Rynearson Tatiana A, Armbrust E Virginia
Marine Molecular Biotechnology Laboratory, School of Oceanography, University of Washington, Box 357940, Seattle, Washington 98195, USA.
Mol Ecol. 2005 May;14(6):1631-40. doi: 10.1111/j.1365-294X.2005.02526.x.
Maintenance of genetic diversity in eukaryotic microbes reflects a synergism between reproductive mode (asexual vs. sexual) and environmental conditions. We determined clonal diversity in field samples of the planktonic marine diatom, Ditylum brightwellii, during a bloom, when cell number increased by seven-fold because of rapid asexual division. The genotypes at three microsatellite loci were determined for 607 individual cell lines isolated during the 11 days of sampling. Genetic diversity remained high during the bloom and 87% of the cells sampled each day were genetically distinct. Sixty-nine clonal lineages were sampled two or more times during the bloom, and two clones were sampled seven times. Based on the frequency of resampled clonal lineages, capture-recapture statistics were used to determine that at least 2400 genetically distinct clonal lineages comprised the bloom population. No significant differences in microsatellite allele frequencies were observed among daily samples indicating that the bloom was comprised of a single population. No sexual stages were observed, although linkage equilibrium at two loci, high levels of allelic and genotypic diversity, and heterozygote deficiencies were all indicative of past sexual reproduction events. At the height of the bloom, a windstorm diluted cell numbers by 51% and coincided with a change in the frequency distribution of some resampled lineages. The extensive clonal diversity generated through past sexual reproduction events coupled with frequent environmental changes appear to prevent individual clonal lineages from becoming numerically dominant, maintaining genetic diversity and the adaptive potential of the population.
真核微生物中遗传多样性的维持反映了生殖模式（无性生殖与有性生殖）与环境条件之间的协同作用。我们测定了浮游海洋硅藻布氏双尾藻在水华期间野外样本中的克隆多样性，在此期间，由于快速的无性分裂，细胞数量增加了七倍。在为期11天的采样过程中，对分离出的607个单细胞系进行了三个微卫星位点的基因型测定。在水华期间，遗传多样性保持较高水平，每天采样的细胞中有87%在基因上是不同的。在水华期间，69个克隆谱系被采样了两次或更多次，两个克隆被采样了七次。根据重新采样的克隆谱系的频率，使用捕获-再捕获统计方法确定，至少2400个基因上不同的克隆谱系构成了水华种群。在每日样本中未观察到微卫星等位基因频率的显著差异，这表明水华由单一群体组成。尽管在两个位点上存在连锁平衡、高水平的等位基因和基因型多样性以及杂合子不足，但均表明过去发生过有性生殖事件，但未观察到有性阶段。在水华高峰期，一场风暴使细胞数量减少了51%，同时一些重新采样谱系的频率分布也发生了变化。过去有性生殖事件产生的广泛克隆多样性，加上频繁的环境变化，似乎阻止了单个克隆谱系在数量上占据主导地位，从而维持了遗传多样性和种群的适应潜力。
