脂类在中华哲水蚤休眠过程中的生理功能

Evidence is accumulating that storage lipids are important energy supplement for herbivorous copepods from higher latitude regions, which spend a long period of food scarcity in a state of diapause. .Calanus sinicus is one of the target species in the China-GLOBEC program, which accounts for as much as 80% of the total zooplankton biomass in the Yellow Sea in some regions in spring. In summer, C. sinicus (mostly CVs) maintains a dormant status in the Yellow Sea Cold Water Mass (YSCWM), where both temperature and food abundance are low. This adaptive oversummering strategy helps C. sinicus to live through the warm and food-limited season. It has been noticed that C. sinicus could deposit a large body of oil sac in the spring phytoplankton bloom before diapause. The decrease of oil sac volume along the oversummering indicates the consumption of storage lipids in the process of diapause. Until now, the role of storage lipids for C. sinicus in diapause is still not clearly identified and is still speculative. .A deep analysis is carried out in this study with emphasis on the role of lipids in the process of oversummering in C. sinicus. We examine the content and composition of lipids with individuals from different development stages to determine the influence of lipids on the gonadal development of C. sinicus. The number and volume of lipid droplets in nauplii from N1 to N6 are measured in order to analyze the utilization of lipids during the development of nauplii. Zooplankton samples for the analysis of lipids are taken and incubation experiments for the determination of feeding rate, respiration rate and growth rate are carried out onboard in order to investigate the contribution of storage lipids and feeding in the process of oversummering. Our interest is also in the role of lipids in the beginning and ending of diapause. For which, lipids are analyzed and subsamples of lipids are separated by thin layer chromatography for the determination of fatty acid composition of each lipid classes. The aim of the present study is to investigate the role of lipids in the process of diapause of C. sinicus.

度夏是中华哲水蚤生活史过程中的关键阶段，关系到其种群在食物短缺胁迫和高温伤害下是否能保存和延续。和高纬度海区桡足类的越冬过程相似，中华哲水蚤在度夏开始前的水华期也会积累大量脂类，但是目前对脂类在中华哲水蚤度夏休眠过程中的具体生理功能研究的还很少。本项目以南黄海中华哲水蚤为研究对象，通过了解脂类在其性腺发育及幼体发育过程中含量和组成的变化研究脂类在繁殖中的作用；通过分析中华哲水蚤在休眠过程中不同阶段脂类组成和含量的变化，结合摄食、代谢、生长和繁殖等生理指标研究中华哲水蚤在休眠过程中对脂类的利用策略；在研究中华哲水蚤休眠状态和脂类的含量、组成变化的基础上，分析脂类积累对中华哲水蚤休眠状态的影响。综合以上研究结果分析脂类在中华哲水蚤休眠过程中的生理功能。该项目将为我们更深入了解中华哲水蚤的生活史过程提供有力依据，并为温带海区桡足类积累脂类应对不利环境胁迫的研究提供新的思路。

度夏是中华哲水蚤生活史过程中的关键阶段，关系到其种群在食物短缺和高温胁迫下是否能保存和延续。项目以中华哲水蚤为研究对象，通过不同条件培养的饵料培养中华哲水蚤，分析饵料对其脂类积累、生长、繁殖的影响。结果表明中肋骨条藻和海洋原甲藻培养下其产卵率和繁殖率无显著差异，但中肋骨条藻培养下中华哲水蚤死亡率更高，这可能是因为中肋骨条藻较低的PUFA和较高的醛类含量导致的。另外，不同浓度配比的饵料会影响浮游植物的生化组成和种群粒径结构，并进而影响中华哲水蚤的生长和繁殖。相对于高纬度海区的飞马哲水蚤，野外中华哲水蚤16:1ω7和18:4ω3的含量均较低，其体内的植食性指标20:1+22:1的含量也较低，综合分析认为中华哲水蚤是一种偏植食性的杂食性桡足类。中华哲水蚤雌体和桡足幼体植食性特征明显，雌体更偏好摄食硅藻，而桡足幼体则倾向于摄食甲藻（18:4ω3含量较高）。对冷水团内外雌体和桡足幼体脂肪酸组成分析发现，冷水团内的雌体和桡足幼体大多数脂肪酸的含量均高于冷水团外的个体。特别是桡足幼体20:1+22:1、20:5ω3、22:6ω3、MUFA、PUFA、∑ω3和TFA的含量与冷水团外的个体差异均达到显著水平（p<0.05）。蜡脂、磷脂和三酰甘油作为中华哲水蚤主要的脂质构成，其总和可以占到总脂含量的98%以上。从6月冷水团开始形成到8月冷水团繁盛期，蜡脂和磷脂的含量均减少，说明中华哲水蚤在冷水团形成后开始消耗体内储存的脂类物质。蜡脂中的PUFA比SFA+MUFA具有更高的消耗速率，说明中华哲水蚤对PUFA具有选择性消耗。由于CV期是中华哲水蚤休眠度夏的主要群体，桡足幼体高含量的脂肪酸更有利于长时间的应对冷水团中饵料稀少的环境和满足度夏过程中的能量需求。随着冷水团的发育，桡足幼体体内的脂肪酸逐渐被代谢消耗，当冷水团消退时，桡足幼体逐渐发育为成熟的个体，中华哲水蚤种群得以延续。由于中华哲水蚤在度夏过程中不存在蜡脂相态的转变，且南黄海水深较浅垂直混合剧烈，综合分析认为垂直混合带来的温度以及饵料条件的变化促使了中华哲水蚤度夏休眠的结束。