背景:线虫是地球上最丰富和多样化的后生动物,并且已知会严重影响生态系统功能。更好地了解他们的生物学和生态学,包括对不同栖息地和生活方式的潜在适应,是了解他们对全球变化情景的反应的关键。线粒体基因组提供了高物种水平的表征,测序成本低,和易于数据处理,可以提供对线虫进化压力的见解。
结果:一般来说,线虫线粒体基因组表现出相似的结构特征(例如,基因大小和GC含量),但围绕这些一般模式显示出显著的可变性。组成链偏差显示出强烈的密码子位置特异性G偏斜,并且与线虫生命特征(尤其是寄生摄食习性)的关系等于或大于与预测的系统发育。平均而言,线虫线粒体基因组显示出低的非同义替换率,而且与这些手段的具体偏差也很高。尽管存在显著的突变饱和,非同义(dN)和同义(dS)替代率仍然可以通过摄食习惯和/或栖息地来解释。dN:dS比率低,特别是与寄生虫的生活方式有关,建议存在强大的净化选择。
结论:线虫线粒体基因组表现出积累成分多样性的能力,结构,和内容,同时仍然保持功能基因。此外,他们展示了快速进化变化的能力,指出多层次选择压力和快速进化之间的潜在相互作用。总之,这项研究有助于为我们理解形成线虫线粒体基因组的潜在进化压力奠定基础,同时概述了未来可能的调查路线。
BACKGROUND: Nematodes are the most abundant and diverse metazoans on Earth, and are known to significantly affect ecosystem functioning. A better understanding of their biology and ecology, including potential adaptations to diverse habitats and lifestyles, is key to understanding their response to global change scenarios. Mitochondrial genomes offer high species level characterization, low cost of sequencing, and an ease of data handling that can provide insights into nematode evolutionary pressures.
RESULTS: Generally, nematode mitochondrial genomes exhibited similar structural characteristics (e.g., gene size and GC content), but displayed remarkable variability around these general patterns. Compositional strand biases showed strong codon position specific G skews and relationships with nematode life traits (especially parasitic feeding habits) equal to or greater than with predicted phylogeny. On average, nematode mitochondrial genomes showed low non-synonymous substitution rates, but also high clade specific deviations from these means. Despite the presence of significant mutational saturation, non-synonymous (dN) and synonymous (dS) substitution rates could still be significantly explained by feeding habit and/or habitat. Low ratios of dN:dS rates, particularly associated with the parasitic lifestyles, suggested the presence of strong purifying selection.
CONCLUSIONS: Nematode mitochondrial genomes demonstrated a capacity to accumulate diversity in composition, structure, and content while still maintaining functional genes. Moreover, they demonstrated a capacity for rapid evolutionary change pointing to a potential interaction between multi-level selection pressures and rapid evolution. In conclusion, this study helps establish a background for our understanding of the potential evolutionary pressures shaping nematode mitochondrial genomes, while outlining likely routes of future inquiry.