摘要
由于研究技术与方法的不断改进 ,人们对海藻 (seaweeds)早期生活史方面的研究兴趣日益增大。评述了近年来海藻有性繁殖过程中配子释放和受精生态学问题。到达一定生理状态的海藻 ,通过对环境暗示应答而诱导配子形成。海藻生殖器官感受另一些特定的环境条件 ,通过有关信号传递机制 ,触发配子释放。海藻配子释放的时间及其所需的环境条件 ,依不同的种类而变化。配子同步释放以及各种适当的环境条件提高了受精频率和受精成功率 ,有利于受精的各种生物的和非生物的因素组合 ,形成了“机会窗 (the window of opportunity)”的概念。近年来的研究表明 ,海藻 (特别是红藻 )的自然受精成功率比以前所认为的要高得多。受精后合子 (胚 )的散布、集落与附着显著地影响其生存以及种群动态。
Seaweeds (marine macroalgae) are distributed in the intertidal and subtidal zones of the coasted areas, being major contributors to primary productivity in these habitats. Although studies of benthic seaweeds have made essential contributions to ecological theory, attention has focused primarily upon adult interactions, and relative little attention is paid on the early stage of life history in seaweeds. One major cause is due to the technical difficult for research. However, new approaches and methods produced significant and innovative data recently on the early stage of life cycle in seaweeds. One stirring point is about the sexual reproduction. Sexual reproduction is a common part of the life cycle in seaweeds, although not always an obligatory step. This review is principally about the recent advances of gamete release and fertilization success in seaweeds from an ecological perspective. Variation in the environmental factors satisfying the physiological requirement for reproduction triggers reproductive seasonality. Seaweeds respond to many environmental cues (e.g. photoperiod, spectral quality and light intensity, temperature, nutrients supply) for timing of gametogenesis. Fucoid algae, being brown seaweeds that are abundant in temperate rocky intertidal zones of the open coast and estuaries, serve as excellent model systems for studies of reproductive ecology and physiology. Receptacles are the their reproductive tissue. The reproductive thalli in seaweeds generally release gametes in response to different environmental cues from the ones that confer an overall seasonality to the life cycle. Gametes release commonly occurs following a change in irradiance (dark after a light-induction period or vice versa). Photosynthesis is required for potentiation of gamete release, which gives the consequence of intracellular accumulation of K^+ and Cl^- by cells in the receptacle. Adult thalli of fucoid living in habitats that are frequently stormy can sense reductions in water motion via the reduced unstirred boundary layer bicarbonate levels and photosynthesis, which provide a signal involved in triggering the release of gametes. A change in salinity or a certain range of salinities may also be needed for gamete release. Moreover, one signal can be modified by a second signal in some species. In many green and brown algae, sexual induction by on one gamete (e.g. the egg) in required for final maturation and release of the other gamete (i.e. the sperm), which may be related to pheromonal signals. It is essential to note that some of the factors appearing from laboratory studies to be involved in gamete release may not appear particularly important in field. Thus both laboratory and field studies of seaweeds are essential to establish the mechanisms influencing gamete release. The recent field data suggest the fertilization success values of 70%~100% for fucoids and 30%~80 % for the red algae, the values frequently high than previously assessed. The red algae are previously viewed as having reproductive disadvantages because both their spermatia and carpogonia are nonmotile. However, they have a number of reproductive adaptations that help to achieve fertilization. Synchronous release of gametes by adult thalli increases concentrations of gametes and the likelihood of gametes encounter and thereby is crucial for fertilization success. Moreover, asynchronous gamete release by closely related species seems to prevent most hybridization. Another factor for the high levels of fertilization success is that adults are exquisitely sensitive to water motion. Dilutions is avoided or reduced as a consequence of gametes releasing under calm conditions. Gametes are also concentrated spatially in some algae through a pheromonal-dependent release of sperm. Indirect evidence for high nature fertilization success in seaweeds comes from the occurrence of plolyspermy and the presence of polyspermy blocks. It was suggested that polyspermy prevention is a widespread adaptation in seaweeds. Results suggest three polyspermy-preventing mech
出处
《生态学报》
CAS
CSCD
北大核心
2004年第12期2870-2877,共8页
Acta Ecologica Sinica
基金
国家 8 63计划青年基金资助项目 ( 2 0 0 2 AA62 80 90 )
国家自然科学基金资助项目 ( 3 0 3 0 0 0 5 0和 3 0 470 3 43 )
广东省自然科学资金资助项目 ( 0 3 2 0 48和 0 40 10 990 )
广东省科技攻关资助项目 ( 2 0 0 2 C3 2 70 5 )~~
关键词
海藻
有性繁殖
配子释放
受精
生态学
seaweeds
sexual reproduction
gamete release
fertilization
ecology
