5.36ng O2embryo-1h-1. Respiration curve of diapause eggs within25days after deposition followed the L-shaped pattern:it increased rapidly during the first2days, and reached a maximum on the3rd day,7.59ng O2 embryo-1h-1, and then declined gradually and maintained at a low level (48%of the maximum).3. The ecdysteroids level of embryo. The relative titers of ecdysteroids in both subitaneous and diapause eggs were measured during development and diapause using ELISA. The trend of relative titers in subitaneous eggs was slow with the maximum0.61at24th h, at limb-bud stage. Another peak was0.57at12th h. The rise of ecdysteroids level might due to the forming of exoskeleton. For diapauses eggs, ecdysteroids level was highest at the1st day, the following two data were0.41,0.46at8th day and17th day relatively, both were below the average level of subitaneous eggs (0.53)...