Tarallo Andrea, Angelini Claudia, Sanges Remo, Yagi Mitsuharu, Agnisola Claudio, D'Onofrio Giuseppe
Genome Evolution and Organization - Department BEOM, Stazione Zoologica Anton Dohrn, Villa Comunale, 80121, Naples, Italy.
Istituto per le Applicazioni del Calcolo "Mauro Picone" - CNR, Via Pietro Castellino, 111, 80131, Naples, Italy.
BMC Genomics. 2016 Mar 2;17:173. doi: 10.1186/s12864-016-2537-1.
The DNA base composition is well known to be highly variable among organisms. Bio-physic studies on the effect of the GC increments on the DNA structure have shown that GC-richer DNA sequences are more bendable. The result was the keystone of the hypothesis proposing the metabolic rate as the major force driving the GC content variability, since an increased resistance to the torsion stress is mainly required during the transcription process to avoid DNA breakage. Hence, the aim of the present work is to test if both salinity and migration, suggested to affect the metabolic rate of teleostean fishes, affect the average genomic GC content as well. Moreover, since the gill surface has been reported to be a major morphological expression of metabolic rate, this parameter was also analyzed in the light of the above hypothesis.
Teleosts living in different environments (freshwater and seawater) and with different lifestyles (migratory and non-migratory) were analyzed studying three variables: routine metabolic rate, gill area and genomic GC-content, none of them showing a phylogenetic signal among fish species. Routine metabolic rate, specific gill area and average genomic GC were higher in seawater than freshwater species. The same trend was observed comparing migratory versus non-migratory species. Crossing salinity and lifestyle, the active migratory species living in seawater show coincidentally the highest routine metabolic rate, the highest specific gill area and the highest average genomic GC content.
The results clearly highlight that environmental factors (salinity) and lifestyle (migration) affect not only the physiology (i.e. the routine metabolic rate), and the morphology (i.e. gill area) of teleosts, but also basic genome feature (i.e. the GC content), thus opening to an interesting liaison among the three variables in the light of the metabolic rate hypothesis.
众所周知，DNA碱基组成在生物体之间具有高度变异性。关于GC含量增加对DNA结构影响的生物物理研究表明，富含GC的DNA序列更易弯曲。这一结果是提出代谢率是驱动GC含量变异性的主要力量这一假说的关键，因为在转录过程中主要需要增加对扭转应力的抗性以避免DNA断裂。因此，本研究的目的是检验盐度和洄游（这两者被认为会影响硬骨鱼类的代谢率）是否也会影响基因组平均GC含量。此外，由于鳃表面据报道是代谢率的主要形态学表现，因此也根据上述假说对该参数进行了分析。
对生活在不同环境（淡水和海水）且具有不同生活方式（洄游和非洄游）的硬骨鱼类进行了分析，研究了三个变量：常规代谢率、鳃面积和基因组GC含量，在鱼类物种中这些变量均未显示出系统发育信号。海水鱼类的常规代谢率、比鳃面积和基因组平均GC含量高于淡水鱼类。在比较洄游鱼类和非洄游鱼类时也观察到了相同的趋势。综合盐度和生活方式来看，生活在海水中的活跃洄游鱼类同时具有最高的常规代谢率、最高的比鳃面积和最高的基因组平均GC含量。
结果清楚地表明，环境因素（盐度）和生活方式（洄游）不仅影响硬骨鱼类的生理学（即常规代谢率）和形态学（即鳃面积），还影响基本的基因组特征（即GC含量），从而根据代谢率假说揭示了这三个变量之间有趣的联系。
