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Sexual reproduction adversely affects the population growth of cyclic parthenogenetic animals. The density-dependent sexual reproduction of a superior competitor could mediate the coexistence. However,the cost of sex may make the inferior competitor more vulnerable. To investigate the effect of sexual reproduction on the inferior competitor,we experimentally paired the competition of one Brachionus angularis clone against three B rachionus calyciflorus clones. One of the B. calyciflorus clones showed a low propensity for sexual reproduction,while the other two showed high propensities. The results show that all B. calyciflorus clones were excluded in the competition for resources at low food level. The increased food level promoted the competition persistence,but the clones did not show a clear pattern. Both the cumulative population density and resting egg production increased with the food level. The cumulative population density decreased with the mixis investment,while the resting egg production increased with the mixis investment. A trade-off between the population growth and sexual reproduction was observed in this research. The results indicate that although higher mixis investment resulted in a lower population density,it would not determinately accelerate the exclusion process of the inferior competitor. On the contrary,higher mixis investment promoted resting egg production before being excluded and thus promised a longterm benefit. In conclusion,our results suggest that mixis investment,to some extent,favored the excluded inferior competitor under fierce competition or some other adverse conditions.  相似文献   
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利用线粒体细胞色素氧化酶亚基Ⅰ(cytochrome oxidaseⅠ,COI)基因序列对北京地区和江汉湖群部分湖泊萼花臂尾轮虫(Brachionus calyciflorus)种群遗传结构进行了初步分析。以特异引物进行PCR扩增,获得了661bp的基因片断序列,所得序列与Genbank中B.calyciflorus COI序列的同源性为82%—93%。在6个种群中,共获得了15种单元型。序列分析结果表明,不同季节单元型之间的遗传距离较大(0.248-0.263),而在同一季节单元型之间遗传距离较小(0.002-0.031)。种群遗传结构分析表明,各种群之间无共享的单元型,同一季节不同湖泊种群之间存在着一定程度的遗传分化,但未按照地理位置形成明显的地理格局。按采样时间分组进行AMOVA分析,组间差异高达94.09%;DH-I与其他种群之间存在着明显的遗传分化。同一湖泊不同季节样品之间,遗传变异较大,这表明在同一湖泊存在着不同基因型的轮虫休眠卵,当环境条件发生了变化后,不同基因型之间会发生更迭。  相似文献   
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Large numbers of rotifer eggs from sediment resting egg banks may hatch simultaneously under appropriate conditions;therefore,natural populations are likely to be multiclonal in a growing season.A recent field investigation showed that subordinate and ephemeral clones were able to establish populations in an environment with several strongly dominant clone populations.However,it was not clear how the subordinate populations maintained their growth under these conditions where the crowding signal would induce high levels of sexual reproduction in the dominant clone populations.In the present study,we conducted a continuous passage to 60 generations for new populations at three different temperatures(15°C,25°C,and 35°C).These populations emerged from resting eggs produced by a clone population.At the first,30th,and 60th generations,the populations were sampled and fitness was assayed using the life-table method.We found a significant short-term fitness advantage for populations newly emerged from resting eggs produced by a clone population of the rotifer Brachionus calyciflorus,followed by a significant decrease in relative fitness with long-term continuous passage.Our results suggested that the early shortterm fitness advantage was important for later-hatched and subordinate clone populations in an environment with multiple sympatric clones.The early short-term fitness might also promote the coexistence of sympatric clones because it could help to offset the cost of early sexual reproduction.  相似文献   
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mtDNA COI基因在轮虫分子系统重建中的意义   总被引:5,自引:0,他引:5  
为分析mtDNA COI基因在轮虫分子系统重建中的作用.扩增并测定了B.calyciflorus和B.quadridentatus mtDNA COI基因部分序列。通过对扩增序列和Genbank中其它轮虫序列进行比较分析.发现COI序列包含丰富的遗传信息。利用Kimura双参数法计算遗传距离,在属和物种水平上间存在不同程度的遗传分化。利用NJ和MP法构建基因树。各物种形成独立进化枝.在属、科水平上与传统分类结果基本一致.这说明COI在轮虫系统重建中具有重要意义。在种内不同的单元型之间存在着遗传差异,部分种类不同地理种群之间存在较大的遗传变异.因此在系统重建过程中要注意种内多态的影响。  相似文献   
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孙栋  牛翠娟 《湖泊科学》2013,25(2):171-187
作为轮虫动物门的主体,单巢类轮虫是淡水浮游动物的重要组成部分.它们通常作为一类主要的初级消费者在淡水生态系统中起着重要作用,因而深入了解它们在自然水体中的种群动态及其决定机制对淡水生态系统理论与应用研究都有重要意义.作为一类具有典型周期性孤雌生殖生活史的动物,有性生殖的发生和进化策略对其种群动态和进化都有重要影响,因而单巢类轮虫有性生殖的机理和进化研究一直是轮虫学研究领域的一个核心内容.本文就当前单巢类轮虫有性生殖的主要研究进展,包括其发生机理、信息素、理论模型、影响因素和相关实证研究等进行了系统综述;特别就单巢类轮虫有性生殖策略的三个理论模型:"bang-bang"模型、中等有性生殖比率模型和非延迟的有性生殖模型进行了详细论述.此外,本文还对影响单巢类有性生殖的内外源因素进行了总结,主要的外源因素包括食物的浓度及种类、温度、盐度和特殊的细菌等,而主要的内源性因素则包括母体年龄、食物浓度诱导的跨代母系效应、延迟的有性生殖和其他一些潜在的母系效应因素等.其中,因为延迟的有性生殖现象广泛存在且可能是轮虫物种共存或克隆共存现象的一种潜在解释,所以就此现象的理论模型、机理和实证研究等方面进行了深入讨论.另外,本文还简要讨论性比率资源分配与单巢类轮虫有性生殖的关系.最后,对未来几个可能的热点方向简单评述,以期为国内轮虫学和相关方面的研究提供帮助.  相似文献   
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