隆线溞[Daphnia(Ctenodaphnia)carinata]卵鞍的超微结构

在不利的环境条件下,枝角类中有一部分种类可以形成卵鞍(ephippium),内含休眠卵。本文应用扫描电镜和透射电镜对隆线溞的卵鞍进行了超微结构的研究。研究表明:卵鞍外面大部分略呈浅的蜂窝状,内面则排布着多数卵石状小突起。卵鞍分为内外两层,两层的超微结构截然不同;各层又可分为三小层。     

若干种枝角类卵鞍表面亚显微结构的比较研究

以扫描电镜对发头裸腹溞、蚤状溞、隆线溞指名亚种以及隆线溞东湖一亚种的卵鞍分别进行了比较研究,发现卵鞍表面的亚显微结构有明显的差异,但亚种之间差异较小。隆线溞指名亚种与隆线溞东湖一亚种二者的卵鞍在光学显微镜下看不出有什么差异,然而亚显微结构却互不相同。这就为东湖一新亚种的确定提供了一项可靠的依据,同时也进一步证实卵鞍的超微结构确可作为枝角类分类的表征。     

The influence of pool volume and summer desiccation on the production of the resting and dispersal stage in a Daphnia metapopulation

Dispersal is a key process in metapopulations, as migrants genetically connect populations and enable the colonization of empty habitat patches. Sub-populations may differ in their numerical contribution of migrants within a metapopulation. This has strong implications on evolutionary and ecological dynamics and has led to two different hypotheses about the Daphnia metapopulation studied here: the assessment by some authors is that sub-populations contribute equally to the production of migrants, while others have postulated long-lived core populations in large "mainland" habitat patches as the dominant source of migrants. We have studied the resting and dispersal stage (ephippium) in a natural Daphnia metapopulation and in mesocosm experiments, and tested for effects of habitat size and summer desiccation. We found that a 1000-fold increase in rock pool volume resulted on average in only in a 2.8-fold increase in ephippium production. Mesocosm experiments confirmed these results: a 1000-fold increase of the mesocosms' volume resulted in a 7.2-fold increase in ephippium production. Additionally, we showed that ephippium production did not depend on the initial population size. Thus, populations in small pools may contribute only marginal fewer potential migrants in the whole metapopulation than populations in large pools. In a second mesocosm experiment we found that summer desiccation, which is a typical occurrence in small pools, is not detrimental for the populations. Daphnia hatched out of ephippia that were produced earlier within the same season and built up viable populations again. The substantial production of ephippia by populations in small pools suggests that these populations might be important for both the dynamics and global stability of metapopulations.     

温度和培养体积对大型溞种群动态和两性生殖影响的研究

研究了5个培养体积(50、100、200、400、1000 mL)和2个温度(20℃、25℃)下大型溞(Daphnia magna Straus)种群动态和两性生殖的变化,结果表明:(1)在相同培养体积下,随温度升高,大型溞首次抱卵时间缩短、首次产幼涵时间提前.在相同温度下,大型涵首次抱卵体长随培养体积的增大而增大.20℃和25℃下,1000 mL组大型溞首次抱卵体长分别是(2.54±0.02)mm和(2.71±0.01)mm.(2)在一定时间内,大型溞种群数量快速增加.但在较小培养体积下大型溞种群增长明显受到抑制.20℃和25℃下1000 mL培养体积组最大种群数量是2152 ind./1000 mL和3085 ind./1000 mL,分别约为50 mL组的4倍和13倍.培养体积与大型溞最大种群数量间存在显著相关性(P<0.01,n=15).(3)所有种群实验组均产生雄体,且雄体数量随种群数量的增加而相应增加.20℃下1000 mL组产生的雄体数量明显高于其他培养体积组,最大比例可达36%,且第一次产幼溞即出现雄性.雄体数量与大型溞最大种群数量之间呈显著的相关性(20℃:P<0.01,n=15;25℃:P<0.05,n=15).(4)20℃和25℃下,1000 mL组大型涵累计产生卵鞍分别为814和359个,且均由母溞后代形成.而其他体积组仅产生少量卵鞍或不产卵鞍,且所产卵鞍均由培养时的母溞形成.20℃和25℃下1000 mL组所产卵鞍的空卵鞍率分别达61.18%和99.16%.实验期间,20℃、1000 mL组所产生的卵鞍中,含休眠卵的比例均在20%以上.     

几种枝角类的卵鞍形态及表面超微结构

用光镜和扫描电镜对浙东地区八种常见淡水枝角类卵鞍形态和表面结构进行了观察和比较。卵鞍形态多为三角形或豆荚形,表面大都具特定的纹饰,内储冬卵1－2枚。卵鞍的形态、表面纹饰、冬卵的数量的排列方向具有种的特异性。枝角类的分类地位相距越远,卵鞍形态和表面结构相差越大,相近种和亚种间的卵鞍在光镜下难以区别,亚显微结构却有一定的差异。卵鞍的形态和结构作为枝角类的分类依据是有意义的。