Department of Human Evolutionary Biology, Harvard University, Cambridge, MA, USA.
Genome Biol Evol. 2012;4(10):1033-43. doi: 10.1093/gbe/evs070.
Intronic DNA is a major component of eukaryotic genes and genomes and can be subject to selective constraint and have functions in gene regulation. Intron size is of particular interest given that it is thought to be the target of a variety of evolutionary forces and has been suggested to be linked ultimately to various phenotypic traits, such as powered flight. Using whole-genome analyses and comparative approaches that account for phylogenetic nonindependence, we examined interspecific variation in intron size variation in three data sets encompassing from 12 to 30 amniotes genomes and allowing for different levels of genome coverage. In addition to confirming that intron size is negatively associated with intron position and correlates with genome size, we found that on average mammals have longer introns than birds and nonavian reptiles, a trend that is correlated with the proliferation of repetitive elements in mammals. Two independent comparisons between flying and nonflying sister groups both showed a reduction of intron size in volant species, supporting an association between powered flight, or possibly the high metabolic rates associated with flight, and reduced intron/genome size. Small intron size in volant lineages is less easily explained as a neutral consequence of large effective population size. In conclusion, we found that the evolution of intron size in amniotes appears to be non-neutral, is correlated with genome size, and is likely influenced by powered flight and associated high metabolic rates.
内含子 DNA 是真核生物基因和基因组的主要组成部分，可能受到选择约束，并具有基因调控的功能。鉴于内含子大小被认为是多种进化力量的目标，并且与各种表型特征（如飞行能力）有关，因此它特别引人注目。本研究使用全基因组分析和考虑系统发育非独立性的比较方法，在三个数据集（涵盖 12 到 30 种羊膜动物基因组）中研究了内含子大小变异的种间变异，同时允许基因组覆盖的不同水平。除了确认内含子大小与内含子位置呈负相关并与基因组大小相关之外，我们还发现哺乳动物的内含子平均比鸟类和非鸟类爬行动物长，这一趋势与哺乳动物中重复元件的增殖有关。在两个独立的飞行和非飞行姊妹群之间的比较中，都显示出飞行物种的内含子大小减小，支持与飞行相关的动力飞行，或者可能与飞行相关的高代谢率之间存在关联，以及内含子/基因组大小减小。飞行谱系中小的内含子大小不太容易解释为大有效种群大小的中性后果。总之，我们发现，羊膜动物中内含子大小的进化似乎不是中性的，与基因组大小相关，并且可能受到动力飞行和相关高代谢率的影响。
