BACKGROUND AND AIMS While nuclear DNA content variation and its phenotypic consequences have been well described for animals, vascular plants and seaweeds, much less about this topic is known regarding unicellular algae and protists in general. The dearth of data is especially pronounced when it comes to intraspecific genome size variation. This study attempts to investigate the extent of intraspecific variability in genome size and its adaptive consequences in a microalgae species. METHODS Propidium iodide flow cytometry was used to estimate the absolute genome size of 131 strains (isolates) of the golden-brown algae Synura petersenii (Chrysophyceae, Stramenopiles), identified by identical ITS rDNA barcodes. Cell size, growth rate and genomic GC content were further assessed on a subset of strains. Geographic location of 67 sampling sites across the Northern hemisphere was used to extract climatic database data and to evaluate ecogeographical distribution of genome size diversity. KEY RESULTS Genome size ranged continuously from 0.97 pg to 2.02 pg of DNA across the investigated strains. The genome size was positively associated with cell size and negatively associated with growth rate. Bioclim variables were not correlated with genome size variation. No clear trends in the geographical distribution of strains of particular genome size were detected and strains of different genome size occasionally coexisted at the same locality. Genomic GC content was significantly associated only with genome size via a quadratic relationship. CONCLUSIONS Genome size variability in Synura petersenii was likely triggered by an evolutionary mechanism operating via gradual changes in genome size accompanied by changes in genomic GC content, such as e.g. proliferation of transposable elements. The variation was reflected in cell size and relative growth rate, possibly with adaptive consequences.

中文翻译：

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金褐藻种内基因组大小的显着变化及其表型后果


背景和目的 虽然动物、维管植物和海藻的核 DNA 含量变异及其表型后果已得到很好的描述，但对于单细胞藻类和原生生物，人们对这一主题的了解却少之又少。当涉及种内基因组大小变异时，数据的缺乏尤其明显。本研究试图研究微藻物种基因组大小的种内变异程度及其适应性后果。方法 使用碘化丙啶流式细胞术估计 131 株金褐藻 Synura petersenii（金藻科、原生藻菌目）菌株（分离株）的绝对基因组大小，这些菌株通过相同的 ITS rDNA 条形码进行鉴定。对一部分菌株的细胞大小、生长速率和基因组 GC 含量进行了进一步评估。使用北半球 67 个采样点的地理位置来提取气候数据库数据并评估基因组大小多样性的生态地理分布。主要结果 在所研究的菌株中，基因组大小连续变化，从 0.97 pg 到 2.02 pg DNA。基因组大小与细胞大小呈正相关，与生长速率呈负相关。 Bioclim 变量与基因组大小变异不相关。没有检测到特定基因组大小的菌株的地理分布的明显趋势，并且不同基因组大小的菌株偶尔在同一地点共存。基因组 GC 含量仅通过二次关系与基因组大小显着相关。结论 Synura petersenii 的基因组大小变异可能是由基因组大小逐渐变化伴随着基因组 GC 含量变化的进化机制触发的，例如 转座因子的增殖。这种变化反映在细胞大小和相对生长速率上，可能会产生适应性后果。