Shedding light upon the complex net of genome size, genome composition and environment in chordates

The nucleotype theory has been advanced on the basis of studies regarding genome size and composition in various plant andanimal species, i.e. the influence that genome can have on the phenotype independently of the informational content ofDNA.It hasalso been noted that during evolution various interactions between different environmental factors and genome structural andfunctional parameters would have occurred. In this review, changes in genome size, transposon content, and base compositionoccurred during the evolution of chordates were examined. Many environmental stresses, such as temperature, can act ontransposons and through these on genome size. Temperature is also one of the most important elements of natural selection ableto interact both with base composition and genome size. It has been evidenced that temperature exerts a direct influence on basecomposition and its increase would have led to an higher content of genome GC-rich components during the evolution ofchordates, in particular in endotherms. Temperature would have controlled the rate of biosynthesis in G1 phase and consequentlythe cell cycle duration which in turn would have interacted with genome size. The combined action of temperature, basecomposition, and genome size would also have been very important in controlling the metabolic rate. Finally, another importantaspect of the nucleotypic effect is the influence that genome size and cell cycle duration, in correlation with environmentaltemperature, would have exert on embryo and larval development, very important for environmental adaptation. In conclusion,studies here reviewed to confirm the existence in chordates of a mutual influence between environment and genome non-codingcomponents that would have played an important role in the evolution of these animals especially in environmental adaptationprocesses.