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黄海中华哲水蚤度夏机制的新探索:温度和饵料的作用
周孔霖
Subtype博士
Thesis Advisor孙松
2016-05-18
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline海洋生态学
Keyword度夏 环境因子 油脂积累 呼吸率 基因表达
Abstract中华哲水蚤是黄东海浮游动物的关键种,在黄东海海洋生态系统中起到重要的支撑作用。中华哲水蚤的数量变动会影响到整个生态系统结构与功能的改变。夏季,中华哲水蚤在黄海冷水团中度夏,是种群保存和延续的关键过程。然而,度夏的启动与终止过程尚不明确。本文通过室内受控实验和野外调查,探讨了中华哲水蚤度夏的启动与终止过程以及温度和饵料的影响作用。
油囊中贮存的油脂是中华哲水蚤在度夏期间的主要能量来源。度夏前,油脂积累的程度关系到中华哲水蚤能否顺利度夏。结合春末黄海冷水团海区的温度和饵料环境,本文系统研究了温度(恒温和变温)、饵料浓度和种类(硅藻和自然饵料)对中华哲水蚤油脂积累的影响。中华哲水蚤的油囊体积在C5期桡足类幼体达到最大,进入成体阶段后减小,性腺随后发育成熟。低温(10°C)能降低个体代谢消耗,从而有利于能量的积累。较大幅度的温差(10-16°C和10-19°C)有利于C5期油脂的积累,其油囊体积百分数(OSV%)是对应高温组(16°C和19°C)的1.8—6.1倍。C5期的油囊体积随着饵料浓度的增加而增大,过低或过高的饵料浓度会掩盖温度的作用。本实验中,硅藻是C5期油脂积累的主要食物来源。
对2014年春末黄海冷水团内外的中华哲水蚤进行比较研究。春末,冷水团区的叶绿素浓度比冷水团外的低;然而,冷水团区的中华哲水蚤C5期呼吸率比冷水团外的低32%,OSV%为其的2.4倍;冷水团区C5期的大颚均处于蜕离前期(Pre-apolysis),蜕皮发育不活跃。由此推测:春末冷水团区的中华哲水蚤抑制个体的蜕皮发育,降低新陈代谢,个体将摄食获得的能量用于油脂积累而非蜕皮发育;度夏前大体积油囊的形成与内源性因素的调控有关。此外,冷水团区底层C5期的OSV%是表层的1.9—4.2倍,积累足够油脂的中华哲水蚤偏向在冷水团底部活动。
在中华哲水蚤度夏期间,通过野外调查和现场实验,从形态特征、呼吸率和相关基因表达三个方面对2013年8月黄海冷水团内外的中华哲水蚤进行了比较研究。结果表明,夏季冷水团内的C5期油囊体积大,呼吸率低,铁蛋白(Ferritin)表达量高而蜕皮激素受体(EcR)表达量低,C5期的蜕皮发育受到抑制,个体处于浅休眠状态——静息(Quiescence)。冷水团内雌体的呼吸率高,处于非休眠状态。冷水团边缘的C5期生理状态介于静息与活跃之间,较高的EcR表达量预示着蜕皮发育的开始。冷水团边缘较好的饵料环境可能是诱导度夏终止的外部信号。
通过模拟秋季冷水团衰退期间的温度和饵料环境,本研究在不同温度、饵料条件下对中华哲水蚤度夏种群的C5期进行连续培养,观察度夏终止以及后续生长发育过程中呼吸率、形态特征以及相关基因表达量的动态变化,揭示了温度和饵料在此过程中的作用。结果表明环境改变,如升温或添加饵料,均能诱导中华哲水蚤终止度夏。静息的C5期能快速响应环境变化,在培养1日后上调EcR表达量,并在3日内增加呼吸率。升温或添加饵料有利于个体的蜕皮发育。Ferritin表达量对饵料环境敏感,仅在投喂饵料组的培养后期下调。度夏终止后,油囊中的脂类可用于蜕皮发育和性腺的初步发育。在添加饵料的实验组,中华哲水蚤上调卵黄原蛋白受体(VgR)的表达量,性腺随后发育成熟。综上所述,环境改变能诱导中华哲水蚤结束度夏,饵料是度夏结束后个体性腺发育以及种群繁殖补充的必需条件,升温能加快这些生理过程。
秋季的野外调查发现,冷水团区中华哲水蚤C5期的呼吸率与春末无异,而OSV%却大幅度降低。此时,冷水团区的成体所占比例增加,约6.7%的C5期出现蜕离现象(Apolysis),这表明蜕皮发育的开始和度夏的终止。环境条件的改善以及油脂消耗到一个低阈值均能诱导C5期结束度夏。
Other AbstractCalanus sinicus is the dominant species of zooplankton in the Yellow Sea and East China Sea, which plays a key role in marine ecosystems of the Yellow Sea and East China Sea. The population dynamics of C. sinicus could affect the structure and function of marine ecosystem. In summer, C. sinicus over-summers inside the Yellow Sea Cold Water Mass (YSCWM) to conserve population abundance. However, the mechanisms of initiation and termination of over-summering are still unknown. Here, we conducted laboratory controlled experiments and field studies to explore the mechanism of over-summering and the effects of temperature and food.
The lipid reserve in oil sacs is the main energy resource for over-summering C. sinicus to survive. The lipid accumulation of C5 copepodids (C5s) would affect the success of the over-summering. Given the temperature and food conditions in the YSCWM in late spring, we systematically studied the effects of temperature (e.g. constant temperature and temperature difference), food concentration and food type (diatom and natural diets) on the lipid accumulation of C. sinicus. The lipid was accumulated most in C5s, and then was consumed as gonad developed. At low temperatures, C. sinicus stored more lipid than at high temperatures by reducing the energy cost at colder temperatures. Larger diurnal temperature differences (10–16 and 10–19 °C) could promote the lipid accumulation, and the oil sac proportions (OSV%) of C5s were 1.8–6.1 time of those at 16 or 19 °C. C5s accumulated more lipid as the food concentration increased. Diatoms were the main food resource for lipid accumulation in C5s.
We compared C. sinicus captured insisde and outside the YSCWM in late spring, 2014. In late spring, the Chl a concentration was lower inside the YSCWM. However, the C5s inside the YSCWM had 32% lower metabolic rates and 1.4 time larger oil sacs than those outside. All the C5s inside the YSCWM were in pre-apolysis, indicating inactive molting development. Therefore, the C5s inside the YSCWM might suppress molting, reduce metabolic activity, and assign most energy to lipid accumulation other than molting. In addition, the OSV% of C5s in the bottom of YSCWM were 1.9—4.2 times of those in the surface layers. Thus, wih enough lipid accumulation, C. sinicus preferred to stay inside the bottom of the YSCWM.
In this study, we compared the metabolic rates, morphological characteristics and relative gene expressions of C. sinicus captured both inside and outside the YSCWM in Aug, 2013. With large oil sacs, low metabolic rates and suppressed molting development, the C5s inside the YSCWM were probably quiescent. When quiescent, the gene associated with molting (ecdysteroid receptor, EcR) was down-regulated, while genes associated with stress tolerance (ferritin) were up-regulated. Females inside the YSCWM were active for higher metabolic rates. C5s at the margin of the YSCWM up-regulated EcR expression, which could be a response to the elevated Chl a concentration, suggesting that improved food condition may serve as a trigger that terminated the over-summering of C. sinicus in the Yellow Sea.
We examined the effects of temperatures and food on metabolic rates, morphological characteristics, and relative gene expressions of six genes involved in molting, gonad development, lipid catabolism and stress tolerance processes of C. sinicus during the termination of over-summering and subsequent development. Both elevated temperature and external food supply rapidly ended over-summering of C. sinicus, accompanied by up-regulation of EcR expression on the 1st day and increased metabolic rates on the 3rd day. The improved temperature or food conditions could ensure the success of molting. Ferritin was sensitive to the food condition and was down-regulated only when copepods fed. During the subsequent development, the lipid reserved in oil sacs could support molting and early gonad development. When fed with food, C. sinicus up-regulated VgR (vitellogenin receptor) expression, and the gonad got mature thereafter. Thus, the environmental changes would induce the termination of over-summering. In addition, food played an indispensable role in population recruitment after the termination of over-summering, whereas the elevated temperature just accelerated these physiological processes.
In autumn, the metabolic rates of C5s were similar to those in spring inside the YSCWM, while the OSV% reduced a lot. Meanwhile, the proportion of adults inside the YSCWM increased, and ~6.7% of C5s were in post-apolysis, suggesting the termination of over-summering and beginning of ecdysis. Both the improved environmental conditions and lipid consumption would trigger the termination of over-summering.
Subject Area海洋科学
Language中文
Document Type学位论文
Identifierhttp://ir.qdio.ac.cn/handle/337002/116968
Collection海洋生态与环境科学重点实验室
Affiliation中国科学院海洋研究所海洋生态与环境科学重点实验室 青岛 260071
Recommended Citation
GB/T 7714
周孔霖. 黄海中华哲水蚤度夏机制的新探索:温度和饵料的作用[D]. 北京. 中国科学院大学,2016.
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